qemu

nbd.c (68618B)

---

 /*
  * QEMU Block driver for  NBD
  *
  * Copyright (c) 2019 Virtuozzo International GmbH.
  * Copyright (C) 2016 Red Hat, Inc.
  * Copyright (C) 2008 Bull S.A.S.
  *     Author: Laurent Vivier <Laurent.Vivier@bull.net>
  *
  * Some parts:
  *    Copyright (C) 2007 Anthony Liguori <anthony@codemonkey.ws>
  *
  * 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 "trace.h"
 #include "qemu/uri.h"
 #include "qemu/option.h"
 #include "qemu/cutils.h"
 #include "qemu/main-loop.h"
 
 #include "qapi/qapi-visit-sockets.h"
 #include "qapi/qmp/qstring.h"
 #include "qapi/clone-visitor.h"
 
 #include "block/qdict.h"
 #include "block/nbd.h"
 #include "block/block_int.h"
 #include "block/coroutines.h"
 
 #include "qemu/yank.h"
 
 #define EN_OPTSTR ":exportname="
 #define MAX_NBD_REQUESTS    16
 
 #define HANDLE_TO_INDEX(bs, handle) ((handle) ^ (uint64_t)(intptr_t)(bs))
 #define INDEX_TO_HANDLE(bs, index)  ((index)  ^ (uint64_t)(intptr_t)(bs))
 
 typedef struct {
     Coroutine *coroutine;
     uint64_t offset;        /* original offset of the request */
     bool receiving;         /* sleeping in the yield in nbd_receive_replies */
 } NBDClientRequest;
 
 typedef enum NBDClientState {
     NBD_CLIENT_CONNECTING_WAIT,
     NBD_CLIENT_CONNECTING_NOWAIT,
     NBD_CLIENT_CONNECTED,
     NBD_CLIENT_QUIT
 } NBDClientState;
 
 typedef struct BDRVNBDState {
     QIOChannel *ioc; /* The current I/O channel */
     NBDExportInfo info;
 
     /*
      * Protects state, free_sema, in_flight, requests[].coroutine,
      * reconnect_delay_timer.
      */
     QemuMutex requests_lock;
     NBDClientState state;
     CoQueue free_sema;
     unsigned in_flight;
     NBDClientRequest requests[MAX_NBD_REQUESTS];
     QEMUTimer *reconnect_delay_timer;
 
     /* Protects sending data on the socket.  */
     CoMutex send_mutex;
 
     /*
      * Protects receiving reply headers from the socket, as well as the
      * fields reply and requests[].receiving
      */
     CoMutex receive_mutex;
     NBDReply reply;
 
     QEMUTimer *open_timer;
 
     BlockDriverState *bs;
 
     /* Connection parameters */
     uint32_t reconnect_delay;
     uint32_t open_timeout;
     SocketAddress *saddr;
     char *export;
     char *tlscredsid;
     QCryptoTLSCreds *tlscreds;
     char *tlshostname;
     char *x_dirty_bitmap;
     bool alloc_depth;
 
     NBDClientConnection *conn;
 } BDRVNBDState;
 
 static void nbd_yank(void *opaque);
 
 static void nbd_clear_bdrvstate(BlockDriverState *bs)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
     nbd_client_connection_release(s->conn);
     s->conn = NULL;
 
     yank_unregister_instance(BLOCKDEV_YANK_INSTANCE(bs->node_name));
 
     /* Must not leave timers behind that would access freed data */
     assert(!s->reconnect_delay_timer);
     assert(!s->open_timer);
 
     object_unref(OBJECT(s->tlscreds));
     qapi_free_SocketAddress(s->saddr);
     s->saddr = NULL;
     g_free(s->export);
     s->export = NULL;
     g_free(s->tlscredsid);
     s->tlscredsid = NULL;
     g_free(s->tlshostname);
     s->tlshostname = NULL;
     g_free(s->x_dirty_bitmap);
     s->x_dirty_bitmap = NULL;
 }
 
 /* Called with s->receive_mutex taken.  */
 static bool coroutine_fn nbd_recv_coroutine_wake_one(NBDClientRequest *req)
 {
     if (req->receiving) {
         req->receiving = false;
         aio_co_wake(req->coroutine);
         return true;
     }
 
     return false;
 }
 
 static void coroutine_fn nbd_recv_coroutines_wake(BDRVNBDState *s)
 {
     int i;
 
     QEMU_LOCK_GUARD(&s->receive_mutex);
     for (i = 0; i < MAX_NBD_REQUESTS; i++) {
         if (nbd_recv_coroutine_wake_one(&s->requests[i])) {
             return;
         }
     }
 }
 
 /* Called with s->requests_lock held.  */
 static void coroutine_fn nbd_channel_error_locked(BDRVNBDState *s, int ret)
 {
     if (s->state == NBD_CLIENT_CONNECTED) {
         qio_channel_shutdown(s->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
     }
 
     if (ret == -EIO) {
         if (s->state == NBD_CLIENT_CONNECTED) {
             s->state = s->reconnect_delay ? NBD_CLIENT_CONNECTING_WAIT :
                                             NBD_CLIENT_CONNECTING_NOWAIT;
         }
     } else {
         s->state = NBD_CLIENT_QUIT;
     }
 }
 
 static void coroutine_fn nbd_channel_error(BDRVNBDState *s, int ret)
 {
     QEMU_LOCK_GUARD(&s->requests_lock);
     nbd_channel_error_locked(s, ret);
 }
 
 static void reconnect_delay_timer_del(BDRVNBDState *s)
 {
     if (s->reconnect_delay_timer) {
         timer_free(s->reconnect_delay_timer);
         s->reconnect_delay_timer = NULL;
     }
 }
 
 static void reconnect_delay_timer_cb(void *opaque)
 {
     BDRVNBDState *s = opaque;
 
     reconnect_delay_timer_del(s);
     WITH_QEMU_LOCK_GUARD(&s->requests_lock) {
         if (s->state != NBD_CLIENT_CONNECTING_WAIT) {
             return;
         }
         s->state = NBD_CLIENT_CONNECTING_NOWAIT;
     }
     nbd_co_establish_connection_cancel(s->conn);
 }
 
 static void reconnect_delay_timer_init(BDRVNBDState *s, uint64_t expire_time_ns)
 {
     assert(!s->reconnect_delay_timer);
     s->reconnect_delay_timer = aio_timer_new(bdrv_get_aio_context(s->bs),
                                              QEMU_CLOCK_REALTIME,
                                              SCALE_NS,
                                              reconnect_delay_timer_cb, s);
     timer_mod(s->reconnect_delay_timer, expire_time_ns);
 }
 
 static void nbd_teardown_connection(BlockDriverState *bs)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
     assert(!s->in_flight);
 
     if (s->ioc) {
         qio_channel_shutdown(s->ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
         yank_unregister_function(BLOCKDEV_YANK_INSTANCE(s->bs->node_name),
                                  nbd_yank, s->bs);
         object_unref(OBJECT(s->ioc));
         s->ioc = NULL;
     }
 
     WITH_QEMU_LOCK_GUARD(&s->requests_lock) {
         s->state = NBD_CLIENT_QUIT;
     }
 }
 
 static void open_timer_del(BDRVNBDState *s)
 {
     if (s->open_timer) {
         timer_free(s->open_timer);
         s->open_timer = NULL;
     }
 }
 
 static void open_timer_cb(void *opaque)
 {
     BDRVNBDState *s = opaque;
 
     nbd_co_establish_connection_cancel(s->conn);
     open_timer_del(s);
 }
 
 static void open_timer_init(BDRVNBDState *s, uint64_t expire_time_ns)
 {
     assert(!s->open_timer);
     s->open_timer = aio_timer_new(bdrv_get_aio_context(s->bs),
                                   QEMU_CLOCK_REALTIME,
                                   SCALE_NS,
                                   open_timer_cb, s);
     timer_mod(s->open_timer, expire_time_ns);
 }
 
 static bool nbd_client_will_reconnect(BDRVNBDState *s)
 {
     /*
      * Called only after a socket error, so this is not performance sensitive.
      */
     QEMU_LOCK_GUARD(&s->requests_lock);
     return s->state == NBD_CLIENT_CONNECTING_WAIT;
 }
 
