]> git.proxmox.com Git - mirror_qemu.git/blobdiff - block/backup.c
block/export: Move writable to BlockExportOptions
[mirror_qemu.git] / block / backup.c
index 03637aeb119ecafe4e2e6293cb9ec9e701ac9e29..9afa0bf3b41229536a5b9e67df8d2965c734406f 100644 (file)
@@ -2,6 +2,7 @@
  * QEMU backup
  *
  * Copyright (C) 2013 Proxmox Server Solutions
+ * Copyright (c) 2019 Virtuozzo International GmbH.
  *
  * Authors:
  *  Dietmar Maurer (dietmar@proxmox.com)
@@ -18,6 +19,7 @@
 #include "block/block_int.h"
 #include "block/blockjob_int.h"
 #include "block/block_backup.h"
+#include "block/block-copy.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qerror.h"
 #include "qemu/ratelimit.h"
 #include "qemu/bitmap.h"
 #include "qemu/error-report.h"
 
-#define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
+#include "block/backup-top.h"
 
-typedef struct CowRequest {
-    int64_t start_byte;
-    int64_t end_byte;
-    QLIST_ENTRY(CowRequest) list;
-    CoQueue wait_queue; /* coroutines blocked on this request */
-} CowRequest;
+#define BACKUP_CLUSTER_SIZE_DEFAULT (1 << 16)
 
 typedef struct BackupBlockJob {
     BlockJob common;
-    BlockBackend *target;
+    BlockDriverState *backup_top;
+    BlockDriverState *source_bs;
 
     BdrvDirtyBitmap *sync_bitmap;
-    BdrvDirtyBitmap *copy_bitmap;
 
     MirrorSyncMode sync_mode;
     BitmapSyncMode bitmap_mode;
     BlockdevOnError on_source_error;
     BlockdevOnError on_target_error;
-    CoRwlock flush_rwlock;
     uint64_t len;
     uint64_t bytes_read;
     int64_t cluster_size;
-    NotifierWithReturn before_write;
-    QLIST_HEAD(, CowRequest) inflight_reqs;
-
-    bool use_copy_range;
-    int64_t copy_range_size;
 
-    BdrvRequestFlags write_flags;
-    bool initializing_bitmap;
+    BlockCopyState *bcs;
 } BackupBlockJob;
 
 static const BlockJobDriver backup_job_driver;
 
