qemu

block.c (245584B)

---

 /*
  * QEMU System Emulator block driver
  *
  * Copyright (c) 2003 Fabrice Bellard
  * Copyright (c) 2020 Virtuozzo International GmbH.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
 
 #include "qemu/osdep.h"
 #include "block/trace.h"
 #include "block/block_int.h"
 #include "block/blockjob.h"
 #include "block/fuse.h"
 #include "block/nbd.h"
 #include "block/qdict.h"
 #include "qemu/error-report.h"
 #include "block/module_block.h"
 #include "qemu/main-loop.h"
 #include "qemu/module.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qjson.h"
 #include "qapi/qmp/qnull.h"
 #include "qapi/qmp/qstring.h"
 #include "qapi/qobject-output-visitor.h"
 #include "qapi/qapi-visit-block-core.h"
 #include "sysemu/block-backend.h"
 #include "qemu/notify.h"
 #include "qemu/option.h"
 #include "qemu/coroutine.h"
 #include "block/qapi.h"
 #include "qemu/timer.h"
 #include "qemu/cutils.h"
 #include "qemu/id.h"
 #include "qemu/range.h"
 #include "qemu/rcu.h"
 #include "block/coroutines.h"
 
 #ifdef CONFIG_BSD
 #include <sys/ioctl.h>
 #include <sys/queue.h>
 #if defined(HAVE_SYS_DISK_H)
 #include <sys/disk.h>
 #endif
 #endif
 
 #ifdef _WIN32
 #include <windows.h>
 #endif
 
 #define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress */
 
 /* Protected by BQL */
 static QTAILQ_HEAD(, BlockDriverState) graph_bdrv_states =
     QTAILQ_HEAD_INITIALIZER(graph_bdrv_states);
 
 /* Protected by BQL */
 static QTAILQ_HEAD(, BlockDriverState) all_bdrv_states =
     QTAILQ_HEAD_INITIALIZER(all_bdrv_states);
 
 /* Protected by BQL */
 static QLIST_HEAD(, BlockDriver) bdrv_drivers =
     QLIST_HEAD_INITIALIZER(bdrv_drivers);
 
 static BlockDriverState *bdrv_open_inherit(const char *filename,
                                            const char *reference,
                                            QDict *options, int flags,
                                            BlockDriverState *parent,
                                            const BdrvChildClass *child_class,
                                            BdrvChildRole child_role,
                                            Error **errp);
 
 static bool bdrv_recurse_has_child(BlockDriverState *bs,
                                    BlockDriverState *child);
 
 static void bdrv_replace_child_noperm(BdrvChild *child,
                                       BlockDriverState *new_bs);
 static void bdrv_remove_child(BdrvChild *child, Transaction *tran);
 static void bdrv_remove_filter_or_cow_child(BlockDriverState *bs,
                                             Transaction *tran);
 
 static int bdrv_reopen_prepare(BDRVReopenState *reopen_state,
                                BlockReopenQueue *queue,
                                Transaction *change_child_tran, Error **errp);
 static void bdrv_reopen_commit(BDRVReopenState *reopen_state);
 static void bdrv_reopen_abort(BDRVReopenState *reopen_state);
 
 static bool bdrv_backing_overridden(BlockDriverState *bs);
 
 static bool bdrv_change_aio_context(BlockDriverState *bs, AioContext *ctx,
                                     GHashTable *visited, Transaction *tran,
                                     Error **errp);
 
 /* If non-zero, use only whitelisted block drivers */
 static int use_bdrv_whitelist;
 
 #ifdef _WIN32
 static int is_windows_drive_prefix(const char *filename)
 {
     return (((filename[0] >= 'a' && filename[0] <= 'z') ||
              (filename[0] >= 'A' && filename[0] <= 'Z')) &&
             filename[1] == ':');
 }
 
 int is_windows_drive(const char *filename)
 {
     if (is_windows_drive_prefix(filename) &&
         filename[2] == '\0')
         return 1;
     if (strstart(filename, "\\\\.\\", NULL) ||
         strstart(filename, "//./", NULL))
         return 1;
     return 0;
 }
 #endif
 
 size_t bdrv_opt_mem_align(BlockDriverState *bs)
 {
     if (!bs || !bs->drv) {
         /* page size or 4k (hdd sector size) should be on the safe side */
         return MAX(4096, qemu_real_host_page_size());
     }
     IO_CODE();
 
     return bs->bl.opt_mem_alignment;
 }
 
 size_t bdrv_min_mem_align(BlockDriverState *bs)
 {
     if (!bs || !bs->drv) {
         /* page size or 4k (hdd sector size) should be on the safe side */
         return MAX(4096, qemu_real_host_page_size());
     }
     IO_CODE();
 
     return bs->bl.min_mem_alignment;
 }
 
 /* check if the path starts with "<protocol>:" */
 int path_has_protocol(const char *path)
 {
     const char *p;
 
 #ifdef _WIN32
     if (is_windows_drive(path) ||
         is_windows_drive_prefix(path)) {
         return 0;
     }
     p = path + strcspn(path, ":/\\");
 #else
     p = path + strcspn(path, ":/");
 #endif
 
     return *p == ':';
 }
 
 int path_is_absolute(const char *path)
 {
 #ifdef _WIN32
     /* specific case for names like: "\\.\d:" */
     if (is_windows_drive(path) || is_windows_drive_prefix(path)) {
         return 1;
     }
     return (*path == '/' || *path == '\\');
 #else
     return (*path == '/');
 #endif
 }
 
 /* if filename is absolute, just return its duplicate. Otherwise, build a
    path to it by considering it is relative to base_path. URL are
    supported. */
 char *path_combine(const char *base_path, const char *filename)
 {
     const char *protocol_stripped = NULL;
     const char *p, *p1;
     char *result;
     int len;
 
     if (path_is_absolute(filename)) {
         return g_strdup(filename);
     }
 
     if (path_has_protocol(base_path)) {
         protocol_stripped = strchr(base_path, ':');
         if (protocol_stripped) {
             protocol_stripped++;
         }
     }
     p = protocol_stripped ?: base_path;
 
     p1 = strrchr(base_path, '/');
 #ifdef _WIN32
     {
         const char *p2;
         p2 = strrchr(base_path, '\\');
         if (!p1 || p2 > p1) {
             p1 = p2;
         }
     }
 #endif
     if (p1) {
         p1++;
     } else {
         p1 = base_path;
     }
     if (p1 > p) {
         p = p1;
     }
     len = p - base_path;
 
     result = g_malloc(len + strlen(filename) + 1);
     memcpy(result, base_path, len);
     strcpy(result + len, filename);
 
     return result;
 }
 
 /*
  * Helper function for bdrv_parse_filename() implementations to remove optional
  * protocol prefixes (especially "file:") from a filename and for putting the
  * stripped filename into the options QDict if there is such a prefix.
  */
 void bdrv_parse_filename_strip_prefix(const char *filename, const char *prefix,
                                       QDict *options)
 {
     if (strstart(filename, prefix, &filename)) {
         /* Stripping the explicit protocol prefix may result in a protocol
          * prefix being (wrongly) detected (if the filename contains a colon) */
         if (path_has_protocol(filename)) {
             GString *fat_filename;
 
             /* This means there is some colon before the first slash; therefore,
              * this cannot be an absolute path */
             assert(!path_is_absolute(filename));
 
             /* And we can thus fix the protocol detection issue by prefixing it
              * by "./" */
             fat_filename = g_string_new("./");
             g_string_append(fat_filename, filename);
 
             assert(!path_has_protocol(fat_filename->str));
 
             qdict_put(options, "filename",
                       qstring_from_gstring(fat_filename));
         } else {
             /* If no protocol prefix was detected, we can use the shortened
              * filename as-is */
             qdict_put_str(options, "filename", filename);
         }
     }
 }
 
 
 /* Returns whether the image file is opened as read-only. Note that this can
  * return false and writing to the image file is still not possible because the
  * image is inactivated. */
 bool bdrv_is_read_only(BlockDriverState *bs)
 {
     IO_CODE();
     return !(bs->open_flags & BDRV_O_RDWR);
 }
 
 int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only,
                            bool ignore_allow_rdw, Error **errp)
 {
     IO_CODE();
 
     /* Do not set read_only if copy_on_read is enabled */
     if (bs->copy_on_read && read_only) {
         error_setg(errp, "Can't set node '%s' to r/o with copy-on-read enabled",
                    bdrv_get_device_or_node_name(bs));
         return -EINVAL;
     }
 
     /* Do not clear read_only if it is prohibited */
     if (!read_only && !(bs->open_flags & BDRV_O_ALLOW_RDWR) &&
         !ignore_allow_rdw)
     {
         error_setg(errp, "Node '%s' is read only",
                    bdrv_get_device_or_node_name(bs));
         return -EPERM;
     }
 
     return 0;
 }
 
 /*
  * Called by a driver that can only provide a read-only image.
  *
  * Returns 0 if the node is already read-only or it could switch the node to
  * read-only because BDRV_O_AUTO_RDONLY is set.
  *
  * Returns -EACCES if the node is read-write and BDRV_O_AUTO_RDONLY is not set
  * or bdrv_can_set_read_only() forbids making the node read-only. If @errmsg
  * is not NULL, it is used as the error message for the Error object.
  */
 int bdrv_apply_auto_read_only(BlockDriverState *bs, const char *errmsg,
                               Error **errp)
 {
     int ret = 0;
     IO_CODE();
 
     if (!(bs->open_flags & BDRV_O_RDWR)) {
         return 0;
     }
     if (!(bs->open_flags & BDRV_O_AUTO_RDONLY)) {
         goto fail;
     }
 
     ret = bdrv_can_set_read_only(bs, true, false, NULL);
     if (ret < 0) {
         goto fail;
     }
 
     bs->open_flags &= ~BDRV_O_RDWR;
 
     return 0;
 
 fail:
     error_setg(errp, "%s", errmsg ?: "Image is read-only");
     return -EACCES;
 }
 
 /*
  * If @backing is empty, this function returns NULL without setting
  * @errp.  In all other cases, NULL will only be returned with @errp
  * set.
  *
  * Therefore, a return value of NULL without @errp set means that
  * there is no backing file; if @errp is set, there is one but its
  * absolute filename cannot be generated.
  */
 char *bdrv_get_full_backing_filename_from_filename(const char *backed,
                                                    const char *backing,
                                                    Error **errp)
 {
     if (backing[0] == '\0') {
         return NULL;
     } else if (path_has_protocol(backing) || path_is_absolute(backing)) {
         return g_strdup(backing);
     } else if (backed[0] == '\0' || strstart(backed, "json:", NULL)) {
         error_setg(errp, "Cannot use relative backing file names for '%s'",
                    backed);
         return NULL;
     } else {
         return path_combine(backed, backing);
     }
 }
 
 /*
  * If @filename is empty or NULL, this function returns NULL without
  * setting @errp.  In all other cases, NULL will only be returned with
  * @errp set.
  */
 static char *bdrv_make_absolute_filename(BlockDriverState *relative_to,
                                          const char *filename, Error **errp)
 {
     char *dir, *full_name;
 
     if (!filename || filename[0] == '\0') {
         return NULL;
     } else if (path_has_protocol(filename) || path_is_absolute(filename)) {
         return g_strdup(filename);
     }
 
     dir = bdrv_dirname(relative_to, errp);
     if (!dir) {
         return NULL;
     }
 
     full_name = g_strconcat(dir, filename, NULL);
     g_free(dir);
     return full_name;
 }
 
 char *bdrv_get_full_backing_filename(BlockDriverState *bs, Error **errp)
 {
     GLOBAL_STATE_CODE();
     return bdrv_make_absolute_filename(bs, bs->backing_file, errp);
 }
 
 void bdrv_register(BlockDriver *bdrv)
 {
     assert(bdrv->format_name);
     GLOBAL_STATE_CODE();
     QLIST_INSERT_HEAD(&bdrv_drivers, bdrv, list);
 }
 
 BlockDriverState *bdrv_new(void)
 {
     BlockDriverState *bs;
     int i;
 
     GLOBAL_STATE_CODE();
 
     bs = g_new0(BlockDriverState, 1);
     QLIST_INIT(&bs->dirty_bitmaps);
     for (i = 0; i < BLOCK_OP_TYPE_MAX; i++) {
         QLIST_INIT(&bs->op_blockers[i]);
     }
     qemu_co_mutex_init(&bs->reqs_lock);
     qemu_mutex_init(&bs->dirty_bitmap_mutex);
     bs->refcnt = 1;
     bs->aio_context = qemu_get_aio_context();
 
     qemu_co_queue_init(&bs->flush_queue);
 
     qemu_co_mutex_init(&bs->bsc_modify_lock);
     bs->block_status_cache = g_new0(BdrvBlockStatusCache, 1);
 
     for (i = 0; i < bdrv_drain_all_count; i++) {
         bdrv_drained_begin(bs);
     }
 
     QTAILQ_INSERT_TAIL(&all_bdrv_states, bs, bs_list);
 
     return bs;
 }
 
 static BlockDriver *bdrv_do_find_format(const char *format_name)
 {
     BlockDriver *drv1;
     GLOBAL_STATE_CODE();
 
     QLIST_FOREACH(drv1, &bdrv_drivers, list) {
         if (!strcmp(drv1->format_name, format_name)) {
             return drv1;
         }
     }
 
     return NULL;
 }
 
 BlockDriver *bdrv_find_format(const char *format_name)
 {
     BlockDriver *drv1;
     int i;
 
     GLOBAL_STATE_CODE();
 
     drv1 = bdrv_do_find_format(format_name);
     if (drv1) {
         return drv1;
     }
 
     /* The driver isn't registered, maybe we need to load a module */
     for (i = 0; i < (int)ARRAY_SIZE(block_driver_modules); ++i) {
         if (!strcmp(block_driver_modules[i].format_name, format_name)) {
             Error *local_err = NULL;
             int rv = block_module_load(block_driver_modules[i].library_name,
                                        &local_err);
             if (rv > 0) {
                 return bdrv_do_find_format(format_name);
             } else if (rv < 0) {
                 error_report_err(local_err);
             }
             break;
         }
     }
     return NULL;
 }
 
 static int bdrv_format_is_whitelisted(const char *format_name, bool read_only)
 {
     static const char *whitelist_rw[] = {
         CONFIG_BDRV_RW_WHITELIST
         NULL
     };
     static const char *whitelist_ro[] = {
         CONFIG_BDRV_RO_WHITELIST
         NULL
     };
     const char **p;
 
     if (!whitelist_rw[0] && !whitelist_ro[0]) {
         return 1;               /* no whitelist, anything goes */
     }
 
     for (p = whitelist_rw; *p; p++) {
         if (!strcmp(format_name, *p)) {
             return 1;
         }
     }
     if (read_only) {
         for (p = whitelist_ro; *p; p++) {
             if (!strcmp(format_name, *p)) {
                 return 1;
             }
         }
     }
     return 0;
 }
 
 int bdrv_is_whitelisted(BlockDriver *drv, bool read_only)
 {
     GLOBAL_STATE_CODE();
     return bdrv_format_is_whitelisted(drv->format_name, read_only);
 }
 
 bool bdrv_uses_whitelist(void)
 {
     return use_bdrv_whitelist;
 }
 
 typedef struct CreateCo {
     BlockDriver *drv;
     char *filename;
     QemuOpts *opts;
     int ret;
     Error *err;
 } CreateCo;
 
 static void coroutine_fn bdrv_create_co_entry(void *opaque)
 {
     Error *local_err = NULL;
     int ret;
 
     CreateCo *cco = opaque;
     assert(cco->drv);
     GLOBAL_STATE_CODE();
 
     ret = cco->drv->bdrv_co_create_opts(cco->drv,
                                         cco->filename, cco->opts, &local_err);
     error_propagate(&cco->err, local_err);
     cco->ret = ret;
 }
 
 int bdrv_create(BlockDriver *drv, const char* filename,
                 QemuOpts *opts, Error **errp)
 {
     int ret;
 
     GLOBAL_STATE_CODE();
 
     Coroutine *co;
     CreateCo cco = {
         .drv = drv,
         .filename = g_strdup(filename),
         .opts = opts,
         .ret = NOT_DONE,
         .err = NULL,
     };
 
     if (!drv->bdrv_co_create_opts) {
         error_setg(errp, "Driver '%s' does not support image creation", drv->format_name);
         ret = -ENOTSUP;
         goto out;
     }
 
     if (qemu_in_coroutine()) {
         /* Fast-path if already in coroutine context */
         bdrv_create_co_entry(&cco);
     } else {
         co = qemu_coroutine_create(bdrv_create_co_entry, &cco);
         qemu_coroutine_enter(co);
         while (cco.ret == NOT_DONE) {
             aio_poll(qemu_get_aio_context(), true);
         }
     }
 
     ret = cco.ret;
     if (ret < 0) {
         if (cco.err) {
             error_propagate(errp, cco.err);
         } else {
             error_setg_errno(errp, -ret, "Could not create image");
         }
     }
 
 out:
     g_free(cco.filename);
     return ret;
 }
 
 /**
  * Helper function for bdrv_create_file_fallback(): Resize @blk to at
  * least the given @minimum_size.
  *
  * On success, return @blk's actual length.
  * Otherwise, return -errno.
  */
 static int64_t create_file_fallback_truncate(BlockBackend *blk,
                                              int64_t minimum_size, Error **errp)
 {
     Error *local_err = NULL;
     int64_t size;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     ret = blk_truncate(blk, minimum_size, false, PREALLOC_MODE_OFF, 0,
                        &local_err);
     if (ret < 0 && ret != -ENOTSUP) {
         error_propagate(errp, local_err);
         return ret;
     }
 
     size = blk_getlength(blk);
     if (size < 0) {
         error_free(local_err);
         error_setg_errno(errp, -size,
                          "Failed to inquire the new image file's length");
         return size;
     }
 
     if (size < minimum_size) {
         /* Need to grow the image, but we failed to do that */
         error_propagate(errp, local_err);
         return -ENOTSUP;
     }
 
     error_free(local_err);
     local_err = NULL;
 
     return size;
 }
 
 /**
  * Helper function for bdrv_create_file_fallback(): Zero the first
  * sector to remove any potentially pre-existing image header.
  */
 static int coroutine_fn
 create_file_fallback_zero_first_sector(BlockBackend *blk,
                                        int64_t current_size,
                                        Error **errp)
 {
     int64_t bytes_to_clear;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     bytes_to_clear = MIN(current_size, BDRV_SECTOR_SIZE);
     if (bytes_to_clear) {
         ret = blk_co_pwrite_zeroes(blk, 0, bytes_to_clear, BDRV_REQ_MAY_UNMAP);
         if (ret < 0) {
             error_setg_errno(errp, -ret,
                              "Failed to clear the new image's first sector");
             return ret;
         }
     }
 
     return 0;
 }
 
 /**
  * Simple implementation of bdrv_co_create_opts for protocol drivers
  * which only support creation via opening a file
  * (usually existing raw storage device)
  */
 int coroutine_fn bdrv_co_create_opts_simple(BlockDriver *drv,
                                             const char *filename,
                                             QemuOpts *opts,
                                             Error **errp)
 {
     BlockBackend *blk;
     QDict *options;
     int64_t size = 0;
     char *buf = NULL;
     PreallocMode prealloc;
     Error *local_err = NULL;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     size = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
     buf = qemu_opt_get_del(opts, BLOCK_OPT_PREALLOC);
     prealloc = qapi_enum_parse(&PreallocMode_lookup, buf,
                                PREALLOC_MODE_OFF, &local_err);
     g_free(buf);
     if (local_err) {
         error_propagate(errp, local_err);
         return -EINVAL;
     }
 
     if (prealloc != PREALLOC_MODE_OFF) {
         error_setg(errp, "Unsupported preallocation mode '%s'",
                    PreallocMode_str(prealloc));
         return -ENOTSUP;
     }
 
     options = qdict_new();
     qdict_put_str(options, "driver", drv->format_name);
 
     blk = blk_new_open(filename, NULL, options,
                        BDRV_O_RDWR | BDRV_O_RESIZE, errp);
     if (!blk) {
         error_prepend(errp, "Protocol driver '%s' does not support image "
                       "creation, and opening the image failed: ",
                       drv->format_name);
         return -EINVAL;
     }
 
     size = create_file_fallback_truncate(blk, size, errp);
     if (size < 0) {
         ret = size;
         goto out;
     }
 
     ret = create_file_fallback_zero_first_sector(blk, size, errp);
     if (ret < 0) {
         goto out;
     }
 
     ret = 0;
 out:
     blk_unref(blk);
     return ret;
 }
 
 int bdrv_create_file(const char *filename, QemuOpts *opts, Error **errp)
 {
     QemuOpts *protocol_opts;
     BlockDriver *drv;
     QDict *qdict;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     drv = bdrv_find_protocol(filename, true, errp);
     if (drv == NULL) {
         return -ENOENT;
     }
 
     if (!drv->create_opts) {
         error_setg(errp, "Driver '%s' does not support image creation",
                    drv->format_name);
         return -ENOTSUP;
     }
 
     /*
      * 'opts' contains a QemuOptsList with a combination of format and protocol
      * default values.
      *
      * The format properly removes its options, but the default values remain
      * in 'opts->list'.  So if the protocol has options with the same name
      * (e.g. rbd has 'cluster_size' as qcow2), it will see the default values
      * of the format, since for overlapping options, the format wins.
      *
      * To avoid this issue, lets convert QemuOpts to QDict, in this way we take
      * only the set options, and then convert it back to QemuOpts, using the
      * create_opts of the protocol. So the new QemuOpts, will contain only the
      * protocol defaults.
      */
     qdict = qemu_opts_to_qdict(opts, NULL);
     protocol_opts = qemu_opts_from_qdict(drv->create_opts, qdict, errp);
     if (protocol_opts == NULL) {
         ret = -EINVAL;
         goto out;
     }
 
     ret = bdrv_create(drv, filename, protocol_opts, errp);
 out:
     qemu_opts_del(protocol_opts);
     qobject_unref(qdict);
     return ret;
 }
 
 int coroutine_fn bdrv_co_delete_file(BlockDriverState *bs, Error **errp)
 {
     Error *local_err = NULL;
     int ret;
 
     IO_CODE();
     assert(bs != NULL);
 
     if (!bs->drv) {
         error_setg(errp, "Block node '%s' is not opened", bs->filename);
         return -ENOMEDIUM;
     }
 
     if (!bs->drv->bdrv_co_delete_file) {
         error_setg(errp, "Driver '%s' does not support image deletion",
                    bs->drv->format_name);
         return -ENOTSUP;
     }
 
     ret = bs->drv->bdrv_co_delete_file(bs, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
     }
 
     return ret;
 }
 
 void coroutine_fn bdrv_co_delete_file_noerr(BlockDriverState *bs)
 {
     Error *local_err = NULL;
     int ret;
     IO_CODE();
 
     if (!bs) {
         return;
     }
 
     ret = bdrv_co_delete_file(bs, &local_err);
     /*
      * ENOTSUP will happen if the block driver doesn't support
      * the 'bdrv_co_delete_file' interface. This is a predictable
      * scenario and shouldn't be reported back to the user.
      */
     if (ret == -ENOTSUP) {
         error_free(local_err);
     } else if (ret < 0) {
         error_report_err(local_err);
     }
 }
 
 /**
  * Try to get @bs's logical and physical block size.
  * On success, store them in @bsz struct and return 0.
  * On failure return -errno.
  * @bs must not be empty.
  */
 int bdrv_probe_blocksizes(BlockDriverState *bs, BlockSizes *bsz)
 {
     BlockDriver *drv = bs->drv;
     BlockDriverState *filtered = bdrv_filter_bs(bs);
     GLOBAL_STATE_CODE();
 
     if (drv && drv->bdrv_probe_blocksizes) {
         return drv->bdrv_probe_blocksizes(bs, bsz);
     } else if (filtered) {
         return bdrv_probe_blocksizes(filtered, bsz);
     }
 
     return -ENOTSUP;
 }
 
 /**
  * Try to get @bs's geometry (cyls, heads, sectors).
  * On success, store them in @geo struct and return 0.
  * On failure return -errno.
  * @bs must not be empty.
  */
 int bdrv_probe_geometry(BlockDriverState *bs, HDGeometry *geo)
 {
     BlockDriver *drv = bs->drv;
     BlockDriverState *filtered = bdrv_filter_bs(bs);
     GLOBAL_STATE_CODE();
 
     if (drv && drv->bdrv_probe_geometry) {
         return drv->bdrv_probe_geometry(bs, geo);
     } else if (filtered) {
         return bdrv_probe_geometry(filtered, geo);
     }
 
     return -ENOTSUP;
 }
 
 /*
  * Create a uniquely-named empty temporary file.
  * Return the actual file name used upon success, otherwise NULL.
  * This string should be freed with g_free() when not needed any longer.
  *
  * Note: creating a temporary file for the caller to (re)open is
  * inherently racy. Use g_file_open_tmp() instead whenever practical.
  */
 char *create_tmp_file(Error **errp)
 {
     int fd;
     const char *tmpdir;
     g_autofree char *filename = NULL;
 
     tmpdir = g_get_tmp_dir();
 #ifndef _WIN32
     /*
      * See commit 69bef79 ("block: use /var/tmp instead of /tmp for -snapshot")
      *
      * This function is used to create temporary disk images (like -snapshot),
      * so the files can become very large. /tmp is often a tmpfs where as
      * /var/tmp is usually on a disk, so more appropriate for disk images.
      */
     if (!g_strcmp0(tmpdir, "/tmp")) {
         tmpdir = "/var/tmp";
     }
 #endif
 
     filename = g_strdup_printf("%s/vl.XXXXXX", tmpdir);
     fd = g_mkstemp(filename);
     if (fd < 0) {
         error_setg_errno(errp, errno, "Could not open temporary file '%s'",
                          filename);
         return NULL;
     }
     close(fd);
 
     return g_steal_pointer(&filename);
 }
 
 /*
  * Detect host devices. By convention, /dev/cdrom[N] is always
  * recognized as a host CDROM.
  */
 static BlockDriver *find_hdev_driver(const char *filename)
 {
     int score_max = 0, score;
     BlockDriver *drv = NULL, *d;
     GLOBAL_STATE_CODE();
 
     QLIST_FOREACH(d, &bdrv_drivers, list) {
         if (d->bdrv_probe_device) {
             score = d->bdrv_probe_device(filename);
             if (score > score_max) {
                 score_max = score;
                 drv = d;
             }
         }
     }
 
     return drv;
 }
 
 static BlockDriver *bdrv_do_find_protocol(const char *protocol)
 {
     BlockDriver *drv1;
     GLOBAL_STATE_CODE();
 
     QLIST_FOREACH(drv1, &bdrv_drivers, list) {
         if (drv1->protocol_name && !strcmp(drv1->protocol_name, protocol)) {
             return drv1;
         }
     }
 
     return NULL;
 }
 
 BlockDriver *bdrv_find_protocol(const char *filename,
                                 bool allow_protocol_prefix,
                                 Error **errp)
 {
     BlockDriver *drv1;
     char protocol[128];
     int len;
     const char *p;
     int i;
 
     GLOBAL_STATE_CODE();
     /* TODO Drivers without bdrv_file_open must be specified explicitly */
 
     /*
      * XXX(hch): we really should not let host device detection
      * override an explicit protocol specification, but moving this
      * later breaks access to device names with colons in them.
      * Thanks to the brain-dead persistent naming schemes on udev-
      * based Linux systems those actually are quite common.
      */
     drv1 = find_hdev_driver(filename);
     if (drv1) {
         return drv1;
     }
 
     if (!path_has_protocol(filename) || !allow_protocol_prefix) {
         return &bdrv_file;
     }
 
     p = strchr(filename, ':');
     assert(p != NULL);
     len = p - filename;
     if (len > sizeof(protocol) - 1)
         len = sizeof(protocol) - 1;
     memcpy(protocol, filename, len);
     protocol[len] = '\0';
 
     drv1 = bdrv_do_find_protocol(protocol);
     if (drv1) {
         return drv1;
     }
 
     for (i = 0; i < (int)ARRAY_SIZE(block_driver_modules); ++i) {
         if (block_driver_modules[i].protocol_name &&
             !strcmp(block_driver_modules[i].protocol_name, protocol)) {
             int rv = block_module_load(block_driver_modules[i].library_name, errp);
             if (rv > 0) {
                 drv1 = bdrv_do_find_protocol(protocol);
             } else if (rv < 0) {
                 return NULL;
             }
             break;
         }
     }
 
     if (!drv1) {
         error_setg(errp, "Unknown protocol '%s'", protocol);
     }
     return drv1;
 }
 
 /*
  * Guess image format by probing its contents.
  * This is not a good idea when your image is raw (CVE-2008-2004), but
  * we do it anyway for backward compatibility.
  *
  * @buf         contains the image's first @buf_size bytes.
  * @buf_size    is the buffer size in bytes (generally BLOCK_PROBE_BUF_SIZE,
  *              but can be smaller if the image file is smaller)
  * @filename    is its filename.
  *
  * For all block drivers, call the bdrv_probe() method to get its
  * probing score.
  * Return the first block driver with the highest probing score.
  */
 BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
                             const char *filename)
 {
     int score_max = 0, score;
     BlockDriver *drv = NULL, *d;
     IO_CODE();
 
     QLIST_FOREACH(d, &bdrv_drivers, list) {
         if (d->bdrv_probe) {
             score = d->bdrv_probe(buf, buf_size, filename);
             if (score > score_max) {
                 score_max = score;
                 drv = d;
             }
         }
     }
 
     return drv;
 }
 
 static int find_image_format(BlockBackend *file, const char *filename,
                              BlockDriver **pdrv, Error **errp)
 {
     BlockDriver *drv;
     uint8_t buf[BLOCK_PROBE_BUF_SIZE];
     int ret = 0;
 
     GLOBAL_STATE_CODE();
 
     /* Return the raw BlockDriver * to scsi-generic devices or empty drives */
     if (blk_is_sg(file) || !blk_is_inserted(file) || blk_getlength(file) == 0) {
         *pdrv = &bdrv_raw;
         return ret;
     }
 
     ret = blk_pread(file, 0, sizeof(buf), buf, 0);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not read image for determining its "
                          "format");
         *pdrv = NULL;
         return ret;
     }
 
     drv = bdrv_probe_all(buf, sizeof(buf), filename);
     if (!drv) {
         error_setg(errp, "Could not determine image format: No compatible "
                    "driver found");
         *pdrv = NULL;
         return -ENOENT;
     }
 
     *pdrv = drv;
     return 0;
 }
 
 /**
  * Set the current 'total_sectors' value
  * Return 0 on success, -errno on error.
  */
 int refresh_total_sectors(BlockDriverState *bs, int64_t hint)
 {
     BlockDriver *drv = bs->drv;
     IO_CODE();
 
     if (!drv) {
         return -ENOMEDIUM;
     }
 
     /* Do not attempt drv->bdrv_getlength() on scsi-generic devices */
     if (bdrv_is_sg(bs))
         return 0;
 