 /*
  * Update @bs with information learned during a completed negotiation process.
  * Return failure if the server's advertised options are incompatible with the
  * client's needs.
  */
 static int nbd_handle_updated_info(BlockDriverState *bs, Error **errp)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     int ret;
 
     if (s->x_dirty_bitmap) {
         if (!s->info.base_allocation) {
             error_setg(errp, "requested x-dirty-bitmap %s not found",
                        s->x_dirty_bitmap);
             return -EINVAL;
         }
         if (strcmp(s->x_dirty_bitmap, "qemu:allocation-depth") == 0) {
             s->alloc_depth = true;
         }
     }
 
     if (s->info.flags & NBD_FLAG_READ_ONLY) {
         ret = bdrv_apply_auto_read_only(bs, "NBD export is read-only", errp);
         if (ret < 0) {
             return ret;
         }
     }
 
     if (s->info.flags & NBD_FLAG_SEND_FUA) {
         bs->supported_write_flags = BDRV_REQ_FUA;
         bs->supported_zero_flags |= BDRV_REQ_FUA;
     }
 
     if (s->info.flags & NBD_FLAG_SEND_WRITE_ZEROES) {
         bs->supported_zero_flags |= BDRV_REQ_MAY_UNMAP;
         if (s->info.flags & NBD_FLAG_SEND_FAST_ZERO) {
             bs->supported_zero_flags |= BDRV_REQ_NO_FALLBACK;
         }
     }
 
     trace_nbd_client_handshake_success(s->export);
 
     return 0;
 }
 
 int coroutine_fn nbd_co_do_establish_connection(BlockDriverState *bs,
                                                 bool blocking, Error **errp)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     int ret;
     IO_CODE();
 
     assert(!s->ioc);
 
     s->ioc = nbd_co_establish_connection(s->conn, &s->info, blocking, errp);
     if (!s->ioc) {
         return -ECONNREFUSED;
     }
 
     yank_register_function(BLOCKDEV_YANK_INSTANCE(s->bs->node_name), nbd_yank,
                            bs);
 
     ret = nbd_handle_updated_info(s->bs, NULL);
     if (ret < 0) {
         /*
          * We have connected, but must fail for other reasons.
          * Send NBD_CMD_DISC as a courtesy to the server.
          */
         NBDRequest request = { .type = NBD_CMD_DISC };
 
         nbd_send_request(s->ioc, &request);
 
         yank_unregister_function(BLOCKDEV_YANK_INSTANCE(s->bs->node_name),
                                  nbd_yank, bs);
         object_unref(OBJECT(s->ioc));
         s->ioc = NULL;
 
         return ret;
     }
 
     qio_channel_set_blocking(s->ioc, false, NULL);
     qio_channel_attach_aio_context(s->ioc, bdrv_get_aio_context(bs));
 
     /* successfully connected */
     WITH_QEMU_LOCK_GUARD(&s->requests_lock) {
         s->state = NBD_CLIENT_CONNECTED;
     }
 
     return 0;
 }
 
 /* Called with s->requests_lock held.  */
 static bool nbd_client_connecting(BDRVNBDState *s)
 {
     return s->state == NBD_CLIENT_CONNECTING_WAIT ||
         s->state == NBD_CLIENT_CONNECTING_NOWAIT;
 }
 
 /* Called with s->requests_lock taken.  */
 static coroutine_fn void nbd_reconnect_attempt(BDRVNBDState *s)
 {
     int ret;
     bool blocking = s->state == NBD_CLIENT_CONNECTING_WAIT;
 
     /*
      * Now we are sure that nobody is accessing the channel, and no one will
      * try until we set the state to CONNECTED.
      */
     assert(nbd_client_connecting(s));
     assert(s->in_flight == 1);
 
     trace_nbd_reconnect_attempt(s->bs->in_flight);
 
     if (blocking && !s->reconnect_delay_timer) {
         /*
          * It's the first reconnect attempt after switching to
          * NBD_CLIENT_CONNECTING_WAIT
          */
         g_assert(s->reconnect_delay);
         reconnect_delay_timer_init(s,
             qemu_clock_get_ns(QEMU_CLOCK_REALTIME) +
             s->reconnect_delay * NANOSECONDS_PER_SECOND);
     }
 
     /* Finalize previous connection if any */
     if (s->ioc) {
         qio_channel_detach_aio_context(QIO_CHANNEL(s->ioc));
         yank_unregister_function(BLOCKDEV_YANK_INSTANCE(s->bs->node_name),
                                  nbd_yank, s->bs);
         object_unref(OBJECT(s->ioc));
         s->ioc = NULL;
     }
 
     qemu_mutex_unlock(&s->requests_lock);
     ret = nbd_co_do_establish_connection(s->bs, blocking, NULL);
     trace_nbd_reconnect_attempt_result(ret, s->bs->in_flight);
     qemu_mutex_lock(&s->requests_lock);
 
     /*
      * The reconnect attempt is done (maybe successfully, maybe not), so
      * we no longer need this timer.  Delete it so it will not outlive
      * this I/O request (so draining removes all timers).
      */
     reconnect_delay_timer_del(s);
 }
 
 static coroutine_fn int nbd_receive_replies(BDRVNBDState *s, uint64_t handle)
 {
     int ret;
     uint64_t ind = HANDLE_TO_INDEX(s, handle), ind2;
     QEMU_LOCK_GUARD(&s->receive_mutex);
 
     while (true) {
         if (s->reply.handle == handle) {
             /* We are done */
             return 0;
         }
 
         if (s->reply.handle != 0) {
             /*
              * Some other request is being handled now. It should already be
              * woken by whoever set s->reply.handle (or never wait in this
              * yield). So, we should not wake it here.
              */
             ind2 = HANDLE_TO_INDEX(s, s->reply.handle);
             assert(!s->requests[ind2].receiving);
 
             s->requests[ind].receiving = true;
             qemu_co_mutex_unlock(&s->receive_mutex);
 
             qemu_coroutine_yield();
             /*
              * We may be woken for 2 reasons:
              * 1. From this function, executing in parallel coroutine, when our
              *    handle is received.
              * 2. From nbd_co_receive_one_chunk(), when previous request is
              *    finished and s->reply.handle set to 0.
              * Anyway, it's OK to lock the mutex and go to the next iteration.
              */
 
             qemu_co_mutex_lock(&s->receive_mutex);
             assert(!s->requests[ind].receiving);
             continue;
         }
 
         /* We are under mutex and handle is 0. We have to do the dirty work. */
         assert(s->reply.handle == 0);
         ret = nbd_receive_reply(s->bs, s->ioc, &s->reply, NULL);
         if (ret <= 0) {
             ret = ret ? ret : -EIO;
             nbd_channel_error(s, ret);
             return ret;
         }
         if (nbd_reply_is_structured(&s->reply) && !s->info.structured_reply) {
             nbd_channel_error(s, -EINVAL);
             return -EINVAL;
         }
         ind2 = HANDLE_TO_INDEX(s, s->reply.handle);
         if (ind2 >= MAX_NBD_REQUESTS || !s->requests[ind2].coroutine) {
             nbd_channel_error(s, -EINVAL);
             return -EINVAL;
         }
         if (s->reply.handle == handle) {
             /* We are done */
             return 0;
         }
         nbd_recv_coroutine_wake_one(&s->requests[ind2]);
     }
 }
 
 static int coroutine_fn nbd_co_send_request(BlockDriverState *bs,
                                             NBDRequest *request,
                                             QEMUIOVector *qiov)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     int rc, i = -1;
 
     qemu_mutex_lock(&s->requests_lock);
     while (s->in_flight == MAX_NBD_REQUESTS ||
            (s->state != NBD_CLIENT_CONNECTED && s->in_flight > 0)) {
         qemu_co_queue_wait(&s->free_sema, &s->requests_lock);
     }
 
     s->in_flight++;
     if (s->state != NBD_CLIENT_CONNECTED) {
         if (nbd_client_connecting(s)) {
             nbd_reconnect_attempt(s);
             qemu_co_queue_restart_all(&s->free_sema);
         }
         if (s->state != NBD_CLIENT_CONNECTED) {
             rc = -EIO;
             goto err;
         }
     }
 
     for (i = 0; i < MAX_NBD_REQUESTS; i++) {
         if (s->requests[i].coroutine == NULL) {
             break;
         }
     }
 
     assert(i < MAX_NBD_REQUESTS);
     s->requests[i].coroutine = qemu_coroutine_self();
     s->requests[i].offset = request->from;
     s->requests[i].receiving = false;
     qemu_mutex_unlock(&s->requests_lock);
 
     qemu_co_mutex_lock(&s->send_mutex);
     request->handle = INDEX_TO_HANDLE(s, i);
 
     assert(s->ioc);
 
     if (qiov) {
         qio_channel_set_cork(s->ioc, true);
         rc = nbd_send_request(s->ioc, request);
         if (rc >= 0 && qio_channel_writev_all(s->ioc, qiov->iov, qiov->niov,
                                               NULL) < 0) {
             rc = -EIO;
         }
         qio_channel_set_cork(s->ioc, false);
     } else {
         rc = nbd_send_request(s->ioc, request);
     }
     qemu_co_mutex_unlock(&s->send_mutex);
 
     if (rc < 0) {
         qemu_mutex_lock(&s->requests_lock);
 err:
         nbd_channel_error_locked(s, rc);
         if (i != -1) {
             s->requests[i].coroutine = NULL;
         }
         s->in_flight--;
         qemu_co_queue_next(&s->free_sema);
         qemu_mutex_unlock(&s->requests_lock);
     }
     return rc;
 }
 
 static inline uint16_t payload_advance16(uint8_t **payload)
 {
     *payload += 2;
     return lduw_be_p(*payload - 2);
 }
 