-/* See if in-flight requests overlap and wait for them to complete */
-static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,
-                                                       int64_t start,
-                                                       int64_t end)
-{
-    CowRequest *req;
-    bool retry;
-
-    do {
-        retry = false;
-        QLIST_FOREACH(req, &job->inflight_reqs, list) {
-            if (end > req->start_byte && start < req->end_byte) {
-                qemu_co_queue_wait(&req->wait_queue, NULL);
-                retry = true;
-                break;
-            }
-        }
-    } while (retry);
-}
-
-/* Keep track of an in-flight request */
-static void cow_request_begin(CowRequest *req, BackupBlockJob *job,
-                              int64_t start, int64_t end)
-{
-    req->start_byte = start;
-    req->end_byte = end;
-    qemu_co_queue_init(&req->wait_queue);
-    QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);
-}
-
-/* Forget about a completed request */
-static void cow_request_end(CowRequest *req)
-{
-    QLIST_REMOVE(req, list);
-    qemu_co_queue_restart_all(&req->wait_queue);
-}
-
-/* Copy range to target with a bounce buffer and return the bytes copied. If
- * error occurred, return a negative error number */
-static int coroutine_fn backup_cow_with_bounce_buffer(BackupBlockJob *job,
-                                                      int64_t start,
-                                                      int64_t end,
-                                                      bool is_write_notifier,
-                                                      bool *error_is_read,
-                                                      void **bounce_buffer)
-{
-    int ret;
-    BlockBackend *blk = job->common.blk;
-    int nbytes;
-    int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
-
-    assert(QEMU_IS_ALIGNED(start, job->cluster_size));
-    bdrv_reset_dirty_bitmap(job->copy_bitmap, start, job->cluster_size);
-    nbytes = MIN(job->cluster_size, job->len - start);
-    if (!*bounce_buffer) {
-        *bounce_buffer = blk_blockalign(blk, job->cluster_size);
-    }
-
-    ret = blk_co_pread(blk, start, nbytes, *bounce_buffer, read_flags);
-    if (ret < 0) {
-        trace_backup_do_cow_read_fail(job, start, ret);
-        if (error_is_read) {
-            *error_is_read = true;
-        }
-        goto fail;
-    }
-
-    ret = blk_co_pwrite(job->target, start, nbytes, *bounce_buffer,
-                        job->write_flags);
-    if (ret < 0) {
-        trace_backup_do_cow_write_fail(job, start, ret);
-        if (error_is_read) {
-            *error_is_read = false;
-        }
-        goto fail;
-    }
-
-    return nbytes;
-fail:
-    bdrv_set_dirty_bitmap(job->copy_bitmap, start, job->cluster_size);
-    return ret;
-
-}
-
-/* Copy range to target and return the bytes copied. If error occurred, return a
- * negative error number. */
-static int coroutine_fn backup_cow_with_offload(BackupBlockJob *job,
-                                                int64_t start,
-                                                int64_t end,
-                                                bool is_write_notifier)
-{
-    int ret;
-    int nr_clusters;
-    BlockBackend *blk = job->common.blk;
-    int nbytes;
-    int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
-
-    assert(QEMU_IS_ALIGNED(job->copy_range_size, job->cluster_size));
-    assert(QEMU_IS_ALIGNED(start, job->cluster_size));
-    nbytes = MIN(job->copy_range_size, end - start);
-    nr_clusters = DIV_ROUND_UP(nbytes, job->cluster_size);
-    bdrv_reset_dirty_bitmap(job->copy_bitmap, start,
-                            job->cluster_size * nr_clusters);
-    ret = blk_co_copy_range(blk, start, job->target, start, nbytes,
-                            read_flags, job->write_flags);
-    if (ret < 0) {
-        trace_backup_do_cow_copy_range_fail(job, start, ret);
-        bdrv_set_dirty_bitmap(job->copy_bitmap, start,
-                              job->cluster_size * nr_clusters);
-        return ret;
-    }
-
-    return nbytes;
-}
-
-/*
- * Check if the cluster starting at offset is allocated or not.
- * return via pnum the number of contiguous clusters sharing this allocation.
- */
-static int backup_is_cluster_allocated(BackupBlockJob *s, int64_t offset,
-                                       int64_t *pnum)
+static void backup_progress_bytes_callback(int64_t bytes, void *opaque)
 {
-    BlockDriverState *bs = blk_bs(s->common.blk);
-    int64_t count, total_count = 0;
-    int64_t bytes = s->len - offset;
-    int ret;
-
-    assert(QEMU_IS_ALIGNED(offset, s->cluster_size));
-
-    while (true) {
-        ret = bdrv_is_allocated(bs, offset, bytes, &count);
-        if (ret < 0) {
-            return ret;
-        }
+    BackupBlockJob *s = opaque;
 
-        total_count += count;
-
-        if (ret || count == 0) {
-            /*
-             * ret: partial segment(s) are considered allocated.
-             * otherwise: unallocated tail is treated as an entire segment.
-             */
-            *pnum = DIV_ROUND_UP(total_count, s->cluster_size);
-            return ret;
-        }
-
-        /* Unallocated segment(s) with uncertain following segment(s) */
-        if (total_count >= s->cluster_size) {
-            *pnum = total_count / s->cluster_size;
-            return 0;
-        }
-
-        offset += count;
-        bytes -= count;
-    }
-}
-
-/**
- * Reset bits in copy_bitmap starting at offset if they represent unallocated
- * data in the image. May reset subsequent contiguous bits.
- * @return 0 when the cluster at @offset was unallocated,
- *         1 otherwise, and -ret on error.
- */
-static int64_t backup_bitmap_reset_unallocated(BackupBlockJob *s,
-                                               int64_t offset, int64_t *count)
-{
-    int ret;
-    int64_t clusters, bytes, estimate;
-
-    ret = backup_is_cluster_allocated(s, offset, &clusters);
-    if (ret < 0) {
-        return ret;
-    }
-
-    bytes = clusters * s->cluster_size;
-
-    if (!ret) {
-        bdrv_reset_dirty_bitmap(s->copy_bitmap, offset, bytes);
-        estimate = bdrv_get_dirty_count(s->copy_bitmap);
-        job_progress_set_remaining(&s->common.job, estimate);
-    }
-
-    *count = bytes;
-    return ret;
+    s->bytes_read += bytes;
 }
 