     /* query actual device if possible, otherwise just trust the hint */
     if (drv->bdrv_getlength) {
         int64_t length = drv->bdrv_getlength(bs);
         if (length < 0) {
             return length;
         }
         hint = DIV_ROUND_UP(length, BDRV_SECTOR_SIZE);
     }
 
     bs->total_sectors = hint;
 
     if (bs->total_sectors * BDRV_SECTOR_SIZE > BDRV_MAX_LENGTH) {
         return -EFBIG;
     }
 
     return 0;
 }
 
 /**
  * Combines a QDict of new block driver @options with any missing options taken
  * from @old_options, so that leaving out an option defaults to its old value.
  */
 static void bdrv_join_options(BlockDriverState *bs, QDict *options,
                               QDict *old_options)
 {
     GLOBAL_STATE_CODE();
     if (bs->drv && bs->drv->bdrv_join_options) {
         bs->drv->bdrv_join_options(options, old_options);
     } else {
         qdict_join(options, old_options, false);
     }
 }
 
 static BlockdevDetectZeroesOptions bdrv_parse_detect_zeroes(QemuOpts *opts,
                                                             int open_flags,
                                                             Error **errp)
 {
     Error *local_err = NULL;
     char *value = qemu_opt_get_del(opts, "detect-zeroes");
     BlockdevDetectZeroesOptions detect_zeroes =
         qapi_enum_parse(&BlockdevDetectZeroesOptions_lookup, value,
                         BLOCKDEV_DETECT_ZEROES_OPTIONS_OFF, &local_err);
     GLOBAL_STATE_CODE();
     g_free(value);
     if (local_err) {
         error_propagate(errp, local_err);
         return detect_zeroes;
     }
 
     if (detect_zeroes == BLOCKDEV_DETECT_ZEROES_OPTIONS_UNMAP &&
         !(open_flags & BDRV_O_UNMAP))
     {
         error_setg(errp, "setting detect-zeroes to unmap is not allowed "
                    "without setting discard operation to unmap");
     }
 
     return detect_zeroes;
 }
 
 /**
  * Set open flags for aio engine
  *
  * Return 0 on success, -1 if the engine specified is invalid
  */
 int bdrv_parse_aio(const char *mode, int *flags)
 {
     if (!strcmp(mode, "threads")) {
         /* do nothing, default */
     } else if (!strcmp(mode, "native")) {
         *flags |= BDRV_O_NATIVE_AIO;
 #ifdef CONFIG_LINUX_IO_URING
     } else if (!strcmp(mode, "io_uring")) {
         *flags |= BDRV_O_IO_URING;
 #endif
     } else {
         return -1;
     }
 
     return 0;
 }
 
 /**
  * Set open flags for a given discard mode
  *
  * Return 0 on success, -1 if the discard mode was invalid.
  */
 int bdrv_parse_discard_flags(const char *mode, int *flags)
 {
     *flags &= ~BDRV_O_UNMAP;
 
     if (!strcmp(mode, "off") || !strcmp(mode, "ignore")) {
         /* do nothing */
     } else if (!strcmp(mode, "on") || !strcmp(mode, "unmap")) {
         *flags |= BDRV_O_UNMAP;
     } else {
         return -1;
     }
 
     return 0;
 }
 
 /**
  * Set open flags for a given cache mode
  *
  * Return 0 on success, -1 if the cache mode was invalid.
  */
 int bdrv_parse_cache_mode(const char *mode, int *flags, bool *writethrough)
 {
     *flags &= ~BDRV_O_CACHE_MASK;
 
     if (!strcmp(mode, "off") || !strcmp(mode, "none")) {
         *writethrough = false;
         *flags |= BDRV_O_NOCACHE;
     } else if (!strcmp(mode, "directsync")) {
         *writethrough = true;
         *flags |= BDRV_O_NOCACHE;
     } else if (!strcmp(mode, "writeback")) {
         *writethrough = false;
     } else if (!strcmp(mode, "unsafe")) {
         *writethrough = false;
         *flags |= BDRV_O_NO_FLUSH;
     } else if (!strcmp(mode, "writethrough")) {
         *writethrough = true;
     } else {
         return -1;
     }
 
     return 0;
 }
 
 static char *bdrv_child_get_parent_desc(BdrvChild *c)
 {
     BlockDriverState *parent = c->opaque;
     return g_strdup_printf("node '%s'", bdrv_get_node_name(parent));
 }
 
 static void bdrv_child_cb_drained_begin(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
     bdrv_do_drained_begin_quiesce(bs, NULL, false);
 }
 
 static bool bdrv_child_cb_drained_poll(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
     return bdrv_drain_poll(bs, false, NULL, false);
 }
 
 static void bdrv_child_cb_drained_end(BdrvChild *child,
                                       int *drained_end_counter)
 {
     BlockDriverState *bs = child->opaque;
     bdrv_drained_end_no_poll(bs, drained_end_counter);
 }
 
 static int bdrv_child_cb_inactivate(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
     GLOBAL_STATE_CODE();
     assert(bs->open_flags & BDRV_O_INACTIVE);
     return 0;
 }
 
 static bool bdrv_child_cb_change_aio_ctx(BdrvChild *child, AioContext *ctx,
                                          GHashTable *visited, Transaction *tran,
                                          Error **errp)
 {
     BlockDriverState *bs = child->opaque;
     return bdrv_change_aio_context(bs, ctx, visited, tran, errp);
 }
 
 /*
  * Returns the options and flags that a temporary snapshot should get, based on
  * the originally requested flags (the originally requested image will have
  * flags like a backing file)
  */
 static void bdrv_temp_snapshot_options(int *child_flags, QDict *child_options,
                                        int parent_flags, QDict *parent_options)
 {
     GLOBAL_STATE_CODE();
     *child_flags = (parent_flags & ~BDRV_O_SNAPSHOT) | BDRV_O_TEMPORARY;
 
     /* For temporary files, unconditional cache=unsafe is fine */
     qdict_set_default_str(child_options, BDRV_OPT_CACHE_DIRECT, "off");
     qdict_set_default_str(child_options, BDRV_OPT_CACHE_NO_FLUSH, "on");
 
     /* Copy the read-only and discard options from the parent */
     qdict_copy_default(child_options, parent_options, BDRV_OPT_READ_ONLY);
     qdict_copy_default(child_options, parent_options, BDRV_OPT_DISCARD);
 
     /* aio=native doesn't work for cache.direct=off, so disable it for the
      * temporary snapshot */
     *child_flags &= ~BDRV_O_NATIVE_AIO;
 }
 
 static void bdrv_backing_attach(BdrvChild *c)
 {
     BlockDriverState *parent = c->opaque;
     BlockDriverState *backing_hd = c->bs;
 
     GLOBAL_STATE_CODE();
     assert(!parent->backing_blocker);
     error_setg(&parent->backing_blocker,
                "node is used as backing hd of '%s'",
                bdrv_get_device_or_node_name(parent));
 
     bdrv_refresh_filename(backing_hd);
 
     parent->open_flags &= ~BDRV_O_NO_BACKING;
 
     bdrv_op_block_all(backing_hd, parent->backing_blocker);
     /* Otherwise we won't be able to commit or stream */
     bdrv_op_unblock(backing_hd, BLOCK_OP_TYPE_COMMIT_TARGET,
                     parent->backing_blocker);
     bdrv_op_unblock(backing_hd, BLOCK_OP_TYPE_STREAM,
                     parent->backing_blocker);
     /*
      * We do backup in 3 ways:
      * 1. drive backup
      *    The target bs is new opened, and the source is top BDS
      * 2. blockdev backup
      *    Both the source and the target are top BDSes.
      * 3. internal backup(used for block replication)
      *    Both the source and the target are backing file
      *
      * In case 1 and 2, neither the source nor the target is the backing file.
      * In case 3, we will block the top BDS, so there is only one block job
      * for the top BDS and its backing chain.
      */
     bdrv_op_unblock(backing_hd, BLOCK_OP_TYPE_BACKUP_SOURCE,
                     parent->backing_blocker);
     bdrv_op_unblock(backing_hd, BLOCK_OP_TYPE_BACKUP_TARGET,
                     parent->backing_blocker);
 }
 
 static void bdrv_backing_detach(BdrvChild *c)
 {
     BlockDriverState *parent = c->opaque;
 
     GLOBAL_STATE_CODE();
     assert(parent->backing_blocker);
     bdrv_op_unblock_all(c->bs, parent->backing_blocker);
     error_free(parent->backing_blocker);
     parent->backing_blocker = NULL;
 }
 
 static int bdrv_backing_update_filename(BdrvChild *c, BlockDriverState *base,
                                         const char *filename, Error **errp)
 {
     BlockDriverState *parent = c->opaque;
     bool read_only = bdrv_is_read_only(parent);
     int ret;
     GLOBAL_STATE_CODE();
 
     if (read_only) {
         ret = bdrv_reopen_set_read_only(parent, false, errp);
         if (ret < 0) {
             return ret;
         }
     }
 
     ret = bdrv_change_backing_file(parent, filename,
                                    base->drv ? base->drv->format_name : "",
                                    false);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not update backing file link");
     }
 
     if (read_only) {
         bdrv_reopen_set_read_only(parent, true, NULL);
     }
 
     return ret;
 }
 
 /*
  * Returns the options and flags that a generic child of a BDS should
  * get, based on the given options and flags for the parent BDS.
  */
 static void bdrv_inherited_options(BdrvChildRole role, bool parent_is_format,
                                    int *child_flags, QDict *child_options,
                                    int parent_flags, QDict *parent_options)
 {
     int flags = parent_flags;
     GLOBAL_STATE_CODE();
 
     /*
      * First, decide whether to set, clear, or leave BDRV_O_PROTOCOL.
      * Generally, the question to answer is: Should this child be
      * format-probed by default?
      */
 
     /*
      * Pure and non-filtered data children of non-format nodes should
      * be probed by default (even when the node itself has BDRV_O_PROTOCOL
      * set).  This only affects a very limited set of drivers (namely
      * quorum and blkverify when this comment was written).
      * Force-clear BDRV_O_PROTOCOL then.
      */
     if (!parent_is_format &&
         (role & BDRV_CHILD_DATA) &&
         !(role & (BDRV_CHILD_METADATA | BDRV_CHILD_FILTERED)))
     {
         flags &= ~BDRV_O_PROTOCOL;
     }
 
     /*
      * All children of format nodes (except for COW children) and all
      * metadata children in general should never be format-probed.
      * Force-set BDRV_O_PROTOCOL then.
      */
     if ((parent_is_format && !(role & BDRV_CHILD_COW)) ||
         (role & BDRV_CHILD_METADATA))
     {
         flags |= BDRV_O_PROTOCOL;
     }
 
     /*
      * If the cache mode isn't explicitly set, inherit direct and no-flush from
      * the parent.
      */
     qdict_copy_default(child_options, parent_options, BDRV_OPT_CACHE_DIRECT);
     qdict_copy_default(child_options, parent_options, BDRV_OPT_CACHE_NO_FLUSH);
     qdict_copy_default(child_options, parent_options, BDRV_OPT_FORCE_SHARE);
 
     if (role & BDRV_CHILD_COW) {
         /* backing files are opened read-only by default */
         qdict_set_default_str(child_options, BDRV_OPT_READ_ONLY, "on");
         qdict_set_default_str(child_options, BDRV_OPT_AUTO_READ_ONLY, "off");
     } else {
         /* Inherit the read-only option from the parent if it's not set */
         qdict_copy_default(child_options, parent_options, BDRV_OPT_READ_ONLY);
         qdict_copy_default(child_options, parent_options,
                            BDRV_OPT_AUTO_READ_ONLY);
     }
 
     /*
      * bdrv_co_pdiscard() respects unmap policy for the parent, so we
      * can default to enable it on lower layers regardless of the
      * parent option.
      */
     qdict_set_default_str(child_options, BDRV_OPT_DISCARD, "unmap");
 
     /* Clear flags that only apply to the top layer */
     flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_COPY_ON_READ);
 
     if (role & BDRV_CHILD_METADATA) {
         flags &= ~BDRV_O_NO_IO;
     }
     if (role & BDRV_CHILD_COW) {
         flags &= ~BDRV_O_TEMPORARY;
     }
 
     *child_flags = flags;
 }
 
 static void bdrv_child_cb_attach(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
 
     assert_bdrv_graph_writable(bs);
     QLIST_INSERT_HEAD(&bs->children, child, next);
     if (bs->drv->is_filter || (child->role & BDRV_CHILD_FILTERED)) {
         /*
          * Here we handle filters and block/raw-format.c when it behave like
          * filter. They generally have a single PRIMARY child, which is also the
          * FILTERED child, and that they may have multiple more children, which
          * are neither PRIMARY nor FILTERED. And never we have a COW child here.
          * So bs->file will be the PRIMARY child, unless the PRIMARY child goes
          * into bs->backing on exceptional cases; and bs->backing will be
          * nothing else.
          */
         assert(!(child->role & BDRV_CHILD_COW));
         if (child->role & BDRV_CHILD_PRIMARY) {
             assert(child->role & BDRV_CHILD_FILTERED);
             assert(!bs->backing);
             assert(!bs->file);
 
             if (bs->drv->filtered_child_is_backing) {
                 bs->backing = child;
             } else {
                 bs->file = child;
             }
         } else {
             assert(!(child->role & BDRV_CHILD_FILTERED));
         }
     } else if (child->role & BDRV_CHILD_COW) {
         assert(bs->drv->supports_backing);
         assert(!(child->role & BDRV_CHILD_PRIMARY));
         assert(!bs->backing);
         bs->backing = child;
         bdrv_backing_attach(child);
     } else if (child->role & BDRV_CHILD_PRIMARY) {
         assert(!bs->file);
         bs->file = child;
     }
 
     bdrv_apply_subtree_drain(child, bs);
 }
 
 static void bdrv_child_cb_detach(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
 
     if (child->role & BDRV_CHILD_COW) {
         bdrv_backing_detach(child);
     }
 
     bdrv_unapply_subtree_drain(child, bs);
 
     assert_bdrv_graph_writable(bs);
     QLIST_REMOVE(child, next);
     if (child == bs->backing) {
         assert(child != bs->file);
         bs->backing = NULL;
     } else if (child == bs->file) {
         bs->file = NULL;
     }
 }
 
 static int bdrv_child_cb_update_filename(BdrvChild *c, BlockDriverState *base,
                                          const char *filename, Error **errp)
 {
     if (c->role & BDRV_CHILD_COW) {
         return bdrv_backing_update_filename(c, base, filename, errp);
     }
     return 0;
 }
 
 AioContext *child_of_bds_get_parent_aio_context(BdrvChild *c)
 {
     BlockDriverState *bs = c->opaque;
     IO_CODE();
 
     return bdrv_get_aio_context(bs);
 }
 
 const BdrvChildClass child_of_bds = {
     .parent_is_bds   = true,
     .get_parent_desc = bdrv_child_get_parent_desc,
     .inherit_options = bdrv_inherited_options,
     .drained_begin   = bdrv_child_cb_drained_begin,
     .drained_poll    = bdrv_child_cb_drained_poll,
     .drained_end     = bdrv_child_cb_drained_end,
     .attach          = bdrv_child_cb_attach,
     .detach          = bdrv_child_cb_detach,
     .inactivate      = bdrv_child_cb_inactivate,
     .change_aio_ctx  = bdrv_child_cb_change_aio_ctx,
     .update_filename = bdrv_child_cb_update_filename,
     .get_parent_aio_context = child_of_bds_get_parent_aio_context,
 };
 
 AioContext *bdrv_child_get_parent_aio_context(BdrvChild *c)
 {
     IO_CODE();
     return c->klass->get_parent_aio_context(c);
 }
 
 static int bdrv_open_flags(BlockDriverState *bs, int flags)
 {
     int open_flags = flags;
     GLOBAL_STATE_CODE();
 
     /*
      * Clear flags that are internal to the block layer before opening the
      * image.
      */
     open_flags &= ~(BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING | BDRV_O_PROTOCOL);
 
     return open_flags;
 }
 
 static void update_flags_from_options(int *flags, QemuOpts *opts)
 {
     GLOBAL_STATE_CODE();
 
     *flags &= ~(BDRV_O_CACHE_MASK | BDRV_O_RDWR | BDRV_O_AUTO_RDONLY);
 
     if (qemu_opt_get_bool_del(opts, BDRV_OPT_CACHE_NO_FLUSH, false)) {
         *flags |= BDRV_O_NO_FLUSH;
     }
 
     if (qemu_opt_get_bool_del(opts, BDRV_OPT_CACHE_DIRECT, false)) {
         *flags |= BDRV_O_NOCACHE;
     }
 
     if (!qemu_opt_get_bool_del(opts, BDRV_OPT_READ_ONLY, false)) {
         *flags |= BDRV_O_RDWR;
     }
 
     if (qemu_opt_get_bool_del(opts, BDRV_OPT_AUTO_READ_ONLY, false)) {
         *flags |= BDRV_O_AUTO_RDONLY;
     }
 }
 
 static void update_options_from_flags(QDict *options, int flags)
 {
     GLOBAL_STATE_CODE();
     if (!qdict_haskey(options, BDRV_OPT_CACHE_DIRECT)) {
         qdict_put_bool(options, BDRV_OPT_CACHE_DIRECT, flags & BDRV_O_NOCACHE);
     }
     if (!qdict_haskey(options, BDRV_OPT_CACHE_NO_FLUSH)) {
         qdict_put_bool(options, BDRV_OPT_CACHE_NO_FLUSH,
                        flags & BDRV_O_NO_FLUSH);
     }
     if (!qdict_haskey(options, BDRV_OPT_READ_ONLY)) {
         qdict_put_bool(options, BDRV_OPT_READ_ONLY, !(flags & BDRV_O_RDWR));
     }
     if (!qdict_haskey(options, BDRV_OPT_AUTO_READ_ONLY)) {
         qdict_put_bool(options, BDRV_OPT_AUTO_READ_ONLY,
                        flags & BDRV_O_AUTO_RDONLY);
     }
 }
 
 static void bdrv_assign_node_name(BlockDriverState *bs,
                                   const char *node_name,
                                   Error **errp)
 {
     char *gen_node_name = NULL;
     GLOBAL_STATE_CODE();
 
     if (!node_name) {
         node_name = gen_node_name = id_generate(ID_BLOCK);
     } else if (!id_wellformed(node_name)) {
         /*
          * Check for empty string or invalid characters, but not if it is
          * generated (generated names use characters not available to the user)
          */
         error_setg(errp, "Invalid node-name: '%s'", node_name);
         return;
     }
 
     /* takes care of avoiding namespaces collisions */
     if (blk_by_name(node_name)) {
         error_setg(errp, "node-name=%s is conflicting with a device id",
                    node_name);
         goto out;
     }
 
     /* takes care of avoiding duplicates node names */
     if (bdrv_find_node(node_name)) {
         error_setg(errp, "Duplicate nodes with node-name='%s'", node_name);
         goto out;
     }
 
     /* Make sure that the node name isn't truncated */
     if (strlen(node_name) >= sizeof(bs->node_name)) {
         error_setg(errp, "Node name too long");
         goto out;
     }
 
     /* copy node name into the bs and insert it into the graph list */
     pstrcpy(bs->node_name, sizeof(bs->node_name), node_name);
     QTAILQ_INSERT_TAIL(&graph_bdrv_states, bs, node_list);
 out:
     g_free(gen_node_name);
 }
 
 static int bdrv_open_driver(BlockDriverState *bs, BlockDriver *drv,
                             const char *node_name, QDict *options,
                             int open_flags, Error **errp)
 {
     Error *local_err = NULL;
     int i, ret;
     GLOBAL_STATE_CODE();
 
     bdrv_assign_node_name(bs, node_name, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         return -EINVAL;
     }
 
     bs->drv = drv;
     bs->opaque = g_malloc0(drv->instance_size);
 
     if (drv->bdrv_file_open) {
         assert(!drv->bdrv_needs_filename || bs->filename[0]);
         ret = drv->bdrv_file_open(bs, options, open_flags, &local_err);
     } else if (drv->bdrv_open) {
         ret = drv->bdrv_open(bs, options, open_flags, &local_err);
     } else {
         ret = 0;
     }
 
     if (ret < 0) {
         if (local_err) {
             error_propagate(errp, local_err);
         } else if (bs->filename[0]) {
             error_setg_errno(errp, -ret, "Could not open '%s'", bs->filename);
         } else {
             error_setg_errno(errp, -ret, "Could not open image");
         }
         goto open_failed;
     }
 
     assert(!(bs->supported_read_flags & ~BDRV_REQ_MASK));
     assert(!(bs->supported_write_flags & ~BDRV_REQ_MASK));
 
     /*
      * Always allow the BDRV_REQ_REGISTERED_BUF optimization hint. This saves
      * drivers that pass read/write requests through to a child the trouble of
      * declaring support explicitly.
      *
      * Drivers must not propagate this flag accidentally when they initiate I/O
      * to a bounce buffer. That case should be rare though.
      */
     bs->supported_read_flags |= BDRV_REQ_REGISTERED_BUF;
     bs->supported_write_flags |= BDRV_REQ_REGISTERED_BUF;
 
     ret = refresh_total_sectors(bs, bs->total_sectors);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not refresh total sector count");
         return ret;
     }
 
     bdrv_refresh_limits(bs, NULL, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         return -EINVAL;
     }
 
     assert(bdrv_opt_mem_align(bs) != 0);
     assert(bdrv_min_mem_align(bs) != 0);
     assert(is_power_of_2(bs->bl.request_alignment));
 
     for (i = 0; i < bs->quiesce_counter; i++) {
         if (drv->bdrv_co_drain_begin) {
             drv->bdrv_co_drain_begin(bs);
         }
     }
 
     return 0;
 open_failed:
     bs->drv = NULL;
     if (bs->file != NULL) {
         bdrv_unref_child(bs, bs->file);
         assert(!bs->file);
     }
     g_free(bs->opaque);
     bs->opaque = NULL;
     return ret;
 }
 
 /*
  * Create and open a block node.
  *
  * @options is a QDict of options to pass to the block drivers, or NULL for an
  * empty set of options. The reference to the QDict belongs to the block layer
  * after the call (even on failure), so if the caller intends to reuse the
  * dictionary, it needs to use qobject_ref() before calling bdrv_open.
  */
 BlockDriverState *bdrv_new_open_driver_opts(BlockDriver *drv,
                                             const char *node_name,
                                             QDict *options, int flags,
                                             Error **errp)
 {
     BlockDriverState *bs;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     bs = bdrv_new();
     bs->open_flags = flags;
     bs->options = options ?: qdict_new();
     bs->explicit_options = qdict_clone_shallow(bs->options);
     bs->opaque = NULL;
 
     update_options_from_flags(bs->options, flags);
 
     ret = bdrv_open_driver(bs, drv, node_name, bs->options, flags, errp);
     if (ret < 0) {
         qobject_unref(bs->explicit_options);
         bs->explicit_options = NULL;
         qobject_unref(bs->options);
         bs->options = NULL;
         bdrv_unref(bs);
         return NULL;
     }
 
     return bs;
 }
 
 /* Create and open a block node. */
 BlockDriverState *bdrv_new_open_driver(BlockDriver *drv, const char *node_name,
                                        int flags, Error **errp)
 {
     GLOBAL_STATE_CODE();
     return bdrv_new_open_driver_opts(drv, node_name, NULL, flags, errp);
 }
 
 QemuOptsList bdrv_runtime_opts = {
     .name = "bdrv_common",
     .head = QTAILQ_HEAD_INITIALIZER(bdrv_runtime_opts.head),
     .desc = {
         {
             .name = "node-name",
             .type = QEMU_OPT_STRING,
             .help = "Node name of the block device node",
         },
         {
             .name = "driver",
             .type = QEMU_OPT_STRING,
             .help = "Block driver to use for the node",
         },
         {
             .name = BDRV_OPT_CACHE_DIRECT,
             .type = QEMU_OPT_BOOL,
             .help = "Bypass software writeback cache on the host",
         },
         {
             .name = BDRV_OPT_CACHE_NO_FLUSH,
             .type = QEMU_OPT_BOOL,
             .help = "Ignore flush requests",
         },
         {
             .name = BDRV_OPT_READ_ONLY,
             .type = QEMU_OPT_BOOL,
             .help = "Node is opened in read-only mode",
         },
         {
             .name = BDRV_OPT_AUTO_READ_ONLY,
             .type = QEMU_OPT_BOOL,
             .help = "Node can become read-only if opening read-write fails",
         },
         {
             .name = "detect-zeroes",
             .type = QEMU_OPT_STRING,
             .help = "try to optimize zero writes (off, on, unmap)",
         },
         {
             .name = BDRV_OPT_DISCARD,
             .type = QEMU_OPT_STRING,
             .help = "discard operation (ignore/off, unmap/on)",
         },
         {
             .name = BDRV_OPT_FORCE_SHARE,
             .type = QEMU_OPT_BOOL,
             .help = "always accept other writers (default: off)",
         },
         { /* end of list */ }
     },
 };
 
 QemuOptsList bdrv_create_opts_simple = {
     .name = "simple-create-opts",
     .head = QTAILQ_HEAD_INITIALIZER(bdrv_create_opts_simple.head),
     .desc = {
         {
             .name = BLOCK_OPT_SIZE,
             .type = QEMU_OPT_SIZE,
             .help = "Virtual disk size"
         },
         {
             .name = BLOCK_OPT_PREALLOC,
             .type = QEMU_OPT_STRING,
             .help = "Preallocation mode (allowed values: off)"
         },
         { /* end of list */ }
     }
 };
 
 /*
  * Common part for opening disk images and files
  *
  * Removes all processed options from *options.
  */
 static int bdrv_open_common(BlockDriverState *bs, BlockBackend *file,
                             QDict *options, Error **errp)
 {
     int ret, open_flags;
     const char *filename;
     const char *driver_name = NULL;
     const char *node_name = NULL;
     const char *discard;
     QemuOpts *opts;
     BlockDriver *drv;
     Error *local_err = NULL;
     bool ro;
 
     assert(bs->file == NULL);
     assert(options != NULL && bs->options != options);
     GLOBAL_STATE_CODE();
 
     opts = qemu_opts_create(&bdrv_runtime_opts, NULL, 0, &error_abort);
     if (!qemu_opts_absorb_qdict(opts, options, errp)) {
         ret = -EINVAL;
         goto fail_opts;
     }
 
     update_flags_from_options(&bs->open_flags, opts);
 
     driver_name = qemu_opt_get(opts, "driver");
     drv = bdrv_find_format(driver_name);
     assert(drv != NULL);
 
     bs->force_share = qemu_opt_get_bool(opts, BDRV_OPT_FORCE_SHARE, false);
 
     if (bs->force_share && (bs->open_flags & BDRV_O_RDWR)) {
         error_setg(errp,
                    BDRV_OPT_FORCE_SHARE
                    "=on can only be used with read-only images");
         ret = -EINVAL;
         goto fail_opts;
     }
 
     if (file != NULL) {
         bdrv_refresh_filename(blk_bs(file));
         filename = blk_bs(file)->filename;
     } else {
         /*
          * Caution: while qdict_get_try_str() is fine, getting
          * non-string types would require more care.  When @options
          * come from -blockdev or blockdev_add, its members are typed
          * according to the QAPI schema, but when they come from
          * -drive, they're all QString.
          */
         filename = qdict_get_try_str(options, "filename");
     }
 
     if (drv->bdrv_needs_filename && (!filename || !filename[0])) {
         error_setg(errp, "The '%s' block driver requires a file name",
                    drv->format_name);
         ret = -EINVAL;
         goto fail_opts;
     }
 
     trace_bdrv_open_common(bs, filename ?: "", bs->open_flags,
                            drv->format_name);
 
     ro = bdrv_is_read_only(bs);
 
     if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv, ro)) {
         if (!ro && bdrv_is_whitelisted(drv, true)) {
             ret = bdrv_apply_auto_read_only(bs, NULL, NULL);
         } else {
             ret = -ENOTSUP;
         }
         if (ret < 0) {
             error_setg(errp,
                        !ro && bdrv_is_whitelisted(drv, true)
                        ? "Driver '%s' can only be used for read-only devices"
                        : "Driver '%s' is not whitelisted",
                        drv->format_name);
             goto fail_opts;
         }
     }
 
     /* bdrv_new() and bdrv_close() make it so */
     assert(qatomic_read(&bs->copy_on_read) == 0);
 
     if (bs->open_flags & BDRV_O_COPY_ON_READ) {
         if (!ro) {
             bdrv_enable_copy_on_read(bs);
         } else {
             error_setg(errp, "Can't use copy-on-read on read-only device");
             ret = -EINVAL;
             goto fail_opts;
         }
     }
 
     discard = qemu_opt_get(opts, BDRV_OPT_DISCARD);
     if (discard != NULL) {
         if (bdrv_parse_discard_flags(discard, &bs->open_flags) != 0) {
             error_setg(errp, "Invalid discard option");
             ret = -EINVAL;
             goto fail_opts;
         }
     }
 
     bs->detect_zeroes =
         bdrv_parse_detect_zeroes(opts, bs->open_flags, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         ret = -EINVAL;
         goto fail_opts;
     }
 
     if (filename != NULL) {
         pstrcpy(bs->filename, sizeof(bs->filename), filename);
     } else {
         bs->filename[0] = '\0';
     }
     pstrcpy(bs->exact_filename, sizeof(bs->exact_filename), bs->filename);
 
     /* Open the image, either directly or using a protocol */
     open_flags = bdrv_open_flags(bs, bs->open_flags);
     node_name = qemu_opt_get(opts, "node-name");
 
     assert(!drv->bdrv_file_open || file == NULL);
     ret = bdrv_open_driver(bs, drv, node_name, options, open_flags, errp);
     if (ret < 0) {
         goto fail_opts;
     }
 
     qemu_opts_del(opts);
     return 0;
 
 fail_opts:
     qemu_opts_del(opts);
     return ret;
 }
 
 static QDict *parse_json_filename(const char *filename, Error **errp)
 {
     QObject *options_obj;
     QDict *options;
     int ret;
     GLOBAL_STATE_CODE();
 
     ret = strstart(filename, "json:", &filename);
     assert(ret);
 
     options_obj = qobject_from_json(filename, errp);
     if (!options_obj) {
         error_prepend(errp, "Could not parse the JSON options: ");
         return NULL;
     }
 
     options = qobject_to(QDict, options_obj);
     if (!options) {
         qobject_unref(options_obj);
         error_setg(errp, "Invalid JSON object given");
         return NULL;
     }
 
     qdict_flatten(options);
 
     return options;
 }
 
 static void parse_json_protocol(QDict *options, const char **pfilename,
                                 Error **errp)
 {
     QDict *json_options;
     Error *local_err = NULL;
     GLOBAL_STATE_CODE();
 
     /* Parse json: pseudo-protocol */
     if (!*pfilename || !g_str_has_prefix(*pfilename, "json:")) {
         return;
     }
 
     json_options = parse_json_filename(*pfilename, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         return;
     }
 
     /* Options given in the filename have lower priority than options
      * specified directly */
     qdict_join(options, json_options, false);
     qobject_unref(json_options);
     *pfilename = NULL;
 }
 
 /*
  * Fills in default options for opening images and converts the legacy
  * filename/flags pair to option QDict entries.
  * The BDRV_O_PROTOCOL flag in *flags will be set or cleared accordingly if a
  * block driver has been specified explicitly.
  */
 static int bdrv_fill_options(QDict **options, const char *filename,
                              int *flags, Error **errp)
 {
     const char *drvname;
     bool protocol = *flags & BDRV_O_PROTOCOL;
     bool parse_filename = false;
     BlockDriver *drv = NULL;
     Error *local_err = NULL;
 
     GLOBAL_STATE_CODE();
 
