qemu

block.c (29665B)

---

 /*
  * QEMU live block migration
  *
  * Copyright IBM, Corp. 2009
  *
  * Authors:
  *  Liran Schour   <lirans@il.ibm.com>
  *
  * This work is licensed under the terms of the GNU GPL, version 2.  See
  * the COPYING file in the top-level directory.
  *
  * Contributions after 2012-01-13 are licensed under the terms of the
  * GNU GPL, version 2 or (at your option) any later version.
  */
 
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
 #include "qemu/cutils.h"
 #include "qemu/queue.h"
 #include "block.h"
 #include "migration/misc.h"
 #include "migration.h"
 #include "migration/register.h"
 #include "qemu-file.h"
 #include "migration/vmstate.h"
 #include "sysemu/block-backend.h"
 #include "trace.h"
 
 #define BLK_MIG_BLOCK_SIZE           (1ULL << 20)
 #define BDRV_SECTORS_PER_DIRTY_CHUNK (BLK_MIG_BLOCK_SIZE >> BDRV_SECTOR_BITS)
 
 #define BLK_MIG_FLAG_DEVICE_BLOCK       0x01
 #define BLK_MIG_FLAG_EOS                0x02
 #define BLK_MIG_FLAG_PROGRESS           0x04
 #define BLK_MIG_FLAG_ZERO_BLOCK         0x08
 
 #define MAX_IS_ALLOCATED_SEARCH (65536 * BDRV_SECTOR_SIZE)
 
 #define MAX_IO_BUFFERS 512
 #define MAX_PARALLEL_IO 16
 
 /* #define DEBUG_BLK_MIGRATION */
 
 #ifdef DEBUG_BLK_MIGRATION
 #define DPRINTF(fmt, ...) \
     do { printf("blk_migration: " fmt, ## __VA_ARGS__); } while (0)
 #else
 #define DPRINTF(fmt, ...) \
     do { } while (0)
 #endif
 
 typedef struct BlkMigDevState {
     /* Written during setup phase.  Can be read without a lock.  */
     BlockBackend *blk;
     char *blk_name;
     int shared_base;
     int64_t total_sectors;
     QSIMPLEQ_ENTRY(BlkMigDevState) entry;
     Error *blocker;
 
     /* Only used by migration thread.  Does not need a lock.  */
     int bulk_completed;
     int64_t cur_sector;
     int64_t cur_dirty;
 
     /* Data in the aio_bitmap is protected by block migration lock.
      * Allocation and free happen during setup and cleanup respectively.
      */
     unsigned long *aio_bitmap;
 
     /* Protected by block migration lock.  */
     int64_t completed_sectors;
 
     /* During migration this is protected by iothread lock / AioContext.
      * Allocation and free happen during setup and cleanup respectively.
      */
     BdrvDirtyBitmap *dirty_bitmap;
 } BlkMigDevState;
 
 typedef struct BlkMigBlock {
     /* Only used by migration thread.  */
     uint8_t *buf;
     BlkMigDevState *bmds;
     int64_t sector;
     int nr_sectors;
     QEMUIOVector qiov;
     BlockAIOCB *aiocb;
 
     /* Protected by block migration lock.  */
     int ret;
     QSIMPLEQ_ENTRY(BlkMigBlock) entry;
 } BlkMigBlock;
 
 typedef struct BlkMigState {
     QSIMPLEQ_HEAD(, BlkMigDevState) bmds_list;
     int64_t total_sector_sum;
     bool zero_blocks;
 
     /* Protected by lock.  */
     QSIMPLEQ_HEAD(, BlkMigBlock) blk_list;
     int submitted;
     int read_done;
 
     /* Only used by migration thread.  Does not need a lock.  */
     int transferred;
     int prev_progress;
     int bulk_completed;
 
     /* Lock must be taken _inside_ the iothread lock and any AioContexts.  */
     QemuMutex lock;
 } BlkMigState;
 
 static BlkMigState block_mig_state;
 
 static void blk_mig_lock(void)
 {
     qemu_mutex_lock(&block_mig_state.lock);
 }
 
 static void blk_mig_unlock(void)
 {
     qemu_mutex_unlock(&block_mig_state.lock);
 }
 