 static int coroutine_fn backup_do_cow(BackupBlockJob *job,
                                       int64_t offset, uint64_t bytes,
-                                      bool *error_is_read,
-                                      bool is_write_notifier)
+                                      bool *error_is_read)
 {
-    CowRequest cow_request;
     int ret = 0;
     int64_t start, end; /* bytes */
-    void *bounce_buffer = NULL;
-    int64_t status_bytes;
-
-    qemu_co_rwlock_rdlock(&job->flush_rwlock);
 
     start = QEMU_ALIGN_DOWN(offset, job->cluster_size);
     end = QEMU_ALIGN_UP(bytes + offset, job->cluster_size);
 
     trace_backup_do_cow_enter(job, start, offset, bytes);
 
-    wait_for_overlapping_requests(job, start, end);
-    cow_request_begin(&cow_request, job, start, end);
-
-    while (start < end) {
-        int64_t dirty_end;
-
-        if (!bdrv_dirty_bitmap_get(job->copy_bitmap, start)) {
-            trace_backup_do_cow_skip(job, start);
-            start += job->cluster_size;
-            continue; /* already copied */
-        }
-
-        dirty_end = bdrv_dirty_bitmap_next_zero(job->copy_bitmap, start,
-                                                (end - start));
-        if (dirty_end < 0) {
-            dirty_end = end;
-        }
-
-        if (job->initializing_bitmap) {
-            ret = backup_bitmap_reset_unallocated(job, start, &status_bytes);
-            if (ret == 0) {
-                trace_backup_do_cow_skip_range(job, start, status_bytes);
-                start += status_bytes;
-                continue;
-            }
-            /* Clamp to known allocated region */
-            dirty_end = MIN(dirty_end, start + status_bytes);
-        }
-
-        trace_backup_do_cow_process(job, start);
-
-        if (job->use_copy_range) {
-            ret = backup_cow_with_offload(job, start, dirty_end,
-                                          is_write_notifier);
-            if (ret < 0) {
-                job->use_copy_range = false;
-            }
-        }
-        if (!job->use_copy_range) {
-            ret = backup_cow_with_bounce_buffer(job, start, dirty_end,
-                                                is_write_notifier,
-                                                error_is_read, &bounce_buffer);
-        }
-        if (ret < 0) {
-            break;
-        }
-
-        /* Publish progress, guest I/O counts as progress too.  Note that the
-         * offset field is an opaque progress value, it is not a disk offset.
-         */
-        start += ret;
-        job->bytes_read += ret;
-        job_progress_update(&job->common.job, ret);
-        ret = 0;
-    }
-
-    if (bounce_buffer) {
-        qemu_vfree(bounce_buffer);
-    }
-
-    cow_request_end(&cow_request);
+    ret = block_copy(job->bcs, start, end - start, error_is_read);
 
     trace_backup_do_cow_return(job, offset, bytes, ret);
 
-    qemu_co_rwlock_unlock(&job->flush_rwlock);
-
     return ret;
 }
 
-static int coroutine_fn backup_before_write_notify(
-        NotifierWithReturn *notifier,
-        void *opaque)
-{
-    BackupBlockJob *job = container_of(notifier, BackupBlockJob, before_write);
-    BdrvTrackedRequest *req = opaque;
-
-    assert(req->bs == blk_bs(job->common.blk));
-    assert(QEMU_IS_ALIGNED(req->offset, BDRV_SECTOR_SIZE));
-    assert(QEMU_IS_ALIGNED(req->bytes, BDRV_SECTOR_SIZE));
-
-    return backup_do_cow(job, req->offset, req->bytes, NULL, true);
-}
-
 static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 {
     BdrvDirtyBitmap *bm;
-    BlockDriverState *bs = blk_bs(job->common.blk);
     bool sync = (((ret == 0) || (job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS)) \
                  && (job->bitmap_mode != BITMAP_SYNC_MODE_NEVER));
 
