diff --git a/include/block/block-copy.h b/include/block/block-copy.h
index d96b097267..753fa663ac 100644
--- a/include/block/block-copy.h
+++ b/include/block/block-copy.h
@@ -18,61 +18,9 @@
 #include "block/block.h"
 #include "qemu/co-shared-resource.h"
 
-typedef struct BlockCopyInFlightReq {
-    int64_t offset;
-    int64_t bytes;
-    QLIST_ENTRY(BlockCopyInFlightReq) list;
-    CoQueue wait_queue; /* coroutines blocked on this request */
-} BlockCopyInFlightReq;
-
 typedef void (*ProgressBytesCallbackFunc)(int64_t bytes, void *opaque);
 typedef void (*ProgressResetCallbackFunc)(void *opaque);
-typedef struct BlockCopyState {
-    /*
-     * BdrvChild objects are not owned or managed by block-copy. They are
-     * provided by block-copy user and user is responsible for appropriate
-     * permissions on these children.
-     */
-    BdrvChild *source;
-    BdrvChild *target;
-    BdrvDirtyBitmap *copy_bitmap;
-    int64_t cluster_size;
-    bool use_copy_range;
-    int64_t copy_size;
-    uint64_t len;
-    QLIST_HEAD(, BlockCopyInFlightReq) inflight_reqs;
-
-    BdrvRequestFlags write_flags;
-
-    /*
-     * skip_unallocated:
-     *
-     * Used by sync=top jobs, which first scan the source node for unallocated
-     * areas and clear them in the copy_bitmap.  During this process, the bitmap
-     * is thus not fully initialized: It may still have bits set for areas that
-     * are unallocated and should actually not be copied.
-     *
-     * This is indicated by skip_unallocated.
-     *
-     * In this case, block_copy() will query the source’s allocation status,
-     * skip unallocated regions, clear them in the copy_bitmap, and invoke
-     * block_copy_reset_unallocated() every time it does.
-     */
-    bool skip_unallocated;
-
-    /* progress_bytes_callback: called when some copying progress is done. */
-    ProgressBytesCallbackFunc progress_bytes_callback;
-
-    /*
-     * progress_reset_callback: called when some bytes reset from copy_bitmap
-     * (see @skip_unallocated above). The callee is assumed to recalculate how
-     * many bytes remain based on the dirty bit count of copy_bitmap.
-     */
-    ProgressResetCallbackFunc progress_reset_callback;
-    void *progress_opaque;
-
-    SharedResource *mem;
-} BlockCopyState;
+typedef struct BlockCopyState BlockCopyState;
 
 BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
                                      int64_t cluster_size,
@@ -93,4 +41,7 @@ int64_t block_copy_reset_unallocated(BlockCopyState *s,
 int coroutine_fn block_copy(BlockCopyState *s, int64_t start, uint64_t bytes,
                             bool *error_is_read);
 
+BdrvDirtyBitmap *block_copy_dirty_bitmap(BlockCopyState *s);
+void block_copy_set_skip_unallocated(BlockCopyState *s, bool skip);
+
 #endif /* BLOCK_COPY_H */
diff --git a/block/backup-top.c b/block/backup-top.c
index 7cdb1f8eba..1026628b57 100644
--- a/block/backup-top.c
+++ b/block/backup-top.c
@@ -38,6 +38,7 @@ typedef struct BDRVBackupTopState {
     BlockCopyState *bcs;
     BdrvChild *target;
     bool active;
+    int64_t cluster_size;
 } BDRVBackupTopState;
 
 static coroutine_fn int backup_top_co_preadv(
@@ -51,8 +52,8 @@ static coroutine_fn int backup_top_cbw(BlockDriverState *bs, uint64_t offset,
                                        uint64_t bytes)
 {
     BDRVBackupTopState *s = bs->opaque;
-    uint64_t end = QEMU_ALIGN_UP(offset + bytes, s->bcs->cluster_size);
-    uint64_t off = QEMU_ALIGN_DOWN(offset, s->bcs->cluster_size);
+    uint64_t end = QEMU_ALIGN_UP(offset + bytes, s->cluster_size);
+    uint64_t off = QEMU_ALIGN_DOWN(offset, s->cluster_size);
 
     return block_copy(s->bcs, off, end - off, NULL);
 }
@@ -227,6 +228,7 @@ BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
         goto failed_after_append;
     }
 