     /*
      * Caution: while qdict_get_try_str() is fine, getting non-string
      * types would require more care.  When @options come from
      * -blockdev or blockdev_add, its members are typed according to
      * the QAPI schema, but when they come from -drive, they're all
      * QString.
      */
     drvname = qdict_get_try_str(*options, "driver");
     if (drvname) {
         drv = bdrv_find_format(drvname);
         if (!drv) {
             error_setg(errp, "Unknown driver '%s'", drvname);
             return -ENOENT;
         }
         /* If the user has explicitly specified the driver, this choice should
          * override the BDRV_O_PROTOCOL flag */
         protocol = drv->bdrv_file_open;
     }
 
     if (protocol) {
         *flags |= BDRV_O_PROTOCOL;
     } else {
         *flags &= ~BDRV_O_PROTOCOL;
     }
 
     /* Translate cache options from flags into options */
     update_options_from_flags(*options, *flags);
 
     /* Fetch the file name from the options QDict if necessary */
     if (protocol && filename) {
         if (!qdict_haskey(*options, "filename")) {
             qdict_put_str(*options, "filename", filename);
             parse_filename = true;
         } else {
             error_setg(errp, "Can't specify 'file' and 'filename' options at "
                              "the same time");
             return -EINVAL;
         }
     }
 
     /* Find the right block driver */
     /* See cautionary note on accessing @options above */
     filename = qdict_get_try_str(*options, "filename");
 
     if (!drvname && protocol) {
         if (filename) {
             drv = bdrv_find_protocol(filename, parse_filename, errp);
             if (!drv) {
                 return -EINVAL;
             }
 
             drvname = drv->format_name;
             qdict_put_str(*options, "driver", drvname);
         } else {
             error_setg(errp, "Must specify either driver or file");
             return -EINVAL;
         }
     }
 
     assert(drv || !protocol);
 
     /* Driver-specific filename parsing */
     if (drv && drv->bdrv_parse_filename && parse_filename) {
         drv->bdrv_parse_filename(filename, *options, &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
             return -EINVAL;
         }
 
         if (!drv->bdrv_needs_filename) {
             qdict_del(*options, "filename");
         }
     }
 
     return 0;
 }
 
 typedef struct BlockReopenQueueEntry {
      bool prepared;
      bool perms_checked;
      BDRVReopenState state;
      QTAILQ_ENTRY(BlockReopenQueueEntry) entry;
 } BlockReopenQueueEntry;
 
 /*
  * Return the flags that @bs will have after the reopens in @q have
  * successfully completed. If @q is NULL (or @bs is not contained in @q),
  * return the current flags.
  */
 static int bdrv_reopen_get_flags(BlockReopenQueue *q, BlockDriverState *bs)
 {
     BlockReopenQueueEntry *entry;
 
     if (q != NULL) {
         QTAILQ_FOREACH(entry, q, entry) {
             if (entry->state.bs == bs) {
                 return entry->state.flags;
             }
         }
     }
 
     return bs->open_flags;
 }
 
 /* Returns whether the image file can be written to after the reopen queue @q
  * has been successfully applied, or right now if @q is NULL. */
 static bool bdrv_is_writable_after_reopen(BlockDriverState *bs,
                                           BlockReopenQueue *q)
 {
     int flags = bdrv_reopen_get_flags(q, bs);
 
     return (flags & (BDRV_O_RDWR | BDRV_O_INACTIVE)) == BDRV_O_RDWR;
 }
 
 /*
  * Return whether the BDS can be written to.  This is not necessarily
  * the same as !bdrv_is_read_only(bs), as inactivated images may not
  * be written to but do not count as read-only images.
  */
 bool bdrv_is_writable(BlockDriverState *bs)
 {
     IO_CODE();
     return bdrv_is_writable_after_reopen(bs, NULL);
 }
 
 static char *bdrv_child_user_desc(BdrvChild *c)
 {
     GLOBAL_STATE_CODE();
     return c->klass->get_parent_desc(c);
 }
 
 /*
  * Check that @a allows everything that @b needs. @a and @b must reference same
  * child node.
  */
 static bool bdrv_a_allow_b(BdrvChild *a, BdrvChild *b, Error **errp)
 {
     const char *child_bs_name;
     g_autofree char *a_user = NULL;
     g_autofree char *b_user = NULL;
     g_autofree char *perms = NULL;
 
     assert(a->bs);
     assert(a->bs == b->bs);
     GLOBAL_STATE_CODE();
 
     if ((b->perm & a->shared_perm) == b->perm) {
         return true;
     }
 
     child_bs_name = bdrv_get_node_name(b->bs);
     a_user = bdrv_child_user_desc(a);
     b_user = bdrv_child_user_desc(b);
     perms = bdrv_perm_names(b->perm & ~a->shared_perm);
 
     error_setg(errp, "Permission conflict on node '%s': permissions '%s' are "
                "both required by %s (uses node '%s' as '%s' child) and "
                "unshared by %s (uses node '%s' as '%s' child).",
                child_bs_name, perms,
                b_user, child_bs_name, b->name,
                a_user, child_bs_name, a->name);
 
     return false;
 }
 
 static bool bdrv_parent_perms_conflict(BlockDriverState *bs, Error **errp)
 {
     BdrvChild *a, *b;
     GLOBAL_STATE_CODE();
 
     /*
      * During the loop we'll look at each pair twice. That's correct because
      * bdrv_a_allow_b() is asymmetric and we should check each pair in both
      * directions.
      */
     QLIST_FOREACH(a, &bs->parents, next_parent) {
         QLIST_FOREACH(b, &bs->parents, next_parent) {
             if (a == b) {
                 continue;
             }
 
             if (!bdrv_a_allow_b(a, b, errp)) {
                 return true;
             }
         }
     }
 
     return false;
 }
 
 static void bdrv_child_perm(BlockDriverState *bs, BlockDriverState *child_bs,
                             BdrvChild *c, BdrvChildRole role,
                             BlockReopenQueue *reopen_queue,
                             uint64_t parent_perm, uint64_t parent_shared,
                             uint64_t *nperm, uint64_t *nshared)
 {
     assert(bs->drv && bs->drv->bdrv_child_perm);
     GLOBAL_STATE_CODE();
     bs->drv->bdrv_child_perm(bs, c, role, reopen_queue,
                              parent_perm, parent_shared,
                              nperm, nshared);
     /* TODO Take force_share from reopen_queue */
     if (child_bs && child_bs->force_share) {
         *nshared = BLK_PERM_ALL;
     }
 }
 
 /*
  * Adds the whole subtree of @bs (including @bs itself) to the @list (except for
  * nodes that are already in the @list, of course) so that final list is
  * topologically sorted. Return the result (GSList @list object is updated, so
  * don't use old reference after function call).
  *
  * On function start @list must be already topologically sorted and for any node
  * in the @list the whole subtree of the node must be in the @list as well. The
  * simplest way to satisfy this criteria: use only result of
  * bdrv_topological_dfs() or NULL as @list parameter.
  */
 static GSList *bdrv_topological_dfs(GSList *list, GHashTable *found,
                                     BlockDriverState *bs)
 {
     BdrvChild *child;
     g_autoptr(GHashTable) local_found = NULL;
 
     GLOBAL_STATE_CODE();
 
     if (!found) {
         assert(!list);
         found = local_found = g_hash_table_new(NULL, NULL);
     }
 
     if (g_hash_table_contains(found, bs)) {
         return list;
     }
     g_hash_table_add(found, bs);
 
     QLIST_FOREACH(child, &bs->children, next) {
         list = bdrv_topological_dfs(list, found, child->bs);
     }
 
     return g_slist_prepend(list, bs);
 }
 
 typedef struct BdrvChildSetPermState {
     BdrvChild *child;
     uint64_t old_perm;
     uint64_t old_shared_perm;
 } BdrvChildSetPermState;
 
 static void bdrv_child_set_perm_abort(void *opaque)
 {
     BdrvChildSetPermState *s = opaque;
 
     GLOBAL_STATE_CODE();
 
     s->child->perm = s->old_perm;
     s->child->shared_perm = s->old_shared_perm;
 }
 
 static TransactionActionDrv bdrv_child_set_pem_drv = {
     .abort = bdrv_child_set_perm_abort,
     .clean = g_free,
 };
 
 static void bdrv_child_set_perm(BdrvChild *c, uint64_t perm,
                                 uint64_t shared, Transaction *tran)
 {
     BdrvChildSetPermState *s = g_new(BdrvChildSetPermState, 1);
     GLOBAL_STATE_CODE();
 
     *s = (BdrvChildSetPermState) {
         .child = c,
         .old_perm = c->perm,
         .old_shared_perm = c->shared_perm,
     };
 
     c->perm = perm;
     c->shared_perm = shared;
 
     tran_add(tran, &bdrv_child_set_pem_drv, s);
 }
 
 static void bdrv_drv_set_perm_commit(void *opaque)
 {
     BlockDriverState *bs = opaque;
     uint64_t cumulative_perms, cumulative_shared_perms;
     GLOBAL_STATE_CODE();
 
     if (bs->drv->bdrv_set_perm) {
         bdrv_get_cumulative_perm(bs, &cumulative_perms,
                                  &cumulative_shared_perms);
         bs->drv->bdrv_set_perm(bs, cumulative_perms, cumulative_shared_perms);
     }
 }
 
 static void bdrv_drv_set_perm_abort(void *opaque)
 {
     BlockDriverState *bs = opaque;
     GLOBAL_STATE_CODE();
 
     if (bs->drv->bdrv_abort_perm_update) {
         bs->drv->bdrv_abort_perm_update(bs);
     }
 }
 
 TransactionActionDrv bdrv_drv_set_perm_drv = {
     .abort = bdrv_drv_set_perm_abort,
     .commit = bdrv_drv_set_perm_commit,
 };
 
 static int bdrv_drv_set_perm(BlockDriverState *bs, uint64_t perm,
                              uint64_t shared_perm, Transaction *tran,
                              Error **errp)
 {
     GLOBAL_STATE_CODE();
     if (!bs->drv) {
         return 0;
     }
 
     if (bs->drv->bdrv_check_perm) {
         int ret = bs->drv->bdrv_check_perm(bs, perm, shared_perm, errp);
         if (ret < 0) {
             return ret;
         }
     }
 
     if (tran) {
         tran_add(tran, &bdrv_drv_set_perm_drv, bs);
     }
 
     return 0;
 }
 
 typedef struct BdrvReplaceChildState {
     BdrvChild *child;
     BlockDriverState *old_bs;
 } BdrvReplaceChildState;
 
 static void bdrv_replace_child_commit(void *opaque)
 {
     BdrvReplaceChildState *s = opaque;
     GLOBAL_STATE_CODE();
 
     bdrv_unref(s->old_bs);
 }
 
 static void bdrv_replace_child_abort(void *opaque)
 {
     BdrvReplaceChildState *s = opaque;
     BlockDriverState *new_bs = s->child->bs;
 
     GLOBAL_STATE_CODE();
     /* old_bs reference is transparently moved from @s to @s->child */
     bdrv_replace_child_noperm(s->child, s->old_bs);
     bdrv_unref(new_bs);
 }
 
 static TransactionActionDrv bdrv_replace_child_drv = {
     .commit = bdrv_replace_child_commit,
     .abort = bdrv_replace_child_abort,
     .clean = g_free,
 };
 
 /*
  * bdrv_replace_child_tran
  *
  * Note: real unref of old_bs is done only on commit.
  *
  * The function doesn't update permissions, caller is responsible for this.
  */
 static void bdrv_replace_child_tran(BdrvChild *child, BlockDriverState *new_bs,
                                     Transaction *tran)
 {
     BdrvReplaceChildState *s = g_new(BdrvReplaceChildState, 1);
     *s = (BdrvReplaceChildState) {
         .child = child,
         .old_bs = child->bs,
     };
     tran_add(tran, &bdrv_replace_child_drv, s);
 
     if (new_bs) {
         bdrv_ref(new_bs);
     }
     bdrv_replace_child_noperm(child, new_bs);
     /* old_bs reference is transparently moved from @child to @s */
 }
 
 /*
  * Refresh permissions in @bs subtree. The function is intended to be called
  * after some graph modification that was done without permission update.
  */
 static int bdrv_node_refresh_perm(BlockDriverState *bs, BlockReopenQueue *q,
                                   Transaction *tran, Error **errp)
 {
     BlockDriver *drv = bs->drv;
     BdrvChild *c;
     int ret;
     uint64_t cumulative_perms, cumulative_shared_perms;
     GLOBAL_STATE_CODE();
 
     bdrv_get_cumulative_perm(bs, &cumulative_perms, &cumulative_shared_perms);
 
     /* Write permissions never work with read-only images */
     if ((cumulative_perms & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED)) &&
         !bdrv_is_writable_after_reopen(bs, q))
     {
         if (!bdrv_is_writable_after_reopen(bs, NULL)) {
             error_setg(errp, "Block node is read-only");
         } else {
             error_setg(errp, "Read-only block node '%s' cannot support "
                        "read-write users", bdrv_get_node_name(bs));
         }
 
         return -EPERM;
     }
 
     /*
      * Unaligned requests will automatically be aligned to bl.request_alignment
      * and without RESIZE we can't extend requests to write to space beyond the
      * end of the image, so it's required that the image size is aligned.
      */
     if ((cumulative_perms & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED)) &&
         !(cumulative_perms & BLK_PERM_RESIZE))
     {
         if ((bs->total_sectors * BDRV_SECTOR_SIZE) % bs->bl.request_alignment) {
             error_setg(errp, "Cannot get 'write' permission without 'resize': "
                              "Image size is not a multiple of request "
                              "alignment");
             return -EPERM;
         }
     }
 
     /* Check this node */
     if (!drv) {
         return 0;
     }
 
     ret = bdrv_drv_set_perm(bs, cumulative_perms, cumulative_shared_perms, tran,
                             errp);
     if (ret < 0) {
         return ret;
     }
 
     /* Drivers that never have children can omit .bdrv_child_perm() */
     if (!drv->bdrv_child_perm) {
         assert(QLIST_EMPTY(&bs->children));
         return 0;
     }
 
     /* Check all children */
     QLIST_FOREACH(c, &bs->children, next) {
         uint64_t cur_perm, cur_shared;
 
         bdrv_child_perm(bs, c->bs, c, c->role, q,
                         cumulative_perms, cumulative_shared_perms,
                         &cur_perm, &cur_shared);
         bdrv_child_set_perm(c, cur_perm, cur_shared, tran);
     }
 
     return 0;
 }
 
 static int bdrv_list_refresh_perms(GSList *list, BlockReopenQueue *q,
                                    Transaction *tran, Error **errp)
 {
     int ret;
     BlockDriverState *bs;
     GLOBAL_STATE_CODE();
 
     for ( ; list; list = list->next) {
         bs = list->data;
 
         if (bdrv_parent_perms_conflict(bs, errp)) {
             return -EINVAL;
         }
 
         ret = bdrv_node_refresh_perm(bs, q, tran, errp);
         if (ret < 0) {
             return ret;
         }
     }
 
     return 0;
 }
 
 void bdrv_get_cumulative_perm(BlockDriverState *bs, uint64_t *perm,
                               uint64_t *shared_perm)
 {
     BdrvChild *c;
     uint64_t cumulative_perms = 0;
     uint64_t cumulative_shared_perms = BLK_PERM_ALL;
 
     GLOBAL_STATE_CODE();
 
     QLIST_FOREACH(c, &bs->parents, next_parent) {
         cumulative_perms |= c->perm;
         cumulative_shared_perms &= c->shared_perm;
     }
 
     *perm = cumulative_perms;
     *shared_perm = cumulative_shared_perms;
 }
 
 char *bdrv_perm_names(uint64_t perm)
 {
     struct perm_name {
         uint64_t perm;
         const char *name;
     } permissions[] = {
         { BLK_PERM_CONSISTENT_READ, "consistent read" },
         { BLK_PERM_WRITE,           "write" },
         { BLK_PERM_WRITE_UNCHANGED, "write unchanged" },
         { BLK_PERM_RESIZE,          "resize" },
         { 0, NULL }
     };
 
     GString *result = g_string_sized_new(30);
     struct perm_name *p;
 
     for (p = permissions; p->name; p++) {
         if (perm & p->perm) {
             if (result->len > 0) {
                 g_string_append(result, ", ");
             }
             g_string_append(result, p->name);
         }
     }
 
     return g_string_free(result, FALSE);
 }
 
 
 static int bdrv_refresh_perms(BlockDriverState *bs, Error **errp)
 {
     int ret;
     Transaction *tran = tran_new();
     g_autoptr(GSList) list = bdrv_topological_dfs(NULL, NULL, bs);
     GLOBAL_STATE_CODE();
 
     ret = bdrv_list_refresh_perms(list, NULL, tran, errp);
     tran_finalize(tran, ret);
 
     return ret;
 }
 
 int bdrv_child_try_set_perm(BdrvChild *c, uint64_t perm, uint64_t shared,
                             Error **errp)
 {
     Error *local_err = NULL;
     Transaction *tran = tran_new();
     int ret;
 
     GLOBAL_STATE_CODE();
 
     bdrv_child_set_perm(c, perm, shared, tran);
 
     ret = bdrv_refresh_perms(c->bs, &local_err);
 
     tran_finalize(tran, ret);
 
     if (ret < 0) {
         if ((perm & ~c->perm) || (c->shared_perm & ~shared)) {
             /* tighten permissions */
             error_propagate(errp, local_err);
         } else {
             /*
              * Our caller may intend to only loosen restrictions and
              * does not expect this function to fail.  Errors are not
              * fatal in such a case, so we can just hide them from our
              * caller.
              */
             error_free(local_err);
             ret = 0;
         }
     }
 
     return ret;
 }
 
 int bdrv_child_refresh_perms(BlockDriverState *bs, BdrvChild *c, Error **errp)
 {
     uint64_t parent_perms, parent_shared;
     uint64_t perms, shared;
 
     GLOBAL_STATE_CODE();
 
     bdrv_get_cumulative_perm(bs, &parent_perms, &parent_shared);
     bdrv_child_perm(bs, c->bs, c, c->role, NULL,
                     parent_perms, parent_shared, &perms, &shared);
 
     return bdrv_child_try_set_perm(c, perms, shared, errp);
 }
 
 /*
  * Default implementation for .bdrv_child_perm() for block filters:
  * Forward CONSISTENT_READ, WRITE, WRITE_UNCHANGED, and RESIZE to the
  * filtered child.
  */
 static void bdrv_filter_default_perms(BlockDriverState *bs, BdrvChild *c,
                                       BdrvChildRole role,
                                       BlockReopenQueue *reopen_queue,
                                       uint64_t perm, uint64_t shared,
                                       uint64_t *nperm, uint64_t *nshared)
 {
     GLOBAL_STATE_CODE();
     *nperm = perm & DEFAULT_PERM_PASSTHROUGH;
     *nshared = (shared & DEFAULT_PERM_PASSTHROUGH) | DEFAULT_PERM_UNCHANGED;
 }
 
 static void bdrv_default_perms_for_cow(BlockDriverState *bs, BdrvChild *c,
                                        BdrvChildRole role,
                                        BlockReopenQueue *reopen_queue,
                                        uint64_t perm, uint64_t shared,
                                        uint64_t *nperm, uint64_t *nshared)
 {
     assert(role & BDRV_CHILD_COW);
     GLOBAL_STATE_CODE();
 
     /*
      * We want consistent read from backing files if the parent needs it.
      * No other operations are performed on backing files.
      */
     perm &= BLK_PERM_CONSISTENT_READ;
 
     /*
      * If the parent can deal with changing data, we're okay with a
      * writable and resizable backing file.
      * TODO Require !(perm & BLK_PERM_CONSISTENT_READ), too?
      */
     if (shared & BLK_PERM_WRITE) {
         shared = BLK_PERM_WRITE | BLK_PERM_RESIZE;
     } else {
         shared = 0;
     }
 
     shared |= BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
 
     if (bs->open_flags & BDRV_O_INACTIVE) {
         shared |= BLK_PERM_WRITE | BLK_PERM_RESIZE;
     }
 
     *nperm = perm;
     *nshared = shared;
 }
 
 static void bdrv_default_perms_for_storage(BlockDriverState *bs, BdrvChild *c,
                                            BdrvChildRole role,
                                            BlockReopenQueue *reopen_queue,
                                            uint64_t perm, uint64_t shared,
                                            uint64_t *nperm, uint64_t *nshared)
 {
     int flags;
 
     GLOBAL_STATE_CODE();
     assert(role & (BDRV_CHILD_METADATA | BDRV_CHILD_DATA));
 
     flags = bdrv_reopen_get_flags(reopen_queue, bs);
 
     /*
      * Apart from the modifications below, the same permissions are
      * forwarded and left alone as for filters
      */
     bdrv_filter_default_perms(bs, c, role, reopen_queue,
                               perm, shared, &perm, &shared);
 
     if (role & BDRV_CHILD_METADATA) {
         /* Format drivers may touch metadata even if the guest doesn't write */
         if (bdrv_is_writable_after_reopen(bs, reopen_queue)) {
             perm |= BLK_PERM_WRITE | BLK_PERM_RESIZE;
         }
 
         /*
          * bs->file always needs to be consistent because of the
          * metadata. We can never allow other users to resize or write
          * to it.
          */
         if (!(flags & BDRV_O_NO_IO)) {
             perm |= BLK_PERM_CONSISTENT_READ;
         }
         shared &= ~(BLK_PERM_WRITE | BLK_PERM_RESIZE);
     }
 
     if (role & BDRV_CHILD_DATA) {
         /*
          * Technically, everything in this block is a subset of the
          * BDRV_CHILD_METADATA path taken above, and so this could
          * be an "else if" branch.  However, that is not obvious, and
          * this function is not performance critical, therefore we let
          * this be an independent "if".
          */
 
         /*
          * We cannot allow other users to resize the file because the
          * format driver might have some assumptions about the size
          * (e.g. because it is stored in metadata, or because the file
          * is split into fixed-size data files).
          */
         shared &= ~BLK_PERM_RESIZE;
 
         /*
          * WRITE_UNCHANGED often cannot be performed as such on the
          * data file.  For example, the qcow2 driver may still need to
          * write copied clusters on copy-on-read.
          */
         if (perm & BLK_PERM_WRITE_UNCHANGED) {
             perm |= BLK_PERM_WRITE;
         }
 
         /*
          * If the data file is written to, the format driver may
          * expect to be able to resize it by writing beyond the EOF.
          */
         if (perm & BLK_PERM_WRITE) {
             perm |= BLK_PERM_RESIZE;
         }
     }
 
     if (bs->open_flags & BDRV_O_INACTIVE) {
         shared |= BLK_PERM_WRITE | BLK_PERM_RESIZE;
     }
 
     *nperm = perm;
     *nshared = shared;
 }
 
 void bdrv_default_perms(BlockDriverState *bs, BdrvChild *c,
                         BdrvChildRole role, BlockReopenQueue *reopen_queue,
                         uint64_t perm, uint64_t shared,
                         uint64_t *nperm, uint64_t *nshared)
 {
     GLOBAL_STATE_CODE();
     if (role & BDRV_CHILD_FILTERED) {
         assert(!(role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA |
                          BDRV_CHILD_COW)));
         bdrv_filter_default_perms(bs, c, role, reopen_queue,
                                   perm, shared, nperm, nshared);
     } else if (role & BDRV_CHILD_COW) {
         assert(!(role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA)));
         bdrv_default_perms_for_cow(bs, c, role, reopen_queue,
                                    perm, shared, nperm, nshared);
     } else if (role & (BDRV_CHILD_METADATA | BDRV_CHILD_DATA)) {
         bdrv_default_perms_for_storage(bs, c, role, reopen_queue,
                                        perm, shared, nperm, nshared);
     } else {
         g_assert_not_reached();
     }
 }
 
 uint64_t bdrv_qapi_perm_to_blk_perm(BlockPermission qapi_perm)
 {
     static const uint64_t permissions[] = {
         [BLOCK_PERMISSION_CONSISTENT_READ]  = BLK_PERM_CONSISTENT_READ,
         [BLOCK_PERMISSION_WRITE]            = BLK_PERM_WRITE,
         [BLOCK_PERMISSION_WRITE_UNCHANGED]  = BLK_PERM_WRITE_UNCHANGED,
         [BLOCK_PERMISSION_RESIZE]           = BLK_PERM_RESIZE,
     };
 
     QEMU_BUILD_BUG_ON(ARRAY_SIZE(permissions) != BLOCK_PERMISSION__MAX);
     QEMU_BUILD_BUG_ON(1UL << ARRAY_SIZE(permissions) != BLK_PERM_ALL + 1);
 
     assert(qapi_perm < BLOCK_PERMISSION__MAX);
 
     return permissions[qapi_perm];
 }
 
 static void bdrv_replace_child_noperm(BdrvChild *child,
                                       BlockDriverState *new_bs)
 {
     BlockDriverState *old_bs = child->bs;
     int new_bs_quiesce_counter;
     int drain_saldo;
 
     assert(!child->frozen);
     assert(old_bs != new_bs);
     GLOBAL_STATE_CODE();
 
     if (old_bs && new_bs) {
         assert(bdrv_get_aio_context(old_bs) == bdrv_get_aio_context(new_bs));
     }
 
     new_bs_quiesce_counter = (new_bs ? new_bs->quiesce_counter : 0);
     drain_saldo = new_bs_quiesce_counter - child->parent_quiesce_counter;
 
     /*
      * If the new child node is drained but the old one was not, flush
      * all outstanding requests to the old child node.
      */
     while (drain_saldo > 0 && child->klass->drained_begin) {
         bdrv_parent_drained_begin_single(child, true);
         drain_saldo--;
     }
 
     if (old_bs) {
         /* Detach first so that the recursive drain sections coming from @child
          * are already gone and we only end the drain sections that came from
          * elsewhere. */
         if (child->klass->detach) {
             child->klass->detach(child);
         }
         assert_bdrv_graph_writable(old_bs);
         QLIST_REMOVE(child, next_parent);
     }
 
     child->bs = new_bs;
 
     if (new_bs) {
         assert_bdrv_graph_writable(new_bs);
         QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
 
         /*
          * Detaching the old node may have led to the new node's
          * quiesce_counter having been decreased.  Not a problem, we
          * just need to recognize this here and then invoke
          * drained_end appropriately more often.
          */
         assert(new_bs->quiesce_counter <= new_bs_quiesce_counter);
         drain_saldo += new_bs->quiesce_counter - new_bs_quiesce_counter;
 
         /* Attach only after starting new drained sections, so that recursive
          * drain sections coming from @child don't get an extra .drained_begin
          * callback. */
         if (child->klass->attach) {
             child->klass->attach(child);
         }
     }
 
     /*
      * If the old child node was drained but the new one is not, allow
      * requests to come in only after the new node has been attached.
      */
     while (drain_saldo < 0 && child->klass->drained_end) {
         bdrv_parent_drained_end_single(child);
         drain_saldo++;
     }
 }
 
 /**
  * Free the given @child.
  *
  * The child must be empty (i.e. `child->bs == NULL`) and it must be
  * unused (i.e. not in a children list).
  */
 static void bdrv_child_free(BdrvChild *child)
 {
     assert(!child->bs);
     GLOBAL_STATE_CODE();
     assert(!child->next.le_prev); /* not in children list */
 
     g_free(child->name);
     g_free(child);
 }
 
 typedef struct BdrvAttachChildCommonState {
     BdrvChild *child;
     AioContext *old_parent_ctx;
     AioContext *old_child_ctx;
 } BdrvAttachChildCommonState;
 
 static void bdrv_attach_child_common_abort(void *opaque)
 {
     BdrvAttachChildCommonState *s = opaque;
     BlockDriverState *bs = s->child->bs;
 
     GLOBAL_STATE_CODE();
     bdrv_replace_child_noperm(s->child, NULL);
 
     if (bdrv_get_aio_context(bs) != s->old_child_ctx) {
         bdrv_try_change_aio_context(bs, s->old_child_ctx, NULL, &error_abort);
     }
 
     if (bdrv_child_get_parent_aio_context(s->child) != s->old_parent_ctx) {
         Transaction *tran;
         GHashTable *visited;
         bool ret;
 
         tran = tran_new();
 
         /* No need to visit `child`, because it has been detached already */
         visited = g_hash_table_new(NULL, NULL);
         ret = s->child->klass->change_aio_ctx(s->child, s->old_parent_ctx,
                                               visited, tran, &error_abort);
         g_hash_table_destroy(visited);
 
         /* transaction is supposed to always succeed */
         assert(ret == true);
         tran_commit(tran);
     }
 
     bdrv_unref(bs);
     bdrv_child_free(s->child);
 }
 
 static TransactionActionDrv bdrv_attach_child_common_drv = {
     .abort = bdrv_attach_child_common_abort,
     .clean = g_free,
 };
 
 /*
  * Common part of attaching bdrv child to bs or to blk or to job
  *
  * Function doesn't update permissions, caller is responsible for this.
  *
  * Returns new created child.
  */
 static BdrvChild *bdrv_attach_child_common(BlockDriverState *child_bs,
                                            const char *child_name,
                                            const BdrvChildClass *child_class,
                                            BdrvChildRole child_role,
                                            uint64_t perm, uint64_t shared_perm,
                                            void *opaque,
                                            Transaction *tran, Error **errp)
 {
     BdrvChild *new_child;
     AioContext *parent_ctx;
     AioContext *child_ctx = bdrv_get_aio_context(child_bs);
 
     assert(child_class->get_parent_desc);
     GLOBAL_STATE_CODE();
 
     new_child = g_new(BdrvChild, 1);
     *new_child = (BdrvChild) {
         .bs             = NULL,
         .name           = g_strdup(child_name),
         .klass          = child_class,
         .role           = child_role,
         .perm           = perm,
         .shared_perm    = shared_perm,
         .opaque         = opaque,
     };
 
     /*
      * If the AioContexts don't match, first try to move the subtree of
      * child_bs into the AioContext of the new parent. If this doesn't work,
      * try moving the parent into the AioContext of child_bs instead.
      */
     parent_ctx = bdrv_child_get_parent_aio_context(new_child);
     if (child_ctx != parent_ctx) {
         Error *local_err = NULL;
         int ret = bdrv_try_change_aio_context(child_bs, parent_ctx, NULL,
                                               &local_err);
 
         if (ret < 0 && child_class->change_aio_ctx) {
             Transaction *tran = tran_new();
             GHashTable *visited = g_hash_table_new(NULL, NULL);
             bool ret_child;
 
             g_hash_table_add(visited, new_child);
             ret_child = child_class->change_aio_ctx(new_child, child_ctx,
                                                     visited, tran, NULL);
             if (ret_child == true) {
                 error_free(local_err);
                 ret = 0;
             }
             tran_finalize(tran, ret_child == true ? 0 : -1);
             g_hash_table_destroy(visited);
         }
 
         if (ret < 0) {
             error_propagate(errp, local_err);
             bdrv_child_free(new_child);
             return NULL;
         }
     }
 
     bdrv_ref(child_bs);
     bdrv_replace_child_noperm(new_child, child_bs);
 