 static inline uint32_t payload_advance32(uint8_t **payload)
 {
     *payload += 4;
     return ldl_be_p(*payload - 4);
 }
 
 static inline uint64_t payload_advance64(uint8_t **payload)
 {
     *payload += 8;
     return ldq_be_p(*payload - 8);
 }
 
 static int nbd_parse_offset_hole_payload(BDRVNBDState *s,
                                          NBDStructuredReplyChunk *chunk,
                                          uint8_t *payload, uint64_t orig_offset,
                                          QEMUIOVector *qiov, Error **errp)
 {
     uint64_t offset;
     uint32_t hole_size;
 
     if (chunk->length != sizeof(offset) + sizeof(hole_size)) {
         error_setg(errp, "Protocol error: invalid payload for "
                          "NBD_REPLY_TYPE_OFFSET_HOLE");
         return -EINVAL;
     }
 
     offset = payload_advance64(&payload);
     hole_size = payload_advance32(&payload);
 
     if (!hole_size || offset < orig_offset || hole_size > qiov->size ||
         offset > orig_offset + qiov->size - hole_size) {
         error_setg(errp, "Protocol error: server sent chunk exceeding requested"
                          " region");
         return -EINVAL;
     }
     if (s->info.min_block &&
         !QEMU_IS_ALIGNED(hole_size, s->info.min_block)) {
         trace_nbd_structured_read_compliance("hole");
     }
 
     qemu_iovec_memset(qiov, offset - orig_offset, 0, hole_size);
 
     return 0;
 }
 
 /*
  * nbd_parse_blockstatus_payload
  * Based on our request, we expect only one extent in reply, for the
  * base:allocation context.
  */
 static int nbd_parse_blockstatus_payload(BDRVNBDState *s,
                                          NBDStructuredReplyChunk *chunk,
                                          uint8_t *payload, uint64_t orig_length,
                                          NBDExtent *extent, Error **errp)
 {
     uint32_t context_id;
 
     /* The server succeeded, so it must have sent [at least] one extent */
     if (chunk->length < sizeof(context_id) + sizeof(*extent)) {
         error_setg(errp, "Protocol error: invalid payload for "
                          "NBD_REPLY_TYPE_BLOCK_STATUS");
         return -EINVAL;
     }
 
     context_id = payload_advance32(&payload);
     if (s->info.context_id != context_id) {
         error_setg(errp, "Protocol error: unexpected context id %d for "
                          "NBD_REPLY_TYPE_BLOCK_STATUS, when negotiated context "
                          "id is %d", context_id,
                          s->info.context_id);
         return -EINVAL;
     }
 
     extent->length = payload_advance32(&payload);
     extent->flags = payload_advance32(&payload);
 
     if (extent->length == 0) {
         error_setg(errp, "Protocol error: server sent status chunk with "
                    "zero length");
         return -EINVAL;
     }
 
     /*
      * A server sending unaligned block status is in violation of the
      * protocol, but as qemu-nbd 3.1 is such a server (at least for
      * POSIX files that are not a multiple of 512 bytes, since qemu
      * rounds files up to 512-byte multiples but lseek(SEEK_HOLE)
      * still sees an implicit hole beyond the real EOF), it's nicer to
      * work around the misbehaving server. If the request included
      * more than the final unaligned block, truncate it back to an
      * aligned result; if the request was only the final block, round
      * up to the full block and change the status to fully-allocated
      * (always a safe status, even if it loses information).
      */
     if (s->info.min_block && !QEMU_IS_ALIGNED(extent->length,
                                                    s->info.min_block)) {
         trace_nbd_parse_blockstatus_compliance("extent length is unaligned");
         if (extent->length > s->info.min_block) {
             extent->length = QEMU_ALIGN_DOWN(extent->length,
                                              s->info.min_block);
         } else {
             extent->length = s->info.min_block;
             extent->flags = 0;
         }
     }
 
     /*
      * We used NBD_CMD_FLAG_REQ_ONE, so the server should not have
      * sent us any more than one extent, nor should it have included
      * status beyond our request in that extent. However, it's easy
      * enough to ignore the server's noncompliance without killing the
      * connection; just ignore trailing extents, and clamp things to
      * the length of our request.
      */
     if (chunk->length > sizeof(context_id) + sizeof(*extent)) {
         trace_nbd_parse_blockstatus_compliance("more than one extent");
     }
     if (extent->length > orig_length) {
         extent->length = orig_length;
         trace_nbd_parse_blockstatus_compliance("extent length too large");
     }
 
     /*
      * HACK: if we are using x-dirty-bitmaps to access
      * qemu:allocation-depth, treat all depths > 2 the same as 2,
      * since nbd_client_co_block_status is only expecting the low two
      * bits to be set.
      */
     if (s->alloc_depth && extent->flags > 2) {
         extent->flags = 2;
     }
 
     return 0;
 }
 
 /*
  * nbd_parse_error_payload
  * on success @errp contains message describing nbd error reply
  */
 static int nbd_parse_error_payload(NBDStructuredReplyChunk *chunk,
                                    uint8_t *payload, int *request_ret,
                                    Error **errp)
 {
     uint32_t error;
     uint16_t message_size;
 
     assert(chunk->type & (1 << 15));
 
     if (chunk->length < sizeof(error) + sizeof(message_size)) {
         error_setg(errp,
                    "Protocol error: invalid payload for structured error");
         return -EINVAL;
     }
 
     error = nbd_errno_to_system_errno(payload_advance32(&payload));
     if (error == 0) {
         error_setg(errp, "Protocol error: server sent structured error chunk "
                          "with error = 0");
         return -EINVAL;
     }
 
     *request_ret = -error;
     message_size = payload_advance16(&payload);
 
     if (message_size > chunk->length - sizeof(error) - sizeof(message_size)) {
         error_setg(errp, "Protocol error: server sent structured error chunk "
                          "with incorrect message size");
         return -EINVAL;
     }
 
     /* TODO: Add a trace point to mention the server complaint */
 
     /* TODO handle ERROR_OFFSET */
 
     return 0;
 }
 
 static int coroutine_fn
 nbd_co_receive_offset_data_payload(BDRVNBDState *s, uint64_t orig_offset,
                                    QEMUIOVector *qiov, Error **errp)
 {
     QEMUIOVector sub_qiov;
     uint64_t offset;
     size_t data_size;
     int ret;
     NBDStructuredReplyChunk *chunk = &s->reply.structured;
 
     assert(nbd_reply_is_structured(&s->reply));
 
     /* The NBD spec requires at least one byte of payload */
     if (chunk->length <= sizeof(offset)) {
         error_setg(errp, "Protocol error: invalid payload for "
                          "NBD_REPLY_TYPE_OFFSET_DATA");
         return -EINVAL;
     }
 
     if (nbd_read64(s->ioc, &offset, "OFFSET_DATA offset", errp) < 0) {
         return -EIO;
     }
 
     data_size = chunk->length - sizeof(offset);
     assert(data_size);
     if (offset < orig_offset || data_size > qiov->size ||
         offset > orig_offset + qiov->size - data_size) {
         error_setg(errp, "Protocol error: server sent chunk exceeding requested"
                          " region");
         return -EINVAL;
     }
     if (s->info.min_block && !QEMU_IS_ALIGNED(data_size, s->info.min_block)) {
         trace_nbd_structured_read_compliance("data");
     }
 
     qemu_iovec_init(&sub_qiov, qiov->niov);
     qemu_iovec_concat(&sub_qiov, qiov, offset - orig_offset, data_size);
     ret = qio_channel_readv_all(s->ioc, sub_qiov.iov, sub_qiov.niov, errp);
     qemu_iovec_destroy(&sub_qiov);
 
     return ret < 0 ? -EIO : 0;
 }
 
 #define NBD_MAX_MALLOC_PAYLOAD 1000
 static coroutine_fn int nbd_co_receive_structured_payload(
         BDRVNBDState *s, void **payload, Error **errp)
 {
     int ret;
     uint32_t len;
 
     assert(nbd_reply_is_structured(&s->reply));
 
     len = s->reply.structured.length;
 
     if (len == 0) {
         return 0;
     }
 
     if (payload == NULL) {
         error_setg(errp, "Unexpected structured payload");
         return -EINVAL;
     }
 
     if (len > NBD_MAX_MALLOC_PAYLOAD) {
         error_setg(errp, "Payload too large");
         return -EINVAL;
     }
 