 /* Must run outside of the iothread lock during the bulk phase,
  * or the VM will stall.
  */
 
 static void blk_send(QEMUFile *f, BlkMigBlock * blk)
 {
     int len;
     uint64_t flags = BLK_MIG_FLAG_DEVICE_BLOCK;
 
     if (block_mig_state.zero_blocks &&
         buffer_is_zero(blk->buf, BLK_MIG_BLOCK_SIZE)) {
         flags |= BLK_MIG_FLAG_ZERO_BLOCK;
     }
 
     /* sector number and flags */
     qemu_put_be64(f, (blk->sector << BDRV_SECTOR_BITS)
                      | flags);
 
     /* device name */
     len = strlen(blk->bmds->blk_name);
     qemu_put_byte(f, len);
     qemu_put_buffer(f, (uint8_t *) blk->bmds->blk_name, len);
 
     /* if a block is zero we need to flush here since the network
      * bandwidth is now a lot higher than the storage device bandwidth.
      * thus if we queue zero blocks we slow down the migration */
     if (flags & BLK_MIG_FLAG_ZERO_BLOCK) {
         qemu_fflush(f);
         return;
     }
 
     qemu_put_buffer(f, blk->buf, BLK_MIG_BLOCK_SIZE);
 }
 
 int blk_mig_active(void)
 {
     return !QSIMPLEQ_EMPTY(&block_mig_state.bmds_list);
 }
 
 int blk_mig_bulk_active(void)
 {
     return blk_mig_active() && !block_mig_state.bulk_completed;
 }
 
 uint64_t blk_mig_bytes_transferred(void)
 {
     BlkMigDevState *bmds;
     uint64_t sum = 0;
 
     blk_mig_lock();
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         sum += bmds->completed_sectors;
     }
     blk_mig_unlock();
     return sum << BDRV_SECTOR_BITS;
 }
 
 uint64_t blk_mig_bytes_remaining(void)
 {
     return blk_mig_bytes_total() - blk_mig_bytes_transferred();
 }
 
 uint64_t blk_mig_bytes_total(void)
 {
     BlkMigDevState *bmds;
     uint64_t sum = 0;
 
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         sum += bmds->total_sectors;
     }
     return sum << BDRV_SECTOR_BITS;
 }
 
 
 /* Called with migration lock held.  */
 
 static int bmds_aio_inflight(BlkMigDevState *bmds, int64_t sector)
 {
     int64_t chunk = sector / (int64_t)BDRV_SECTORS_PER_DIRTY_CHUNK;
 
     if (sector < blk_nb_sectors(bmds->blk)) {
         return !!(bmds->aio_bitmap[chunk / (sizeof(unsigned long) * 8)] &
             (1UL << (chunk % (sizeof(unsigned long) * 8))));
     } else {
         return 0;
     }
 }
 
 /* Called with migration lock held.  */
 
 static void bmds_set_aio_inflight(BlkMigDevState *bmds, int64_t sector_num,
                              int nb_sectors, int set)
 {
     int64_t start, end;
     unsigned long val, idx, bit;
 
     start = sector_num / BDRV_SECTORS_PER_DIRTY_CHUNK;
     end = (sector_num + nb_sectors - 1) / BDRV_SECTORS_PER_DIRTY_CHUNK;
 
     for (; start <= end; start++) {
         idx = start / (sizeof(unsigned long) * 8);
         bit = start % (sizeof(unsigned long) * 8);
         val = bmds->aio_bitmap[idx];
         if (set) {
             val |= 1UL << bit;
         } else {
             val &= ~(1UL << bit);
         }
         bmds->aio_bitmap[idx] = val;
     }
 }
 
 static void alloc_aio_bitmap(BlkMigDevState *bmds)
 {
     BlockBackend *bb = bmds->blk;
     int64_t bitmap_size;
 
     bitmap_size = blk_nb_sectors(bb) + BDRV_SECTORS_PER_DIRTY_CHUNK * 8 - 1;
     bitmap_size /= BDRV_SECTORS_PER_DIRTY_CHUNK * 8;
 
     bmds->aio_bitmap = g_malloc0(bitmap_size);
 }
 
 /* Never hold migration lock when yielding to the main loop!  */
 
 static void blk_mig_read_cb(void *opaque, int ret)
 {
     BlkMigBlock *blk = opaque;
 
     blk_mig_lock();
     blk->ret = ret;
 