     BdrvAttachChildCommonState *s = g_new(BdrvAttachChildCommonState, 1);
     *s = (BdrvAttachChildCommonState) {
         .child = new_child,
         .old_parent_ctx = parent_ctx,
         .old_child_ctx = child_ctx,
     };
     tran_add(tran, &bdrv_attach_child_common_drv, s);
 
     return new_child;
 }
 
 /*
  * Function doesn't update permissions, caller is responsible for this.
  */
 static BdrvChild *bdrv_attach_child_noperm(BlockDriverState *parent_bs,
                                            BlockDriverState *child_bs,
                                            const char *child_name,
                                            const BdrvChildClass *child_class,
                                            BdrvChildRole child_role,
                                            Transaction *tran,
                                            Error **errp)
 {
     uint64_t perm, shared_perm;
 
     assert(parent_bs->drv);
     GLOBAL_STATE_CODE();
 
     if (bdrv_recurse_has_child(child_bs, parent_bs)) {
         error_setg(errp, "Making '%s' a %s child of '%s' would create a cycle",
                    child_bs->node_name, child_name, parent_bs->node_name);
         return NULL;
     }
 
     bdrv_get_cumulative_perm(parent_bs, &perm, &shared_perm);
     bdrv_child_perm(parent_bs, child_bs, NULL, child_role, NULL,
                     perm, shared_perm, &perm, &shared_perm);
 
     return bdrv_attach_child_common(child_bs, child_name, child_class,
                                     child_role, perm, shared_perm, parent_bs,
                                     tran, errp);
 }
 
 static void bdrv_detach_child(BdrvChild *child)
 {
     BlockDriverState *old_bs = child->bs;
 
     GLOBAL_STATE_CODE();
     bdrv_replace_child_noperm(child, NULL);
     bdrv_child_free(child);
 
     if (old_bs) {
         /*
          * Update permissions for old node. We're just taking a parent away, so
          * we're loosening restrictions. Errors of permission update are not
          * fatal in this case, ignore them.
          */
         bdrv_refresh_perms(old_bs, NULL);
 
         /*
          * When the parent requiring a non-default AioContext is removed, the
          * node moves back to the main AioContext
          */
         bdrv_try_change_aio_context(old_bs, qemu_get_aio_context(), NULL, NULL);
     }
 }
 
 /*
  * This function steals the reference to child_bs from the caller.
  * That reference is later dropped by bdrv_root_unref_child().
  *
  * On failure NULL is returned, errp is set and the reference to
  * child_bs is also dropped.
  *
  * The caller must hold the AioContext lock @child_bs, but not that of @ctx
  * (unless @child_bs is already in @ctx).
  */
 BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
                                   const char *child_name,
                                   const BdrvChildClass *child_class,
                                   BdrvChildRole child_role,
                                   uint64_t perm, uint64_t shared_perm,
                                   void *opaque, Error **errp)
 {
     int ret;
     BdrvChild *child;
     Transaction *tran = tran_new();
 
     GLOBAL_STATE_CODE();
 
     child = bdrv_attach_child_common(child_bs, child_name, child_class,
                                    child_role, perm, shared_perm, opaque,
                                    tran, errp);
     if (!child) {
         ret = -EINVAL;
         goto out;
     }
 
     ret = bdrv_refresh_perms(child_bs, errp);
 
 out:
     tran_finalize(tran, ret);
 
     bdrv_unref(child_bs);
 
     return ret < 0 ? NULL : child;
 }
 
 /*
  * This function transfers the reference to child_bs from the caller
  * to parent_bs. That reference is later dropped by parent_bs on
  * bdrv_close() or if someone calls bdrv_unref_child().
  *
  * On failure NULL is returned, errp is set and the reference to
  * child_bs is also dropped.
  *
  * If @parent_bs and @child_bs are in different AioContexts, the caller must
  * hold the AioContext lock for @child_bs, but not for @parent_bs.
  */
 BdrvChild *bdrv_attach_child(BlockDriverState *parent_bs,
                              BlockDriverState *child_bs,
                              const char *child_name,
                              const BdrvChildClass *child_class,
                              BdrvChildRole child_role,
                              Error **errp)
 {
     int ret;
     BdrvChild *child;
     Transaction *tran = tran_new();
 
     GLOBAL_STATE_CODE();
 
     child = bdrv_attach_child_noperm(parent_bs, child_bs, child_name,
                                      child_class, child_role, tran, errp);
     if (!child) {
         ret = -EINVAL;
         goto out;
     }
 
     ret = bdrv_refresh_perms(parent_bs, errp);
     if (ret < 0) {
         goto out;
     }
 
 out:
     tran_finalize(tran, ret);
 
     bdrv_unref(child_bs);
 
     return ret < 0 ? NULL : child;
 }
 
 /* Callers must ensure that child->frozen is false. */
 void bdrv_root_unref_child(BdrvChild *child)
 {
     BlockDriverState *child_bs;
 
     GLOBAL_STATE_CODE();
 
     child_bs = child->bs;
     bdrv_detach_child(child);
     bdrv_unref(child_bs);
 }
 
 typedef struct BdrvSetInheritsFrom {
     BlockDriverState *bs;
     BlockDriverState *old_inherits_from;
 } BdrvSetInheritsFrom;
 
 static void bdrv_set_inherits_from_abort(void *opaque)
 {
     BdrvSetInheritsFrom *s = opaque;
 
     s->bs->inherits_from = s->old_inherits_from;
 }
 
 static TransactionActionDrv bdrv_set_inherits_from_drv = {
     .abort = bdrv_set_inherits_from_abort,
     .clean = g_free,
 };
 
 /* @tran is allowed to be NULL. In this case no rollback is possible */
 static void bdrv_set_inherits_from(BlockDriverState *bs,
                                    BlockDriverState *new_inherits_from,
                                    Transaction *tran)
 {
     if (tran) {
         BdrvSetInheritsFrom *s = g_new(BdrvSetInheritsFrom, 1);
 
         *s = (BdrvSetInheritsFrom) {
             .bs = bs,
             .old_inherits_from = bs->inherits_from,
         };
 
         tran_add(tran, &bdrv_set_inherits_from_drv, s);
     }
 
     bs->inherits_from = new_inherits_from;
 }
 
 /**
  * Clear all inherits_from pointers from children and grandchildren of
  * @root that point to @root, where necessary.
  * @tran is allowed to be NULL. In this case no rollback is possible
  */
 static void bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child,
                                      Transaction *tran)
 {
     BdrvChild *c;
 
     if (child->bs->inherits_from == root) {
         /*
          * Remove inherits_from only when the last reference between root and
          * child->bs goes away.
          */
         QLIST_FOREACH(c, &root->children, next) {
             if (c != child && c->bs == child->bs) {
                 break;
             }
         }
         if (c == NULL) {
             bdrv_set_inherits_from(child->bs, NULL, tran);
         }
     }
 
     QLIST_FOREACH(c, &child->bs->children, next) {
         bdrv_unset_inherits_from(root, c, tran);
     }
 }
 
 /* Callers must ensure that child->frozen is false. */
 void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child)
 {
     GLOBAL_STATE_CODE();
     if (child == NULL) {
         return;
     }
 
     bdrv_unset_inherits_from(parent, child, NULL);
     bdrv_root_unref_child(child);
 }
 
 
 static void bdrv_parent_cb_change_media(BlockDriverState *bs, bool load)
 {
     BdrvChild *c;
     GLOBAL_STATE_CODE();
     QLIST_FOREACH(c, &bs->parents, next_parent) {
         if (c->klass->change_media) {
             c->klass->change_media(c, load);
         }
     }
 }
 
 /* Return true if you can reach parent going through child->inherits_from
  * recursively. If parent or child are NULL, return false */
 static bool bdrv_inherits_from_recursive(BlockDriverState *child,
                                          BlockDriverState *parent)
 {
     while (child && child != parent) {
         child = child->inherits_from;
     }
 
     return child != NULL;
 }
 
 /*
  * Return the BdrvChildRole for @bs's backing child.  bs->backing is
  * mostly used for COW backing children (role = COW), but also for
  * filtered children (role = FILTERED | PRIMARY).
  */
 static BdrvChildRole bdrv_backing_role(BlockDriverState *bs)
 {
     if (bs->drv && bs->drv->is_filter) {
         return BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY;
     } else {
         return BDRV_CHILD_COW;
     }
 }
 
 /*
  * Sets the bs->backing or bs->file link of a BDS. A new reference is created;
  * callers which don't need their own reference any more must call bdrv_unref().
  *
  * Function doesn't update permissions, caller is responsible for this.
  */
 static int bdrv_set_file_or_backing_noperm(BlockDriverState *parent_bs,
                                            BlockDriverState *child_bs,
                                            bool is_backing,
                                            Transaction *tran, Error **errp)
 {
     bool update_inherits_from =
         bdrv_inherits_from_recursive(child_bs, parent_bs);
     BdrvChild *child = is_backing ? parent_bs->backing : parent_bs->file;
     BdrvChildRole role;
 
     GLOBAL_STATE_CODE();
 
     if (!parent_bs->drv) {
         /*
          * Node without drv is an object without a class :/. TODO: finally fix
          * qcow2 driver to never clear bs->drv and implement format corruption
          * handling in other way.
          */
         error_setg(errp, "Node corrupted");
         return -EINVAL;
     }
 
     if (child && child->frozen) {
         error_setg(errp, "Cannot change frozen '%s' link from '%s' to '%s'",
                    child->name, parent_bs->node_name, child->bs->node_name);
         return -EPERM;
     }
 
     if (is_backing && !parent_bs->drv->is_filter &&
         !parent_bs->drv->supports_backing)
     {
         error_setg(errp, "Driver '%s' of node '%s' does not support backing "
                    "files", parent_bs->drv->format_name, parent_bs->node_name);
         return -EINVAL;
     }
 
     if (parent_bs->drv->is_filter) {
         role = BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY;
     } else if (is_backing) {
         role = BDRV_CHILD_COW;
     } else {
         /*
          * We only can use same role as it is in existing child. We don't have
          * infrastructure to determine role of file child in generic way
          */
         if (!child) {
             error_setg(errp, "Cannot set file child to format node without "
                        "file child");
             return -EINVAL;
         }
         role = child->role;
     }
 
     if (child) {
         bdrv_unset_inherits_from(parent_bs, child, tran);
         bdrv_remove_child(child, tran);
     }
 
     if (!child_bs) {
         goto out;
     }
 
     child = bdrv_attach_child_noperm(parent_bs, child_bs,
                                      is_backing ? "backing" : "file",
                                      &child_of_bds, role,
                                      tran, errp);
     if (!child) {
         return -EINVAL;
     }
 
 
     /*
      * If inherits_from pointed recursively to bs then let's update it to
      * point directly to bs (else it will become NULL).
      */
     if (update_inherits_from) {
         bdrv_set_inherits_from(child_bs, parent_bs, tran);
     }
 
 out:
     bdrv_refresh_limits(parent_bs, tran, NULL);
 
     return 0;
 }
 
 static int bdrv_set_backing_noperm(BlockDriverState *bs,
                                    BlockDriverState *backing_hd,
                                    Transaction *tran, Error **errp)
 {
     GLOBAL_STATE_CODE();
     return bdrv_set_file_or_backing_noperm(bs, backing_hd, true, tran, errp);
 }
 
 int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
                         Error **errp)
 {
     int ret;
     Transaction *tran = tran_new();
 
     GLOBAL_STATE_CODE();
     bdrv_drained_begin(bs);
 
     ret = bdrv_set_backing_noperm(bs, backing_hd, tran, errp);
     if (ret < 0) {
         goto out;
     }
 
     ret = bdrv_refresh_perms(bs, errp);
 out:
     tran_finalize(tran, ret);
 
     bdrv_drained_end(bs);
 
     return ret;
 }
 
 /*
  * Opens the backing file for a BlockDriverState if not yet open
  *
  * bdref_key specifies the key for the image's BlockdevRef in the options QDict.
  * That QDict has to be flattened; therefore, if the BlockdevRef is a QDict
  * itself, all options starting with "${bdref_key}." are considered part of the
  * BlockdevRef.
  *
  * TODO Can this be unified with bdrv_open_image()?
  */
 int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
                            const char *bdref_key, Error **errp)
 {
     char *backing_filename = NULL;
     char *bdref_key_dot;
     const char *reference = NULL;
     int ret = 0;
     bool implicit_backing = false;
     BlockDriverState *backing_hd;
     QDict *options;
     QDict *tmp_parent_options = NULL;
     Error *local_err = NULL;
 
     GLOBAL_STATE_CODE();
 
     if (bs->backing != NULL) {
         goto free_exit;
     }
 
     /* NULL means an empty set of options */
     if (parent_options == NULL) {
         tmp_parent_options = qdict_new();
         parent_options = tmp_parent_options;
     }
 
     bs->open_flags &= ~BDRV_O_NO_BACKING;
 
     bdref_key_dot = g_strdup_printf("%s.", bdref_key);
     qdict_extract_subqdict(parent_options, &options, bdref_key_dot);
     g_free(bdref_key_dot);
 
     /*
      * Caution: while qdict_get_try_str() is fine, getting non-string
      * types would require more care.  When @parent_options come from
      * -blockdev or blockdev_add, its members are typed according to
      * the QAPI schema, but when they come from -drive, they're all
      * QString.
      */
     reference = qdict_get_try_str(parent_options, bdref_key);
     if (reference || qdict_haskey(options, "file.filename")) {
         /* keep backing_filename NULL */
     } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) {
         qobject_unref(options);
         goto free_exit;
     } else {
         if (qdict_size(options) == 0) {
             /* If the user specifies options that do not modify the
              * backing file's behavior, we might still consider it the
              * implicit backing file.  But it's easier this way, and
              * just specifying some of the backing BDS's options is
              * only possible with -drive anyway (otherwise the QAPI
              * schema forces the user to specify everything). */
             implicit_backing = !strcmp(bs->auto_backing_file, bs->backing_file);
         }
 
         backing_filename = bdrv_get_full_backing_filename(bs, &local_err);
         if (local_err) {
             ret = -EINVAL;
             error_propagate(errp, local_err);
             qobject_unref(options);
             goto free_exit;
         }
     }
 
     if (!bs->drv || !bs->drv->supports_backing) {
         ret = -EINVAL;
         error_setg(errp, "Driver doesn't support backing files");
         qobject_unref(options);
         goto free_exit;
     }
 
     if (!reference &&
         bs->backing_format[0] != '\0' && !qdict_haskey(options, "driver")) {
         qdict_put_str(options, "driver", bs->backing_format);
     }
 
     backing_hd = bdrv_open_inherit(backing_filename, reference, options, 0, bs,
                                    &child_of_bds, bdrv_backing_role(bs), errp);
     if (!backing_hd) {
         bs->open_flags |= BDRV_O_NO_BACKING;
         error_prepend(errp, "Could not open backing file: ");
         ret = -EINVAL;
         goto free_exit;
     }
 
     if (implicit_backing) {
         bdrv_refresh_filename(backing_hd);
         pstrcpy(bs->auto_backing_file, sizeof(bs->auto_backing_file),
                 backing_hd->filename);
     }
 
     /* Hook up the backing file link; drop our reference, bs owns the
      * backing_hd reference now */
     ret = bdrv_set_backing_hd(bs, backing_hd, errp);
     bdrv_unref(backing_hd);
     if (ret < 0) {
         goto free_exit;
     }
 
     qdict_del(parent_options, bdref_key);
 
 free_exit:
     g_free(backing_filename);
     qobject_unref(tmp_parent_options);
     return ret;
 }
 
 static BlockDriverState *
 bdrv_open_child_bs(const char *filename, QDict *options, const char *bdref_key,
                    BlockDriverState *parent, const BdrvChildClass *child_class,
                    BdrvChildRole child_role, bool allow_none, Error **errp)
 {
     BlockDriverState *bs = NULL;
     QDict *image_options;
     char *bdref_key_dot;
     const char *reference;
 
     assert(child_class != NULL);
 
     bdref_key_dot = g_strdup_printf("%s.", bdref_key);
     qdict_extract_subqdict(options, &image_options, bdref_key_dot);
     g_free(bdref_key_dot);
 
     /*
      * Caution: while qdict_get_try_str() is fine, getting non-string
      * types would require more care.  When @options come from
      * -blockdev or blockdev_add, its members are typed according to
      * the QAPI schema, but when they come from -drive, they're all
      * QString.
      */
     reference = qdict_get_try_str(options, bdref_key);
     if (!filename && !reference && !qdict_size(image_options)) {
         if (!allow_none) {
             error_setg(errp, "A block device must be specified for \"%s\"",
                        bdref_key);
         }
         qobject_unref(image_options);
         goto done;
     }
 
     bs = bdrv_open_inherit(filename, reference, image_options, 0,
                            parent, child_class, child_role, errp);
     if (!bs) {
         goto done;
     }
 
 done:
     qdict_del(options, bdref_key);
     return bs;
 }
 
 /*
  * Opens a disk image whose options are given as BlockdevRef in another block
  * device's options.
  *
  * If allow_none is true, no image will be opened if filename is false and no
  * BlockdevRef is given. NULL will be returned, but errp remains unset.
  *
  * bdrev_key specifies the key for the image's BlockdevRef in the options QDict.
  * That QDict has to be flattened; therefore, if the BlockdevRef is a QDict
  * itself, all options starting with "${bdref_key}." are considered part of the
  * BlockdevRef.
  *
  * The BlockdevRef will be removed from the options QDict.
  */
 BdrvChild *bdrv_open_child(const char *filename,
                            QDict *options, const char *bdref_key,
                            BlockDriverState *parent,
                            const BdrvChildClass *child_class,
                            BdrvChildRole child_role,
                            bool allow_none, Error **errp)
 {
     BlockDriverState *bs;
 
     GLOBAL_STATE_CODE();
 
     bs = bdrv_open_child_bs(filename, options, bdref_key, parent, child_class,
                             child_role, allow_none, errp);
     if (bs == NULL) {
         return NULL;
     }
 
     return bdrv_attach_child(parent, bs, bdref_key, child_class, child_role,
                              errp);
 }
 
 /*
  * Wrapper on bdrv_open_child() for most popular case: open primary child of bs.
  */
 int bdrv_open_file_child(const char *filename,
                          QDict *options, const char *bdref_key,
                          BlockDriverState *parent, Error **errp)
 {
     BdrvChildRole role;
 
     /* commit_top and mirror_top don't use this function */
     assert(!parent->drv->filtered_child_is_backing);
     role = parent->drv->is_filter ?
         (BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY) : BDRV_CHILD_IMAGE;
 
     if (!bdrv_open_child(filename, options, bdref_key, parent,
                          &child_of_bds, role, false, errp))
     {
         return -EINVAL;
     }
 
     return 0;
 }
 
 /*
  * TODO Future callers may need to specify parent/child_class in order for
  * option inheritance to work. Existing callers use it for the root node.
  */
 BlockDriverState *bdrv_open_blockdev_ref(BlockdevRef *ref, Error **errp)
 {
     BlockDriverState *bs = NULL;
     QObject *obj = NULL;
     QDict *qdict = NULL;
     const char *reference = NULL;
     Visitor *v = NULL;
 
     GLOBAL_STATE_CODE();
 
     if (ref->type == QTYPE_QSTRING) {
         reference = ref->u.reference;
     } else {
         BlockdevOptions *options = &ref->u.definition;
         assert(ref->type == QTYPE_QDICT);
 
         v = qobject_output_visitor_new(&obj);
         visit_type_BlockdevOptions(v, NULL, &options, &error_abort);
         visit_complete(v, &obj);
 
         qdict = qobject_to(QDict, obj);
         qdict_flatten(qdict);
 
         /* bdrv_open_inherit() defaults to the values in bdrv_flags (for
          * compatibility with other callers) rather than what we want as the
          * real defaults. Apply the defaults here instead. */
         qdict_set_default_str(qdict, BDRV_OPT_CACHE_DIRECT, "off");
         qdict_set_default_str(qdict, BDRV_OPT_CACHE_NO_FLUSH, "off");
         qdict_set_default_str(qdict, BDRV_OPT_READ_ONLY, "off");
         qdict_set_default_str(qdict, BDRV_OPT_AUTO_READ_ONLY, "off");
 
     }
 
     bs = bdrv_open_inherit(NULL, reference, qdict, 0, NULL, NULL, 0, errp);
     obj = NULL;
     qobject_unref(obj);
     visit_free(v);
     return bs;
 }
 
 static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
                                                    int flags,
                                                    QDict *snapshot_options,
                                                    Error **errp)
 {
     g_autofree char *tmp_filename = NULL;
     int64_t total_size;
     QemuOpts *opts = NULL;
     BlockDriverState *bs_snapshot = NULL;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     /* if snapshot, we create a temporary backing file and open it
        instead of opening 'filename' directly */
 
     /* Get the required size from the image */
     total_size = bdrv_getlength(bs);
     if (total_size < 0) {
         error_setg_errno(errp, -total_size, "Could not get image size");
         goto out;
     }
 
     /* Create the temporary image */
     tmp_filename = create_tmp_file(errp);
     if (!tmp_filename) {
         goto out;
     }
 
     opts = qemu_opts_create(bdrv_qcow2.create_opts, NULL, 0,
                             &error_abort);
     qemu_opt_set_number(opts, BLOCK_OPT_SIZE, total_size, &error_abort);
     ret = bdrv_create(&bdrv_qcow2, tmp_filename, opts, errp);
     qemu_opts_del(opts);
     if (ret < 0) {
         error_prepend(errp, "Could not create temporary overlay '%s': ",
                       tmp_filename);
         goto out;
     }
 
     /* Prepare options QDict for the temporary file */
     qdict_put_str(snapshot_options, "file.driver", "file");
     qdict_put_str(snapshot_options, "file.filename", tmp_filename);
     qdict_put_str(snapshot_options, "driver", "qcow2");
 
     bs_snapshot = bdrv_open(NULL, NULL, snapshot_options, flags, errp);
     snapshot_options = NULL;
     if (!bs_snapshot) {
         goto out;
     }
 
     ret = bdrv_append(bs_snapshot, bs, errp);
     if (ret < 0) {
         bs_snapshot = NULL;
         goto out;
     }
 
 out:
     qobject_unref(snapshot_options);
     return bs_snapshot;
 }
 
 /*
  * Opens a disk image (raw, qcow2, vmdk, ...)
  *
  * options is a QDict of options to pass to the block drivers, or NULL for an
  * empty set of options. The reference to the QDict belongs to the block layer
  * after the call (even on failure), so if the caller intends to reuse the
  * dictionary, it needs to use qobject_ref() before calling bdrv_open.
  *
  * If *pbs is NULL, a new BDS will be created with a pointer to it stored there.
  * If it is not NULL, the referenced BDS will be reused.
  *
  * The reference parameter may be used to specify an existing block device which
  * should be opened. If specified, neither options nor a filename may be given,
  * nor can an existing BDS be reused (that is, *pbs has to be NULL).
  */
 static BlockDriverState *bdrv_open_inherit(const char *filename,
                                            const char *reference,
                                            QDict *options, int flags,
                                            BlockDriverState *parent,
                                            const BdrvChildClass *child_class,
                                            BdrvChildRole child_role,
                                            Error **errp)
 {
     int ret;
     BlockBackend *file = NULL;
     BlockDriverState *bs;
     BlockDriver *drv = NULL;
     BdrvChild *child;
     const char *drvname;
     const char *backing;
     Error *local_err = NULL;
     QDict *snapshot_options = NULL;
     int snapshot_flags = 0;
 
     assert(!child_class || !flags);
     assert(!child_class == !parent);
     GLOBAL_STATE_CODE();
 
     if (reference) {
         bool options_non_empty = options ? qdict_size(options) : false;
         qobject_unref(options);
 
         if (filename || options_non_empty) {
             error_setg(errp, "Cannot reference an existing block device with "
                        "additional options or a new filename");
             return NULL;
         }
 
         bs = bdrv_lookup_bs(reference, reference, errp);
         if (!bs) {
             return NULL;
         }
 
         bdrv_ref(bs);
         return bs;
     }
 
     bs = bdrv_new();
 
     /* NULL means an empty set of options */
     if (options == NULL) {
         options = qdict_new();
     }
 
     /* json: syntax counts as explicit options, as if in the QDict */
     parse_json_protocol(options, &filename, &local_err);
     if (local_err) {
         goto fail;
     }
 
     bs->explicit_options = qdict_clone_shallow(options);
 
     if (child_class) {
         bool parent_is_format;
 
         if (parent->drv) {
             parent_is_format = parent->drv->is_format;
         } else {
             /*
              * parent->drv is not set yet because this node is opened for
              * (potential) format probing.  That means that @parent is going
              * to be a format node.
              */
             parent_is_format = true;
         }
 
         bs->inherits_from = parent;
         child_class->inherit_options(child_role, parent_is_format,
                                      &flags, options,
                                      parent->open_flags, parent->options);
     }
 
     ret = bdrv_fill_options(&options, filename, &flags, &local_err);
     if (ret < 0) {
         goto fail;
     }
 
     /*
      * Set the BDRV_O_RDWR and BDRV_O_ALLOW_RDWR flags.
      * Caution: getting a boolean member of @options requires care.
      * When @options come from -blockdev or blockdev_add, members are
      * typed according to the QAPI schema, but when they come from
      * -drive, they're all QString.
      */
     if (g_strcmp0(qdict_get_try_str(options, BDRV_OPT_READ_ONLY), "on") &&
         !qdict_get_try_bool(options, BDRV_OPT_READ_ONLY, false)) {
         flags |= (BDRV_O_RDWR | BDRV_O_ALLOW_RDWR);
     } else {
         flags &= ~BDRV_O_RDWR;
     }
 
     if (flags & BDRV_O_SNAPSHOT) {
         snapshot_options = qdict_new();
         bdrv_temp_snapshot_options(&snapshot_flags, snapshot_options,
                                    flags, options);
         /* Let bdrv_backing_options() override "read-only" */
         qdict_del(options, BDRV_OPT_READ_ONLY);
         bdrv_inherited_options(BDRV_CHILD_COW, true,
                                &flags, options, flags, options);
     }
 
     bs->open_flags = flags;
     bs->options = options;
     options = qdict_clone_shallow(options);
 
     /* Find the right image format driver */
     /* See cautionary note on accessing @options above */
     drvname = qdict_get_try_str(options, "driver");
     if (drvname) {
         drv = bdrv_find_format(drvname);
         if (!drv) {
             error_setg(errp, "Unknown driver: '%s'", drvname);
             goto fail;
         }
     }
 
     assert(drvname || !(flags & BDRV_O_PROTOCOL));
 
     /* See cautionary note on accessing @options above */
     backing = qdict_get_try_str(options, "backing");
     if (qobject_to(QNull, qdict_get(options, "backing")) != NULL ||
         (backing && *backing == '\0'))
     {
         if (backing) {
             warn_report("Use of \"backing\": \"\" is deprecated; "
                         "use \"backing\": null instead");
         }
         flags |= BDRV_O_NO_BACKING;
         qdict_del(bs->explicit_options, "backing");
         qdict_del(bs->options, "backing");
         qdict_del(options, "backing");
     }
 
     /* Open image file without format layer. This BlockBackend is only used for
      * probing, the block drivers will do their own bdrv_open_child() for the
      * same BDS, which is why we put the node name back into options. */
     if ((flags & BDRV_O_PROTOCOL) == 0) {
         BlockDriverState *file_bs;
 
         file_bs = bdrv_open_child_bs(filename, options, "file", bs,
                                      &child_of_bds, BDRV_CHILD_IMAGE,
                                      true, &local_err);
         if (local_err) {
             goto fail;
         }
         if (file_bs != NULL) {
             /* Not requesting BLK_PERM_CONSISTENT_READ because we're only
              * looking at the header to guess the image format. This works even
              * in cases where a guest would not see a consistent state. */
             file = blk_new(bdrv_get_aio_context(file_bs), 0, BLK_PERM_ALL);
             blk_insert_bs(file, file_bs, &local_err);
             bdrv_unref(file_bs);
             if (local_err) {
                 goto fail;
             }
 
             qdict_put_str(options, "file", bdrv_get_node_name(file_bs));
         }
     }
 
     /* Image format probing */
     bs->probed = !drv;
     if (!drv && file) {
         ret = find_image_format(file, filename, &drv, &local_err);
         if (ret < 0) {
             goto fail;
         }
         /*
          * This option update would logically belong in bdrv_fill_options(),
          * but we first need to open bs->file for the probing to work, while
          * opening bs->file already requires the (mostly) final set of options
          * so that cache mode etc. can be inherited.
          *
          * Adding the driver later is somewhat ugly, but it's not an option
          * that would ever be inherited, so it's correct. We just need to make
          * sure to update both bs->options (which has the full effective
          * options for bs) and options (which has file.* already removed).
          */
         qdict_put_str(bs->options, "driver", drv->format_name);
         qdict_put_str(options, "driver", drv->format_name);
     } else if (!drv) {
         error_setg(errp, "Must specify either driver or file");
         goto fail;
     }
 
     /* BDRV_O_PROTOCOL must be set iff a protocol BDS is about to be created */
     assert(!!(flags & BDRV_O_PROTOCOL) == !!drv->bdrv_file_open);
     /* file must be NULL if a protocol BDS is about to be created
      * (the inverse results in an error message from bdrv_open_common()) */
     assert(!(flags & BDRV_O_PROTOCOL) || !file);
 
     /* Open the image */
     ret = bdrv_open_common(bs, file, options, &local_err);
     if (ret < 0) {
         goto fail;
     }
 
     if (file) {
         blk_unref(file);
         file = NULL;
     }
 
     /* If there is a backing file, use it */
     if ((flags & BDRV_O_NO_BACKING) == 0) {
         ret = bdrv_open_backing_file(bs, options, "backing", &local_err);
         if (ret < 0) {
             goto close_and_fail;
         }
     }
 
     /* Remove all children options and references
      * from bs->options and bs->explicit_options */
     QLIST_FOREACH(child, &bs->children, next) {
         char *child_key_dot;
         child_key_dot = g_strdup_printf("%s.", child->name);
         qdict_extract_subqdict(bs->explicit_options, NULL, child_key_dot);
         qdict_extract_subqdict(bs->options, NULL, child_key_dot);
         qdict_del(bs->explicit_options, child->name);
         qdict_del(bs->options, child->name);
         g_free(child_key_dot);
     }
 
     /* Check if any unknown options were used */
     if (qdict_size(options) != 0) {
         const QDictEntry *entry = qdict_first(options);
         if (flags & BDRV_O_PROTOCOL) {
             error_setg(errp, "Block protocol '%s' doesn't support the option "
                        "'%s'", drv->format_name, entry->key);
         } else {
             error_setg(errp,
                        "Block format '%s' does not support the option '%s'",
                        drv->format_name, entry->key);
         }
 
         goto close_and_fail;
     }
 
     bdrv_parent_cb_change_media(bs, true);
 
     qobject_unref(options);
     options = NULL;
 
     /* For snapshot=on, create a temporary qcow2 overlay. bs points to the
      * temporary snapshot afterwards. */
     if (snapshot_flags) {
         BlockDriverState *snapshot_bs;
         snapshot_bs = bdrv_append_temp_snapshot(bs, snapshot_flags,
                                                 snapshot_options, &local_err);
         snapshot_options = NULL;
         if (local_err) {
             goto close_and_fail;
         }
         /* We are not going to return bs but the overlay on top of it
          * (snapshot_bs); thus, we have to drop the strong reference to bs
          * (which we obtained by calling bdrv_new()). bs will not be deleted,
          * though, because the overlay still has a reference to it. */
         bdrv_unref(bs);
         bs = snapshot_bs;
     }
 
     return bs;
 
 fail:
     blk_unref(file);
     qobject_unref(snapshot_options);
     qobject_unref(bs->explicit_options);
     qobject_unref(bs->options);
     qobject_unref(options);
     bs->options = NULL;
     bs->explicit_options = NULL;
     bdrv_unref(bs);
     error_propagate(errp, local_err);
     return NULL;
 
 close_and_fail:
     bdrv_unref(bs);
     qobject_unref(snapshot_options);
     qobject_unref(options);
     error_propagate(errp, local_err);
     return NULL;
 }
 