     *payload = g_new(char, len);
     ret = nbd_read(s->ioc, *payload, len, "structured payload", errp);
     if (ret < 0) {
         g_free(*payload);
         *payload = NULL;
         return ret;
     }
 
     return 0;
 }
 
 /*
  * nbd_co_do_receive_one_chunk
  * for simple reply:
  *   set request_ret to received reply error
  *   if qiov is not NULL: read payload to @qiov
  * for structured reply chunk:
  *   if error chunk: read payload, set @request_ret, do not set @payload
  *   else if offset_data chunk: read payload data to @qiov, do not set @payload
  *   else: read payload to @payload
  *
  * If function fails, @errp contains corresponding error message, and the
  * connection with the server is suspect.  If it returns 0, then the
  * transaction succeeded (although @request_ret may be a negative errno
  * corresponding to the server's error reply), and errp is unchanged.
  */
 static coroutine_fn int nbd_co_do_receive_one_chunk(
         BDRVNBDState *s, uint64_t handle, bool only_structured,
         int *request_ret, QEMUIOVector *qiov, void **payload, Error **errp)
 {
     int ret;
     int i = HANDLE_TO_INDEX(s, handle);
     void *local_payload = NULL;
     NBDStructuredReplyChunk *chunk;
 
     if (payload) {
         *payload = NULL;
     }
     *request_ret = 0;
 
     ret = nbd_receive_replies(s, handle);
     if (ret < 0) {
         error_setg(errp, "Connection closed");
         return -EIO;
     }
     assert(s->ioc);
 
     assert(s->reply.handle == handle);
 
     if (nbd_reply_is_simple(&s->reply)) {
         if (only_structured) {
             error_setg(errp, "Protocol error: simple reply when structured "
                              "reply chunk was expected");
             return -EINVAL;
         }
 
         *request_ret = -nbd_errno_to_system_errno(s->reply.simple.error);
         if (*request_ret < 0 || !qiov) {
             return 0;
         }
 
         return qio_channel_readv_all(s->ioc, qiov->iov, qiov->niov,
                                      errp) < 0 ? -EIO : 0;
     }
 
     /* handle structured reply chunk */
     assert(s->info.structured_reply);
     chunk = &s->reply.structured;
 
     if (chunk->type == NBD_REPLY_TYPE_NONE) {
         if (!(chunk->flags & NBD_REPLY_FLAG_DONE)) {
             error_setg(errp, "Protocol error: NBD_REPLY_TYPE_NONE chunk without"
                        " NBD_REPLY_FLAG_DONE flag set");
             return -EINVAL;
         }
         if (chunk->length) {
             error_setg(errp, "Protocol error: NBD_REPLY_TYPE_NONE chunk with"
                        " nonzero length");
             return -EINVAL;
         }
         return 0;
     }
 
     if (chunk->type == NBD_REPLY_TYPE_OFFSET_DATA) {
         if (!qiov) {
             error_setg(errp, "Unexpected NBD_REPLY_TYPE_OFFSET_DATA chunk");
             return -EINVAL;
         }
 
         return nbd_co_receive_offset_data_payload(s, s->requests[i].offset,
                                                   qiov, errp);
     }
 
     if (nbd_reply_type_is_error(chunk->type)) {
         payload = &local_payload;
     }
 
     ret = nbd_co_receive_structured_payload(s, payload, errp);
     if (ret < 0) {
         return ret;
     }
 
     if (nbd_reply_type_is_error(chunk->type)) {
         ret = nbd_parse_error_payload(chunk, local_payload, request_ret, errp);
         g_free(local_payload);
         return ret;
     }
 
     return 0;
 }
 
 /*
  * nbd_co_receive_one_chunk
  * Read reply, wake up connection_co and set s->quit if needed.
  * Return value is a fatal error code or normal nbd reply error code
  */
 static coroutine_fn int nbd_co_receive_one_chunk(
         BDRVNBDState *s, uint64_t handle, bool only_structured,
         int *request_ret, QEMUIOVector *qiov, NBDReply *reply, void **payload,
         Error **errp)
 {
     int ret = nbd_co_do_receive_one_chunk(s, handle, only_structured,
                                           request_ret, qiov, payload, errp);
 
     if (ret < 0) {
         memset(reply, 0, sizeof(*reply));
         nbd_channel_error(s, ret);
     } else {
         /* For assert at loop start in nbd_connection_entry */
         *reply = s->reply;
     }
     s->reply.handle = 0;
 
     nbd_recv_coroutines_wake(s);
 
     return ret;
 }
 
 typedef struct NBDReplyChunkIter {
     int ret;
     int request_ret;
     Error *err;
     bool done, only_structured;
 } NBDReplyChunkIter;
 
 static void nbd_iter_channel_error(NBDReplyChunkIter *iter,
                                    int ret, Error **local_err)
 {
     assert(local_err && *local_err);
     assert(ret < 0);
 
     if (!iter->ret) {
         iter->ret = ret;
         error_propagate(&iter->err, *local_err);
     } else {
         error_free(*local_err);
     }
 
     *local_err = NULL;
 }
 
 static void nbd_iter_request_error(NBDReplyChunkIter *iter, int ret)
 {
     assert(ret < 0);
 
     if (!iter->request_ret) {
         iter->request_ret = ret;
     }
 }
 
 /*
  * NBD_FOREACH_REPLY_CHUNK
  * The pointer stored in @payload requires g_free() to free it.
  */
 #define NBD_FOREACH_REPLY_CHUNK(s, iter, handle, structured, \
                                 qiov, reply, payload) \
     for (iter = (NBDReplyChunkIter) { .only_structured = structured }; \
          nbd_reply_chunk_iter_receive(s, &iter, handle, qiov, reply, payload);)
 
 /*
  * nbd_reply_chunk_iter_receive
  * The pointer stored in @payload requires g_free() to free it.
  */
 static bool coroutine_fn nbd_reply_chunk_iter_receive(BDRVNBDState *s,
                                                       NBDReplyChunkIter *iter,
                                                       uint64_t handle,
                                                       QEMUIOVector *qiov,
                                                       NBDReply *reply,
                                                       void **payload)
 {
     int ret, request_ret;
     NBDReply local_reply;
     NBDStructuredReplyChunk *chunk;
     Error *local_err = NULL;
 
     if (iter->done) {
         /* Previous iteration was last. */
         goto break_loop;
     }
 
     if (reply == NULL) {
         reply = &local_reply;
     }
 
     ret = nbd_co_receive_one_chunk(s, handle, iter->only_structured,
                                    &request_ret, qiov, reply, payload,
                                    &local_err);
     if (ret < 0) {
         nbd_iter_channel_error(iter, ret, &local_err);
     } else if (request_ret < 0) {
         nbd_iter_request_error(iter, request_ret);
     }
 
     /* Do not execute the body of NBD_FOREACH_REPLY_CHUNK for simple reply. */
     if (nbd_reply_is_simple(reply) || iter->ret < 0) {
         goto break_loop;
     }
 
     chunk = &reply->structured;
     iter->only_structured = true;
 
     if (chunk->type == NBD_REPLY_TYPE_NONE) {
         /* NBD_REPLY_FLAG_DONE is already checked in nbd_co_receive_one_chunk */
         assert(chunk->flags & NBD_REPLY_FLAG_DONE);
         goto break_loop;
     }
 
     if (chunk->flags & NBD_REPLY_FLAG_DONE) {
         /* This iteration is last. */
         iter->done = true;
     }
 
     /* Execute the loop body */
     return true;
 
 break_loop:
     qemu_mutex_lock(&s->requests_lock);
     s->requests[HANDLE_TO_INDEX(s, handle)].coroutine = NULL;
     s->in_flight--;
     qemu_co_queue_next(&s->free_sema);
     qemu_mutex_unlock(&s->requests_lock);
 
     return false;
 }
 
 static int coroutine_fn nbd_co_receive_return_code(BDRVNBDState *s, uint64_t handle,
                                                    int *request_ret, Error **errp)
 {
     NBDReplyChunkIter iter;
 
     NBD_FOREACH_REPLY_CHUNK(s, iter, handle, false, NULL, NULL, NULL) {
         /* nbd_reply_chunk_iter_receive does all the work */
     }
 
     error_propagate(errp, iter.err);
     *request_ret = iter.request_ret;
     return iter.ret;
 }
 
 static int coroutine_fn nbd_co_receive_cmdread_reply(BDRVNBDState *s, uint64_t handle,
                                                      uint64_t offset, QEMUIOVector *qiov,
                                                      int *request_ret, Error **errp)
 {
     NBDReplyChunkIter iter;
     NBDReply reply;
     void *payload = NULL;
     Error *local_err = NULL;
 