     QSIMPLEQ_INSERT_TAIL(&block_mig_state.blk_list, blk, entry);
     bmds_set_aio_inflight(blk->bmds, blk->sector, blk->nr_sectors, 0);
 
     block_mig_state.submitted--;
     block_mig_state.read_done++;
     assert(block_mig_state.submitted >= 0);
     blk_mig_unlock();
 }
 
 /* Called with no lock taken.  */
 
 static int mig_save_device_bulk(QEMUFile *f, BlkMigDevState *bmds)
 {
     int64_t total_sectors = bmds->total_sectors;
     int64_t cur_sector = bmds->cur_sector;
     BlockBackend *bb = bmds->blk;
     BlkMigBlock *blk;
     int nr_sectors;
     int64_t count;
 
     if (bmds->shared_base) {
         qemu_mutex_lock_iothread();
         aio_context_acquire(blk_get_aio_context(bb));
         /* Skip unallocated sectors; intentionally treats failure or
          * partial sector as an allocated sector */
         while (cur_sector < total_sectors &&
                !bdrv_is_allocated(blk_bs(bb), cur_sector * BDRV_SECTOR_SIZE,
                                   MAX_IS_ALLOCATED_SEARCH, &count)) {
             if (count < BDRV_SECTOR_SIZE) {
                 break;
             }
             cur_sector += count >> BDRV_SECTOR_BITS;
         }
         aio_context_release(blk_get_aio_context(bb));
         qemu_mutex_unlock_iothread();
     }
 
     if (cur_sector >= total_sectors) {
         bmds->cur_sector = bmds->completed_sectors = total_sectors;
         return 1;
     }
 
     bmds->completed_sectors = cur_sector;
 
     cur_sector &= ~((int64_t)BDRV_SECTORS_PER_DIRTY_CHUNK - 1);
 
     /* we are going to transfer a full block even if it is not allocated */
     nr_sectors = BDRV_SECTORS_PER_DIRTY_CHUNK;
 
     if (total_sectors - cur_sector < BDRV_SECTORS_PER_DIRTY_CHUNK) {
         nr_sectors = total_sectors - cur_sector;
     }
 
     blk = g_new(BlkMigBlock, 1);
     blk->buf = g_malloc(BLK_MIG_BLOCK_SIZE);
     blk->bmds = bmds;
     blk->sector = cur_sector;
     blk->nr_sectors = nr_sectors;
 
     qemu_iovec_init_buf(&blk->qiov, blk->buf, nr_sectors * BDRV_SECTOR_SIZE);
 
     blk_mig_lock();
     block_mig_state.submitted++;
     blk_mig_unlock();
 
     /* We do not know if bs is under the main thread (and thus does
      * not acquire the AioContext when doing AIO) or rather under
      * dataplane.  Thus acquire both the iothread mutex and the
      * AioContext.
      *
      * This is ugly and will disappear when we make bdrv_* thread-safe,
      * without the need to acquire the AioContext.
      */
     qemu_mutex_lock_iothread();
     aio_context_acquire(blk_get_aio_context(bmds->blk));
     bdrv_reset_dirty_bitmap(bmds->dirty_bitmap, cur_sector * BDRV_SECTOR_SIZE,
                             nr_sectors * BDRV_SECTOR_SIZE);
     blk->aiocb = blk_aio_preadv(bb, cur_sector * BDRV_SECTOR_SIZE, &blk->qiov,
                                 0, blk_mig_read_cb, blk);
     aio_context_release(blk_get_aio_context(bmds->blk));
     qemu_mutex_unlock_iothread();
 
     bmds->cur_sector = cur_sector + nr_sectors;
     return (bmds->cur_sector >= total_sectors);
 }
 
 /* Called with iothread lock taken.  */
 
 static int set_dirty_tracking(void)
 {
     BlkMigDevState *bmds;
     int ret;
 
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         bmds->dirty_bitmap = bdrv_create_dirty_bitmap(blk_bs(bmds->blk),
                                                       BLK_MIG_BLOCK_SIZE,
                                                       NULL, NULL);
         if (!bmds->dirty_bitmap) {
             ret = -errno;
             goto fail;
         }
     }
     return 0;
 
 fail:
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         if (bmds->dirty_bitmap) {
             bdrv_release_dirty_bitmap(bmds->dirty_bitmap);
         }
     }
     return ret;
 }
 