 BlockDriverState *bdrv_open(const char *filename, const char *reference,
                             QDict *options, int flags, Error **errp)
 {
     GLOBAL_STATE_CODE();
 
     return bdrv_open_inherit(filename, reference, options, flags, NULL,
                              NULL, 0, errp);
 }
 
 /* Return true if the NULL-terminated @list contains @str */
 static bool is_str_in_list(const char *str, const char *const *list)
 {
     if (str && list) {
         int i;
         for (i = 0; list[i] != NULL; i++) {
             if (!strcmp(str, list[i])) {
                 return true;
             }
         }
     }
     return false;
 }
 
 /*
  * Check that every option set in @bs->options is also set in
  * @new_opts.
  *
  * Options listed in the common_options list and in
  * @bs->drv->mutable_opts are skipped.
  *
  * Return 0 on success, otherwise return -EINVAL and set @errp.
  */
 static int bdrv_reset_options_allowed(BlockDriverState *bs,
                                       const QDict *new_opts, Error **errp)
 {
     const QDictEntry *e;
     /* These options are common to all block drivers and are handled
      * in bdrv_reopen_prepare() so they can be left out of @new_opts */
     const char *const common_options[] = {
         "node-name", "discard", "cache.direct", "cache.no-flush",
         "read-only", "auto-read-only", "detect-zeroes", NULL
     };
 
     for (e = qdict_first(bs->options); e; e = qdict_next(bs->options, e)) {
         if (!qdict_haskey(new_opts, e->key) &&
             !is_str_in_list(e->key, common_options) &&
             !is_str_in_list(e->key, bs->drv->mutable_opts)) {
             error_setg(errp, "Option '%s' cannot be reset "
                        "to its default value", e->key);
             return -EINVAL;
         }
     }
 
     return 0;
 }
 
 /*
  * Returns true if @child can be reached recursively from @bs
  */
 static bool bdrv_recurse_has_child(BlockDriverState *bs,
                                    BlockDriverState *child)
 {
     BdrvChild *c;
 
     if (bs == child) {
         return true;
     }
 
     QLIST_FOREACH(c, &bs->children, next) {
         if (bdrv_recurse_has_child(c->bs, child)) {
             return true;
         }
     }
 
     return false;
 }
 
 /*
  * Adds a BlockDriverState to a simple queue for an atomic, transactional
  * reopen of multiple devices.
  *
  * bs_queue can either be an existing BlockReopenQueue that has had QTAILQ_INIT
  * already performed, or alternatively may be NULL a new BlockReopenQueue will
  * be created and initialized. This newly created BlockReopenQueue should be
  * passed back in for subsequent calls that are intended to be of the same
  * atomic 'set'.
  *
  * bs is the BlockDriverState to add to the reopen queue.
  *
  * options contains the changed options for the associated bs
  * (the BlockReopenQueue takes ownership)
  *
  * flags contains the open flags for the associated bs
  *
  * returns a pointer to bs_queue, which is either the newly allocated
  * bs_queue, or the existing bs_queue being used.
  *
  * bs must be drained between bdrv_reopen_queue() and bdrv_reopen_multiple().
  */
 static BlockReopenQueue *bdrv_reopen_queue_child(BlockReopenQueue *bs_queue,
                                                  BlockDriverState *bs,
                                                  QDict *options,
                                                  const BdrvChildClass *klass,
                                                  BdrvChildRole role,
                                                  bool parent_is_format,
                                                  QDict *parent_options,
                                                  int parent_flags,
                                                  bool keep_old_opts)
 {
     assert(bs != NULL);
 
     BlockReopenQueueEntry *bs_entry;
     BdrvChild *child;
     QDict *old_options, *explicit_options, *options_copy;
     int flags;
     QemuOpts *opts;
 
     /* Make sure that the caller remembered to use a drained section. This is
      * important to avoid graph changes between the recursive queuing here and
      * bdrv_reopen_multiple(). */
     assert(bs->quiesce_counter > 0);
     GLOBAL_STATE_CODE();
 
     if (bs_queue == NULL) {
         bs_queue = g_new0(BlockReopenQueue, 1);
         QTAILQ_INIT(bs_queue);
     }
 
     if (!options) {
         options = qdict_new();
     }
 
     /* Check if this BlockDriverState is already in the queue */
     QTAILQ_FOREACH(bs_entry, bs_queue, entry) {
         if (bs == bs_entry->state.bs) {
             break;
         }
     }
 
     /*
      * Precedence of options:
      * 1. Explicitly passed in options (highest)
      * 2. Retained from explicitly set options of bs
      * 3. Inherited from parent node
      * 4. Retained from effective options of bs
      */
 
     /* Old explicitly set values (don't overwrite by inherited value) */
     if (bs_entry || keep_old_opts) {
         old_options = qdict_clone_shallow(bs_entry ?
                                           bs_entry->state.explicit_options :
                                           bs->explicit_options);
         bdrv_join_options(bs, options, old_options);
         qobject_unref(old_options);
     }
 
     explicit_options = qdict_clone_shallow(options);
 
     /* Inherit from parent node */
     if (parent_options) {
         flags = 0;
         klass->inherit_options(role, parent_is_format, &flags, options,
                                parent_flags, parent_options);
     } else {
         flags = bdrv_get_flags(bs);
     }
 
     if (keep_old_opts) {
         /* Old values are used for options that aren't set yet */
         old_options = qdict_clone_shallow(bs->options);
         bdrv_join_options(bs, options, old_options);
         qobject_unref(old_options);
     }
 
     /* We have the final set of options so let's update the flags */
     options_copy = qdict_clone_shallow(options);
     opts = qemu_opts_create(&bdrv_runtime_opts, NULL, 0, &error_abort);
     qemu_opts_absorb_qdict(opts, options_copy, NULL);
     update_flags_from_options(&flags, opts);
     qemu_opts_del(opts);
     qobject_unref(options_copy);
 
     /* bdrv_open_inherit() sets and clears some additional flags internally */
     flags &= ~BDRV_O_PROTOCOL;
     if (flags & BDRV_O_RDWR) {
         flags |= BDRV_O_ALLOW_RDWR;
     }
 
     if (!bs_entry) {
         bs_entry = g_new0(BlockReopenQueueEntry, 1);
         QTAILQ_INSERT_TAIL(bs_queue, bs_entry, entry);
     } else {
         qobject_unref(bs_entry->state.options);
         qobject_unref(bs_entry->state.explicit_options);
     }
 
     bs_entry->state.bs = bs;
     bs_entry->state.options = options;
     bs_entry->state.explicit_options = explicit_options;
     bs_entry->state.flags = flags;
 
     /*
      * If keep_old_opts is false then it means that unspecified
      * options must be reset to their original value. We don't allow
      * resetting 'backing' but we need to know if the option is
      * missing in order to decide if we have to return an error.
      */
     if (!keep_old_opts) {
         bs_entry->state.backing_missing =
             !qdict_haskey(options, "backing") &&
             !qdict_haskey(options, "backing.driver");
     }
 
     QLIST_FOREACH(child, &bs->children, next) {
         QDict *new_child_options = NULL;
         bool child_keep_old = keep_old_opts;
 
         /* reopen can only change the options of block devices that were
          * implicitly created and inherited options. For other (referenced)
          * block devices, a syntax like "backing.foo" results in an error. */
         if (child->bs->inherits_from != bs) {
             continue;
         }
 
         /* Check if the options contain a child reference */
         if (qdict_haskey(options, child->name)) {
             const char *childref = qdict_get_try_str(options, child->name);
             /*
              * The current child must not be reopened if the child
              * reference is null or points to a different node.
              */
             if (g_strcmp0(childref, child->bs->node_name)) {
                 continue;
             }
             /*
              * If the child reference points to the current child then
              * reopen it with its existing set of options (note that
              * it can still inherit new options from the parent).
              */
             child_keep_old = true;
         } else {
             /* Extract child options ("child-name.*") */
             char *child_key_dot = g_strdup_printf("%s.", child->name);
             qdict_extract_subqdict(explicit_options, NULL, child_key_dot);
             qdict_extract_subqdict(options, &new_child_options, child_key_dot);
             g_free(child_key_dot);
         }
 
         bdrv_reopen_queue_child(bs_queue, child->bs, new_child_options,
                                 child->klass, child->role, bs->drv->is_format,
                                 options, flags, child_keep_old);
     }
 
     return bs_queue;
 }
 
 BlockReopenQueue *bdrv_reopen_queue(BlockReopenQueue *bs_queue,
                                     BlockDriverState *bs,
                                     QDict *options, bool keep_old_opts)
 {
     GLOBAL_STATE_CODE();
 
     return bdrv_reopen_queue_child(bs_queue, bs, options, NULL, 0, false,
                                    NULL, 0, keep_old_opts);
 }
 
 void bdrv_reopen_queue_free(BlockReopenQueue *bs_queue)
 {
     GLOBAL_STATE_CODE();
     if (bs_queue) {
         BlockReopenQueueEntry *bs_entry, *next;
         QTAILQ_FOREACH_SAFE(bs_entry, bs_queue, entry, next) {
             qobject_unref(bs_entry->state.explicit_options);
             qobject_unref(bs_entry->state.options);
             g_free(bs_entry);
         }
         g_free(bs_queue);
     }
 }
 
 /*
  * Reopen multiple BlockDriverStates atomically & transactionally.
  *
  * The queue passed in (bs_queue) must have been built up previous
  * via bdrv_reopen_queue().
  *
  * Reopens all BDS specified in the queue, with the appropriate
  * flags.  All devices are prepared for reopen, and failure of any
  * device will cause all device changes to be abandoned, and intermediate
  * data cleaned up.
  *
  * If all devices prepare successfully, then the changes are committed
  * to all devices.
  *
  * All affected nodes must be drained between bdrv_reopen_queue() and
  * bdrv_reopen_multiple().
  *
  * To be called from the main thread, with all other AioContexts unlocked.
  */
 int bdrv_reopen_multiple(BlockReopenQueue *bs_queue, Error **errp)
 {
     int ret = -1;
     BlockReopenQueueEntry *bs_entry, *next;
     AioContext *ctx;
     Transaction *tran = tran_new();
     g_autoptr(GHashTable) found = NULL;
     g_autoptr(GSList) refresh_list = NULL;
 
     assert(qemu_get_current_aio_context() == qemu_get_aio_context());
     assert(bs_queue != NULL);
     GLOBAL_STATE_CODE();
 
     QTAILQ_FOREACH(bs_entry, bs_queue, entry) {
         ctx = bdrv_get_aio_context(bs_entry->state.bs);
         aio_context_acquire(ctx);
         ret = bdrv_flush(bs_entry->state.bs);
         aio_context_release(ctx);
         if (ret < 0) {
             error_setg_errno(errp, -ret, "Error flushing drive");
             goto abort;
         }
     }
 
     QTAILQ_FOREACH(bs_entry, bs_queue, entry) {
         assert(bs_entry->state.bs->quiesce_counter > 0);
         ctx = bdrv_get_aio_context(bs_entry->state.bs);
         aio_context_acquire(ctx);
         ret = bdrv_reopen_prepare(&bs_entry->state, bs_queue, tran, errp);
         aio_context_release(ctx);
         if (ret < 0) {
             goto abort;
         }
         bs_entry->prepared = true;
     }
 
     found = g_hash_table_new(NULL, NULL);
     QTAILQ_FOREACH(bs_entry, bs_queue, entry) {
         BDRVReopenState *state = &bs_entry->state;
 
         refresh_list = bdrv_topological_dfs(refresh_list, found, state->bs);
         if (state->old_backing_bs) {
             refresh_list = bdrv_topological_dfs(refresh_list, found,
                                                 state->old_backing_bs);
         }
         if (state->old_file_bs) {
             refresh_list = bdrv_topological_dfs(refresh_list, found,
                                                 state->old_file_bs);
         }
     }
 
     /*
      * Note that file-posix driver rely on permission update done during reopen
      * (even if no permission changed), because it wants "new" permissions for
      * reconfiguring the fd and that's why it does it in raw_check_perm(), not
      * in raw_reopen_prepare() which is called with "old" permissions.
      */
     ret = bdrv_list_refresh_perms(refresh_list, bs_queue, tran, errp);
     if (ret < 0) {
         goto abort;
     }
 
     /*
      * If we reach this point, we have success and just need to apply the
      * changes.
      *
      * Reverse order is used to comfort qcow2 driver: on commit it need to write
      * IN_USE flag to the image, to mark bitmaps in the image as invalid. But
      * children are usually goes after parents in reopen-queue, so go from last
      * to first element.
      */
     QTAILQ_FOREACH_REVERSE(bs_entry, bs_queue, entry) {
         ctx = bdrv_get_aio_context(bs_entry->state.bs);
         aio_context_acquire(ctx);
         bdrv_reopen_commit(&bs_entry->state);
         aio_context_release(ctx);
     }
 
     tran_commit(tran);
 
     QTAILQ_FOREACH_REVERSE(bs_entry, bs_queue, entry) {
         BlockDriverState *bs = bs_entry->state.bs;
 
         if (bs->drv->bdrv_reopen_commit_post) {
             ctx = bdrv_get_aio_context(bs);
             aio_context_acquire(ctx);
             bs->drv->bdrv_reopen_commit_post(&bs_entry->state);
             aio_context_release(ctx);
         }
     }
 
     ret = 0;
     goto cleanup;
 
 abort:
     tran_abort(tran);
     QTAILQ_FOREACH_SAFE(bs_entry, bs_queue, entry, next) {
         if (bs_entry->prepared) {
             ctx = bdrv_get_aio_context(bs_entry->state.bs);
             aio_context_acquire(ctx);
             bdrv_reopen_abort(&bs_entry->state);
             aio_context_release(ctx);
         }
     }
 
 cleanup:
     bdrv_reopen_queue_free(bs_queue);
 
     return ret;
 }
 
 int bdrv_reopen(BlockDriverState *bs, QDict *opts, bool keep_old_opts,
                 Error **errp)
 {
     AioContext *ctx = bdrv_get_aio_context(bs);
     BlockReopenQueue *queue;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     bdrv_subtree_drained_begin(bs);
     if (ctx != qemu_get_aio_context()) {
         aio_context_release(ctx);
     }
 
     queue = bdrv_reopen_queue(NULL, bs, opts, keep_old_opts);
     ret = bdrv_reopen_multiple(queue, errp);
 
     if (ctx != qemu_get_aio_context()) {
         aio_context_acquire(ctx);
     }
     bdrv_subtree_drained_end(bs);
 
     return ret;
 }
 
 int bdrv_reopen_set_read_only(BlockDriverState *bs, bool read_only,
                               Error **errp)
 {
     QDict *opts = qdict_new();
 
     GLOBAL_STATE_CODE();
 
     qdict_put_bool(opts, BDRV_OPT_READ_ONLY, read_only);
 
     return bdrv_reopen(bs, opts, true, errp);
 }
 
 /*
  * Take a BDRVReopenState and check if the value of 'backing' in the
  * reopen_state->options QDict is valid or not.
  *
  * If 'backing' is missing from the QDict then return 0.
  *
  * If 'backing' contains the node name of the backing file of
  * reopen_state->bs then return 0.
  *
  * If 'backing' contains a different node name (or is null) then check
  * whether the current backing file can be replaced with the new one.
  * If that's the case then reopen_state->replace_backing_bs is set to
  * true and reopen_state->new_backing_bs contains a pointer to the new
  * backing BlockDriverState (or NULL).
  *
  * Return 0 on success, otherwise return < 0 and set @errp.
  */
 static int bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
                                              bool is_backing, Transaction *tran,
                                              Error **errp)
 {
     BlockDriverState *bs = reopen_state->bs;
     BlockDriverState *new_child_bs;
     BlockDriverState *old_child_bs = is_backing ? child_bs(bs->backing) :
                                                   child_bs(bs->file);
     const char *child_name = is_backing ? "backing" : "file";
     QObject *value;
     const char *str;
 
     GLOBAL_STATE_CODE();
 
     value = qdict_get(reopen_state->options, child_name);
     if (value == NULL) {
         return 0;
     }
 
     switch (qobject_type(value)) {
     case QTYPE_QNULL:
         assert(is_backing); /* The 'file' option does not allow a null value */
         new_child_bs = NULL;
         break;
     case QTYPE_QSTRING:
         str = qstring_get_str(qobject_to(QString, value));
         new_child_bs = bdrv_lookup_bs(NULL, str, errp);
         if (new_child_bs == NULL) {
             return -EINVAL;
         } else if (bdrv_recurse_has_child(new_child_bs, bs)) {
             error_setg(errp, "Making '%s' a %s child of '%s' would create a "
                        "cycle", str, child_name, bs->node_name);
             return -EINVAL;
         }
         break;
     default:
         /*
          * The options QDict has been flattened, so 'backing' and 'file'
          * do not allow any other data type here.
          */
         g_assert_not_reached();
     }
 
     if (old_child_bs == new_child_bs) {
         return 0;
     }
 
     if (old_child_bs) {
         if (bdrv_skip_implicit_filters(old_child_bs) == new_child_bs) {
             return 0;
         }
 
         if (old_child_bs->implicit) {
             error_setg(errp, "Cannot replace implicit %s child of %s",
                        child_name, bs->node_name);
             return -EPERM;
         }
     }
 
     if (bs->drv->is_filter && !old_child_bs) {
         /*
          * Filters always have a file or a backing child, so we are trying to
          * change wrong child
          */
         error_setg(errp, "'%s' is a %s filter node that does not support a "
                    "%s child", bs->node_name, bs->drv->format_name, child_name);
         return -EINVAL;
     }
 
     if (is_backing) {
         reopen_state->old_backing_bs = old_child_bs;
     } else {
         reopen_state->old_file_bs = old_child_bs;
     }
 
     return bdrv_set_file_or_backing_noperm(bs, new_child_bs, is_backing,
                                            tran, errp);
 }
 
 /*
  * Prepares a BlockDriverState for reopen. All changes are staged in the
  * 'opaque' field of the BDRVReopenState, which is used and allocated by
  * the block driver layer .bdrv_reopen_prepare()
  *
  * bs is the BlockDriverState to reopen
  * flags are the new open flags
  * queue is the reopen queue
  *
  * Returns 0 on success, non-zero on error.  On error errp will be set
  * as well.
  *
  * On failure, bdrv_reopen_abort() will be called to clean up any data.
  * It is the responsibility of the caller to then call the abort() or
  * commit() for any other BDS that have been left in a prepare() state
  *
  */
 static int bdrv_reopen_prepare(BDRVReopenState *reopen_state,
                                BlockReopenQueue *queue,
                                Transaction *change_child_tran, Error **errp)
 {
     int ret = -1;
     int old_flags;
     Error *local_err = NULL;
     BlockDriver *drv;
     QemuOpts *opts;
     QDict *orig_reopen_opts;
     char *discard = NULL;
     bool read_only;
     bool drv_prepared = false;
 
     assert(reopen_state != NULL);
     assert(reopen_state->bs->drv != NULL);
     GLOBAL_STATE_CODE();
     drv = reopen_state->bs->drv;
 
     /* This function and each driver's bdrv_reopen_prepare() remove
      * entries from reopen_state->options as they are processed, so
      * we need to make a copy of the original QDict. */
     orig_reopen_opts = qdict_clone_shallow(reopen_state->options);
 
     /* Process generic block layer options */
     opts = qemu_opts_create(&bdrv_runtime_opts, NULL, 0, &error_abort);
     if (!qemu_opts_absorb_qdict(opts, reopen_state->options, errp)) {
         ret = -EINVAL;
         goto error;
     }
 
     /* This was already called in bdrv_reopen_queue_child() so the flags
      * are up-to-date. This time we simply want to remove the options from
      * QemuOpts in order to indicate that they have been processed. */
     old_flags = reopen_state->flags;
     update_flags_from_options(&reopen_state->flags, opts);
     assert(old_flags == reopen_state->flags);
 
     discard = qemu_opt_get_del(opts, BDRV_OPT_DISCARD);
     if (discard != NULL) {
         if (bdrv_parse_discard_flags(discard, &reopen_state->flags) != 0) {
             error_setg(errp, "Invalid discard option");
             ret = -EINVAL;
             goto error;
         }
     }
 
     reopen_state->detect_zeroes =
         bdrv_parse_detect_zeroes(opts, reopen_state->flags, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         ret = -EINVAL;
         goto error;
     }
 
     /* All other options (including node-name and driver) must be unchanged.
      * Put them back into the QDict, so that they are checked at the end
      * of this function. */
     qemu_opts_to_qdict(opts, reopen_state->options);
 
     /* If we are to stay read-only, do not allow permission change
      * to r/w. Attempting to set to r/w may fail if either BDRV_O_ALLOW_RDWR is
      * not set, or if the BDS still has copy_on_read enabled */
     read_only = !(reopen_state->flags & BDRV_O_RDWR);
     ret = bdrv_can_set_read_only(reopen_state->bs, read_only, true, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         goto error;
     }
 
     if (drv->bdrv_reopen_prepare) {
         /*
          * If a driver-specific option is missing, it means that we
          * should reset it to its default value.
          * But not all options allow that, so we need to check it first.
          */
         ret = bdrv_reset_options_allowed(reopen_state->bs,
                                          reopen_state->options, errp);
         if (ret) {
             goto error;
         }
 
         ret = drv->bdrv_reopen_prepare(reopen_state, queue, &local_err);
         if (ret) {
             if (local_err != NULL) {
                 error_propagate(errp, local_err);
             } else {
                 bdrv_refresh_filename(reopen_state->bs);
                 error_setg(errp, "failed while preparing to reopen image '%s'",
                            reopen_state->bs->filename);
             }
             goto error;
         }
     } else {
         /* It is currently mandatory to have a bdrv_reopen_prepare()
          * handler for each supported drv. */
         error_setg(errp, "Block format '%s' used by node '%s' "
                    "does not support reopening files", drv->format_name,
                    bdrv_get_device_or_node_name(reopen_state->bs));
         ret = -1;
         goto error;
     }
 
     drv_prepared = true;
 
     /*
      * We must provide the 'backing' option if the BDS has a backing
      * file or if the image file has a backing file name as part of
      * its metadata. Otherwise the 'backing' option can be omitted.
      */
     if (drv->supports_backing && reopen_state->backing_missing &&
         (reopen_state->bs->backing || reopen_state->bs->backing_file[0])) {
         error_setg(errp, "backing is missing for '%s'",
                    reopen_state->bs->node_name);
         ret = -EINVAL;
         goto error;
     }
 
     /*
      * Allow changing the 'backing' option. The new value can be
      * either a reference to an existing node (using its node name)
      * or NULL to simply detach the current backing file.
      */
     ret = bdrv_reopen_parse_file_or_backing(reopen_state, true,
                                             change_child_tran, errp);
     if (ret < 0) {
         goto error;
     }
     qdict_del(reopen_state->options, "backing");
 
     /* Allow changing the 'file' option. In this case NULL is not allowed */
     ret = bdrv_reopen_parse_file_or_backing(reopen_state, false,
                                             change_child_tran, errp);
     if (ret < 0) {
         goto error;
     }
     qdict_del(reopen_state->options, "file");
 
     /* Options that are not handled are only okay if they are unchanged
      * compared to the old state. It is expected that some options are only
      * used for the initial open, but not reopen (e.g. filename) */
     if (qdict_size(reopen_state->options)) {
         const QDictEntry *entry = qdict_first(reopen_state->options);
 
         do {
             QObject *new = entry->value;
             QObject *old = qdict_get(reopen_state->bs->options, entry->key);
 
             /* Allow child references (child_name=node_name) as long as they
              * point to the current child (i.e. everything stays the same). */
             if (qobject_type(new) == QTYPE_QSTRING) {
                 BdrvChild *child;
                 QLIST_FOREACH(child, &reopen_state->bs->children, next) {
                     if (!strcmp(child->name, entry->key)) {
                         break;
                     }
                 }
 
                 if (child) {
                     if (!strcmp(child->bs->node_name,
                                 qstring_get_str(qobject_to(QString, new)))) {
                         continue; /* Found child with this name, skip option */
                     }
                 }
             }
 
             /*
              * TODO: When using -drive to specify blockdev options, all values
              * will be strings; however, when using -blockdev, blockdev-add or
              * filenames using the json:{} pseudo-protocol, they will be
              * correctly typed.
              * In contrast, reopening options are (currently) always strings
              * (because you can only specify them through qemu-io; all other
              * callers do not specify any options).
              * Therefore, when using anything other than -drive to create a BDS,
              * this cannot detect non-string options as unchanged, because
              * qobject_is_equal() always returns false for objects of different
              * type.  In the future, this should be remedied by correctly typing
              * all options.  For now, this is not too big of an issue because
              * the user can simply omit options which cannot be changed anyway,
              * so they will stay unchanged.
              */
             if (!qobject_is_equal(new, old)) {
                 error_setg(errp, "Cannot change the option '%s'", entry->key);
                 ret = -EINVAL;
                 goto error;
             }
         } while ((entry = qdict_next(reopen_state->options, entry)));
     }
 
     ret = 0;
 
     /* Restore the original reopen_state->options QDict */
     qobject_unref(reopen_state->options);
     reopen_state->options = qobject_ref(orig_reopen_opts);
 
 error:
     if (ret < 0 && drv_prepared) {
         /* drv->bdrv_reopen_prepare() has succeeded, so we need to
          * call drv->bdrv_reopen_abort() before signaling an error
          * (bdrv_reopen_multiple() will not call bdrv_reopen_abort()
          * when the respective bdrv_reopen_prepare() has failed) */
         if (drv->bdrv_reopen_abort) {
             drv->bdrv_reopen_abort(reopen_state);
         }
     }
     qemu_opts_del(opts);
     qobject_unref(orig_reopen_opts);
     g_free(discard);
     return ret;
 }
 
 /*
  * Takes the staged changes for the reopen from bdrv_reopen_prepare(), and
  * makes them final by swapping the staging BlockDriverState contents into
  * the active BlockDriverState contents.
  */
 static void bdrv_reopen_commit(BDRVReopenState *reopen_state)
 {
     BlockDriver *drv;
     BlockDriverState *bs;
     BdrvChild *child;
 
     assert(reopen_state != NULL);
     bs = reopen_state->bs;
     drv = bs->drv;
     assert(drv != NULL);
     GLOBAL_STATE_CODE();
 
     /* If there are any driver level actions to take */
     if (drv->bdrv_reopen_commit) {
         drv->bdrv_reopen_commit(reopen_state);
     }
 
     /* set BDS specific flags now */
     qobject_unref(bs->explicit_options);
     qobject_unref(bs->options);
     qobject_ref(reopen_state->explicit_options);
     qobject_ref(reopen_state->options);
 
     bs->explicit_options   = reopen_state->explicit_options;
     bs->options            = reopen_state->options;
     bs->open_flags         = reopen_state->flags;
     bs->detect_zeroes      = reopen_state->detect_zeroes;
 
     /* Remove child references from bs->options and bs->explicit_options.
      * Child options were already removed in bdrv_reopen_queue_child() */
     QLIST_FOREACH(child, &bs->children, next) {
         qdict_del(bs->explicit_options, child->name);
         qdict_del(bs->options, child->name);
     }
     /* backing is probably removed, so it's not handled by previous loop */
     qdict_del(bs->explicit_options, "backing");
     qdict_del(bs->options, "backing");
 
     bdrv_refresh_limits(bs, NULL, NULL);
 }
 
 /*
  * Abort the reopen, and delete and free the staged changes in
  * reopen_state
  */
 static void bdrv_reopen_abort(BDRVReopenState *reopen_state)
 {
     BlockDriver *drv;
 
     assert(reopen_state != NULL);
     drv = reopen_state->bs->drv;
     assert(drv != NULL);
     GLOBAL_STATE_CODE();
 
     if (drv->bdrv_reopen_abort) {
         drv->bdrv_reopen_abort(reopen_state);
     }
 }
 
 
 static void bdrv_close(BlockDriverState *bs)
 {
     BdrvAioNotifier *ban, *ban_next;
     BdrvChild *child, *next;
 
     GLOBAL_STATE_CODE();
     assert(!bs->refcnt);
 
     bdrv_drained_begin(bs); /* complete I/O */
     bdrv_flush(bs);
     bdrv_drain(bs); /* in case flush left pending I/O */
 
     if (bs->drv) {
         if (bs->drv->bdrv_close) {
             /* Must unfreeze all children, so bdrv_unref_child() works */
             bs->drv->bdrv_close(bs);
         }
         bs->drv = NULL;
     }
 
     QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
         bdrv_unref_child(bs, child);
     }
 
     assert(!bs->backing);
     assert(!bs->file);
     g_free(bs->opaque);
     bs->opaque = NULL;
     qatomic_set(&bs->copy_on_read, 0);
     bs->backing_file[0] = '\0';
     bs->backing_format[0] = '\0';
     bs->total_sectors = 0;
     bs->encrypted = false;
     bs->sg = false;
     qobject_unref(bs->options);
     qobject_unref(bs->explicit_options);
     bs->options = NULL;
     bs->explicit_options = NULL;
     qobject_unref(bs->full_open_options);
     bs->full_open_options = NULL;
     g_free(bs->block_status_cache);
     bs->block_status_cache = NULL;
 
     bdrv_release_named_dirty_bitmaps(bs);
     assert(QLIST_EMPTY(&bs->dirty_bitmaps));
 
     QLIST_FOREACH_SAFE(ban, &bs->aio_notifiers, list, ban_next) {
         g_free(ban);
     }
     QLIST_INIT(&bs->aio_notifiers);
     bdrv_drained_end(bs);
 
     /*
      * If we're still inside some bdrv_drain_all_begin()/end() sections, end
      * them now since this BDS won't exist anymore when bdrv_drain_all_end()
      * gets called.
      */
     if (bs->quiesce_counter) {
         bdrv_drain_all_end_quiesce(bs);
     }
 }
 
 void bdrv_close_all(void)
 {
     GLOBAL_STATE_CODE();
     assert(job_next(NULL) == NULL);
 