+    state->cluster_size = cluster_size;
     state->bcs = block_copy_state_new(top->backing, state->target,
                                       cluster_size, write_flags, &local_err);
     if (local_err) {
diff --git a/block/backup.c b/block/backup.c
index cf62b1a38c..acab0d08da 100644
--- a/block/backup.c
+++ b/block/backup.c
@@ -48,6 +48,7 @@ typedef struct BackupBlockJob {
     int64_t cluster_size;
 
     BlockCopyState *bcs;
+    BdrvDirtyBitmap *bcs_bitmap;
 } BackupBlockJob;
 
 static const BlockJobDriver backup_job_driver;
@@ -63,7 +64,7 @@ static void backup_progress_bytes_callback(int64_t bytes, void *opaque)
 static void backup_progress_reset_callback(void *opaque)
 {
     BackupBlockJob *s = opaque;
-    uint64_t estimate = bdrv_get_dirty_count(s->bcs->copy_bitmap);
+    uint64_t estimate = bdrv_get_dirty_count(s->bcs_bitmap);
 
     job_progress_set_remaining(&s->common.job, estimate);
 }
@@ -111,8 +112,7 @@ static void backup_cleanup_sync_bitmap(BackupBlockJob *job, int ret)
 
     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->bcs->copy_bitmap,
-                                         NULL, true);
+        bdrv_dirty_bitmap_merge_internal(bm, job->bcs_bitmap, NULL, true);
     }
 }
 
@@ -151,7 +151,7 @@ void backup_do_checkpoint(BlockJob *job, Error **errp)
         return;
     }
 
-    bdrv_set_dirty_bitmap(backup_job->bcs->copy_bitmap, 0, backup_job->len);
+    bdrv_set_dirty_bitmap(backup_job->bcs_bitmap, 0, backup_job->len);
 }
 
 static BlockErrorAction backup_error_action(BackupBlockJob *job,
@@ -196,7 +196,7 @@ static int coroutine_fn backup_loop(BackupBlockJob *job)
     BdrvDirtyBitmapIter *bdbi;
     int ret = 0;
 
-    bdbi = bdrv_dirty_iter_new(job->bcs->copy_bitmap);
+    bdbi = bdrv_dirty_iter_new(job->bcs_bitmap);
     while ((offset = bdrv_dirty_iter_next(bdbi)) != -1) {
         do {
             if (yield_and_check(job)) {
@@ -216,13 +216,13 @@ 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;
 
     if (job->sync_mode == MIRROR_SYNC_MODE_BITMAP) {
-        ret = bdrv_dirty_bitmap_merge_internal(job->bcs->copy_bitmap,
+        ret = bdrv_dirty_bitmap_merge_internal(job->bcs_bitmap,
                                                job->sync_bitmap,
                                                NULL, true);
         assert(ret);
@@ -232,12 +232,12 @@ 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->bcs->skip_unallocated = true;
+            block_copy_set_skip_unallocated(job->bcs, true);
         }
-        bdrv_set_dirty_bitmap(job->bcs->copy_bitmap, 0, job->len);
+        bdrv_set_dirty_bitmap(job->bcs_bitmap, 0, job->len);
     }
 
-    estimate = bdrv_get_dirty_count(job->bcs->copy_bitmap);
+    estimate = bdrv_get_dirty_count(job->bcs_bitmap);
     job_progress_set_remaining(&job->common.job, estimate);
 }
 