@@ -361,20 +89,20 @@ static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
          * We succeeded, or we always intended to sync the bitmap.
          * Delete this bitmap and install the child.
          */
-        bm = bdrv_dirty_bitmap_abdicate(bs, job->sync_bitmap, NULL);
+        bm = bdrv_dirty_bitmap_abdicate(job->sync_bitmap, NULL);
     } else {
         /*
          * We failed, or we never intended to sync the bitmap anyway.
          * Merge the successor back into the parent, keeping all data.
          */
-        bm = bdrv_reclaim_dirty_bitmap(bs, job->sync_bitmap, NULL);
+        bm = bdrv_reclaim_dirty_bitmap(job->sync_bitmap, NULL);
     }
 
     assert(bm);
 
     if (ret < 0 && job->bitmap_mode == BITMAP_SYNC_MODE_ALWAYS) {
         /* If we failed and synced, merge in the bits we didn't copy: */
-        bdrv_dirty_bitmap_merge_internal(bm, job->copy_bitmap,
+        bdrv_dirty_bitmap_merge_internal(bm, block_copy_dirty_bitmap(job->bcs),
                                          NULL, true);
     }
 }
@@ -398,16 +126,7 @@ static void backup_abort(Job *job)
 static void backup_clean(Job *job)
 {
     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
-    BlockDriverState *bs = blk_bs(s->common.blk);
-
-    if (s->copy_bitmap) {
-        bdrv_release_dirty_bitmap(bs, s->copy_bitmap);
-        s->copy_bitmap = NULL;
-    }
-
-    assert(s->target);
-    blk_unref(s->target);
-    s->target = NULL;
+    bdrv_backup_top_drop(s->backup_top);
 }
 
 void backup_do_checkpoint(BlockJob *job, Error **errp)
@@ -422,22 +141,8 @@ void backup_do_checkpoint(BlockJob *job, Error **errp)
         return;
     }
 
-    bdrv_set_dirty_bitmap(backup_job->copy_bitmap, 0, backup_job->len);
-}
-
-static void backup_drain(BlockJob *job)
-{
-    BackupBlockJob *s = container_of(job, BackupBlockJob, common);
-
-    /* Need to keep a reference in case blk_drain triggers execution
-     * of backup_complete...
-     */
-    if (s->target) {
-        BlockBackend *target = s->target;
-        blk_ref(target);
-        blk_drain(target);
-        blk_unref(target);
-    }
+    bdrv_set_dirty_bitmap(block_copy_dirty_bitmap(backup_job->bcs), 0,
+                          backup_job->len);
 }
 
 static BlockErrorAction backup_error_action(BackupBlockJob *job,
@@ -460,8 +165,10 @@ static bool coroutine_fn yield_and_check(BackupBlockJob *job)
         return true;
     }
 
-    /* We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
-     * return. Without a yield, the VM would not reboot. */
+    /*
+     * We need to yield even for delay_ns = 0 so that bdrv_drain_all() can
+     * return. Without a yield, the VM would not reboot.
+     */
     delay_ns = block_job_ratelimit_get_delay(&job->common, job->bytes_read);
     job->bytes_read = 0;
     job_sleep_ns(&job->common.job, delay_ns);
@@ -480,14 +187,13 @@ static int coroutine_fn backup_loop(BackupBlockJob *job)
     BdrvDirtyBitmapIter *bdbi;
     int ret = 0;
 
-    bdbi = bdrv_dirty_iter_new(job->copy_bitmap);
+    bdbi = bdrv_dirty_iter_new(block_copy_dirty_bitmap(job->bcs));
     while ((offset = bdrv_dirty_iter_next(bdbi)) != -1) {
         do {
             if (yield_and_check(job)) {
                 goto out;
             }
-            ret = backup_do_cow(job, offset,
-                                job->cluster_size, &error_is_read, false);
+            ret = backup_do_cow(job, offset, job->cluster_size, &error_is_read);
             if (ret < 0 && backup_error_action(job, error_is_read, -ret) ==
                            BLOCK_ERROR_ACTION_REPORT)
             {
@@ -501,14 +207,14 @@ static int coroutine_fn backup_loop(BackupBlockJob *job)
     return ret;
 }
 