 /* Called with iothread lock taken.  */
 
 static void unset_dirty_tracking(void)
 {
     BlkMigDevState *bmds;
 
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         bdrv_release_dirty_bitmap(bmds->dirty_bitmap);
     }
 }
 
 static int init_blk_migration(QEMUFile *f)
 {
     BlockDriverState *bs;
     BlkMigDevState *bmds;
     int64_t sectors;
     BdrvNextIterator it;
     int i, num_bs = 0;
     struct {
         BlkMigDevState *bmds;
         BlockDriverState *bs;
     } *bmds_bs;
     Error *local_err = NULL;
     int ret;
 
     block_mig_state.submitted = 0;
     block_mig_state.read_done = 0;
     block_mig_state.transferred = 0;
     block_mig_state.total_sector_sum = 0;
     block_mig_state.prev_progress = -1;
     block_mig_state.bulk_completed = 0;
     block_mig_state.zero_blocks = migrate_zero_blocks();
 
     for (bs = bdrv_first(&it); bs; bs = bdrv_next(&it)) {
         num_bs++;
     }
     bmds_bs = g_malloc0(num_bs * sizeof(*bmds_bs));
 
     for (i = 0, bs = bdrv_first(&it); bs; bs = bdrv_next(&it), i++) {
         if (bdrv_is_read_only(bs)) {
             continue;
         }
 
         sectors = bdrv_nb_sectors(bs);
         if (sectors <= 0) {
             ret = sectors;
             bdrv_next_cleanup(&it);
             goto out;
         }
 
         bmds = g_new0(BlkMigDevState, 1);
         bmds->blk = blk_new(qemu_get_aio_context(),
                             BLK_PERM_CONSISTENT_READ, BLK_PERM_ALL);
         bmds->blk_name = g_strdup(bdrv_get_device_name(bs));
         bmds->bulk_completed = 0;
         bmds->total_sectors = sectors;
         bmds->completed_sectors = 0;
         bmds->shared_base = migrate_use_block_incremental();
 
         assert(i < num_bs);
         bmds_bs[i].bmds = bmds;
         bmds_bs[i].bs = bs;
 
         block_mig_state.total_sector_sum += sectors;
 
         if (bmds->shared_base) {
             trace_migration_block_init_shared(bdrv_get_device_name(bs));
         } else {
             trace_migration_block_init_full(bdrv_get_device_name(bs));
         }
 
         QSIMPLEQ_INSERT_TAIL(&block_mig_state.bmds_list, bmds, entry);
     }
 
     /* Can only insert new BDSes now because doing so while iterating block
      * devices may end up in a deadlock (iterating the new BDSes, too). */
     for (i = 0; i < num_bs; i++) {
         BlkMigDevState *bmds = bmds_bs[i].bmds;
         BlockDriverState *bs = bmds_bs[i].bs;
 
         if (bmds) {
             ret = blk_insert_bs(bmds->blk, bs, &local_err);
             if (ret < 0) {
                 error_report_err(local_err);
                 goto out;
             }
 
             alloc_aio_bitmap(bmds);
             error_setg(&bmds->blocker, "block device is in use by migration");
             bdrv_op_block_all(bs, bmds->blocker);
         }
     }
 
     ret = 0;
 out:
     g_free(bmds_bs);
     return ret;
 }
 
 /* Called with no lock taken.  */
 
 static int blk_mig_save_bulked_block(QEMUFile *f)
 {
     int64_t completed_sector_sum = 0;
     BlkMigDevState *bmds;
     int progress;
     int ret = 0;
 
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         if (bmds->bulk_completed == 0) {
             if (mig_save_device_bulk(f, bmds) == 1) {
                 /* completed bulk section for this device */
                 bmds->bulk_completed = 1;
             }
             completed_sector_sum += bmds->completed_sectors;
             ret = 1;
             break;
         } else {
             completed_sector_sum += bmds->completed_sectors;
         }
     }
 
     if (block_mig_state.total_sector_sum != 0) {
         progress = completed_sector_sum * 100 /
                    block_mig_state.total_sector_sum;
     } else {
         progress = 100;
     }
     if (progress != block_mig_state.prev_progress) {
         block_mig_state.prev_progress = progress;
         qemu_put_be64(f, (progress << BDRV_SECTOR_BITS)
                          | BLK_MIG_FLAG_PROGRESS);
         DPRINTF("Completed %d %%\r", progress);
     }
 
     return ret;
 }
 
 static void blk_mig_reset_dirty_cursor(void)
 {
     BlkMigDevState *bmds;
 