     /* Drop references from requests still in flight, such as canceled block
      * jobs whose AIO context has not been polled yet */
     bdrv_drain_all();
 
     blk_remove_all_bs();
     blockdev_close_all_bdrv_states();
 
     assert(QTAILQ_EMPTY(&all_bdrv_states));
 }
 
 static bool should_update_child(BdrvChild *c, BlockDriverState *to)
 {
     GQueue *queue;
     GHashTable *found;
     bool ret;
 
     if (c->klass->stay_at_node) {
         return false;
     }
 
     /* If the child @c belongs to the BDS @to, replacing the current
      * c->bs by @to would mean to create a loop.
      *
      * Such a case occurs when appending a BDS to a backing chain.
      * For instance, imagine the following chain:
      *
      *   guest device -> node A -> further backing chain...
      *
      * Now we create a new BDS B which we want to put on top of this
      * chain, so we first attach A as its backing node:
      *
      *                   node B
      *                     |
      *                     v
      *   guest device -> node A -> further backing chain...
      *
      * Finally we want to replace A by B.  When doing that, we want to
      * replace all pointers to A by pointers to B -- except for the
      * pointer from B because (1) that would create a loop, and (2)
      * that pointer should simply stay intact:
      *
      *   guest device -> node B
      *                     |
      *                     v
      *                   node A -> further backing chain...
      *
      * In general, when replacing a node A (c->bs) by a node B (@to),
      * if A is a child of B, that means we cannot replace A by B there
      * because that would create a loop.  Silently detaching A from B
      * is also not really an option.  So overall just leaving A in
      * place there is the most sensible choice.
      *
      * We would also create a loop in any cases where @c is only
      * indirectly referenced by @to. Prevent this by returning false
      * if @c is found (by breadth-first search) anywhere in the whole
      * subtree of @to.
      */
 
     ret = true;
     found = g_hash_table_new(NULL, NULL);
     g_hash_table_add(found, to);
     queue = g_queue_new();
     g_queue_push_tail(queue, to);
 
     while (!g_queue_is_empty(queue)) {
         BlockDriverState *v = g_queue_pop_head(queue);
         BdrvChild *c2;
 
         QLIST_FOREACH(c2, &v->children, next) {
             if (c2 == c) {
                 ret = false;
                 break;
             }
 
             if (g_hash_table_contains(found, c2->bs)) {
                 continue;
             }
 
             g_queue_push_tail(queue, c2->bs);
             g_hash_table_add(found, c2->bs);
         }
     }
 
     g_queue_free(queue);
     g_hash_table_destroy(found);
 
     return ret;
 }
 
 static void bdrv_remove_child_commit(void *opaque)
 {
     GLOBAL_STATE_CODE();
     bdrv_child_free(opaque);
 }
 
 static TransactionActionDrv bdrv_remove_child_drv = {
     .commit = bdrv_remove_child_commit,
 };
 
 /* Function doesn't update permissions, caller is responsible for this. */
 static void bdrv_remove_child(BdrvChild *child, Transaction *tran)
 {
     if (!child) {
         return;
     }
 
     if (child->bs) {
         bdrv_replace_child_tran(child, NULL, tran);
     }
 
     tran_add(tran, &bdrv_remove_child_drv, child);
 }
 
 /*
  * A function to remove backing-chain child of @bs if exists: cow child for
  * format nodes (always .backing) and filter child for filters (may be .file or
  * .backing)
  */
 static void bdrv_remove_filter_or_cow_child(BlockDriverState *bs,
                                             Transaction *tran)
 {
     bdrv_remove_child(bdrv_filter_or_cow_child(bs), tran);
 }
 
 static int bdrv_replace_node_noperm(BlockDriverState *from,
                                     BlockDriverState *to,
                                     bool auto_skip, Transaction *tran,
                                     Error **errp)
 {
     BdrvChild *c, *next;
 
     GLOBAL_STATE_CODE();
 
     QLIST_FOREACH_SAFE(c, &from->parents, next_parent, next) {
         assert(c->bs == from);
         if (!should_update_child(c, to)) {
             if (auto_skip) {
                 continue;
             }
             error_setg(errp, "Should not change '%s' link to '%s'",
                        c->name, from->node_name);
             return -EINVAL;
         }
         if (c->frozen) {
             error_setg(errp, "Cannot change '%s' link to '%s'",
                        c->name, from->node_name);
             return -EPERM;
         }
         bdrv_replace_child_tran(c, to, tran);
     }
 
     return 0;
 }
 
 /*
  * With auto_skip=true bdrv_replace_node_common skips updating from parents
  * if it creates a parent-child relation loop or if parent is block-job.
  *
  * With auto_skip=false the error is returned if from has a parent which should
  * not be updated.
  *
  * With @detach_subchain=true @to must be in a backing chain of @from. In this
  * case backing link of the cow-parent of @to is removed.
  */
 static int bdrv_replace_node_common(BlockDriverState *from,
                                     BlockDriverState *to,
                                     bool auto_skip, bool detach_subchain,
                                     Error **errp)
 {
     Transaction *tran = tran_new();
     g_autoptr(GHashTable) found = NULL;
     g_autoptr(GSList) refresh_list = NULL;
     BlockDriverState *to_cow_parent = NULL;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     if (detach_subchain) {
         assert(bdrv_chain_contains(from, to));
         assert(from != to);
         for (to_cow_parent = from;
              bdrv_filter_or_cow_bs(to_cow_parent) != to;
              to_cow_parent = bdrv_filter_or_cow_bs(to_cow_parent))
         {
             ;
         }
     }
 
     /* Make sure that @from doesn't go away until we have successfully attached
      * all of its parents to @to. */
     bdrv_ref(from);
 
     assert(qemu_get_current_aio_context() == qemu_get_aio_context());
     assert(bdrv_get_aio_context(from) == bdrv_get_aio_context(to));
     bdrv_drained_begin(from);
 
     /*
      * Do the replacement without permission update.
      * Replacement may influence the permissions, we should calculate new
      * permissions based on new graph. If we fail, we'll roll-back the
      * replacement.
      */
     ret = bdrv_replace_node_noperm(from, to, auto_skip, tran, errp);
     if (ret < 0) {
         goto out;
     }
 
     if (detach_subchain) {
         bdrv_remove_filter_or_cow_child(to_cow_parent, tran);
     }
 
     found = g_hash_table_new(NULL, NULL);
 
     refresh_list = bdrv_topological_dfs(refresh_list, found, to);
     refresh_list = bdrv_topological_dfs(refresh_list, found, from);
 
     ret = bdrv_list_refresh_perms(refresh_list, NULL, tran, errp);
     if (ret < 0) {
         goto out;
     }
 
     ret = 0;
 
 out:
     tran_finalize(tran, ret);
 
     bdrv_drained_end(from);
     bdrv_unref(from);
 
     return ret;
 }
 
 int bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
                       Error **errp)
 {
     GLOBAL_STATE_CODE();
 
     return bdrv_replace_node_common(from, to, true, false, errp);
 }
 
 int bdrv_drop_filter(BlockDriverState *bs, Error **errp)
 {
     GLOBAL_STATE_CODE();
 
     return bdrv_replace_node_common(bs, bdrv_filter_or_cow_bs(bs), true, true,
                                     errp);
 }
 
 /*
  * Add new bs contents at the top of an image chain while the chain is
  * live, while keeping required fields on the top layer.
  *
  * This will modify the BlockDriverState fields, and swap contents
  * between bs_new and bs_top. Both bs_new and bs_top are modified.
  *
  * bs_new must not be attached to a BlockBackend and must not have backing
  * child.
  *
  * This function does not create any image files.
  */
 int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
                 Error **errp)
 {
     int ret;
     BdrvChild *child;
     Transaction *tran = tran_new();
 
     GLOBAL_STATE_CODE();
 
     assert(!bs_new->backing);
 
     child = bdrv_attach_child_noperm(bs_new, bs_top, "backing",
                                      &child_of_bds, bdrv_backing_role(bs_new),
                                      tran, errp);
     if (!child) {
         ret = -EINVAL;
         goto out;
     }
 
     ret = bdrv_replace_node_noperm(bs_top, bs_new, true, tran, errp);
     if (ret < 0) {
         goto out;
     }
 
     ret = bdrv_refresh_perms(bs_new, errp);
 out:
     tran_finalize(tran, ret);
 
     bdrv_refresh_limits(bs_top, NULL, NULL);
 
     return ret;
 }
 
 /* Not for empty child */
 int bdrv_replace_child_bs(BdrvChild *child, BlockDriverState *new_bs,
                           Error **errp)
 {
     int ret;
     Transaction *tran = tran_new();
     g_autoptr(GHashTable) found = NULL;
     g_autoptr(GSList) refresh_list = NULL;
     BlockDriverState *old_bs = child->bs;
 
     GLOBAL_STATE_CODE();
 
     bdrv_ref(old_bs);
     bdrv_drained_begin(old_bs);
     bdrv_drained_begin(new_bs);
 
     bdrv_replace_child_tran(child, new_bs, tran);
 
     found = g_hash_table_new(NULL, NULL);
     refresh_list = bdrv_topological_dfs(refresh_list, found, old_bs);
     refresh_list = bdrv_topological_dfs(refresh_list, found, new_bs);
 
     ret = bdrv_list_refresh_perms(refresh_list, NULL, tran, errp);
 
     tran_finalize(tran, ret);
 
     bdrv_drained_end(old_bs);
     bdrv_drained_end(new_bs);
     bdrv_unref(old_bs);
 
     return ret;
 }
 
 static void bdrv_delete(BlockDriverState *bs)
 {
     assert(bdrv_op_blocker_is_empty(bs));
     assert(!bs->refcnt);
     GLOBAL_STATE_CODE();
 
     /* remove from list, if necessary */
     if (bs->node_name[0] != '\0') {
         QTAILQ_REMOVE(&graph_bdrv_states, bs, node_list);
     }
     QTAILQ_REMOVE(&all_bdrv_states, bs, bs_list);
 
     bdrv_close(bs);
 
     g_free(bs);
 }
 
 
 /*
  * Replace @bs by newly created block node.
  *
  * @options is a QDict of options to pass to the block drivers, or NULL for an
  * empty set of options. The reference to the QDict belongs to the block layer
  * after the call (even on failure), so if the caller intends to reuse the
  * dictionary, it needs to use qobject_ref() before calling bdrv_open.
  */
 BlockDriverState *bdrv_insert_node(BlockDriverState *bs, QDict *options,
                                    int flags, Error **errp)
 {
     ERRP_GUARD();
     int ret;
     BlockDriverState *new_node_bs = NULL;
     const char *drvname, *node_name;
     BlockDriver *drv;
 
     drvname = qdict_get_try_str(options, "driver");
     if (!drvname) {
         error_setg(errp, "driver is not specified");
         goto fail;
     }
 
     drv = bdrv_find_format(drvname);
     if (!drv) {
         error_setg(errp, "Unknown driver: '%s'", drvname);
         goto fail;
     }
 
     node_name = qdict_get_try_str(options, "node-name");
 
     GLOBAL_STATE_CODE();
 
     new_node_bs = bdrv_new_open_driver_opts(drv, node_name, options, flags,
                                             errp);
     options = NULL; /* bdrv_new_open_driver() eats options */
     if (!new_node_bs) {
         error_prepend(errp, "Could not create node: ");
         goto fail;
     }
 
     bdrv_drained_begin(bs);
     ret = bdrv_replace_node(bs, new_node_bs, errp);
     bdrv_drained_end(bs);
 
     if (ret < 0) {
         error_prepend(errp, "Could not replace node: ");
         goto fail;
     }
 
     return new_node_bs;
 
 fail:
     qobject_unref(options);
     bdrv_unref(new_node_bs);
     return NULL;
 }
 
 /*
  * Run consistency checks on an image
  *
  * Returns 0 if the check could be completed (it doesn't mean that the image is
  * free of errors) or -errno when an internal error occurred. The results of the
  * check are stored in res.
  */
 int coroutine_fn bdrv_co_check(BlockDriverState *bs,
                                BdrvCheckResult *res, BdrvCheckMode fix)
 {
     IO_CODE();
     if (bs->drv == NULL) {
         return -ENOMEDIUM;
     }
     if (bs->drv->bdrv_co_check == NULL) {
         return -ENOTSUP;
     }
 
     memset(res, 0, sizeof(*res));
     return bs->drv->bdrv_co_check(bs, res, fix);
 }
 
 /*
  * Return values:
  * 0        - success
  * -EINVAL  - backing format specified, but no file
  * -ENOSPC  - can't update the backing file because no space is left in the
  *            image file header
  * -ENOTSUP - format driver doesn't support changing the backing file
  */
 int bdrv_change_backing_file(BlockDriverState *bs, const char *backing_file,
                              const char *backing_fmt, bool require)
 {
     BlockDriver *drv = bs->drv;
     int ret;
 
     GLOBAL_STATE_CODE();
 
     if (!drv) {
         return -ENOMEDIUM;
     }
 
     /* Backing file format doesn't make sense without a backing file */
     if (backing_fmt && !backing_file) {
         return -EINVAL;
     }
 
     if (require && backing_file && !backing_fmt) {
         return -EINVAL;
     }
 
     if (drv->bdrv_change_backing_file != NULL) {
         ret = drv->bdrv_change_backing_file(bs, backing_file, backing_fmt);
     } else {
         ret = -ENOTSUP;
     }
 
     if (ret == 0) {
         pstrcpy(bs->backing_file, sizeof(bs->backing_file), backing_file ?: "");
         pstrcpy(bs->backing_format, sizeof(bs->backing_format), backing_fmt ?: "");
         pstrcpy(bs->auto_backing_file, sizeof(bs->auto_backing_file),
                 backing_file ?: "");
     }
     return ret;
 }
 
 /*
  * Finds the first non-filter node above bs in the chain between
  * active and bs.  The returned node is either an immediate parent of
  * bs, or there are only filter nodes between the two.
  *
  * Returns NULL if bs is not found in active's image chain,
  * or if active == bs.
  *
  * Returns the bottommost base image if bs == NULL.
  */
 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
                                     BlockDriverState *bs)
 {
 
     GLOBAL_STATE_CODE();
 
     bs = bdrv_skip_filters(bs);
     active = bdrv_skip_filters(active);
 
     while (active) {
         BlockDriverState *next = bdrv_backing_chain_next(active);
         if (bs == next) {
             return active;
         }
         active = next;
     }
 
     return NULL;
 }
 
 /* Given a BDS, searches for the base layer. */
 BlockDriverState *bdrv_find_base(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
 
     return bdrv_find_overlay(bs, NULL);
 }
 
 /*
  * Return true if at least one of the COW (backing) and filter links
  * between @bs and @base is frozen. @errp is set if that's the case.
  * @base must be reachable from @bs, or NULL.
  */
 bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
                                   Error **errp)
 {
     BlockDriverState *i;
     BdrvChild *child;
 
     GLOBAL_STATE_CODE();
 
     for (i = bs; i != base; i = child_bs(child)) {
         child = bdrv_filter_or_cow_child(i);
 
         if (child && child->frozen) {
             error_setg(errp, "Cannot change '%s' link from '%s' to '%s'",
                        child->name, i->node_name, child->bs->node_name);
             return true;
         }
     }
 
     return false;
 }
 
 /*
  * Freeze all COW (backing) and filter links between @bs and @base.
  * If any of the links is already frozen the operation is aborted and
  * none of the links are modified.
  * @base must be reachable from @bs, or NULL.
  * Returns 0 on success. On failure returns < 0 and sets @errp.
  */
 int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
                               Error **errp)
 {
     BlockDriverState *i;
     BdrvChild *child;
 
     GLOBAL_STATE_CODE();
 
     if (bdrv_is_backing_chain_frozen(bs, base, errp)) {
         return -EPERM;
     }
 
     for (i = bs; i != base; i = child_bs(child)) {
         child = bdrv_filter_or_cow_child(i);
         if (child && child->bs->never_freeze) {
             error_setg(errp, "Cannot freeze '%s' link to '%s'",
                        child->name, child->bs->node_name);
             return -EPERM;
         }
     }
 
     for (i = bs; i != base; i = child_bs(child)) {
         child = bdrv_filter_or_cow_child(i);
         if (child) {
             child->frozen = true;
         }
     }
 
     return 0;
 }
 
 /*
  * Unfreeze all COW (backing) and filter links between @bs and @base.
  * The caller must ensure that all links are frozen before using this
  * function.
  * @base must be reachable from @bs, or NULL.
  */
 void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base)
 {
     BlockDriverState *i;
     BdrvChild *child;
 
     GLOBAL_STATE_CODE();
 
     for (i = bs; i != base; i = child_bs(child)) {
         child = bdrv_filter_or_cow_child(i);
         if (child) {
             assert(child->frozen);
             child->frozen = false;
         }
     }
 }
 
 /*
  * Drops images above 'base' up to and including 'top', and sets the image
  * above 'top' to have base as its backing file.
  *
  * Requires that the overlay to 'top' is opened r/w, so that the backing file
  * information in 'bs' can be properly updated.
  *
  * E.g., this will convert the following chain:
  * bottom <- base <- intermediate <- top <- active
  *
  * to
  *
  * bottom <- base <- active
  *
  * It is allowed for bottom==base, in which case it converts:
  *
  * base <- intermediate <- top <- active
  *
  * to
  *
  * base <- active
  *
  * If backing_file_str is non-NULL, it will be used when modifying top's
  * overlay image metadata.
  *
  * Error conditions:
  *  if active == top, that is considered an error
  *
  */
 int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
                            const char *backing_file_str)
 {
     BlockDriverState *explicit_top = top;
     bool update_inherits_from;
     BdrvChild *c;
     Error *local_err = NULL;
     int ret = -EIO;
     g_autoptr(GSList) updated_children = NULL;
     GSList *p;
 
     GLOBAL_STATE_CODE();
 
     bdrv_ref(top);
     bdrv_subtree_drained_begin(top);
 
     if (!top->drv || !base->drv) {
         goto exit;
     }
 
     /* Make sure that base is in the backing chain of top */
     if (!bdrv_chain_contains(top, base)) {
         goto exit;
     }
 
     /* If 'base' recursively inherits from 'top' then we should set
      * base->inherits_from to top->inherits_from after 'top' and all
      * other intermediate nodes have been dropped.
      * If 'top' is an implicit node (e.g. "commit_top") we should skip
      * it because no one inherits from it. We use explicit_top for that. */
     explicit_top = bdrv_skip_implicit_filters(explicit_top);
     update_inherits_from = bdrv_inherits_from_recursive(base, explicit_top);
 
     /* success - we can delete the intermediate states, and link top->base */
     if (!backing_file_str) {
         bdrv_refresh_filename(base);
         backing_file_str = base->filename;
     }
 
     QLIST_FOREACH(c, &top->parents, next_parent) {
         updated_children = g_slist_prepend(updated_children, c);
     }
 
     /*
      * It seems correct to pass detach_subchain=true here, but it triggers
      * one more yet not fixed bug, when due to nested aio_poll loop we switch to
      * another drained section, which modify the graph (for example, removing
      * the child, which we keep in updated_children list). So, it's a TODO.
      *
      * Note, bug triggered if pass detach_subchain=true here and run
      * test-bdrv-drain. test_drop_intermediate_poll() test-case will crash.
      * That's a FIXME.
      */
     bdrv_replace_node_common(top, base, false, false, &local_err);
     if (local_err) {
         error_report_err(local_err);
         goto exit;
     }
 
     for (p = updated_children; p; p = p->next) {
         c = p->data;
 
         if (c->klass->update_filename) {
             ret = c->klass->update_filename(c, base, backing_file_str,
                                             &local_err);
             if (ret < 0) {
                 /*
                  * TODO: Actually, we want to rollback all previous iterations
                  * of this loop, and (which is almost impossible) previous
                  * bdrv_replace_node()...
                  *
                  * Note, that c->klass->update_filename may lead to permission
                  * update, so it's a bad idea to call it inside permission
                  * update transaction of bdrv_replace_node.
                  */
                 error_report_err(local_err);
                 goto exit;
             }
         }
     }
 
     if (update_inherits_from) {
         base->inherits_from = explicit_top->inherits_from;
     }
 
     ret = 0;
 exit:
     bdrv_subtree_drained_end(top);
     bdrv_unref(top);
     return ret;
 }
 
 /**
  * Implementation of BlockDriver.bdrv_get_allocated_file_size() that
  * sums the size of all data-bearing children.  (This excludes backing
  * children.)
  */
 static int64_t bdrv_sum_allocated_file_size(BlockDriverState *bs)
 {
     BdrvChild *child;
     int64_t child_size, sum = 0;
 
     QLIST_FOREACH(child, &bs->children, next) {
         if (child->role & (BDRV_CHILD_DATA | BDRV_CHILD_METADATA |
                            BDRV_CHILD_FILTERED))
         {
             child_size = bdrv_get_allocated_file_size(child->bs);
             if (child_size < 0) {
                 return child_size;
             }
             sum += child_size;
         }
     }
 
     return sum;
 }
 
 /**
  * Length of a allocated file in bytes. Sparse files are counted by actual
  * allocated space. Return < 0 if error or unknown.
  */
 int64_t bdrv_get_allocated_file_size(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
     IO_CODE();
 
     if (!drv) {
         return -ENOMEDIUM;
     }
     if (drv->bdrv_get_allocated_file_size) {
         return drv->bdrv_get_allocated_file_size(bs);
     }
 
     if (drv->bdrv_file_open) {
         /*
          * Protocol drivers default to -ENOTSUP (most of their data is
          * not stored in any of their children (if they even have any),
          * so there is no generic way to figure it out).
          */
         return -ENOTSUP;
     } else if (drv->is_filter) {
         /* Filter drivers default to the size of their filtered child */
         return bdrv_get_allocated_file_size(bdrv_filter_bs(bs));
     } else {
         /* Other drivers default to summing their children's sizes */
         return bdrv_sum_allocated_file_size(bs);
     }
 }
 
 /*
  * bdrv_measure:
  * @drv: Format driver
  * @opts: Creation options for new image
  * @in_bs: Existing image containing data for new image (may be NULL)
  * @errp: Error object
  * Returns: A #BlockMeasureInfo (free using qapi_free_BlockMeasureInfo())
  *          or NULL on error
  *
  * Calculate file size required to create a new image.
  *
  * If @in_bs is given then space for allocated clusters and zero clusters
  * from that image are included in the calculation.  If @opts contains a
  * backing file that is shared by @in_bs then backing clusters may be omitted
  * from the calculation.
  *
  * If @in_bs is NULL then the calculation includes no allocated clusters
  * unless a preallocation option is given in @opts.
  *
  * Note that @in_bs may use a different BlockDriver from @drv.
  *
  * If an error occurs the @errp pointer is set.
  */
 BlockMeasureInfo *bdrv_measure(BlockDriver *drv, QemuOpts *opts,
                                BlockDriverState *in_bs, Error **errp)
 {
     IO_CODE();
     if (!drv->bdrv_measure) {
         error_setg(errp, "Block driver '%s' does not support size measurement",
                    drv->format_name);
         return NULL;
     }
 
     return drv->bdrv_measure(opts, in_bs, errp);
 }
 
 /**
  * Return number of sectors on success, -errno on error.
  */
 int64_t bdrv_nb_sectors(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
     IO_CODE();
 
     if (!drv)
         return -ENOMEDIUM;
 
     if (drv->has_variable_length) {
         int ret = refresh_total_sectors(bs, bs->total_sectors);
         if (ret < 0) {
             return ret;
         }
     }
     return bs->total_sectors;
 }
 
 /**
  * Return length in bytes on success, -errno on error.
  * The length is always a multiple of BDRV_SECTOR_SIZE.
  */
 int64_t bdrv_getlength(BlockDriverState *bs)
 {
     int64_t ret = bdrv_nb_sectors(bs);
     IO_CODE();
 
     if (ret < 0) {
         return ret;
     }
     if (ret > INT64_MAX / BDRV_SECTOR_SIZE) {
         return -EFBIG;
     }
     return ret * BDRV_SECTOR_SIZE;
 }
 
 /* return 0 as number of sectors if no device present or error */
 void bdrv_get_geometry(BlockDriverState *bs, uint64_t *nb_sectors_ptr)
 {
     int64_t nb_sectors = bdrv_nb_sectors(bs);
     IO_CODE();
 
     *nb_sectors_ptr = nb_sectors < 0 ? 0 : nb_sectors;
 }
 
 bool bdrv_is_sg(BlockDriverState *bs)
 {
     IO_CODE();
     return bs->sg;
 }
 
 /**
  * Return whether the given node supports compressed writes.
  */
 bool bdrv_supports_compressed_writes(BlockDriverState *bs)
 {
     BlockDriverState *filtered;
     IO_CODE();
 
     if (!bs->drv || !block_driver_can_compress(bs->drv)) {
         return false;
     }
 
     filtered = bdrv_filter_bs(bs);
     if (filtered) {
         /*
          * Filters can only forward compressed writes, so we have to
          * check the child.
          */
         return bdrv_supports_compressed_writes(filtered);
     }
 
     return true;
 }
 
 const char *bdrv_get_format_name(BlockDriverState *bs)
 {
     IO_CODE();
     return bs->drv ? bs->drv->format_name : NULL;
 }
 
 static int qsort_strcmp(const void *a, const void *b)
 {
     return strcmp(*(char *const *)a, *(char *const *)b);
 }
 
 void bdrv_iterate_format(void (*it)(void *opaque, const char *name),
                          void *opaque, bool read_only)
 {
     BlockDriver *drv;
     int count = 0;
     int i;
     const char **formats = NULL;
 
     GLOBAL_STATE_CODE();
 
     QLIST_FOREACH(drv, &bdrv_drivers, list) {
         if (drv->format_name) {
             bool found = false;
             int i = count;
 
             if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv, read_only)) {
                 continue;
             }
 
             while (formats && i && !found) {
                 found = !strcmp(formats[--i], drv->format_name);
             }
 
             if (!found) {
                 formats = g_renew(const char *, formats, count + 1);
                 formats[count++] = drv->format_name;
             }
         }
     }
 
     for (i = 0; i < (int)ARRAY_SIZE(block_driver_modules); i++) {
         const char *format_name = block_driver_modules[i].format_name;
 
         if (format_name) {
             bool found = false;
             int j = count;
 
             if (use_bdrv_whitelist &&
                 !bdrv_format_is_whitelisted(format_name, read_only)) {
                 continue;
             }
 
             while (formats && j && !found) {
                 found = !strcmp(formats[--j], format_name);
             }
 
             if (!found) {
                 formats = g_renew(const char *, formats, count + 1);
                 formats[count++] = format_name;
             }
         }
     }
 
     qsort(formats, count, sizeof(formats[0]), qsort_strcmp);
 
     for (i = 0; i < count; i++) {
         it(opaque, formats[i]);
     }
 
     g_free(formats);
 }
 
 /* This function is to find a node in the bs graph */
 BlockDriverState *bdrv_find_node(const char *node_name)
 {
     BlockDriverState *bs;
 
     assert(node_name);
     GLOBAL_STATE_CODE();
 
     QTAILQ_FOREACH(bs, &graph_bdrv_states, node_list) {
         if (!strcmp(node_name, bs->node_name)) {
             return bs;
         }
     }
     return NULL;
 }
 
 /* Put this QMP function here so it can access the static graph_bdrv_states. */
 BlockDeviceInfoList *bdrv_named_nodes_list(bool flat,
                                            Error **errp)
 {
     BlockDeviceInfoList *list;
     BlockDriverState *bs;
 
     GLOBAL_STATE_CODE();
 
     list = NULL;
     QTAILQ_FOREACH(bs, &graph_bdrv_states, node_list) {
         BlockDeviceInfo *info = bdrv_block_device_info(NULL, bs, flat, errp);
         if (!info) {
             qapi_free_BlockDeviceInfoList(list);
             return NULL;
         }
         QAPI_LIST_PREPEND(list, info);
     }
 
     return list;
 }
 
 typedef struct XDbgBlockGraphConstructor {
     XDbgBlockGraph *graph;
     GHashTable *graph_nodes;
 } XDbgBlockGraphConstructor;
 
 static XDbgBlockGraphConstructor *xdbg_graph_new(void)
 {
     XDbgBlockGraphConstructor *gr = g_new(XDbgBlockGraphConstructor, 1);
 
     gr->graph = g_new0(XDbgBlockGraph, 1);
     gr->graph_nodes = g_hash_table_new(NULL, NULL);
 
     return gr;
 }
 
 static XDbgBlockGraph *xdbg_graph_finalize(XDbgBlockGraphConstructor *gr)
 {
     XDbgBlockGraph *graph = gr->graph;
 
     g_hash_table_destroy(gr->graph_nodes);
     g_free(gr);
 
     return graph;
 }
 
 static uintptr_t xdbg_graph_node_num(XDbgBlockGraphConstructor *gr, void *node)
 {
     uintptr_t ret = (uintptr_t)g_hash_table_lookup(gr->graph_nodes, node);
 
     if (ret != 0) {
         return ret;
     }
 
     /*
      * Start counting from 1, not 0, because 0 interferes with not-found (NULL)
      * answer of g_hash_table_lookup.
      */
     ret = g_hash_table_size(gr->graph_nodes) + 1;
     g_hash_table_insert(gr->graph_nodes, node, (void *)ret);
 
     return ret;
 }
 
 static void xdbg_graph_add_node(XDbgBlockGraphConstructor *gr, void *node,
                                 XDbgBlockGraphNodeType type, const char *name)
 {
     XDbgBlockGraphNode *n;
 
     n = g_new0(XDbgBlockGraphNode, 1);
 
     n->id = xdbg_graph_node_num(gr, node);
     n->type = type;
     n->name = g_strdup(name);
 
     QAPI_LIST_PREPEND(gr->graph->nodes, n);
 }
 
 static void xdbg_graph_add_edge(XDbgBlockGraphConstructor *gr, void *parent,
                                 const BdrvChild *child)
 {
     BlockPermission qapi_perm;
     XDbgBlockGraphEdge *edge;
     GLOBAL_STATE_CODE();
 
     edge = g_new0(XDbgBlockGraphEdge, 1);
 
     edge->parent = xdbg_graph_node_num(gr, parent);
     edge->child = xdbg_graph_node_num(gr, child->bs);
     edge->name = g_strdup(child->name);
 
     for (qapi_perm = 0; qapi_perm < BLOCK_PERMISSION__MAX; qapi_perm++) {
         uint64_t flag = bdrv_qapi_perm_to_blk_perm(qapi_perm);
 
         if (flag & child->perm) {
             QAPI_LIST_PREPEND(edge->perm, qapi_perm);
         }
         if (flag & child->shared_perm) {
             QAPI_LIST_PREPEND(edge->shared_perm, qapi_perm);
         }
     }
 
     QAPI_LIST_PREPEND(gr->graph->edges, edge);
 }
 
 
 XDbgBlockGraph *bdrv_get_xdbg_block_graph(Error **errp)
 {
     BlockBackend *blk;
     BlockJob *job;
     BlockDriverState *bs;
     BdrvChild *child;
     XDbgBlockGraphConstructor *gr = xdbg_graph_new();
 
     GLOBAL_STATE_CODE();
 
     for (blk = blk_all_next(NULL); blk; blk = blk_all_next(blk)) {
         char *allocated_name = NULL;
         const char *name = blk_name(blk);
 
         if (!*name) {
             name = allocated_name = blk_get_attached_dev_id(blk);
         }
         xdbg_graph_add_node(gr, blk, X_DBG_BLOCK_GRAPH_NODE_TYPE_BLOCK_BACKEND,
                            name);
         g_free(allocated_name);
         if (blk_root(blk)) {
             xdbg_graph_add_edge(gr, blk, blk_root(blk));
         }
     }
 
     WITH_JOB_LOCK_GUARD() {
         for (job = block_job_next_locked(NULL); job;
              job = block_job_next_locked(job)) {
             GSList *el;
 
             xdbg_graph_add_node(gr, job, X_DBG_BLOCK_GRAPH_NODE_TYPE_BLOCK_JOB,
                                 job->job.id);
             for (el = job->nodes; el; el = el->next) {
                 xdbg_graph_add_edge(gr, job, (BdrvChild *)el->data);
             }
         }
     }
 