     NBD_FOREACH_REPLY_CHUNK(s, iter, handle, s->info.structured_reply,
                             qiov, &reply, &payload)
     {
         int ret;
         NBDStructuredReplyChunk *chunk = &reply.structured;
 
         assert(nbd_reply_is_structured(&reply));
 
         switch (chunk->type) {
         case NBD_REPLY_TYPE_OFFSET_DATA:
             /*
              * special cased in nbd_co_receive_one_chunk, data is already
              * in qiov
              */
             break;
         case NBD_REPLY_TYPE_OFFSET_HOLE:
             ret = nbd_parse_offset_hole_payload(s, &reply.structured, payload,
                                                 offset, qiov, &local_err);
             if (ret < 0) {
                 nbd_channel_error(s, ret);
                 nbd_iter_channel_error(&iter, ret, &local_err);
             }
             break;
         default:
             if (!nbd_reply_type_is_error(chunk->type)) {
                 /* not allowed reply type */
                 nbd_channel_error(s, -EINVAL);
                 error_setg(&local_err,
                            "Unexpected reply type: %d (%s) for CMD_READ",
                            chunk->type, nbd_reply_type_lookup(chunk->type));
                 nbd_iter_channel_error(&iter, -EINVAL, &local_err);
             }
         }
 
         g_free(payload);
         payload = NULL;
     }
 
     error_propagate(errp, iter.err);
     *request_ret = iter.request_ret;
     return iter.ret;
 }
 
 static int coroutine_fn nbd_co_receive_blockstatus_reply(BDRVNBDState *s,
                                                          uint64_t handle, uint64_t length,
                                                          NBDExtent *extent,
                                                          int *request_ret, Error **errp)
 {
     NBDReplyChunkIter iter;
     NBDReply reply;
     void *payload = NULL;
     Error *local_err = NULL;
     bool received = false;
 
     assert(!extent->length);
     NBD_FOREACH_REPLY_CHUNK(s, iter, handle, false, NULL, &reply, &payload) {
         int ret;
         NBDStructuredReplyChunk *chunk = &reply.structured;
 
         assert(nbd_reply_is_structured(&reply));
 
         switch (chunk->type) {
         case NBD_REPLY_TYPE_BLOCK_STATUS:
             if (received) {
                 nbd_channel_error(s, -EINVAL);
                 error_setg(&local_err, "Several BLOCK_STATUS chunks in reply");
                 nbd_iter_channel_error(&iter, -EINVAL, &local_err);
             }
             received = true;
 
             ret = nbd_parse_blockstatus_payload(s, &reply.structured,
                                                 payload, length, extent,
                                                 &local_err);
             if (ret < 0) {
                 nbd_channel_error(s, ret);
                 nbd_iter_channel_error(&iter, ret, &local_err);
             }
             break;
         default:
             if (!nbd_reply_type_is_error(chunk->type)) {
                 nbd_channel_error(s, -EINVAL);
                 error_setg(&local_err,
                            "Unexpected reply type: %d (%s) "
                            "for CMD_BLOCK_STATUS",
                            chunk->type, nbd_reply_type_lookup(chunk->type));
                 nbd_iter_channel_error(&iter, -EINVAL, &local_err);
             }
         }
 
         g_free(payload);
         payload = NULL;
     }
 
     if (!extent->length && !iter.request_ret) {
         error_setg(&local_err, "Server did not reply with any status extents");
         nbd_iter_channel_error(&iter, -EIO, &local_err);
     }
 
     error_propagate(errp, iter.err);
     *request_ret = iter.request_ret;
     return iter.ret;
 }
 
 static int coroutine_fn nbd_co_request(BlockDriverState *bs, NBDRequest *request,
                                        QEMUIOVector *write_qiov)
 {
     int ret, request_ret;
     Error *local_err = NULL;
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
     assert(request->type != NBD_CMD_READ);
     if (write_qiov) {
         assert(request->type == NBD_CMD_WRITE);
         assert(request->len == iov_size(write_qiov->iov, write_qiov->niov));
     } else {
         assert(request->type != NBD_CMD_WRITE);
     }
 
     do {
         ret = nbd_co_send_request(bs, request, write_qiov);
         if (ret < 0) {
             continue;
         }
 
         ret = nbd_co_receive_return_code(s, request->handle,
                                          &request_ret, &local_err);
         if (local_err) {
             trace_nbd_co_request_fail(request->from, request->len,
                                       request->handle, request->flags,
                                       request->type,
                                       nbd_cmd_lookup(request->type),
                                       ret, error_get_pretty(local_err));
             error_free(local_err);
             local_err = NULL;
         }
     } while (ret < 0 && nbd_client_will_reconnect(s));
 
     return ret ? ret : request_ret;
 }
 
 static int coroutine_fn nbd_client_co_preadv(BlockDriverState *bs, int64_t offset,
                                              int64_t bytes, QEMUIOVector *qiov,
                                              BdrvRequestFlags flags)
 {
     int ret, request_ret;
     Error *local_err = NULL;
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     NBDRequest request = {
         .type = NBD_CMD_READ,
         .from = offset,
         .len = bytes,
     };
 
     assert(bytes <= NBD_MAX_BUFFER_SIZE);
 
     if (!bytes) {
         return 0;
     }
     /*
      * Work around the fact that the block layer doesn't do
      * byte-accurate sizing yet - if the read exceeds the server's
      * advertised size because the block layer rounded size up, then
      * truncate the request to the server and tail-pad with zero.
      */
     if (offset >= s->info.size) {
         assert(bytes < BDRV_SECTOR_SIZE);
         qemu_iovec_memset(qiov, 0, 0, bytes);
         return 0;
     }
     if (offset + bytes > s->info.size) {
         uint64_t slop = offset + bytes - s->info.size;
 
         assert(slop < BDRV_SECTOR_SIZE);
         qemu_iovec_memset(qiov, bytes - slop, 0, slop);
         request.len -= slop;
     }
 
     do {
         ret = nbd_co_send_request(bs, &request, NULL);
         if (ret < 0) {
             continue;
         }
 
         ret = nbd_co_receive_cmdread_reply(s, request.handle, offset, qiov,
                                            &request_ret, &local_err);
         if (local_err) {
             trace_nbd_co_request_fail(request.from, request.len, request.handle,
                                       request.flags, request.type,
                                       nbd_cmd_lookup(request.type),
                                       ret, error_get_pretty(local_err));
             error_free(local_err);
             local_err = NULL;
         }
     } while (ret < 0 && nbd_client_will_reconnect(s));
 
     return ret ? ret : request_ret;
 }
 
 static int coroutine_fn nbd_client_co_pwritev(BlockDriverState *bs, int64_t offset,
                                               int64_t bytes, QEMUIOVector *qiov,
                                               BdrvRequestFlags flags)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     NBDRequest request = {
         .type = NBD_CMD_WRITE,
         .from = offset,
         .len = bytes,
     };
 
     assert(!(s->info.flags & NBD_FLAG_READ_ONLY));
     if (flags & BDRV_REQ_FUA) {
         assert(s->info.flags & NBD_FLAG_SEND_FUA);
         request.flags |= NBD_CMD_FLAG_FUA;
     }
 
     assert(bytes <= NBD_MAX_BUFFER_SIZE);
 
     if (!bytes) {
         return 0;
     }
     return nbd_co_request(bs, &request, qiov);
 }
 
 static int coroutine_fn nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
                                                     int64_t bytes, BdrvRequestFlags flags)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     NBDRequest request = {
         .type = NBD_CMD_WRITE_ZEROES,
         .from = offset,
         .len = bytes,  /* .len is uint32_t actually */
     };
 
     assert(bytes <= UINT32_MAX); /* rely on max_pwrite_zeroes */
 
     assert(!(s->info.flags & NBD_FLAG_READ_ONLY));
     if (!(s->info.flags & NBD_FLAG_SEND_WRITE_ZEROES)) {
         return -ENOTSUP;
     }
 
     if (flags & BDRV_REQ_FUA) {
         assert(s->info.flags & NBD_FLAG_SEND_FUA);
         request.flags |= NBD_CMD_FLAG_FUA;
     }
     if (!(flags & BDRV_REQ_MAY_UNMAP)) {
         request.flags |= NBD_CMD_FLAG_NO_HOLE;
     }
     if (flags & BDRV_REQ_NO_FALLBACK) {
         assert(s->info.flags & NBD_FLAG_SEND_FAST_ZERO);
         request.flags |= NBD_CMD_FLAG_FAST_ZERO;
     }
 
     if (!bytes) {
         return 0;
     }
     return nbd_co_request(bs, &request, NULL);
 }
 
 static int coroutine_fn nbd_client_co_flush(BlockDriverState *bs)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     NBDRequest request = { .type = NBD_CMD_FLUSH };
 
     if (!(s->info.flags & NBD_FLAG_SEND_FLUSH)) {
         return 0;
     }
 
     request.from = 0;
     request.len = 0;
 
     return nbd_co_request(bs, &request, NULL);
 }
 
 static int coroutine_fn nbd_client_co_pdiscard(BlockDriverState *bs, int64_t offset,
                                                int64_t bytes)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     NBDRequest request = {
         .type = NBD_CMD_TRIM,
         .from = offset,
         .len = bytes, /* len is uint32_t */
     };
 
     assert(bytes <= UINT32_MAX); /* rely on max_pdiscard */
 
     assert(!(s->info.flags & NBD_FLAG_READ_ONLY));
     if (!(s->info.flags & NBD_FLAG_SEND_TRIM) || !bytes) {
         return 0;
     }
 
     return nbd_co_request(bs, &request, NULL);
 }
 
 static int coroutine_fn nbd_client_co_block_status(
         BlockDriverState *bs, bool want_zero, int64_t offset, int64_t bytes,
         int64_t *pnum, int64_t *map, BlockDriverState **file)
 {
     int ret, request_ret;
     NBDExtent extent = { 0 };
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     Error *local_err = NULL;
 