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         bmds->cur_dirty = 0;
     }
 }
 
 /* Called with iothread lock and AioContext taken.  */
 
 static int mig_save_device_dirty(QEMUFile *f, BlkMigDevState *bmds,
                                  int is_async)
 {
     BlkMigBlock *blk;
     int64_t total_sectors = bmds->total_sectors;
     int64_t sector;
     int nr_sectors;
     int ret = -EIO;
 
     for (sector = bmds->cur_dirty; sector < bmds->total_sectors;) {
         blk_mig_lock();
         if (bmds_aio_inflight(bmds, sector)) {
             blk_mig_unlock();
             blk_drain(bmds->blk);
         } else {
             blk_mig_unlock();
         }
         bdrv_dirty_bitmap_lock(bmds->dirty_bitmap);
         if (bdrv_dirty_bitmap_get_locked(bmds->dirty_bitmap,
                                          sector * BDRV_SECTOR_SIZE)) {
             if (total_sectors - sector < BDRV_SECTORS_PER_DIRTY_CHUNK) {
                 nr_sectors = total_sectors - sector;
             } else {
                 nr_sectors = BDRV_SECTORS_PER_DIRTY_CHUNK;
             }
             bdrv_reset_dirty_bitmap_locked(bmds->dirty_bitmap,
                                            sector * BDRV_SECTOR_SIZE,
                                            nr_sectors * BDRV_SECTOR_SIZE);
             bdrv_dirty_bitmap_unlock(bmds->dirty_bitmap);
 
             blk = g_new(BlkMigBlock, 1);
             blk->buf = g_malloc(BLK_MIG_BLOCK_SIZE);
             blk->bmds = bmds;
             blk->sector = sector;
             blk->nr_sectors = nr_sectors;
 
             if (is_async) {
                 qemu_iovec_init_buf(&blk->qiov, blk->buf,
                                     nr_sectors * BDRV_SECTOR_SIZE);
 
                 blk->aiocb = blk_aio_preadv(bmds->blk,
                                             sector * BDRV_SECTOR_SIZE,
                                             &blk->qiov, 0, blk_mig_read_cb,
                                             blk);
 
                 blk_mig_lock();
                 block_mig_state.submitted++;
                 bmds_set_aio_inflight(bmds, sector, nr_sectors, 1);
                 blk_mig_unlock();
             } else {
                 ret = blk_pread(bmds->blk, sector * BDRV_SECTOR_SIZE,
                                 nr_sectors * BDRV_SECTOR_SIZE, blk->buf, 0);
                 if (ret < 0) {
                     goto error;
                 }
                 blk_send(f, blk);
 
                 g_free(blk->buf);
                 g_free(blk);
             }
 
             sector += nr_sectors;
             bmds->cur_dirty = sector;
             break;
         }
 
         bdrv_dirty_bitmap_unlock(bmds->dirty_bitmap);
         sector += BDRV_SECTORS_PER_DIRTY_CHUNK;
         bmds->cur_dirty = sector;
     }
 
     return (bmds->cur_dirty >= bmds->total_sectors);
 
 error:
     trace_migration_block_save_device_dirty(sector);
     g_free(blk->buf);
     g_free(blk);
     return ret;
 }
 
 /* Called with iothread lock taken.
  *
  * return value:
  * 0: too much data for max_downtime
  * 1: few enough data for max_downtime
 */
 static int blk_mig_save_dirty_block(QEMUFile *f, int is_async)
 {
     BlkMigDevState *bmds;
     int ret = 1;
 
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         aio_context_acquire(blk_get_aio_context(bmds->blk));
         ret = mig_save_device_dirty(f, bmds, is_async);
         aio_context_release(blk_get_aio_context(bmds->blk));
         if (ret <= 0) {
             break;
         }
     }
 
     return ret;
 }
 
 /* Called with no locks taken.  */
 
 static int flush_blks(QEMUFile *f)
 {
     BlkMigBlock *blk;
     int ret = 0;
 
     trace_migration_block_flush_blks("Enter", block_mig_state.submitted,
                                      block_mig_state.read_done,
                                      block_mig_state.transferred);
 
     blk_mig_lock();
     while ((blk = QSIMPLEQ_FIRST(&block_mig_state.blk_list)) != NULL) {
         if (qemu_file_rate_limit(f)) {
             break;
         }
         if (blk->ret < 0) {
             ret = blk->ret;
             break;
         }
 