     QTAILQ_FOREACH(bs, &graph_bdrv_states, node_list) {
         xdbg_graph_add_node(gr, bs, X_DBG_BLOCK_GRAPH_NODE_TYPE_BLOCK_DRIVER,
                            bs->node_name);
         QLIST_FOREACH(child, &bs->children, next) {
             xdbg_graph_add_edge(gr, bs, child);
         }
     }
 
     return xdbg_graph_finalize(gr);
 }
 
 BlockDriverState *bdrv_lookup_bs(const char *device,
                                  const char *node_name,
                                  Error **errp)
 {
     BlockBackend *blk;
     BlockDriverState *bs;
 
     GLOBAL_STATE_CODE();
 
     if (device) {
         blk = blk_by_name(device);
 
         if (blk) {
             bs = blk_bs(blk);
             if (!bs) {
                 error_setg(errp, "Device '%s' has no medium", device);
             }
 
             return bs;
         }
     }
 
     if (node_name) {
         bs = bdrv_find_node(node_name);
 
         if (bs) {
             return bs;
         }
     }
 
     error_setg(errp, "Cannot find device=\'%s\' nor node-name=\'%s\'",
                      device ? device : "",
                      node_name ? node_name : "");
     return NULL;
 }
 
 /* If 'base' is in the same chain as 'top', return true. Otherwise,
  * return false.  If either argument is NULL, return false. */
 bool bdrv_chain_contains(BlockDriverState *top, BlockDriverState *base)
 {
 
     GLOBAL_STATE_CODE();
 
     while (top && top != base) {
         top = bdrv_filter_or_cow_bs(top);
     }
 
     return top != NULL;
 }
 
 BlockDriverState *bdrv_next_node(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     if (!bs) {
         return QTAILQ_FIRST(&graph_bdrv_states);
     }
     return QTAILQ_NEXT(bs, node_list);
 }
 
 BlockDriverState *bdrv_next_all_states(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     if (!bs) {
         return QTAILQ_FIRST(&all_bdrv_states);
     }
     return QTAILQ_NEXT(bs, bs_list);
 }
 
 const char *bdrv_get_node_name(const BlockDriverState *bs)
 {
     IO_CODE();
     return bs->node_name;
 }
 
 const char *bdrv_get_parent_name(const BlockDriverState *bs)
 {
     BdrvChild *c;
     const char *name;
     IO_CODE();
 
     /* If multiple parents have a name, just pick the first one. */
     QLIST_FOREACH(c, &bs->parents, next_parent) {
         if (c->klass->get_name) {
             name = c->klass->get_name(c);
             if (name && *name) {
                 return name;
             }
         }
     }
 
     return NULL;
 }
 
 /* TODO check what callers really want: bs->node_name or blk_name() */
 const char *bdrv_get_device_name(const BlockDriverState *bs)
 {
     IO_CODE();
     return bdrv_get_parent_name(bs) ?: "";
 }
 
 /* This can be used to identify nodes that might not have a device
  * name associated. Since node and device names live in the same
  * namespace, the result is unambiguous. The exception is if both are
  * absent, then this returns an empty (non-null) string. */
 const char *bdrv_get_device_or_node_name(const BlockDriverState *bs)
 {
     IO_CODE();
     return bdrv_get_parent_name(bs) ?: bs->node_name;
 }
 
 int bdrv_get_flags(BlockDriverState *bs)
 {
     IO_CODE();
     return bs->open_flags;
 }
 
 int bdrv_has_zero_init_1(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     return 1;
 }
 
 int bdrv_has_zero_init(BlockDriverState *bs)
 {
     BlockDriverState *filtered;
     GLOBAL_STATE_CODE();
 
     if (!bs->drv) {
         return 0;
     }
 
     /* If BS is a copy on write image, it is initialized to
        the contents of the base image, which may not be zeroes.  */
     if (bdrv_cow_child(bs)) {
         return 0;
     }
     if (bs->drv->bdrv_has_zero_init) {
         return bs->drv->bdrv_has_zero_init(bs);
     }
 
     filtered = bdrv_filter_bs(bs);
     if (filtered) {
         return bdrv_has_zero_init(filtered);
     }
 
     /* safe default */
     return 0;
 }
 
 bool bdrv_can_write_zeroes_with_unmap(BlockDriverState *bs)
 {
     IO_CODE();
     if (!(bs->open_flags & BDRV_O_UNMAP)) {
         return false;
     }
 
     return bs->supported_zero_flags & BDRV_REQ_MAY_UNMAP;
 }
 
 void bdrv_get_backing_filename(BlockDriverState *bs,
                                char *filename, int filename_size)
 {
     IO_CODE();
     pstrcpy(filename, filename_size, bs->backing_file);
 }
 
 int bdrv_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
 {
     int ret;
     BlockDriver *drv = bs->drv;
     IO_CODE();
     /* if bs->drv == NULL, bs is closed, so there's nothing to do here */
     if (!drv) {
         return -ENOMEDIUM;
     }
     if (!drv->bdrv_get_info) {
         BlockDriverState *filtered = bdrv_filter_bs(bs);
         if (filtered) {
             return bdrv_get_info(filtered, bdi);
         }
         return -ENOTSUP;
     }
     memset(bdi, 0, sizeof(*bdi));
     ret = drv->bdrv_get_info(bs, bdi);
     if (ret < 0) {
         return ret;
     }
 
     if (bdi->cluster_size > BDRV_MAX_ALIGNMENT) {
         return -EINVAL;
     }
 
     return 0;
 }
 
 ImageInfoSpecific *bdrv_get_specific_info(BlockDriverState *bs,
                                           Error **errp)
 {
     BlockDriver *drv = bs->drv;
     IO_CODE();
     if (drv && drv->bdrv_get_specific_info) {
         return drv->bdrv_get_specific_info(bs, errp);
     }
     return NULL;
 }
 
 BlockStatsSpecific *bdrv_get_specific_stats(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
     IO_CODE();
     if (!drv || !drv->bdrv_get_specific_stats) {
         return NULL;
     }
     return drv->bdrv_get_specific_stats(bs);
 }
 
 void bdrv_debug_event(BlockDriverState *bs, BlkdebugEvent event)
 {
     IO_CODE();
     if (!bs || !bs->drv || !bs->drv->bdrv_debug_event) {
         return;
     }
 
     bs->drv->bdrv_debug_event(bs, event);
 }
 
 static BlockDriverState *bdrv_find_debug_node(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     while (bs && bs->drv && !bs->drv->bdrv_debug_breakpoint) {
         bs = bdrv_primary_bs(bs);
     }
 
     if (bs && bs->drv && bs->drv->bdrv_debug_breakpoint) {
         assert(bs->drv->bdrv_debug_remove_breakpoint);
         return bs;
     }
 
     return NULL;
 }
 
 int bdrv_debug_breakpoint(BlockDriverState *bs, const char *event,
                           const char *tag)
 {
     GLOBAL_STATE_CODE();
     bs = bdrv_find_debug_node(bs);
     if (bs) {
         return bs->drv->bdrv_debug_breakpoint(bs, event, tag);
     }
 
     return -ENOTSUP;
 }
 
 int bdrv_debug_remove_breakpoint(BlockDriverState *bs, const char *tag)
 {
     GLOBAL_STATE_CODE();
     bs = bdrv_find_debug_node(bs);
     if (bs) {
         return bs->drv->bdrv_debug_remove_breakpoint(bs, tag);
     }
 
     return -ENOTSUP;
 }
 
 int bdrv_debug_resume(BlockDriverState *bs, const char *tag)
 {
     GLOBAL_STATE_CODE();
     while (bs && (!bs->drv || !bs->drv->bdrv_debug_resume)) {
         bs = bdrv_primary_bs(bs);
     }
 
     if (bs && bs->drv && bs->drv->bdrv_debug_resume) {
         return bs->drv->bdrv_debug_resume(bs, tag);
     }
 
     return -ENOTSUP;
 }
 
 bool bdrv_debug_is_suspended(BlockDriverState *bs, const char *tag)
 {
     GLOBAL_STATE_CODE();
     while (bs && bs->drv && !bs->drv->bdrv_debug_is_suspended) {
         bs = bdrv_primary_bs(bs);
     }
 
     if (bs && bs->drv && bs->drv->bdrv_debug_is_suspended) {
         return bs->drv->bdrv_debug_is_suspended(bs, tag);
     }
 
     return false;
 }
 
 /* backing_file can either be relative, or absolute, or a protocol.  If it is
  * relative, it must be relative to the chain.  So, passing in bs->filename
  * from a BDS as backing_file should not be done, as that may be relative to
  * the CWD rather than the chain. */
 BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
         const char *backing_file)
 {
     char *filename_full = NULL;
     char *backing_file_full = NULL;
     char *filename_tmp = NULL;
     int is_protocol = 0;
     bool filenames_refreshed = false;
     BlockDriverState *curr_bs = NULL;
     BlockDriverState *retval = NULL;
     BlockDriverState *bs_below;
 
     GLOBAL_STATE_CODE();
 
     if (!bs || !bs->drv || !backing_file) {
         return NULL;
     }
 
     filename_full     = g_malloc(PATH_MAX);
     backing_file_full = g_malloc(PATH_MAX);
 
     is_protocol = path_has_protocol(backing_file);
 
     /*
      * Being largely a legacy function, skip any filters here
      * (because filters do not have normal filenames, so they cannot
      * match anyway; and allowing json:{} filenames is a bit out of
      * scope).
      */
     for (curr_bs = bdrv_skip_filters(bs);
          bdrv_cow_child(curr_bs) != NULL;
          curr_bs = bs_below)
     {
         bs_below = bdrv_backing_chain_next(curr_bs);
 
         if (bdrv_backing_overridden(curr_bs)) {
             /*
              * If the backing file was overridden, we can only compare
              * directly against the backing node's filename.
              */
 
             if (!filenames_refreshed) {
                 /*
                  * This will automatically refresh all of the
                  * filenames in the rest of the backing chain, so we
                  * only need to do this once.
                  */
                 bdrv_refresh_filename(bs_below);
                 filenames_refreshed = true;
             }
 
             if (strcmp(backing_file, bs_below->filename) == 0) {
                 retval = bs_below;
                 break;
             }
         } else if (is_protocol || path_has_protocol(curr_bs->backing_file)) {
             /*
              * If either of the filename paths is actually a protocol, then
              * compare unmodified paths; otherwise make paths relative.
              */
             char *backing_file_full_ret;
 
             if (strcmp(backing_file, curr_bs->backing_file) == 0) {
                 retval = bs_below;
                 break;
             }
             /* Also check against the full backing filename for the image */
             backing_file_full_ret = bdrv_get_full_backing_filename(curr_bs,
                                                                    NULL);
             if (backing_file_full_ret) {
                 bool equal = strcmp(backing_file, backing_file_full_ret) == 0;
                 g_free(backing_file_full_ret);
                 if (equal) {
                     retval = bs_below;
                     break;
                 }
             }
         } else {
             /* If not an absolute filename path, make it relative to the current
              * image's filename path */
             filename_tmp = bdrv_make_absolute_filename(curr_bs, backing_file,
                                                        NULL);
             /* We are going to compare canonicalized absolute pathnames */
             if (!filename_tmp || !realpath(filename_tmp, filename_full)) {
                 g_free(filename_tmp);
                 continue;
             }
             g_free(filename_tmp);
 
             /* We need to make sure the backing filename we are comparing against
              * is relative to the current image filename (or absolute) */
             filename_tmp = bdrv_get_full_backing_filename(curr_bs, NULL);
             if (!filename_tmp || !realpath(filename_tmp, backing_file_full)) {
                 g_free(filename_tmp);
                 continue;
             }
             g_free(filename_tmp);
 
             if (strcmp(backing_file_full, filename_full) == 0) {
                 retval = bs_below;
                 break;
             }
         }
     }
 
     g_free(filename_full);
     g_free(backing_file_full);
     return retval;
 }
 
 void bdrv_init(void)
 {
 #ifdef CONFIG_BDRV_WHITELIST_TOOLS
     use_bdrv_whitelist = 1;
 #endif
     module_call_init(MODULE_INIT_BLOCK);
 }
 
 void bdrv_init_with_whitelist(void)
 {
     use_bdrv_whitelist = 1;
     bdrv_init();
 }
 
 int bdrv_activate(BlockDriverState *bs, Error **errp)
 {
     BdrvChild *child, *parent;
     Error *local_err = NULL;
     int ret;
     BdrvDirtyBitmap *bm;
 
     GLOBAL_STATE_CODE();
 
     if (!bs->drv)  {
         return -ENOMEDIUM;
     }
 
     QLIST_FOREACH(child, &bs->children, next) {
         bdrv_activate(child->bs, &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
             return -EINVAL;
         }
     }
 
     /*
      * Update permissions, they may differ for inactive nodes.
      *
      * Note that the required permissions of inactive images are always a
      * subset of the permissions required after activating the image. This
      * allows us to just get the permissions upfront without restricting
      * bdrv_co_invalidate_cache().
      *
      * It also means that in error cases, we don't have to try and revert to
      * the old permissions (which is an operation that could fail, too). We can
      * just keep the extended permissions for the next time that an activation
      * of the image is tried.
      */
     if (bs->open_flags & BDRV_O_INACTIVE) {
         bs->open_flags &= ~BDRV_O_INACTIVE;
         ret = bdrv_refresh_perms(bs, errp);
         if (ret < 0) {
             bs->open_flags |= BDRV_O_INACTIVE;
             return ret;
         }
 
         ret = bdrv_invalidate_cache(bs, errp);
         if (ret < 0) {
             bs->open_flags |= BDRV_O_INACTIVE;
             return ret;
         }
 
         FOR_EACH_DIRTY_BITMAP(bs, bm) {
             bdrv_dirty_bitmap_skip_store(bm, false);
         }
 
         ret = refresh_total_sectors(bs, bs->total_sectors);
         if (ret < 0) {
             bs->open_flags |= BDRV_O_INACTIVE;
             error_setg_errno(errp, -ret, "Could not refresh total sector count");
             return ret;
         }
     }
 
     QLIST_FOREACH(parent, &bs->parents, next_parent) {
         if (parent->klass->activate) {
             parent->klass->activate(parent, &local_err);
             if (local_err) {
                 bs->open_flags |= BDRV_O_INACTIVE;
                 error_propagate(errp, local_err);
                 return -EINVAL;
             }
         }
     }
 
     return 0;
 }
 
 int coroutine_fn bdrv_co_invalidate_cache(BlockDriverState *bs, Error **errp)
 {
     Error *local_err = NULL;
     IO_CODE();
 
     assert(!(bs->open_flags & BDRV_O_INACTIVE));
 
     if (bs->drv->bdrv_co_invalidate_cache) {
         bs->drv->bdrv_co_invalidate_cache(bs, &local_err);
         if (local_err) {
             error_propagate(errp, local_err);
             return -EINVAL;
         }
     }
 
     return 0;
 }
 
 void bdrv_activate_all(Error **errp)
 {
     BlockDriverState *bs;
     BdrvNextIterator it;
 
     GLOBAL_STATE_CODE();
 
     for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *aio_context = bdrv_get_aio_context(bs);
         int ret;
 
         aio_context_acquire(aio_context);
         ret = bdrv_activate(bs, errp);
         aio_context_release(aio_context);
         if (ret < 0) {
             bdrv_next_cleanup(&it);
             return;
         }
     }
 }
 
 static bool bdrv_has_bds_parent(BlockDriverState *bs, bool only_active)
 {
     BdrvChild *parent;
     GLOBAL_STATE_CODE();
 
     QLIST_FOREACH(parent, &bs->parents, next_parent) {
         if (parent->klass->parent_is_bds) {
             BlockDriverState *parent_bs = parent->opaque;
             if (!only_active || !(parent_bs->open_flags & BDRV_O_INACTIVE)) {
                 return true;
             }
         }
     }
 
     return false;
 }
 
 static int bdrv_inactivate_recurse(BlockDriverState *bs)
 {
     BdrvChild *child, *parent;
     int ret;
     uint64_t cumulative_perms, cumulative_shared_perms;
 
     GLOBAL_STATE_CODE();
 
     if (!bs->drv) {
         return -ENOMEDIUM;
     }
 
     /* Make sure that we don't inactivate a child before its parent.
      * It will be covered by recursion from the yet active parent. */
     if (bdrv_has_bds_parent(bs, true)) {
         return 0;
     }
 
     assert(!(bs->open_flags & BDRV_O_INACTIVE));
 
     /* Inactivate this node */
     if (bs->drv->bdrv_inactivate) {
         ret = bs->drv->bdrv_inactivate(bs);
         if (ret < 0) {
             return ret;
         }
     }
 
     QLIST_FOREACH(parent, &bs->parents, next_parent) {
         if (parent->klass->inactivate) {
             ret = parent->klass->inactivate(parent);
             if (ret < 0) {
                 return ret;
             }
         }
     }
 
     bdrv_get_cumulative_perm(bs, &cumulative_perms,
                              &cumulative_shared_perms);
     if (cumulative_perms & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED)) {
         /* Our inactive parents still need write access. Inactivation failed. */
         return -EPERM;
     }
 
     bs->open_flags |= BDRV_O_INACTIVE;
 
     /*
      * Update permissions, they may differ for inactive nodes.
      * We only tried to loosen restrictions, so errors are not fatal, ignore
      * them.
      */
     bdrv_refresh_perms(bs, NULL);
 
     /* Recursively inactivate children */
     QLIST_FOREACH(child, &bs->children, next) {
         ret = bdrv_inactivate_recurse(child->bs);
         if (ret < 0) {
             return ret;
         }
     }
 
     return 0;
 }
 
 int bdrv_inactivate_all(void)
 {
     BlockDriverState *bs = NULL;
     BdrvNextIterator it;
     int ret = 0;
     GSList *aio_ctxs = NULL, *ctx;
 
     GLOBAL_STATE_CODE();
 
     for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         AioContext *aio_context = bdrv_get_aio_context(bs);
 
         if (!g_slist_find(aio_ctxs, aio_context)) {
             aio_ctxs = g_slist_prepend(aio_ctxs, aio_context);
             aio_context_acquire(aio_context);
         }
     }
 
     for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         /* Nodes with BDS parents are covered by recursion from the last
          * parent that gets inactivated. Don't inactivate them a second
          * time if that has already happened. */
         if (bdrv_has_bds_parent(bs, false)) {
             continue;
         }
         ret = bdrv_inactivate_recurse(bs);
         if (ret < 0) {
             bdrv_next_cleanup(&it);
             goto out;
         }
     }
 
 out:
     for (ctx = aio_ctxs; ctx != NULL; ctx = ctx->next) {
         AioContext *aio_context = ctx->data;
         aio_context_release(aio_context);
     }
     g_slist_free(aio_ctxs);
 
     return ret;
 }
 
 /**************************************************************/
 /* removable device support */
 
 /**
  * Return TRUE if the media is present
  */
 bool bdrv_is_inserted(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
     BdrvChild *child;
     IO_CODE();
 
     if (!drv) {
         return false;
     }
     if (drv->bdrv_is_inserted) {
         return drv->bdrv_is_inserted(bs);
     }
     QLIST_FOREACH(child, &bs->children, next) {
         if (!bdrv_is_inserted(child->bs)) {
             return false;
         }
     }
     return true;
 }
 
 /**
  * If eject_flag is TRUE, eject the media. Otherwise, close the tray
  */
 void bdrv_eject(BlockDriverState *bs, bool eject_flag)
 {
     BlockDriver *drv = bs->drv;
     IO_CODE();
 
     if (drv && drv->bdrv_eject) {
         drv->bdrv_eject(bs, eject_flag);
     }
 }
 
 /**
  * Lock or unlock the media (if it is locked, the user won't be able
  * to eject it manually).
  */
 void bdrv_lock_medium(BlockDriverState *bs, bool locked)
 {
     BlockDriver *drv = bs->drv;
     IO_CODE();
     trace_bdrv_lock_medium(bs, locked);
 
     if (drv && drv->bdrv_lock_medium) {
         drv->bdrv_lock_medium(bs, locked);
     }
 }
 
 /* Get a reference to bs */
 void bdrv_ref(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     bs->refcnt++;
 }
 
 /* Release a previously grabbed reference to bs.
  * If after releasing, reference count is zero, the BlockDriverState is
  * deleted. */
 void bdrv_unref(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     if (!bs) {
         return;
     }
     assert(bs->refcnt > 0);
     if (--bs->refcnt == 0) {
         bdrv_delete(bs);
     }
 }
 
 struct BdrvOpBlocker {
     Error *reason;
     QLIST_ENTRY(BdrvOpBlocker) list;
 };
 
 bool bdrv_op_is_blocked(BlockDriverState *bs, BlockOpType op, Error **errp)
 {
     BdrvOpBlocker *blocker;
     GLOBAL_STATE_CODE();
     assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
     if (!QLIST_EMPTY(&bs->op_blockers[op])) {
         blocker = QLIST_FIRST(&bs->op_blockers[op]);
         error_propagate_prepend(errp, error_copy(blocker->reason),
                                 "Node '%s' is busy: ",
                                 bdrv_get_device_or_node_name(bs));
         return true;
     }
     return false;
 }
 
 void bdrv_op_block(BlockDriverState *bs, BlockOpType op, Error *reason)
 {
     BdrvOpBlocker *blocker;
     GLOBAL_STATE_CODE();
     assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
 
     blocker = g_new0(BdrvOpBlocker, 1);
     blocker->reason = reason;
     QLIST_INSERT_HEAD(&bs->op_blockers[op], blocker, list);
 }
 
 void bdrv_op_unblock(BlockDriverState *bs, BlockOpType op, Error *reason)
 {
     BdrvOpBlocker *blocker, *next;
     GLOBAL_STATE_CODE();
     assert((int) op >= 0 && op < BLOCK_OP_TYPE_MAX);
     QLIST_FOREACH_SAFE(blocker, &bs->op_blockers[op], list, next) {
         if (blocker->reason == reason) {
             QLIST_REMOVE(blocker, list);
             g_free(blocker);
         }
     }
 }
 
 void bdrv_op_block_all(BlockDriverState *bs, Error *reason)
 {
     int i;
     GLOBAL_STATE_CODE();
     for (i = 0; i < BLOCK_OP_TYPE_MAX; i++) {
         bdrv_op_block(bs, i, reason);
     }
 }
 
 void bdrv_op_unblock_all(BlockDriverState *bs, Error *reason)
 {
     int i;
     GLOBAL_STATE_CODE();
     for (i = 0; i < BLOCK_OP_TYPE_MAX; i++) {
         bdrv_op_unblock(bs, i, reason);
     }
 }
 
 bool bdrv_op_blocker_is_empty(BlockDriverState *bs)
 {
     int i;
     GLOBAL_STATE_CODE();
     for (i = 0; i < BLOCK_OP_TYPE_MAX; i++) {
         if (!QLIST_EMPTY(&bs->op_blockers[i])) {
             return false;
         }
     }
     return true;
 }
 
 void bdrv_img_create(const char *filename, const char *fmt,
                      const char *base_filename, const char *base_fmt,
                      char *options, uint64_t img_size, int flags, bool quiet,
                      Error **errp)
 {
     QemuOptsList *create_opts = NULL;
     QemuOpts *opts = NULL;
     const char *backing_fmt, *backing_file;
     int64_t size;
     BlockDriver *drv, *proto_drv;
     Error *local_err = NULL;
     int ret = 0;
 
     GLOBAL_STATE_CODE();
 
     /* Find driver and parse its options */
     drv = bdrv_find_format(fmt);
     if (!drv) {
         error_setg(errp, "Unknown file format '%s'", fmt);
         return;
     }
 
     proto_drv = bdrv_find_protocol(filename, true, errp);
     if (!proto_drv) {
         return;
     }
 
     if (!drv->create_opts) {
         error_setg(errp, "Format driver '%s' does not support image creation",
                    drv->format_name);
         return;
     }
 
     if (!proto_drv->create_opts) {
         error_setg(errp, "Protocol driver '%s' does not support image creation",
                    proto_drv->format_name);
         return;
     }
 
     /* Create parameter list */
     create_opts = qemu_opts_append(create_opts, drv->create_opts);
     create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
 
     opts = qemu_opts_create(create_opts, NULL, 0, &error_abort);
 
     /* Parse -o options */
     if (options) {
         if (!qemu_opts_do_parse(opts, options, NULL, errp)) {
             goto out;
         }
     }
 
     if (!qemu_opt_get(opts, BLOCK_OPT_SIZE)) {
         qemu_opt_set_number(opts, BLOCK_OPT_SIZE, img_size, &error_abort);
     } else if (img_size != UINT64_C(-1)) {
         error_setg(errp, "The image size must be specified only once");
         goto out;
     }
 
     if (base_filename) {
         if (!qemu_opt_set(opts, BLOCK_OPT_BACKING_FILE, base_filename,
                           NULL)) {
             error_setg(errp, "Backing file not supported for file format '%s'",
                        fmt);
             goto out;
         }
     }
 
     if (base_fmt) {
         if (!qemu_opt_set(opts, BLOCK_OPT_BACKING_FMT, base_fmt, NULL)) {
             error_setg(errp, "Backing file format not supported for file "
                              "format '%s'", fmt);
             goto out;
         }
     }
 
     backing_file = qemu_opt_get(opts, BLOCK_OPT_BACKING_FILE);
     if (backing_file) {
         if (!strcmp(filename, backing_file)) {
             error_setg(errp, "Error: Trying to create an image with the "
                              "same filename as the backing file");
             goto out;
         }
         if (backing_file[0] == '\0') {
             error_setg(errp, "Expected backing file name, got empty string");
             goto out;
         }
     }
 
     backing_fmt = qemu_opt_get(opts, BLOCK_OPT_BACKING_FMT);
 
     /* The size for the image must always be specified, unless we have a backing
      * file and we have not been forbidden from opening it. */
     size = qemu_opt_get_size(opts, BLOCK_OPT_SIZE, img_size);
     if (backing_file && !(flags & BDRV_O_NO_BACKING)) {
         BlockDriverState *bs;
         char *full_backing;
         int back_flags;
         QDict *backing_options = NULL;
 
         full_backing =
             bdrv_get_full_backing_filename_from_filename(filename, backing_file,
                                                          &local_err);
         if (local_err) {
             goto out;
         }
         assert(full_backing);
 
         /*
          * No need to do I/O here, which allows us to open encrypted
          * backing images without needing the secret
          */
         back_flags = flags;
         back_flags &= ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
         back_flags |= BDRV_O_NO_IO;
 
         backing_options = qdict_new();
         if (backing_fmt) {
             qdict_put_str(backing_options, "driver", backing_fmt);
         }
         qdict_put_bool(backing_options, BDRV_OPT_FORCE_SHARE, true);
 
         bs = bdrv_open(full_backing, NULL, backing_options, back_flags,
                        &local_err);
         g_free(full_backing);
         if (!bs) {
             error_append_hint(&local_err, "Could not open backing image.\n");
             goto out;
         } else {
             if (!backing_fmt) {
                 error_setg(&local_err,
                            "Backing file specified without backing format");
                 error_append_hint(&local_err, "Detected format of %s.",
                                   bs->drv->format_name);
                 goto out;
             }
             if (size == -1) {
                 /* Opened BS, have no size */
                 size = bdrv_getlength(bs);
                 if (size < 0) {
                     error_setg_errno(errp, -size, "Could not get size of '%s'",
                                      backing_file);
                     bdrv_unref(bs);
                     goto out;
                 }
                 qemu_opt_set_number(opts, BLOCK_OPT_SIZE, size, &error_abort);
             }
             bdrv_unref(bs);
         }
         /* (backing_file && !(flags & BDRV_O_NO_BACKING)) */
     } else if (backing_file && !backing_fmt) {
         error_setg(&local_err,
                    "Backing file specified without backing format");
         goto out;
     }
 
     if (size == -1) {
         error_setg(errp, "Image creation needs a size parameter");
         goto out;
     }
 
     if (!quiet) {
         printf("Formatting '%s', fmt=%s ", filename, fmt);
         qemu_opts_print(opts, " ");
         puts("");
         fflush(stdout);
     }
 
     ret = bdrv_create(drv, filename, opts, &local_err);
 
     if (ret == -EFBIG) {
         /* This is generally a better message than whatever the driver would
          * deliver (especially because of the cluster_size_hint), since that
          * is most probably not much different from "image too large". */
         const char *cluster_size_hint = "";
         if (qemu_opt_get_size(opts, BLOCK_OPT_CLUSTER_SIZE, 0)) {
             cluster_size_hint = " (try using a larger cluster size)";
         }
         error_setg(errp, "The image size is too large for file format '%s'"
                    "%s", fmt, cluster_size_hint);
         error_free(local_err);
         local_err = NULL;
     }
 
 out:
     qemu_opts_del(opts);
     qemu_opts_free(create_opts);
     error_propagate(errp, local_err);
 }
 
 AioContext *bdrv_get_aio_context(BlockDriverState *bs)
 {
     IO_CODE();
     return bs ? bs->aio_context : qemu_get_aio_context();
 }
 
 AioContext *coroutine_fn bdrv_co_enter(BlockDriverState *bs)
 {
     Coroutine *self = qemu_coroutine_self();
     AioContext *old_ctx = qemu_coroutine_get_aio_context(self);
     AioContext *new_ctx;
     IO_CODE();
 
     /*
      * Increase bs->in_flight to ensure that this operation is completed before
      * moving the node to a different AioContext. Read new_ctx only afterwards.
      */
     bdrv_inc_in_flight(bs);
 
     new_ctx = bdrv_get_aio_context(bs);
     aio_co_reschedule_self(new_ctx);
     return old_ctx;
 }
 
 void coroutine_fn bdrv_co_leave(BlockDriverState *bs, AioContext *old_ctx)
 {
     IO_CODE();
     aio_co_reschedule_self(old_ctx);
     bdrv_dec_in_flight(bs);
 }
 
 void coroutine_fn bdrv_co_lock(BlockDriverState *bs)
 {
     AioContext *ctx = bdrv_get_aio_context(bs);
 
     /* In the main thread, bs->aio_context won't change concurrently */
     assert(qemu_get_current_aio_context() == qemu_get_aio_context());
 