@@ -246,7 +246,7 @@ static int coroutine_fn backup_run(Job *job, Error **errp)
     BackupBlockJob *s = container_of(job, BackupBlockJob, common.job);
     int ret = 0;
 
-    backup_init_copy_bitmap(s);
+    backup_init_bcs_bitmap(s);
 
     if (s->sync_mode == MIRROR_SYNC_MODE_TOP) {
         int64_t offset = 0;
@@ -265,12 +265,12 @@ static int coroutine_fn backup_run(Job *job, Error **errp)
 
             offset += count;
         }
-        s->bcs->skip_unallocated = 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.
+         * 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)) {
@@ -458,6 +458,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
     job->sync_bitmap = sync_bitmap;
     job->bitmap_mode = bitmap_mode;
     job->bcs = bcs;
+    job->bcs_bitmap = block_copy_dirty_bitmap(bcs);
     job->cluster_size = cluster_size;
     job->len = len;
 
diff --git a/block/block-copy.c b/block/block-copy.c
index aca44b13fb..7e14e86a2d 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -24,6 +24,60 @@
 #define BLOCK_COPY_MAX_BUFFER (1 * MiB)
 #define BLOCK_COPY_MAX_MEM (128 * MiB)
 
+typedef struct BlockCopyInFlightReq {
+    int64_t offset;
+    int64_t bytes;
+    QLIST_ENTRY(BlockCopyInFlightReq) list;
+    CoQueue wait_queue; /* coroutines blocked on this request */
+} BlockCopyInFlightReq;
+
+typedef struct BlockCopyState {
+    /*
+     * BdrvChild objects are not owned or managed by block-copy. They are
+     * provided by block-copy user and user is responsible for appropriate
+     * permissions on these children.
+     */
+    BdrvChild *source;
+    BdrvChild *target;
+    BdrvDirtyBitmap *copy_bitmap;
+    int64_t cluster_size;
+    bool use_copy_range;
+    int64_t copy_size;
+    uint64_t len;
+    QLIST_HEAD(, BlockCopyInFlightReq) inflight_reqs;
+
+    BdrvRequestFlags write_flags;
+
+    /*
+     * skip_unallocated:
+     *
+     * Used by sync=top jobs, which first scan the source node for unallocated
+     * areas and clear them in the copy_bitmap.  During this process, the bitmap
+     * is thus not fully initialized: It may still have bits set for areas that
+     * are unallocated and should actually not be copied.
+     *
+     * This is indicated by skip_unallocated.
+     *
+     * In this case, block_copy() will query the source’s allocation status,
+     * skip unallocated regions, clear them in the copy_bitmap, and invoke
+     * block_copy_reset_unallocated() every time it does.
+     */
+    bool skip_unallocated;
+
+    /* progress_bytes_callback: called when some copying progress is done. */
+    ProgressBytesCallbackFunc progress_bytes_callback;
+
+    /*
+     * progress_reset_callback: called when some bytes reset from copy_bitmap
+     * (see @skip_unallocated above). The callee is assumed to recalculate how
+     * many bytes remain based on the dirty bit count of copy_bitmap.
+     */
+    ProgressResetCallbackFunc progress_reset_callback;
+    void *progress_opaque;
+
+    SharedResource *mem;
+} BlockCopyState;
+
 static BlockCopyInFlightReq *block_copy_find_inflight_req(BlockCopyState *s,
                                                           int64_t offset,
                                                           int64_t bytes)
@@ -492,3 +546,13 @@ int coroutine_fn block_copy(BlockCopyState *s, int64_t start, uint64_t bytes,
 
     return 0;
 }
+
+BdrvDirtyBitmap *block_copy_dirty_bitmap(BlockCopyState *s)
+{
+    return s->copy_bitmap;
+}
+
+void block_copy_set_skip_unallocated(BlockCopyState *s, bool skip)
+{
+    s->skip_unallocated = skip;
+}