         QSIMPLEQ_REMOVE_HEAD(&block_mig_state.blk_list, entry);
         blk_mig_unlock();
         blk_send(f, blk);
         blk_mig_lock();
 
         g_free(blk->buf);
         g_free(blk);
 
         block_mig_state.read_done--;
         block_mig_state.transferred++;
         assert(block_mig_state.read_done >= 0);
     }
     blk_mig_unlock();
 
     trace_migration_block_flush_blks("Exit", block_mig_state.submitted,
                                      block_mig_state.read_done,
                                      block_mig_state.transferred);
     return ret;
 }
 
 /* Called with iothread lock taken.  */
 
 static int64_t get_remaining_dirty(void)
 {
     BlkMigDevState *bmds;
     int64_t dirty = 0;
 
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
         aio_context_acquire(blk_get_aio_context(bmds->blk));
         dirty += bdrv_get_dirty_count(bmds->dirty_bitmap);
         aio_context_release(blk_get_aio_context(bmds->blk));
     }
 
     return dirty;
 }
 
 
 
 /* Called with iothread lock taken.  */
 static void block_migration_cleanup_bmds(void)
 {
     BlkMigDevState *bmds;
     AioContext *ctx;
 
     unset_dirty_tracking();
 
     while ((bmds = QSIMPLEQ_FIRST(&block_mig_state.bmds_list)) != NULL) {
         QSIMPLEQ_REMOVE_HEAD(&block_mig_state.bmds_list, entry);
         bdrv_op_unblock_all(blk_bs(bmds->blk), bmds->blocker);
         error_free(bmds->blocker);
 
         /* Save ctx, because bmds->blk can disappear during blk_unref.  */
         ctx = blk_get_aio_context(bmds->blk);
         aio_context_acquire(ctx);
         blk_unref(bmds->blk);
         aio_context_release(ctx);
 
         g_free(bmds->blk_name);
         g_free(bmds->aio_bitmap);
         g_free(bmds);
     }
 }
 
 /* Called with iothread lock taken.  */
 static void block_migration_cleanup(void *opaque)
 {
     BlkMigBlock *blk;
 
     bdrv_drain_all();
 
     block_migration_cleanup_bmds();
 
     blk_mig_lock();
     while ((blk = QSIMPLEQ_FIRST(&block_mig_state.blk_list)) != NULL) {
         QSIMPLEQ_REMOVE_HEAD(&block_mig_state.blk_list, entry);
         g_free(blk->buf);
         g_free(blk);
     }
     blk_mig_unlock();
 }
 
 static int block_save_setup(QEMUFile *f, void *opaque)
 {
     int ret;
 
     trace_migration_block_save("setup", block_mig_state.submitted,
                                block_mig_state.transferred);
 
     qemu_mutex_lock_iothread();
     ret = init_blk_migration(f);
     if (ret < 0) {
         qemu_mutex_unlock_iothread();
         return ret;
     }
 
     /* start track dirty blocks */
     ret = set_dirty_tracking();
 
     qemu_mutex_unlock_iothread();
 
     if (ret) {
         return ret;
     }
 
     ret = flush_blks(f);
     blk_mig_reset_dirty_cursor();
     qemu_put_be64(f, BLK_MIG_FLAG_EOS);
 
     return ret;
 }
 
 static int block_save_iterate(QEMUFile *f, void *opaque)
 {
     int ret;
     int64_t last_bytes = qemu_file_total_transferred(f);
     int64_t delta_bytes;
 
     trace_migration_block_save("iterate", block_mig_state.submitted,
                                block_mig_state.transferred);
 
     ret = flush_blks(f);
     if (ret) {
         return ret;
     }
 
     blk_mig_reset_dirty_cursor();
 