-static void backup_init_copy_bitmap(BackupBlockJob *job)
+static void backup_init_bcs_bitmap(BackupBlockJob *job)
 {
     bool ret;
     uint64_t estimate;
+    BdrvDirtyBitmap *bcs_bitmap = block_copy_dirty_bitmap(job->bcs);
 
     if (job->sync_mode == MIRROR_SYNC_MODE_BITMAP) {
-        ret = bdrv_dirty_bitmap_merge_internal(job->copy_bitmap,
-                                               job->sync_bitmap,
+        ret = bdrv_dirty_bitmap_merge_internal(bcs_bitmap, job->sync_bitmap,
                                                NULL, true);
         assert(ret);
     } else {
@@ -517,28 +223,21 @@ static void backup_init_copy_bitmap(BackupBlockJob *job)
              * We can't hog the coroutine to initialize this thoroughly.
              * Set a flag and resume work when we are able to yield safely.
              */
-            job->initializing_bitmap = true;
+            block_copy_set_skip_unallocated(job->bcs, true);
         }
-        bdrv_set_dirty_bitmap(job->copy_bitmap, 0, job->len);
+        bdrv_set_dirty_bitmap(bcs_bitmap, 0, job->len);
     }
 
-    estimate = bdrv_get_dirty_count(job->copy_bitmap);
+    estimate = bdrv_get_dirty_count(bcs_bitmap);
     job_progress_set_remaining(&job->common.job, estimate);
 }
 
 static int coroutine_fn backup_run(Job *job, Error **errp)
 {
     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
-    BlockDriverState *bs = blk_bs(s->common.blk);
     int ret = 0;
 
-    QLIST_INIT(&s->inflight_reqs);
-    qemu_co_rwlock_init(&s->flush_rwlock);
-
-    backup_init_copy_bitmap(s);
-
-    s->before_write.notify = backup_before_write_notify;
-    bdrv_add_before_write_notifier(bs, &s->before_write);
+    backup_init_bcs_bitmap(s);
 
     if (s->sync_mode == MIRROR_SYNC_MODE_TOP) {
         int64_t offset = 0;
@@ -550,22 +249,26 @@ static int coroutine_fn backup_run(Job *job, Error **errp)
                 goto out;
             }
 
-            ret = backup_bitmap_reset_unallocated(s, offset, &count);
+            ret = block_copy_reset_unallocated(s->bcs, offset, &count);
             if (ret < 0) {
                 goto out;
             }
 
             offset += count;
         }
-        s->initializing_bitmap = false;
+        block_copy_set_skip_unallocated(s->bcs, false);
     }
 
     if (s->sync_mode == MIRROR_SYNC_MODE_NONE) {
-        /* All bits are set in copy_bitmap to allow any cluster to be copied.
-         * This does not actually require them to be copied. */
+        /*
+         * All bits are set in bcs bitmap to allow any cluster to be copied.
+         * This does not actually require them to be copied.
+         */
         while (!job_is_cancelled(job)) {
-            /* Yield until the job is cancelled.  We just let our before_write
-             * notify callback service CoW requests. */
+            /*
+             * Yield until the job is cancelled.  We just let our before_write
+             * notify callback service CoW requests.
+             */
             job_yield(job);
         }
     } else {
@@ -573,12 +276,6 @@ static int coroutine_fn backup_run(Job *job, Error **errp)
     }
 
  out:
-    notifier_with_return_remove(&s->before_write);
-
-    /* wait until pending backup_do_cow() calls have completed */
-    qemu_co_rwlock_wrlock(&s->flush_rwlock);
-    qemu_co_rwlock_unlock(&s->flush_rwlock);
-
     return ret;
 }
 
@@ -588,13 +285,11 @@ static const BlockJobDriver backup_job_driver = {
         .job_type               = JOB_TYPE_BACKUP,
         .free                   = block_job_free,
         .user_resume            = block_job_user_resume,
-        .drain                  = block_job_drain,
         .run                    = backup_run,
         .commit                 = backup_commit,
         .abort                  = backup_abort,
         .clean                  = backup_clean,
-    },
-    .drain                  = backup_drain,
+    }
 };
 
 static int64_t backup_calculate_cluster_size(BlockDriverState *target,
@@ -602,6 +297,7 @@ static int64_t backup_calculate_cluster_size(BlockDriverState *target,
 {
     int ret;
     BlockDriverInfo bdi;
+    bool target_does_cow = bdrv_backing_chain_next(target);
 