     NBDRequest request = {
         .type = NBD_CMD_BLOCK_STATUS,
         .from = offset,
         .len = MIN(QEMU_ALIGN_DOWN(INT_MAX, bs->bl.request_alignment),
                    MIN(bytes, s->info.size - offset)),
         .flags = NBD_CMD_FLAG_REQ_ONE,
     };
 
     if (!s->info.base_allocation) {
         *pnum = bytes;
         *map = offset;
         *file = bs;
         return BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID;
     }
 
     /*
      * Work around the fact that the block layer doesn't do
      * byte-accurate sizing yet - if the status request exceeds the
      * server's advertised size because the block layer rounded size
      * up, we truncated the request to the server (above), or are
      * called on just the hole.
      */
     if (offset >= s->info.size) {
         *pnum = bytes;
         assert(bytes < BDRV_SECTOR_SIZE);
         /* Intentionally don't report offset_valid for the hole */
         return BDRV_BLOCK_ZERO;
     }
 
     if (s->info.min_block) {
         assert(QEMU_IS_ALIGNED(request.len, s->info.min_block));
     }
     do {
         ret = nbd_co_send_request(bs, &request, NULL);
         if (ret < 0) {
             continue;
         }
 
         ret = nbd_co_receive_blockstatus_reply(s, request.handle, bytes,
                                                &extent, &request_ret,
                                                &local_err);
         if (local_err) {
             trace_nbd_co_request_fail(request.from, request.len, request.handle,
                                       request.flags, request.type,
                                       nbd_cmd_lookup(request.type),
                                       ret, error_get_pretty(local_err));
             error_free(local_err);
             local_err = NULL;
         }
     } while (ret < 0 && nbd_client_will_reconnect(s));
 
     if (ret < 0 || request_ret < 0) {
         return ret ? ret : request_ret;
     }
 
     assert(extent.length);
     *pnum = extent.length;
     *map = offset;
     *file = bs;
     return (extent.flags & NBD_STATE_HOLE ? 0 : BDRV_BLOCK_DATA) |
         (extent.flags & NBD_STATE_ZERO ? BDRV_BLOCK_ZERO : 0) |
         BDRV_BLOCK_OFFSET_VALID;
 }
 
 static int nbd_client_reopen_prepare(BDRVReopenState *state,
                                      BlockReopenQueue *queue, Error **errp)
 {
     BDRVNBDState *s = (BDRVNBDState *)state->bs->opaque;
 
     if ((state->flags & BDRV_O_RDWR) && (s->info.flags & NBD_FLAG_READ_ONLY)) {
         error_setg(errp, "Can't reopen read-only NBD mount as read/write");
         return -EACCES;
     }
     return 0;
 }
 
 static void nbd_yank(void *opaque)
 {
     BlockDriverState *bs = opaque;
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
     QEMU_LOCK_GUARD(&s->requests_lock);
     qio_channel_shutdown(QIO_CHANNEL(s->ioc), QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
     s->state = NBD_CLIENT_QUIT;
 }
 
 static void nbd_client_close(BlockDriverState *bs)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     NBDRequest request = { .type = NBD_CMD_DISC };
 
     if (s->ioc) {
         nbd_send_request(s->ioc, &request);
     }
 
     nbd_teardown_connection(bs);
 }
 
 
 /*
  * Parse nbd_open options
  */
 
 static int nbd_parse_uri(const char *filename, QDict *options)
 {
     URI *uri;
     const char *p;
     QueryParams *qp = NULL;
     int ret = 0;
     bool is_unix;
 
     uri = uri_parse(filename);
     if (!uri) {
         return -EINVAL;
     }
 
     /* transport */
     if (!g_strcmp0(uri->scheme, "nbd")) {
         is_unix = false;
     } else if (!g_strcmp0(uri->scheme, "nbd+tcp")) {
         is_unix = false;
     } else if (!g_strcmp0(uri->scheme, "nbd+unix")) {
         is_unix = true;
     } else {
         ret = -EINVAL;
         goto out;
     }
 
     p = uri->path ? uri->path : "";
     if (p[0] == '/') {
         p++;
     }
     if (p[0]) {
         qdict_put_str(options, "export", p);
     }
 
     qp = query_params_parse(uri->query);
     if (qp->n > 1 || (is_unix && !qp->n) || (!is_unix && qp->n)) {
         ret = -EINVAL;
         goto out;
     }
 
     if (is_unix) {
         /* nbd+unix:///export?socket=path */
         if (uri->server || uri->port || strcmp(qp->p[0].name, "socket")) {
             ret = -EINVAL;
             goto out;
         }
         qdict_put_str(options, "server.type", "unix");
         qdict_put_str(options, "server.path", qp->p[0].value);
     } else {
         QString *host;
         char *port_str;
 
         /* nbd[+tcp]://host[:port]/export */
         if (!uri->server) {
             ret = -EINVAL;
             goto out;
         }
 
         /* strip braces from literal IPv6 address */
         if (uri->server[0] == '[') {
             host = qstring_from_substr(uri->server, 1,
                                        strlen(uri->server) - 1);
         } else {
             host = qstring_from_str(uri->server);
         }
 
         qdict_put_str(options, "server.type", "inet");
         qdict_put(options, "server.host", host);
 
         port_str = g_strdup_printf("%d", uri->port ?: NBD_DEFAULT_PORT);
         qdict_put_str(options, "server.port", port_str);
         g_free(port_str);
     }
 
 out:
     if (qp) {
         query_params_free(qp);
     }
     uri_free(uri);
     return ret;
 }
 
 static bool nbd_has_filename_options_conflict(QDict *options, Error **errp)
 {
     const QDictEntry *e;
 
     for (e = qdict_first(options); e; e = qdict_next(options, e)) {
         if (!strcmp(e->key, "host") ||
             !strcmp(e->key, "port") ||
             !strcmp(e->key, "path") ||
             !strcmp(e->key, "export") ||
             strstart(e->key, "server.", NULL))
         {
             error_setg(errp, "Option '%s' cannot be used with a file name",
                        e->key);
             return true;
         }
     }
 
     return false;
 }
 
 static void nbd_parse_filename(const char *filename, QDict *options,
                                Error **errp)
 {
     g_autofree char *file = NULL;
     char *export_name;
     const char *host_spec;
     const char *unixpath;
 
     if (nbd_has_filename_options_conflict(options, errp)) {
         return;
     }
 
     if (strstr(filename, "://")) {
         int ret = nbd_parse_uri(filename, options);
         if (ret < 0) {
             error_setg(errp, "No valid URL specified");
         }
         return;
     }
 
     file = g_strdup(filename);
 
     export_name = strstr(file, EN_OPTSTR);
     if (export_name) {
         if (export_name[strlen(EN_OPTSTR)] == 0) {
             return;
         }
         export_name[0] = 0; /* truncate 'file' */
         export_name += strlen(EN_OPTSTR);
 
         qdict_put_str(options, "export", export_name);
     }
 
     /* extract the host_spec - fail if it's not nbd:... */
     if (!strstart(file, "nbd:", &host_spec)) {
         error_setg(errp, "File name string for NBD must start with 'nbd:'");
         return;
     }
 
     if (!*host_spec) {
         return;
     }
 
     /* are we a UNIX or TCP socket? */
     if (strstart(host_spec, "unix:", &unixpath)) {
         qdict_put_str(options, "server.type", "unix");
         qdict_put_str(options, "server.path", unixpath);
     } else {
         InetSocketAddress *addr = g_new(InetSocketAddress, 1);
 
         if (inet_parse(addr, host_spec, errp)) {
             goto out_inet;
         }
 
         qdict_put_str(options, "server.type", "inet");
         qdict_put_str(options, "server.host", addr->host);
         qdict_put_str(options, "server.port", addr->port);
     out_inet:
         qapi_free_InetSocketAddress(addr);
     }
 }
 
 static bool nbd_process_legacy_socket_options(QDict *output_options,
                                               QemuOpts *legacy_opts,
                                               Error **errp)
 {
     const char *path = qemu_opt_get(legacy_opts, "path");
     const char *host = qemu_opt_get(legacy_opts, "host");
     const char *port = qemu_opt_get(legacy_opts, "port");
     const QDictEntry *e;
 
     if (!path && !host && !port) {
         return true;
     }
 
     for (e = qdict_first(output_options); e; e = qdict_next(output_options, e))
     {
         if (strstart(e->key, "server.", NULL)) {
             error_setg(errp, "Cannot use 'server' and path/host/port at the "
                        "same time");
             return false;
         }
     }
 
     if (path && host) {
         error_setg(errp, "path and host may not be used at the same time");
         return false;
     } else if (path) {
         if (port) {
             error_setg(errp, "port may not be used without host");
             return false;
         }
 
         qdict_put_str(output_options, "server.type", "unix");
         qdict_put_str(output_options, "server.path", path);
     } else if (host) {
         qdict_put_str(output_options, "server.type", "inet");
         qdict_put_str(output_options, "server.host", host);
         qdict_put_str(output_options, "server.port",
                       port ?: stringify(NBD_DEFAULT_PORT));
     }
 