     /* control the rate of transfer */
     blk_mig_lock();
     while (block_mig_state.read_done * BLK_MIG_BLOCK_SIZE <
            qemu_file_get_rate_limit(f) &&
            block_mig_state.submitted < MAX_PARALLEL_IO &&
            (block_mig_state.submitted + block_mig_state.read_done) <
            MAX_IO_BUFFERS) {
         blk_mig_unlock();
         if (block_mig_state.bulk_completed == 0) {
             /* first finish the bulk phase */
             if (blk_mig_save_bulked_block(f) == 0) {
                 /* finished saving bulk on all devices */
                 block_mig_state.bulk_completed = 1;
             }
             ret = 0;
         } else {
             /* Always called with iothread lock taken for
              * simplicity, block_save_complete also calls it.
              */
             qemu_mutex_lock_iothread();
             ret = blk_mig_save_dirty_block(f, 1);
             qemu_mutex_unlock_iothread();
         }
         if (ret < 0) {
             return ret;
         }
         blk_mig_lock();
         if (ret != 0) {
             /* no more dirty blocks */
             break;
         }
     }
     blk_mig_unlock();
 
     ret = flush_blks(f);
     if (ret) {
         return ret;
     }
 
     qemu_put_be64(f, BLK_MIG_FLAG_EOS);
     delta_bytes = qemu_file_total_transferred(f) - last_bytes;
     if (delta_bytes > 0) {
         return 1;
     } else if (delta_bytes < 0) {
         return -1;
     } else {
         return 0;
     }
 }
 
 /* Called with iothread lock taken.  */
 
 static int block_save_complete(QEMUFile *f, void *opaque)
 {
     int ret;
 
     trace_migration_block_save("complete", block_mig_state.submitted,
                                block_mig_state.transferred);
 
     ret = flush_blks(f);
     if (ret) {
         return ret;
     }
 
     blk_mig_reset_dirty_cursor();
 
     /* we know for sure that save bulk is completed and
        all async read completed */
     blk_mig_lock();
     assert(block_mig_state.submitted == 0);
     blk_mig_unlock();
 
     do {
         ret = blk_mig_save_dirty_block(f, 0);
         if (ret < 0) {
             return ret;
         }
     } while (ret == 0);
 
     /* report completion */
     qemu_put_be64(f, (100 << BDRV_SECTOR_BITS) | BLK_MIG_FLAG_PROGRESS);
 
     trace_migration_block_save_complete();
 
     qemu_put_be64(f, BLK_MIG_FLAG_EOS);
 
     /* Make sure that our BlockBackends are gone, so that the block driver
      * nodes can be inactivated. */
     block_migration_cleanup_bmds();
 
     return 0;
 }
 
 static void block_save_pending(QEMUFile *f, void *opaque, uint64_t max_size,
                                uint64_t *res_precopy_only,
                                uint64_t *res_compatible,
                                uint64_t *res_postcopy_only)
 {
     /* Estimate pending number of bytes to send */
     uint64_t pending;
 
     qemu_mutex_lock_iothread();
     pending = get_remaining_dirty();
     qemu_mutex_unlock_iothread();
 
     blk_mig_lock();
     pending += block_mig_state.submitted * BLK_MIG_BLOCK_SIZE +
                block_mig_state.read_done * BLK_MIG_BLOCK_SIZE;
     blk_mig_unlock();
 
     /* Report at least one block pending during bulk phase */
     if (!pending && !block_mig_state.bulk_completed) {
         pending = BLK_MIG_BLOCK_SIZE;
     }
 
     trace_migration_block_save_pending(pending);
     /* We don't do postcopy */
     *res_precopy_only += pending;
 }
 
 static int block_load(QEMUFile *f, void *opaque, int version_id)
 {
     static int banner_printed;
     int len, flags;
     char device_name[256];
     int64_t addr;
     BlockBackend *blk, *blk_prev = NULL;
     Error *local_err = NULL;
     uint8_t *buf;
     int64_t total_sectors = 0;
     int nr_sectors;
     int ret;
     BlockDriverInfo bdi;
     int cluster_size = BLK_MIG_BLOCK_SIZE;
 
     do {
         addr = qemu_get_be64(f);
 
         flags = addr & (BDRV_SECTOR_SIZE - 1);
         addr >>= BDRV_SECTOR_BITS;
 
         if (flags & BLK_MIG_FLAG_DEVICE_BLOCK) {
             /* get device name */
             len = qemu_get_byte(f);
             qemu_get_buffer(f, (uint8_t *)device_name, len);
             device_name[len] = '\0';
 