     /*
      * If there is no backing file on the target, we cannot rely on COW if our
@@ -609,7 +305,7 @@ static int64_t backup_calculate_cluster_size(BlockDriverState *target,
      * targets with a backing file, try to avoid COW if possible.
      */
     ret = bdrv_get_info(target, &bdi);
-    if (ret == -ENOTSUP && !target->backing) {
+    if (ret == -ENOTSUP && !target_does_cow) {
         /* Cluster size is not defined */
         warn_report("The target block device doesn't provide "
                     "information about the block size and it doesn't have a "
@@ -618,14 +314,14 @@ static int64_t backup_calculate_cluster_size(BlockDriverState *target,
                     "this default, the backup may be unusable",
                     BACKUP_CLUSTER_SIZE_DEFAULT);
         return BACKUP_CLUSTER_SIZE_DEFAULT;
-    } else if (ret < 0 && !target->backing) {
+    } else if (ret < 0 && !target_does_cow) {
         error_setg_errno(errp, -ret,
             "Couldn't determine the cluster size of the target image, "
             "which has no backing file");
         error_append_hint(errp,
             "Aborting, since this may create an unusable destination image\n");
         return ret;
-    } else if (ret < 0 && target->backing) {
+    } else if (ret < 0 && target_does_cow) {
         /* Not fatal; just trudge on ahead. */
         return BACKUP_CLUSTER_SIZE_DEFAULT;
     }
@@ -638,17 +334,19 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
                   MirrorSyncMode sync_mode, BdrvDirtyBitmap *sync_bitmap,
                   BitmapSyncMode bitmap_mode,
                   bool compress,
+                  const char *filter_node_name,
                   BlockdevOnError on_source_error,
                   BlockdevOnError on_target_error,
                   int creation_flags,
                   BlockCompletionFunc *cb, void *opaque,
                   JobTxn *txn, Error **errp)
 {
-    int64_t len;
+    int64_t len, target_len;
     BackupBlockJob *job = NULL;
-    int ret;
     int64_t cluster_size;
-    BdrvDirtyBitmap *copy_bitmap = NULL;
+    BdrvRequestFlags write_flags;
+    BlockDriverState *backup_top = NULL;
+    BlockCopyState *bcs = NULL;
 
     assert(bs);
     assert(target);
@@ -674,7 +372,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         return NULL;
     }
 
-    if (compress && !block_driver_can_compress(target->drv)) {
+    if (compress && !bdrv_supports_compressed_writes(target)) {
         error_setg(errp, "Compression is not supported for this drive %s",
                    bdrv_get_device_name(target));
         return NULL;
@@ -696,15 +394,27 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         }
 
         /* Create a new bitmap, and freeze/disable this one. */
-        if (bdrv_dirty_bitmap_create_successor(bs, sync_bitmap, errp) < 0) {
+        if (bdrv_dirty_bitmap_create_successor(sync_bitmap, errp) < 0) {
             return NULL;
         }
     }
 
     len = bdrv_getlength(bs);
     if (len < 0) {
-        error_setg_errno(errp, -len, "unable to get length for '%s'",
-                         bdrv_get_device_name(bs));
+        error_setg_errno(errp, -len, "Unable to get length for '%s'",
+                         bdrv_get_device_or_node_name(bs));
+        goto error;
+    }
+
+    target_len = bdrv_getlength(target);
+    if (target_len < 0) {
+        error_setg_errno(errp, -target_len, "Unable to get length for '%s'",
+                         bdrv_get_device_or_node_name(bs));
+        goto error;
+    }
+
+    if (target_len != len) {
+        error_setg(errp, "Source and target image have different sizes");
         goto error;
     }
 
@@ -713,76 +423,63 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         goto error;
     }
 