     return true;
 }
 
 static SocketAddress *nbd_config(BDRVNBDState *s, QDict *options,
                                  Error **errp)
 {
     SocketAddress *saddr = NULL;
     QDict *addr = NULL;
     Visitor *iv = NULL;
 
     qdict_extract_subqdict(options, &addr, "server.");
     if (!qdict_size(addr)) {
         error_setg(errp, "NBD server address missing");
         goto done;
     }
 
     iv = qobject_input_visitor_new_flat_confused(addr, errp);
     if (!iv) {
         goto done;
     }
 
     if (!visit_type_SocketAddress(iv, NULL, &saddr, errp)) {
         goto done;
     }
 
     if (socket_address_parse_named_fd(saddr, errp) < 0) {
         qapi_free_SocketAddress(saddr);
         saddr = NULL;
         goto done;
     }
 
 done:
     qobject_unref(addr);
     visit_free(iv);
     return saddr;
 }
 
 static QCryptoTLSCreds *nbd_get_tls_creds(const char *id, Error **errp)
 {
     Object *obj;
     QCryptoTLSCreds *creds;
 
     obj = object_resolve_path_component(
         object_get_objects_root(), id);
     if (!obj) {
         error_setg(errp, "No TLS credentials with id '%s'",
                    id);
         return NULL;
     }
     creds = (QCryptoTLSCreds *)
         object_dynamic_cast(obj, TYPE_QCRYPTO_TLS_CREDS);
     if (!creds) {
         error_setg(errp, "Object with id '%s' is not TLS credentials",
                    id);
         return NULL;
     }
 
     if (!qcrypto_tls_creds_check_endpoint(creds,
                                           QCRYPTO_TLS_CREDS_ENDPOINT_CLIENT,
                                           errp)) {
         return NULL;
     }
     object_ref(obj);
     return creds;
 }
 
 
 static QemuOptsList nbd_runtime_opts = {
     .name = "nbd",
     .head = QTAILQ_HEAD_INITIALIZER(nbd_runtime_opts.head),
     .desc = {
         {
             .name = "host",
             .type = QEMU_OPT_STRING,
             .help = "TCP host to connect to",
         },
         {
             .name = "port",
             .type = QEMU_OPT_STRING,
             .help = "TCP port to connect to",
         },
         {
             .name = "path",
             .type = QEMU_OPT_STRING,
             .help = "Unix socket path to connect to",
         },
         {
             .name = "export",
             .type = QEMU_OPT_STRING,
             .help = "Name of the NBD export to open",
         },
         {
             .name = "tls-creds",
             .type = QEMU_OPT_STRING,
             .help = "ID of the TLS credentials to use",
         },
         {
             .name = "tls-hostname",
             .type = QEMU_OPT_STRING,
             .help = "Override hostname for validating TLS x509 certificate",
         },
         {
             .name = "x-dirty-bitmap",
             .type = QEMU_OPT_STRING,
             .help = "experimental: expose named dirty bitmap in place of "
                     "block status",
         },
         {
             .name = "reconnect-delay",
             .type = QEMU_OPT_NUMBER,
             .help = "On an unexpected disconnect, the nbd client tries to "
                     "connect again until succeeding or encountering a serious "
                     "error.  During the first @reconnect-delay seconds, all "
                     "requests are paused and will be rerun on a successful "
                     "reconnect. After that time, any delayed requests and all "
                     "future requests before a successful reconnect will "
                     "immediately fail. Default 0",
         },
         {
             .name = "open-timeout",
             .type = QEMU_OPT_NUMBER,
             .help = "In seconds. If zero, the nbd driver tries the connection "
                     "only once, and fails to open if the connection fails. "
                     "If non-zero, the nbd driver will repeat connection "
                     "attempts until successful or until @open-timeout seconds "
                     "have elapsed. Default 0",
         },
         { /* end of list */ }
     },
 };
 
 static int nbd_process_options(BlockDriverState *bs, QDict *options,
                                Error **errp)
 {
     BDRVNBDState *s = bs->opaque;
     QemuOpts *opts;
     int ret = -EINVAL;
 
     opts = qemu_opts_create(&nbd_runtime_opts, NULL, 0, &error_abort);
     if (!qemu_opts_absorb_qdict(opts, options, errp)) {
         goto error;
     }
 
     /* Translate @host, @port, and @path to a SocketAddress */
     if (!nbd_process_legacy_socket_options(options, opts, errp)) {
         goto error;
     }
 
     /* Pop the config into our state object. Exit if invalid. */
     s->saddr = nbd_config(s, options, errp);
     if (!s->saddr) {
         goto error;
     }
 
     s->export = g_strdup(qemu_opt_get(opts, "export"));
     if (s->export && strlen(s->export) > NBD_MAX_STRING_SIZE) {
         error_setg(errp, "export name too long to send to server");
         goto error;
     }
 
     s->tlscredsid = g_strdup(qemu_opt_get(opts, "tls-creds"));
     if (s->tlscredsid) {
         s->tlscreds = nbd_get_tls_creds(s->tlscredsid, errp);
         if (!s->tlscreds) {
             goto error;
         }
 
         s->tlshostname = g_strdup(qemu_opt_get(opts, "tls-hostname"));
         if (!s->tlshostname &&
             s->saddr->type == SOCKET_ADDRESS_TYPE_INET) {
             s->tlshostname = g_strdup(s->saddr->u.inet.host);
         }
     }
 
     s->x_dirty_bitmap = g_strdup(qemu_opt_get(opts, "x-dirty-bitmap"));
     if (s->x_dirty_bitmap && strlen(s->x_dirty_bitmap) > NBD_MAX_STRING_SIZE) {
         error_setg(errp, "x-dirty-bitmap query too long to send to server");
         goto error;
     }
 
     s->reconnect_delay = qemu_opt_get_number(opts, "reconnect-delay", 0);
     s->open_timeout = qemu_opt_get_number(opts, "open-timeout", 0);
 
     ret = 0;
 
  error:
     qemu_opts_del(opts);
     return ret;
 }
 
 static int nbd_open(BlockDriverState *bs, QDict *options, int flags,
                     Error **errp)
 {
     int ret;
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
     s->bs = bs;
     qemu_mutex_init(&s->requests_lock);
     qemu_co_queue_init(&s->free_sema);
     qemu_co_mutex_init(&s->send_mutex);
     qemu_co_mutex_init(&s->receive_mutex);
 
     if (!yank_register_instance(BLOCKDEV_YANK_INSTANCE(bs->node_name), errp)) {
         return -EEXIST;
     }
 
     ret = nbd_process_options(bs, options, errp);
     if (ret < 0) {
         goto fail;
     }
 
     s->conn = nbd_client_connection_new(s->saddr, true, s->export,
                                         s->x_dirty_bitmap, s->tlscreds,
                                         s->tlshostname);
 
     if (s->open_timeout) {
         nbd_client_connection_enable_retry(s->conn);
         open_timer_init(s, qemu_clock_get_ns(QEMU_CLOCK_REALTIME) +
                         s->open_timeout * NANOSECONDS_PER_SECOND);
     }
 
     s->state = NBD_CLIENT_CONNECTING_WAIT;
     ret = nbd_do_establish_connection(bs, true, errp);
     if (ret < 0) {
         goto fail;
     }
 
     /*
      * The connect attempt is done, so we no longer need this timer.
      * Delete it, because we do not want it to be around when this node
      * is drained or closed.
      */
     open_timer_del(s);
 
     nbd_client_connection_enable_retry(s->conn);
 
     return 0;
 
 fail:
     open_timer_del(s);
     nbd_clear_bdrvstate(bs);
     return ret;
 }
 
 static int coroutine_fn nbd_co_flush(BlockDriverState *bs)
 {
     return nbd_client_co_flush(bs);
 }
 
 static void nbd_refresh_limits(BlockDriverState *bs, Error **errp)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     uint32_t min = s->info.min_block;
     uint32_t max = MIN_NON_ZERO(NBD_MAX_BUFFER_SIZE, s->info.max_block);
 
     /*
      * If the server did not advertise an alignment:
      * - a size that is not sector-aligned implies that an alignment
      *   of 1 can be used to access those tail bytes
      * - advertisement of block status requires an alignment of 1, so
      *   that we don't violate block layer constraints that block
      *   status is always aligned (as we can't control whether the
      *   server will report sub-sector extents, such as a hole at EOF
      *   on an unaligned POSIX file)
      * - otherwise, assume the server is so old that we are safer avoiding
      *   sub-sector requests
      */
     if (!min) {
         min = (!QEMU_IS_ALIGNED(s->info.size, BDRV_SECTOR_SIZE) ||
                s->info.base_allocation) ? 1 : BDRV_SECTOR_SIZE;
     }
 
     bs->bl.request_alignment = min;
     bs->bl.max_pdiscard = QEMU_ALIGN_DOWN(INT_MAX, min);
     bs->bl.max_pwrite_zeroes = max;
     bs->bl.max_transfer = max;
 
     if (s->info.opt_block &&
         s->info.opt_block > bs->bl.opt_transfer) {
         bs->bl.opt_transfer = s->info.opt_block;
     }
 }
 
 static void nbd_close(BlockDriverState *bs)
 {
     nbd_client_close(bs);
     nbd_clear_bdrvstate(bs);
 }
 