             blk = blk_by_name(device_name);
             if (!blk) {
                 fprintf(stderr, "Error unknown block device %s\n",
                         device_name);
                 return -EINVAL;
             }
 
             if (blk != blk_prev) {
                 blk_prev = blk;
                 total_sectors = blk_nb_sectors(blk);
                 if (total_sectors <= 0) {
                     error_report("Error getting length of block device %s",
                                  device_name);
                     return -EINVAL;
                 }
 
                 blk_activate(blk, &local_err);
                 if (local_err) {
                     error_report_err(local_err);
                     return -EINVAL;
                 }
 
                 ret = bdrv_get_info(blk_bs(blk), &bdi);
                 if (ret == 0 && bdi.cluster_size > 0 &&
                     bdi.cluster_size <= BLK_MIG_BLOCK_SIZE &&
                     BLK_MIG_BLOCK_SIZE % bdi.cluster_size == 0) {
                     cluster_size = bdi.cluster_size;
                 } else {
                     cluster_size = BLK_MIG_BLOCK_SIZE;
                 }
             }
 
             if (total_sectors - addr < BDRV_SECTORS_PER_DIRTY_CHUNK) {
                 nr_sectors = total_sectors - addr;
             } else {
                 nr_sectors = BDRV_SECTORS_PER_DIRTY_CHUNK;
             }
 
             if (flags & BLK_MIG_FLAG_ZERO_BLOCK) {
                 ret = blk_pwrite_zeroes(blk, addr * BDRV_SECTOR_SIZE,
                                         nr_sectors * BDRV_SECTOR_SIZE,
                                         BDRV_REQ_MAY_UNMAP);
             } else {
                 int i;
                 int64_t cur_addr;
                 uint8_t *cur_buf;
 
                 buf = g_malloc(BLK_MIG_BLOCK_SIZE);
                 qemu_get_buffer(f, buf, BLK_MIG_BLOCK_SIZE);
                 for (i = 0; i < BLK_MIG_BLOCK_SIZE / cluster_size; i++) {
                     cur_addr = addr * BDRV_SECTOR_SIZE + i * cluster_size;
                     cur_buf = buf + i * cluster_size;
 
                     if ((!block_mig_state.zero_blocks ||
                         cluster_size < BLK_MIG_BLOCK_SIZE) &&
                         buffer_is_zero(cur_buf, cluster_size)) {
                         ret = blk_pwrite_zeroes(blk, cur_addr,
                                                 cluster_size,
                                                 BDRV_REQ_MAY_UNMAP);
                     } else {
                         ret = blk_pwrite(blk, cur_addr, cluster_size, cur_buf,
                                          0);
                     }
                     if (ret < 0) {
                         break;
                     }
                 }
                 g_free(buf);
             }
 
             if (ret < 0) {
                 return ret;
             }
         } else if (flags & BLK_MIG_FLAG_PROGRESS) {
             if (!banner_printed) {
                 printf("Receiving block device images\n");
                 banner_printed = 1;
             }
             printf("Completed %d %%%c", (int)addr,
                    (addr == 100) ? '\n' : '\r');
             fflush(stdout);
         } else if (!(flags & BLK_MIG_FLAG_EOS)) {
             fprintf(stderr, "Unknown block migration flags: 0x%x\n", flags);
             return -EINVAL;
         }
         ret = qemu_file_get_error(f);
         if (ret != 0) {
             return ret;
         }
     } while (!(flags & BLK_MIG_FLAG_EOS));
 
     return 0;
 }
 
 static bool block_is_active(void *opaque)
 {
     return migrate_use_block();
 }
 
 static SaveVMHandlers savevm_block_handlers = {
     .save_setup = block_save_setup,
     .save_live_iterate = block_save_iterate,
     .save_live_complete_precopy = block_save_complete,
     .save_live_pending = block_save_pending,
     .load_state = block_load,
     .save_cleanup = block_migration_cleanup,
     .is_active = block_is_active,
 };
 
 void blk_mig_init(void)
 {
     QSIMPLEQ_INIT(&block_mig_state.bmds_list);
     QSIMPLEQ_INIT(&block_mig_state.blk_list);
     qemu_mutex_init(&block_mig_state.lock);
 
     register_savevm_live("block", 0, 1, &savevm_block_handlers,
                          &block_mig_state);
 }