     /*
      * We're in coroutine context, so we already hold the lock of the main
      * loop AioContext. Don't lock it twice to avoid deadlocks.
      */
     assert(qemu_in_coroutine());
     if (ctx != qemu_get_aio_context()) {
         aio_context_acquire(ctx);
     }
 }
 
 void coroutine_fn bdrv_co_unlock(BlockDriverState *bs)
 {
     AioContext *ctx = bdrv_get_aio_context(bs);
 
     assert(qemu_in_coroutine());
     if (ctx != qemu_get_aio_context()) {
         aio_context_release(ctx);
     }
 }
 
 void bdrv_coroutine_enter(BlockDriverState *bs, Coroutine *co)
 {
     IO_CODE();
     aio_co_enter(bdrv_get_aio_context(bs), co);
 }
 
 static void bdrv_do_remove_aio_context_notifier(BdrvAioNotifier *ban)
 {
     GLOBAL_STATE_CODE();
     QLIST_REMOVE(ban, list);
     g_free(ban);
 }
 
 static void bdrv_detach_aio_context(BlockDriverState *bs)
 {
     BdrvAioNotifier *baf, *baf_tmp;
 
     assert(!bs->walking_aio_notifiers);
     GLOBAL_STATE_CODE();
     bs->walking_aio_notifiers = true;
     QLIST_FOREACH_SAFE(baf, &bs->aio_notifiers, list, baf_tmp) {
         if (baf->deleted) {
             bdrv_do_remove_aio_context_notifier(baf);
         } else {
             baf->detach_aio_context(baf->opaque);
         }
     }
     /* Never mind iterating again to check for ->deleted.  bdrv_close() will
      * remove remaining aio notifiers if we aren't called again.
      */
     bs->walking_aio_notifiers = false;
 
     if (bs->drv && bs->drv->bdrv_detach_aio_context) {
         bs->drv->bdrv_detach_aio_context(bs);
     }
 
     if (bs->quiesce_counter) {
         aio_enable_external(bs->aio_context);
     }
     assert_bdrv_graph_writable(bs);
     bs->aio_context = NULL;
 }
 
 static void bdrv_attach_aio_context(BlockDriverState *bs,
                                     AioContext *new_context)
 {
     BdrvAioNotifier *ban, *ban_tmp;
     GLOBAL_STATE_CODE();
 
     if (bs->quiesce_counter) {
         aio_disable_external(new_context);
     }
 
     assert_bdrv_graph_writable(bs);
     bs->aio_context = new_context;
 
     if (bs->drv && bs->drv->bdrv_attach_aio_context) {
         bs->drv->bdrv_attach_aio_context(bs, new_context);
     }
 
     assert(!bs->walking_aio_notifiers);
     bs->walking_aio_notifiers = true;
     QLIST_FOREACH_SAFE(ban, &bs->aio_notifiers, list, ban_tmp) {
         if (ban->deleted) {
             bdrv_do_remove_aio_context_notifier(ban);
         } else {
             ban->attached_aio_context(new_context, ban->opaque);
         }
     }
     bs->walking_aio_notifiers = false;
 }
 
 typedef struct BdrvStateSetAioContext {
     AioContext *new_ctx;
     BlockDriverState *bs;
 } BdrvStateSetAioContext;
 
 static bool bdrv_parent_change_aio_context(BdrvChild *c, AioContext *ctx,
                                            GHashTable *visited,
                                            Transaction *tran,
                                            Error **errp)
 {
     GLOBAL_STATE_CODE();
     if (g_hash_table_contains(visited, c)) {
         return true;
     }
     g_hash_table_add(visited, c);
 
     /*
      * A BdrvChildClass that doesn't handle AioContext changes cannot
      * tolerate any AioContext changes
      */
     if (!c->klass->change_aio_ctx) {
         char *user = bdrv_child_user_desc(c);
         error_setg(errp, "Changing iothreads is not supported by %s", user);
         g_free(user);
         return false;
     }
     if (!c->klass->change_aio_ctx(c, ctx, visited, tran, errp)) {
         assert(!errp || *errp);
         return false;
     }
     return true;
 }
 
 bool bdrv_child_change_aio_context(BdrvChild *c, AioContext *ctx,
                                    GHashTable *visited, Transaction *tran,
                                    Error **errp)
 {
     GLOBAL_STATE_CODE();
     if (g_hash_table_contains(visited, c)) {
         return true;
     }
     g_hash_table_add(visited, c);
     return bdrv_change_aio_context(c->bs, ctx, visited, tran, errp);
 }
 
 static void bdrv_set_aio_context_clean(void *opaque)
 {
     BdrvStateSetAioContext *state = (BdrvStateSetAioContext *) opaque;
     BlockDriverState *bs = (BlockDriverState *) state->bs;
 
     /* Paired with bdrv_drained_begin in bdrv_change_aio_context() */
     bdrv_drained_end(bs);
 
     g_free(state);
 }
 
 static void bdrv_set_aio_context_commit(void *opaque)
 {
     BdrvStateSetAioContext *state = (BdrvStateSetAioContext *) opaque;
     BlockDriverState *bs = (BlockDriverState *) state->bs;
     AioContext *new_context = state->new_ctx;
     AioContext *old_context = bdrv_get_aio_context(bs);
     assert_bdrv_graph_writable(bs);
 
     /*
      * Take the old AioContex when detaching it from bs.
      * At this point, new_context lock is already acquired, and we are now
      * also taking old_context. This is safe as long as bdrv_detach_aio_context
      * does not call AIO_POLL_WHILE().
      */
     if (old_context != qemu_get_aio_context()) {
         aio_context_acquire(old_context);
     }
     bdrv_detach_aio_context(bs);
     if (old_context != qemu_get_aio_context()) {
         aio_context_release(old_context);
     }
     bdrv_attach_aio_context(bs, new_context);
 }
 
 static TransactionActionDrv set_aio_context = {
     .commit = bdrv_set_aio_context_commit,
     .clean = bdrv_set_aio_context_clean,
 };
 
 /*
  * Changes the AioContext used for fd handlers, timers, and BHs by this
  * BlockDriverState and all its children and parents.
  *
  * Must be called from the main AioContext.
  *
  * The caller must own the AioContext lock for the old AioContext of bs, but it
  * must not own the AioContext lock for new_context (unless new_context is the
  * same as the current context of bs).
  *
  * @visited will accumulate all visited BdrvChild objects. The caller is
  * responsible for freeing the list afterwards.
  */
 static bool bdrv_change_aio_context(BlockDriverState *bs, AioContext *ctx,
                                     GHashTable *visited, Transaction *tran,
                                     Error **errp)
 {
     BdrvChild *c;
     BdrvStateSetAioContext *state;
 
     GLOBAL_STATE_CODE();
 
     if (bdrv_get_aio_context(bs) == ctx) {
         return true;
     }
 
     QLIST_FOREACH(c, &bs->parents, next_parent) {
         if (!bdrv_parent_change_aio_context(c, ctx, visited, tran, errp)) {
             return false;
         }
     }
 
     QLIST_FOREACH(c, &bs->children, next) {
         if (!bdrv_child_change_aio_context(c, ctx, visited, tran, errp)) {
             return false;
         }
     }
 
     state = g_new(BdrvStateSetAioContext, 1);
     *state = (BdrvStateSetAioContext) {
         .new_ctx = ctx,
         .bs = bs,
     };
 
     /* Paired with bdrv_drained_end in bdrv_set_aio_context_clean() */
     bdrv_drained_begin(bs);
 
     tran_add(tran, &set_aio_context, state);
 
     return true;
 }
 
 /*
  * Change bs's and recursively all of its parents' and children's AioContext
  * to the given new context, returning an error if that isn't possible.
  *
  * If ignore_child is not NULL, that child (and its subgraph) will not
  * be touched.
  *
  * This function still requires the caller to take the bs current
  * AioContext lock, otherwise draining will fail since AIO_WAIT_WHILE
  * assumes the lock is always held if bs is in another AioContext.
  * For the same reason, it temporarily also holds the new AioContext, since
  * bdrv_drained_end calls BDRV_POLL_WHILE that assumes the lock is taken too.
  * Therefore the new AioContext lock must not be taken by the caller.
  */
 int bdrv_try_change_aio_context(BlockDriverState *bs, AioContext *ctx,
                                 BdrvChild *ignore_child, Error **errp)
 {
     Transaction *tran;
     GHashTable *visited;
     int ret;
     AioContext *old_context = bdrv_get_aio_context(bs);
     GLOBAL_STATE_CODE();
 
     /*
      * Recursion phase: go through all nodes of the graph.
      * Take care of checking that all nodes support changing AioContext
      * and drain them, builing a linear list of callbacks to run if everything
      * is successful (the transaction itself).
      */
     tran = tran_new();
     visited = g_hash_table_new(NULL, NULL);
     if (ignore_child) {
         g_hash_table_add(visited, ignore_child);
     }
     ret = bdrv_change_aio_context(bs, ctx, visited, tran, errp);
     g_hash_table_destroy(visited);
 
     /*
      * Linear phase: go through all callbacks collected in the transaction.
      * Run all callbacks collected in the recursion to switch all nodes
      * AioContext lock (transaction commit), or undo all changes done in the
      * recursion (transaction abort).
      */
 
     if (!ret) {
         /* Just run clean() callbacks. No AioContext changed. */
         tran_abort(tran);
         return -EPERM;
     }
 
     /*
      * Release old AioContext, it won't be needed anymore, as all
      * bdrv_drained_begin() have been called already.
      */
     if (qemu_get_aio_context() != old_context) {
         aio_context_release(old_context);
     }
 
     /*
      * Acquire new AioContext since bdrv_drained_end() is going to be called
      * after we switched all nodes in the new AioContext, and the function
      * assumes that the lock of the bs is always taken.
      */
     if (qemu_get_aio_context() != ctx) {
         aio_context_acquire(ctx);
     }
 
     tran_commit(tran);
 
     if (qemu_get_aio_context() != ctx) {
         aio_context_release(ctx);
     }
 
     /* Re-acquire the old AioContext, since the caller takes and releases it. */
     if (qemu_get_aio_context() != old_context) {
         aio_context_acquire(old_context);
     }
 
     return 0;
 }
 
 void bdrv_add_aio_context_notifier(BlockDriverState *bs,
         void (*attached_aio_context)(AioContext *new_context, void *opaque),
         void (*detach_aio_context)(void *opaque), void *opaque)
 {
     BdrvAioNotifier *ban = g_new(BdrvAioNotifier, 1);
     *ban = (BdrvAioNotifier){
         .attached_aio_context = attached_aio_context,
         .detach_aio_context   = detach_aio_context,
         .opaque               = opaque
     };
     GLOBAL_STATE_CODE();
 
     QLIST_INSERT_HEAD(&bs->aio_notifiers, ban, list);
 }
 
 void bdrv_remove_aio_context_notifier(BlockDriverState *bs,
                                       void (*attached_aio_context)(AioContext *,
                                                                    void *),
                                       void (*detach_aio_context)(void *),
                                       void *opaque)
 {
     BdrvAioNotifier *ban, *ban_next;
     GLOBAL_STATE_CODE();
 
     QLIST_FOREACH_SAFE(ban, &bs->aio_notifiers, list, ban_next) {
         if (ban->attached_aio_context == attached_aio_context &&
             ban->detach_aio_context   == detach_aio_context   &&
             ban->opaque               == opaque               &&
             ban->deleted              == false)
         {
             if (bs->walking_aio_notifiers) {
                 ban->deleted = true;
             } else {
                 bdrv_do_remove_aio_context_notifier(ban);
             }
             return;
         }
     }
 
     abort();
 }
 
 int bdrv_amend_options(BlockDriverState *bs, QemuOpts *opts,
                        BlockDriverAmendStatusCB *status_cb, void *cb_opaque,
                        bool force,
                        Error **errp)
 {
     GLOBAL_STATE_CODE();
     if (!bs->drv) {
         error_setg(errp, "Node is ejected");
         return -ENOMEDIUM;
     }
     if (!bs->drv->bdrv_amend_options) {
         error_setg(errp, "Block driver '%s' does not support option amendment",
                    bs->drv->format_name);
         return -ENOTSUP;
     }
     return bs->drv->bdrv_amend_options(bs, opts, status_cb,
                                        cb_opaque, force, errp);
 }
 
 /*
  * This function checks whether the given @to_replace is allowed to be
  * replaced by a node that always shows the same data as @bs.  This is
  * used for example to verify whether the mirror job can replace
  * @to_replace by the target mirrored from @bs.
  * To be replaceable, @bs and @to_replace may either be guaranteed to
  * always show the same data (because they are only connected through
  * filters), or some driver may allow replacing one of its children
  * because it can guarantee that this child's data is not visible at
  * all (for example, for dissenting quorum children that have no other
  * parents).
  */
 bool bdrv_recurse_can_replace(BlockDriverState *bs,
                               BlockDriverState *to_replace)
 {
     BlockDriverState *filtered;
 
     GLOBAL_STATE_CODE();
 
     if (!bs || !bs->drv) {
         return false;
     }
 
     if (bs == to_replace) {
         return true;
     }
 
     /* See what the driver can do */
     if (bs->drv->bdrv_recurse_can_replace) {
         return bs->drv->bdrv_recurse_can_replace(bs, to_replace);
     }
 
     /* For filters without an own implementation, we can recurse on our own */
     filtered = bdrv_filter_bs(bs);
     if (filtered) {
         return bdrv_recurse_can_replace(filtered, to_replace);
     }
 
     /* Safe default */
     return false;
 }
 
 /*
  * Check whether the given @node_name can be replaced by a node that
  * has the same data as @parent_bs.  If so, return @node_name's BDS;
  * NULL otherwise.
  *
  * @node_name must be a (recursive) *child of @parent_bs (or this
  * function will return NULL).
  *
  * The result (whether the node can be replaced or not) is only valid
  * for as long as no graph or permission changes occur.
  */
 BlockDriverState *check_to_replace_node(BlockDriverState *parent_bs,
                                         const char *node_name, Error **errp)
 {
     BlockDriverState *to_replace_bs = bdrv_find_node(node_name);
     AioContext *aio_context;
 
     GLOBAL_STATE_CODE();
 
     if (!to_replace_bs) {
         error_setg(errp, "Failed to find node with node-name='%s'", node_name);
         return NULL;
     }
 
     aio_context = bdrv_get_aio_context(to_replace_bs);
     aio_context_acquire(aio_context);
 
     if (bdrv_op_is_blocked(to_replace_bs, BLOCK_OP_TYPE_REPLACE, errp)) {
         to_replace_bs = NULL;
         goto out;
     }
 
     /* We don't want arbitrary node of the BDS chain to be replaced only the top
      * most non filter in order to prevent data corruption.
      * Another benefit is that this tests exclude backing files which are
      * blocked by the backing blockers.
      */
     if (!bdrv_recurse_can_replace(parent_bs, to_replace_bs)) {
         error_setg(errp, "Cannot replace '%s' by a node mirrored from '%s', "
                    "because it cannot be guaranteed that doing so would not "
                    "lead to an abrupt change of visible data",
                    node_name, parent_bs->node_name);
         to_replace_bs = NULL;
         goto out;
     }
 
 out:
     aio_context_release(aio_context);
     return to_replace_bs;
 }
 
 /**
  * Iterates through the list of runtime option keys that are said to
  * be "strong" for a BDS.  An option is called "strong" if it changes
  * a BDS's data.  For example, the null block driver's "size" and
  * "read-zeroes" options are strong, but its "latency-ns" option is
  * not.
  *
  * If a key returned by this function ends with a dot, all options
  * starting with that prefix are strong.
  */
 static const char *const *strong_options(BlockDriverState *bs,
                                          const char *const *curopt)
 {
     static const char *const global_options[] = {
         "driver", "filename", NULL
     };
 
     if (!curopt) {
         return &global_options[0];
     }
 
     curopt++;
     if (curopt == &global_options[ARRAY_SIZE(global_options) - 1] && bs->drv) {
         curopt = bs->drv->strong_runtime_opts;
     }
 
     return (curopt && *curopt) ? curopt : NULL;
 }
 
 /**
  * Copies all strong runtime options from bs->options to the given
  * QDict.  The set of strong option keys is determined by invoking
  * strong_options().
  *
  * Returns true iff any strong option was present in bs->options (and
  * thus copied to the target QDict) with the exception of "filename"
  * and "driver".  The caller is expected to use this value to decide
  * whether the existence of strong options prevents the generation of
  * a plain filename.
  */
 static bool append_strong_runtime_options(QDict *d, BlockDriverState *bs)
 {
     bool found_any = false;
     const char *const *option_name = NULL;
 
     if (!bs->drv) {
         return false;
     }
 
     while ((option_name = strong_options(bs, option_name))) {
         bool option_given = false;
 
         assert(strlen(*option_name) > 0);
         if ((*option_name)[strlen(*option_name) - 1] != '.') {
             QObject *entry = qdict_get(bs->options, *option_name);
             if (!entry) {
                 continue;
             }
 
             qdict_put_obj(d, *option_name, qobject_ref(entry));
             option_given = true;
         } else {
             const QDictEntry *entry;
             for (entry = qdict_first(bs->options); entry;
                  entry = qdict_next(bs->options, entry))
             {
                 if (strstart(qdict_entry_key(entry), *option_name, NULL)) {
                     qdict_put_obj(d, qdict_entry_key(entry),
                                   qobject_ref(qdict_entry_value(entry)));
                     option_given = true;
                 }
             }
         }
 
         /* While "driver" and "filename" need to be included in a JSON filename,
          * their existence does not prohibit generation of a plain filename. */
         if (!found_any && option_given &&
             strcmp(*option_name, "driver") && strcmp(*option_name, "filename"))
         {
             found_any = true;
         }
     }
 
     if (!qdict_haskey(d, "driver")) {
         /* Drivers created with bdrv_new_open_driver() may not have a
          * @driver option.  Add it here. */
         qdict_put_str(d, "driver", bs->drv->format_name);
     }
 
     return found_any;
 }
 
 /* Note: This function may return false positives; it may return true
  * even if opening the backing file specified by bs's image header
  * would result in exactly bs->backing. */
 static bool bdrv_backing_overridden(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     if (bs->backing) {
         return strcmp(bs->auto_backing_file,
                       bs->backing->bs->filename);
     } else {
         /* No backing BDS, so if the image header reports any backing
          * file, it must have been suppressed */
         return bs->auto_backing_file[0] != '\0';
     }
 }
 
 /* Updates the following BDS fields:
  *  - exact_filename: A filename which may be used for opening a block device
  *                    which (mostly) equals the given BDS (even without any
  *                    other options; so reading and writing must return the same
  *                    results, but caching etc. may be different)
  *  - full_open_options: Options which, when given when opening a block device
  *                       (without a filename), result in a BDS (mostly)
  *                       equalling the given one
  *  - filename: If exact_filename is set, it is copied here. Otherwise,
  *              full_open_options is converted to a JSON object, prefixed with
  *              "json:" (for use through the JSON pseudo protocol) and put here.
  */
 void bdrv_refresh_filename(BlockDriverState *bs)
 {
     BlockDriver *drv = bs->drv;
     BdrvChild *child;
     BlockDriverState *primary_child_bs;
     QDict *opts;
     bool backing_overridden;
     bool generate_json_filename; /* Whether our default implementation should
                                     fill exact_filename (false) or not (true) */
 
     GLOBAL_STATE_CODE();
 
     if (!drv) {
         return;
     }
 
     /* This BDS's file name may depend on any of its children's file names, so
      * refresh those first */
     QLIST_FOREACH(child, &bs->children, next) {
         bdrv_refresh_filename(child->bs);
     }
 
     if (bs->implicit) {
         /* For implicit nodes, just copy everything from the single child */
         child = QLIST_FIRST(&bs->children);
         assert(QLIST_NEXT(child, next) == NULL);
 
         pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
                 child->bs->exact_filename);
         pstrcpy(bs->filename, sizeof(bs->filename), child->bs->filename);
 
         qobject_unref(bs->full_open_options);
         bs->full_open_options = qobject_ref(child->bs->full_open_options);
 
         return;
     }
 
     backing_overridden = bdrv_backing_overridden(bs);
 
     if (bs->open_flags & BDRV_O_NO_IO) {
         /* Without I/O, the backing file does not change anything.
          * Therefore, in such a case (primarily qemu-img), we can
          * pretend the backing file has not been overridden even if
          * it technically has been. */
         backing_overridden = false;
     }
 
     /* Gather the options QDict */
     opts = qdict_new();
     generate_json_filename = append_strong_runtime_options(opts, bs);
     generate_json_filename |= backing_overridden;
 
     if (drv->bdrv_gather_child_options) {
         /* Some block drivers may not want to present all of their children's
          * options, or name them differently from BdrvChild.name */
         drv->bdrv_gather_child_options(bs, opts, backing_overridden);
     } else {
         QLIST_FOREACH(child, &bs->children, next) {
             if (child == bs->backing && !backing_overridden) {
                 /* We can skip the backing BDS if it has not been overridden */
                 continue;
             }
 
             qdict_put(opts, child->name,
                       qobject_ref(child->bs->full_open_options));
         }
 
         if (backing_overridden && !bs->backing) {
             /* Force no backing file */
             qdict_put_null(opts, "backing");
         }
     }
 
     qobject_unref(bs->full_open_options);
     bs->full_open_options = opts;
 
     primary_child_bs = bdrv_primary_bs(bs);
 
     if (drv->bdrv_refresh_filename) {
         /* Obsolete information is of no use here, so drop the old file name
          * information before refreshing it */
         bs->exact_filename[0] = '\0';
 
         drv->bdrv_refresh_filename(bs);
     } else if (primary_child_bs) {
         /*
          * Try to reconstruct valid information from the underlying
          * file -- this only works for format nodes (filter nodes
          * cannot be probed and as such must be selected by the user
          * either through an options dict, or through a special
          * filename which the filter driver must construct in its
          * .bdrv_refresh_filename() implementation).
          */
 
         bs->exact_filename[0] = '\0';
 
         /*
          * We can use the underlying file's filename if:
          * - it has a filename,
          * - the current BDS is not a filter,
          * - the file is a protocol BDS, and
          * - opening that file (as this BDS's format) will automatically create
          *   the BDS tree we have right now, that is:
          *   - the user did not significantly change this BDS's behavior with
          *     some explicit (strong) options
          *   - no non-file child of this BDS has been overridden by the user
          *   Both of these conditions are represented by generate_json_filename.
          */
         if (primary_child_bs->exact_filename[0] &&
             primary_child_bs->drv->bdrv_file_open &&
             !drv->is_filter && !generate_json_filename)
         {
             strcpy(bs->exact_filename, primary_child_bs->exact_filename);
         }
     }
 
     if (bs->exact_filename[0]) {
         pstrcpy(bs->filename, sizeof(bs->filename), bs->exact_filename);
     } else {
         GString *json = qobject_to_json(QOBJECT(bs->full_open_options));
         if (snprintf(bs->filename, sizeof(bs->filename), "json:%s",
                      json->str) >= sizeof(bs->filename)) {
             /* Give user a hint if we truncated things. */
             strcpy(bs->filename + sizeof(bs->filename) - 4, "...");
         }
         g_string_free(json, true);
     }
 }
 
 char *bdrv_dirname(BlockDriverState *bs, Error **errp)
 {
     BlockDriver *drv = bs->drv;
     BlockDriverState *child_bs;
 
     GLOBAL_STATE_CODE();
 
     if (!drv) {
         error_setg(errp, "Node '%s' is ejected", bs->node_name);
         return NULL;
     }
 
     if (drv->bdrv_dirname) {
         return drv->bdrv_dirname(bs, errp);
     }
 
     child_bs = bdrv_primary_bs(bs);
     if (child_bs) {
         return bdrv_dirname(child_bs, errp);
     }
 
     bdrv_refresh_filename(bs);
     if (bs->exact_filename[0] != '\0') {
         return path_combine(bs->exact_filename, "");
     }
 
     error_setg(errp, "Cannot generate a base directory for %s nodes",
                drv->format_name);
     return NULL;
 }
 
 /*
  * Hot add/remove a BDS's child. So the user can take a child offline when
  * it is broken and take a new child online
  */
 void bdrv_add_child(BlockDriverState *parent_bs, BlockDriverState *child_bs,
                     Error **errp)
 {
     GLOBAL_STATE_CODE();
     if (!parent_bs->drv || !parent_bs->drv->bdrv_add_child) {
         error_setg(errp, "The node %s does not support adding a child",
                    bdrv_get_device_or_node_name(parent_bs));
         return;
     }
 
     if (!QLIST_EMPTY(&child_bs->parents)) {
         error_setg(errp, "The node %s already has a parent",
                    child_bs->node_name);
         return;
     }
 
     parent_bs->drv->bdrv_add_child(parent_bs, child_bs, errp);
 }
 
 void bdrv_del_child(BlockDriverState *parent_bs, BdrvChild *child, Error **errp)
 {
     BdrvChild *tmp;
 
     GLOBAL_STATE_CODE();
     if (!parent_bs->drv || !parent_bs->drv->bdrv_del_child) {
         error_setg(errp, "The node %s does not support removing a child",
                    bdrv_get_device_or_node_name(parent_bs));
         return;
     }
 
     QLIST_FOREACH(tmp, &parent_bs->children, next) {
         if (tmp == child) {
             break;
         }
     }
 
     if (!tmp) {
         error_setg(errp, "The node %s does not have a child named %s",
                    bdrv_get_device_or_node_name(parent_bs),
                    bdrv_get_device_or_node_name(child->bs));
         return;
     }
 
     parent_bs->drv->bdrv_del_child(parent_bs, child, errp);
 }
 
 int bdrv_make_empty(BdrvChild *c, Error **errp)
 {
     BlockDriver *drv = c->bs->drv;
     int ret;
 
     GLOBAL_STATE_CODE();
     assert(c->perm & (BLK_PERM_WRITE | BLK_PERM_WRITE_UNCHANGED));
 
     if (!drv->bdrv_make_empty) {
         error_setg(errp, "%s does not support emptying nodes",
                    drv->format_name);
         return -ENOTSUP;
     }
 
     ret = drv->bdrv_make_empty(c->bs);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Failed to empty %s",
                          c->bs->filename);
         return ret;
     }
 
     return 0;
 }
 
 /*
  * Return the child that @bs acts as an overlay for, and from which data may be
  * copied in COW or COR operations.  Usually this is the backing file.
  */
 BdrvChild *bdrv_cow_child(BlockDriverState *bs)
 {
     IO_CODE();
 
     if (!bs || !bs->drv) {
         return NULL;
     }
 
     if (bs->drv->is_filter) {
         return NULL;
     }
 
     if (!bs->backing) {
         return NULL;
     }
 
     assert(bs->backing->role & BDRV_CHILD_COW);
     return bs->backing;
 }
 
 /*
  * If @bs acts as a filter for exactly one of its children, return
  * that child.
  */
 BdrvChild *bdrv_filter_child(BlockDriverState *bs)
 {
     BdrvChild *c;
     IO_CODE();
 
     if (!bs || !bs->drv) {
         return NULL;
     }
 
     if (!bs->drv->is_filter) {
         return NULL;
     }
 
     /* Only one of @backing or @file may be used */
     assert(!(bs->backing && bs->file));
 
     c = bs->backing ?: bs->file;
     if (!c) {
         return NULL;
     }
 
     assert(c->role & BDRV_CHILD_FILTERED);
     return c;
 }
 
 /*
  * Return either the result of bdrv_cow_child() or bdrv_filter_child(),
  * whichever is non-NULL.
  *
  * Return NULL if both are NULL.
  */
 BdrvChild *bdrv_filter_or_cow_child(BlockDriverState *bs)
 {
     BdrvChild *cow_child = bdrv_cow_child(bs);
     BdrvChild *filter_child = bdrv_filter_child(bs);
     IO_CODE();
 
     /* Filter nodes cannot have COW backing files */
     assert(!(cow_child && filter_child));
 
     return cow_child ?: filter_child;
 }
 
 /*
  * Return the primary child of this node: For filters, that is the
  * filtered child.  For other nodes, that is usually the child storing
  * metadata.
  * (A generally more helpful description is that this is (usually) the
  * child that has the same filename as @bs.)
  *
  * Drivers do not necessarily have a primary child; for example quorum
  * does not.
  */
 BdrvChild *bdrv_primary_child(BlockDriverState *bs)
 {
     BdrvChild *c, *found = NULL;
     IO_CODE();
 
     QLIST_FOREACH(c, &bs->children, next) {
         if (c->role & BDRV_CHILD_PRIMARY) {
             assert(!found);
             found = c;
         }
     }
 
     return found;
 }
 
 static BlockDriverState *bdrv_do_skip_filters(BlockDriverState *bs,
                                               bool stop_on_explicit_filter)
 {
     BdrvChild *c;
 
     if (!bs) {
         return NULL;
     }
 
     while (!(stop_on_explicit_filter && !bs->implicit)) {
         c = bdrv_filter_child(bs);
         if (!c) {
             /*
              * A filter that is embedded in a working block graph must
              * have a child.  Assert this here so this function does
              * not return a filter node that is not expected by the
              * caller.
              */
             assert(!bs->drv || !bs->drv->is_filter);
             break;
         }
         bs = c->bs;
     }
     /*
      * Note that this treats nodes with bs->drv == NULL as not being
      * filters (bs->drv == NULL should be replaced by something else
      * anyway).
      * The advantage of this behavior is that this function will thus
      * always return a non-NULL value (given a non-NULL @bs).
      */
 
     return bs;
 }
 
 /*
  * Return the first BDS that has not been added implicitly or that
  * does not have a filtered child down the chain starting from @bs
  * (including @bs itself).
  */
 BlockDriverState *bdrv_skip_implicit_filters(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     return bdrv_do_skip_filters(bs, true);
 }
 
 /*
  * Return the first BDS that does not have a filtered child down the
  * chain starting from @bs (including @bs itself).
  */
 BlockDriverState *bdrv_skip_filters(BlockDriverState *bs)
 {
     IO_CODE();
     return bdrv_do_skip_filters(bs, false);
 }
 
 /*
  * For a backing chain, return the first non-filter backing image of
  * the first non-filter image.
  */
 BlockDriverState *bdrv_backing_chain_next(BlockDriverState *bs)
 {
     IO_CODE();
     return bdrv_skip_filters(bdrv_cow_bs(bdrv_skip_filters(bs)));
 }
 
 /**
  * Check whether [offset, offset + bytes) overlaps with the cached
  * block-status data region.
  *
  * If so, and @pnum is not NULL, set *pnum to `bsc.data_end - offset`,
  * which is what bdrv_bsc_is_data()'s interface needs.
  * Otherwise, *pnum is not touched.
  */
 static bool bdrv_bsc_range_overlaps_locked(BlockDriverState *bs,
                                            int64_t offset, int64_t bytes,
                                            int64_t *pnum)
 {
     BdrvBlockStatusCache *bsc = qatomic_rcu_read(&bs->block_status_cache);
     bool overlaps;
 
     overlaps =
         qatomic_read(&bsc->valid) &&
         ranges_overlap(offset, bytes, bsc->data_start,
                        bsc->data_end - bsc->data_start);
 
     if (overlaps && pnum) {
         *pnum = bsc->data_end - offset;
     }
 
     return overlaps;
 }
 
 /**
  * See block_int.h for this function's documentation.
  */
 bool bdrv_bsc_is_data(BlockDriverState *bs, int64_t offset, int64_t *pnum)
 {
     IO_CODE();
     RCU_READ_LOCK_GUARD();
     return bdrv_bsc_range_overlaps_locked(bs, offset, 1, pnum);
 }
 
 /**
  * See block_int.h for this function's documentation.
  */
 void bdrv_bsc_invalidate_range(BlockDriverState *bs,
                                int64_t offset, int64_t bytes)
 {
     IO_CODE();
     RCU_READ_LOCK_GUARD();
 
     if (bdrv_bsc_range_overlaps_locked(bs, offset, bytes, NULL)) {
         qatomic_set(&bs->block_status_cache->valid, false);
     }
 }
 
 /**
  * See block_int.h for this function's documentation.
  */
 void bdrv_bsc_fill(BlockDriverState *bs, int64_t offset, int64_t bytes)
 {
     BdrvBlockStatusCache *new_bsc = g_new(BdrvBlockStatusCache, 1);
     BdrvBlockStatusCache *old_bsc;
     IO_CODE();
 
     *new_bsc = (BdrvBlockStatusCache) {
         .valid = true,
         .data_start = offset,
         .data_end = offset + bytes,
     };
 
     QEMU_LOCK_GUARD(&bs->bsc_modify_lock);
 
     old_bsc = qatomic_rcu_read(&bs->block_status_cache);
     qatomic_rcu_set(&bs->block_status_cache, new_bsc);
     if (old_bsc) {
         g_free_rcu(old_bsc, rcu);
     }
 }