 /*
  * NBD cannot truncate, but if the caller asks to truncate to the same size, or
  * to a smaller size with exact=false, there is no reason to fail the
  * operation.
  *
  * Preallocation mode is ignored since it does not seems useful to fail when
  * we never change anything.
  */
 static int coroutine_fn nbd_co_truncate(BlockDriverState *bs, int64_t offset,
                                         bool exact, PreallocMode prealloc,
                                         BdrvRequestFlags flags, Error **errp)
 {
     BDRVNBDState *s = bs->opaque;
 
     if (offset != s->info.size && exact) {
         error_setg(errp, "Cannot resize NBD nodes");
         return -ENOTSUP;
     }
 
     if (offset > s->info.size) {
         error_setg(errp, "Cannot grow NBD nodes");
         return -EINVAL;
     }
 
     return 0;
 }
 
 static int64_t nbd_getlength(BlockDriverState *bs)
 {
     BDRVNBDState *s = bs->opaque;
 
     return s->info.size;
 }
 
 static void nbd_refresh_filename(BlockDriverState *bs)
 {
     BDRVNBDState *s = bs->opaque;
     const char *host = NULL, *port = NULL, *path = NULL;
     size_t len = 0;
 
     if (s->saddr->type == SOCKET_ADDRESS_TYPE_INET) {
         const InetSocketAddress *inet = &s->saddr->u.inet;
         if (!inet->has_ipv4 && !inet->has_ipv6 && !inet->has_to) {
             host = inet->host;
             port = inet->port;
         }
     } else if (s->saddr->type == SOCKET_ADDRESS_TYPE_UNIX) {
         path = s->saddr->u.q_unix.path;
     } /* else can't represent as pseudo-filename */
 
     if (path && s->export) {
         len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),
                        "nbd+unix:///%s?socket=%s", s->export, path);
     } else if (path && !s->export) {
         len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),
                        "nbd+unix://?socket=%s", path);
     } else if (host && s->export) {
         len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),
                        "nbd://%s:%s/%s", host, port, s->export);
     } else if (host && !s->export) {
         len = snprintf(bs->exact_filename, sizeof(bs->exact_filename),
                        "nbd://%s:%s", host, port);
     }
     if (len >= sizeof(bs->exact_filename)) {
         /* Name is too long to represent exactly, so leave it empty. */
         bs->exact_filename[0] = '\0';
     }
 }
 
 static char *nbd_dirname(BlockDriverState *bs, Error **errp)
 {
     /* The generic bdrv_dirname() implementation is able to work out some
      * directory name for NBD nodes, but that would be wrong. So far there is no
      * specification for how "export paths" would work, so NBD does not have
      * directory names. */
     error_setg(errp, "Cannot generate a base directory for NBD nodes");
     return NULL;
 }
 
 static const char *const nbd_strong_runtime_opts[] = {
     "path",
     "host",
     "port",
     "export",
     "tls-creds",
     "tls-hostname",
     "server.",
 
     NULL
 };
 
 static void nbd_cancel_in_flight(BlockDriverState *bs)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
 
     reconnect_delay_timer_del(s);
 
     qemu_mutex_lock(&s->requests_lock);
     if (s->state == NBD_CLIENT_CONNECTING_WAIT) {
         s->state = NBD_CLIENT_CONNECTING_NOWAIT;
     }
     qemu_mutex_unlock(&s->requests_lock);
 
     nbd_co_establish_connection_cancel(s->conn);
 }
 
 static void nbd_attach_aio_context(BlockDriverState *bs,
                                    AioContext *new_context)
 {
     BDRVNBDState *s = bs->opaque;
 
     /* The open_timer is used only during nbd_open() */
     assert(!s->open_timer);
 
     /*
      * The reconnect_delay_timer is scheduled in I/O paths when the
      * connection is lost, to cancel the reconnection attempt after a
      * given time.  Once this attempt is done (successfully or not),
      * nbd_reconnect_attempt() ensures the timer is deleted before the
      * respective I/O request is resumed.
      * Since the AioContext can only be changed when a node is drained,
      * the reconnect_delay_timer cannot be active here.
      */
     assert(!s->reconnect_delay_timer);
 
     if (s->ioc) {
         qio_channel_attach_aio_context(s->ioc, new_context);
     }
 }
 
 static void nbd_detach_aio_context(BlockDriverState *bs)
 {
     BDRVNBDState *s = bs->opaque;
 
     assert(!s->open_timer);
     assert(!s->reconnect_delay_timer);
 
     if (s->ioc) {
         qio_channel_detach_aio_context(s->ioc);
     }
 }
 
 static BlockDriver bdrv_nbd = {
     .format_name                = "nbd",
     .protocol_name              = "nbd",
     .instance_size              = sizeof(BDRVNBDState),
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_co_create_opts        = bdrv_co_create_opts_simple,
     .create_opts                = &bdrv_create_opts_simple,
     .bdrv_file_open             = nbd_open,
     .bdrv_reopen_prepare        = nbd_client_reopen_prepare,
     .bdrv_co_preadv             = nbd_client_co_preadv,
     .bdrv_co_pwritev            = nbd_client_co_pwritev,
     .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_pdiscard           = nbd_client_co_pdiscard,
     .bdrv_refresh_limits        = nbd_refresh_limits,
     .bdrv_co_truncate           = nbd_co_truncate,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_refresh_filename      = nbd_refresh_filename,
     .bdrv_co_block_status       = nbd_client_co_block_status,
     .bdrv_dirname               = nbd_dirname,
     .strong_runtime_opts        = nbd_strong_runtime_opts,
     .bdrv_cancel_in_flight      = nbd_cancel_in_flight,
 
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
 };
 
 static BlockDriver bdrv_nbd_tcp = {
     .format_name                = "nbd",
     .protocol_name              = "nbd+tcp",
     .instance_size              = sizeof(BDRVNBDState),
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_co_create_opts        = bdrv_co_create_opts_simple,
     .create_opts                = &bdrv_create_opts_simple,
     .bdrv_file_open             = nbd_open,
     .bdrv_reopen_prepare        = nbd_client_reopen_prepare,
     .bdrv_co_preadv             = nbd_client_co_preadv,
     .bdrv_co_pwritev            = nbd_client_co_pwritev,
     .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_pdiscard           = nbd_client_co_pdiscard,
     .bdrv_refresh_limits        = nbd_refresh_limits,
     .bdrv_co_truncate           = nbd_co_truncate,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_refresh_filename      = nbd_refresh_filename,
     .bdrv_co_block_status       = nbd_client_co_block_status,
     .bdrv_dirname               = nbd_dirname,
     .strong_runtime_opts        = nbd_strong_runtime_opts,
     .bdrv_cancel_in_flight      = nbd_cancel_in_flight,
 
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
 };
 
 static BlockDriver bdrv_nbd_unix = {
     .format_name                = "nbd",
     .protocol_name              = "nbd+unix",
     .instance_size              = sizeof(BDRVNBDState),
     .bdrv_parse_filename        = nbd_parse_filename,
     .bdrv_co_create_opts        = bdrv_co_create_opts_simple,
     .create_opts                = &bdrv_create_opts_simple,
     .bdrv_file_open             = nbd_open,
     .bdrv_reopen_prepare        = nbd_client_reopen_prepare,
     .bdrv_co_preadv             = nbd_client_co_preadv,
     .bdrv_co_pwritev            = nbd_client_co_pwritev,
     .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,
     .bdrv_close                 = nbd_close,
     .bdrv_co_flush_to_os        = nbd_co_flush,
     .bdrv_co_pdiscard           = nbd_client_co_pdiscard,
     .bdrv_refresh_limits        = nbd_refresh_limits,
     .bdrv_co_truncate           = nbd_co_truncate,
     .bdrv_getlength             = nbd_getlength,
     .bdrv_refresh_filename      = nbd_refresh_filename,
     .bdrv_co_block_status       = nbd_client_co_block_status,
     .bdrv_dirname               = nbd_dirname,
     .strong_runtime_opts        = nbd_strong_runtime_opts,
     .bdrv_cancel_in_flight      = nbd_cancel_in_flight,
 
     .bdrv_attach_aio_context    = nbd_attach_aio_context,
     .bdrv_detach_aio_context    = nbd_detach_aio_context,
 };
 
 static void bdrv_nbd_init(void)
 {
     bdrv_register(&bdrv_nbd);
     bdrv_register(&bdrv_nbd_tcp);
     bdrv_register(&bdrv_nbd_unix);
 }
 
 block_init(bdrv_nbd_init);