-    copy_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
-    if (!copy_bitmap) {
+    /*
+     * If source is in backing chain of target assume that target is going to be
+     * used for "image fleecing", i.e. it should represent a kind of snapshot of
+     * source at backup-start point in time. And target is going to be read by
+     * somebody (for example, used as NBD export) during backup job.
+     *
+     * In this case, we need to add BDRV_REQ_SERIALISING write flag to avoid
+     * intersection of backup writes and third party reads from target,
+     * otherwise reading from target we may occasionally read already updated by
+     * guest data.
+     *
+     * For more information see commit f8d59dfb40bb and test
+     * tests/qemu-iotests/222
+     */
+    write_flags = (bdrv_chain_contains(target, bs) ? BDRV_REQ_SERIALISING : 0) |
+                  (compress ? BDRV_REQ_WRITE_COMPRESSED : 0),
+
+    backup_top = bdrv_backup_top_append(bs, target, filter_node_name,
+                                        cluster_size, write_flags, &bcs, errp);
+    if (!backup_top) {
         goto error;
     }
-    bdrv_disable_dirty_bitmap(copy_bitmap);
 
     /* job->len is fixed, so we can't allow resize */
-    job = block_job_create(job_id, &backup_job_driver, txn, bs,
-                           BLK_PERM_CONSISTENT_READ,
-                           BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
-                           BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD,
+    job = block_job_create(job_id, &backup_job_driver, txn, backup_top,
+                           0, BLK_PERM_ALL,
                            speed, creation_flags, cb, opaque, errp);
     if (!job) {
         goto error;
     }
 
-    /* The target must match the source in size, so no resize here either */
-    job->target = blk_new(job->common.job.aio_context,
-                          BLK_PERM_WRITE,
-                          BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE |
-                          BLK_PERM_WRITE_UNCHANGED | BLK_PERM_GRAPH_MOD);
-    ret = blk_insert_bs(job->target, target, errp);
-    if (ret < 0) {
-        goto error;
-    }
-    blk_set_disable_request_queuing(job->target, true);
-
+    job->backup_top = backup_top;
+    job->source_bs = bs;
     job->on_source_error = on_source_error;
     job->on_target_error = on_target_error;
     job->sync_mode = sync_mode;
     job->sync_bitmap = sync_bitmap;
     job->bitmap_mode = bitmap_mode;
+    job->bcs = bcs;
+    job->cluster_size = cluster_size;
+    job->len = len;
 
-    /*
-     * Set write flags:
-     * 1. Detect image-fleecing (and similar) schemes
-     * 2. Handle compression
-     */
-    job->write_flags =
-        (bdrv_chain_contains(target, bs) ? BDRV_REQ_SERIALISING : 0) |
-        (compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
+    block_copy_set_progress_callback(bcs, backup_progress_bytes_callback, job);
+    block_copy_set_progress_meter(bcs, &job->common.job.progress);
 
-    job->cluster_size = cluster_size;
-    job->copy_bitmap = copy_bitmap;
-    copy_bitmap = NULL;
-    job->use_copy_range = !compress; /* compression isn't supported for it */
-    job->copy_range_size = MIN_NON_ZERO(blk_get_max_transfer(job->common.blk),
-                                        blk_get_max_transfer(job->target));
-    job->copy_range_size = MAX(job->cluster_size,
-                               QEMU_ALIGN_UP(job->copy_range_size,
-                                             job->cluster_size));
-
-    /* Required permissions are already taken with target's blk_new() */
+    /* Required permissions are already taken by backup-top target */
     block_job_add_bdrv(&job->common, "target", target, 0, BLK_PERM_ALL,
                        &error_abort);
-    job->len = len;
 
     return &job->common;
 
  error:
-    if (copy_bitmap) {
-        assert(!job || !job->copy_bitmap);
-        bdrv_release_dirty_bitmap(bs, copy_bitmap);
-    }
     if (sync_bitmap) {
-        bdrv_reclaim_dirty_bitmap(bs, sync_bitmap, NULL);
+        bdrv_reclaim_dirty_bitmap(sync_bitmap, NULL);
     }
-    if (job) {
-        backup_clean(&job->common.job);
-        job_early_fail(&job->common.job);
+    if (backup_top) {
+        bdrv_backup_top_drop(backup_top);
     }
 
     return NULL;