diff --git a/block/blkreplay.c b/block/blkreplay.c
index 196b8d0..70650e4 100755
--- a/block/blkreplay.c
+++ b/block/blkreplay.c
@@ -85,7 +85,7 @@
     uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
 {
     uint64_t reqid = request_id++;
-    int ret = bdrv_co_preadv(bs->file->bs, offset, bytes, qiov, flags);
+    int ret = bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
     block_request_create(reqid, bs, qemu_coroutine_self());
     qemu_coroutine_yield();
 
@@ -96,7 +96,7 @@
     uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
 {
     uint64_t reqid = request_id++;
-    int ret = bdrv_co_pwritev(bs->file->bs, offset, bytes, qiov, flags);
+    int ret = bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
     block_request_create(reqid, bs, qemu_coroutine_self());
     qemu_coroutine_yield();
 
@@ -107,7 +107,7 @@
     int64_t offset, int count, BdrvRequestFlags flags)
 {
     uint64_t reqid = request_id++;
-    int ret = bdrv_co_pwrite_zeroes(bs->file->bs, offset, count, flags);
+    int ret = bdrv_co_pwrite_zeroes(bs->file, offset, count, flags);
     block_request_create(reqid, bs, qemu_coroutine_self());
     qemu_coroutine_yield();
 
diff --git a/block/block-backend.c b/block/block-backend.c
index 4bc7265..a862f65 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -760,7 +760,7 @@
         throttle_group_co_io_limits_intercept(blk, bytes, false);
     }
 
-    return bdrv_co_preadv(blk_bs(blk), offset, bytes, qiov, flags);
+    return bdrv_co_preadv(blk->root, offset, bytes, qiov, flags);
 }
 
 int coroutine_fn blk_co_pwritev(BlockBackend *blk, int64_t offset,
@@ -785,7 +785,7 @@
         flags |= BDRV_REQ_FUA;
     }
 
-    return bdrv_co_pwritev(blk_bs(blk), offset, bytes, qiov, flags);
+    return bdrv_co_pwritev(blk->root, offset, bytes, qiov, flags);
 }
 
 typedef struct BlkRwCo {
diff --git a/block/bochs.c b/block/bochs.c
index 46f635f..8c9652e 100644
--- a/block/bochs.c
+++ b/block/bochs.c
@@ -255,7 +255,7 @@
         qemu_iovec_concat(&local_qiov, qiov, bytes_done, 512);
 
         if (block_offset > 0) {
-            ret = bdrv_co_preadv(bs->file->bs, block_offset, 512,
+            ret = bdrv_co_preadv(bs->file, block_offset, 512,
                                  &local_qiov, 0);
             if (ret < 0) {
                 goto fail;
diff --git a/block/io.c b/block/io.c
index f702efc..7086908 100644
--- a/block/io.c
+++ b/block/io.c
@@ -566,11 +566,11 @@
     RwCo *rwco = opaque;
 
     if (!rwco->is_write) {
-        rwco->ret = bdrv_co_preadv(rwco->child->bs, rwco->offset,
+        rwco->ret = bdrv_co_preadv(rwco->child, rwco->offset,
                                    rwco->qiov->size, rwco->qiov,
                                    rwco->flags);
     } else {
-        rwco->ret = bdrv_co_pwritev(rwco->child->bs, rwco->offset,
+        rwco->ret = bdrv_co_pwritev(rwco->child, rwco->offset,
                                     rwco->qiov->size, rwco->qiov,
                                     rwco->flags);
     }
@@ -1061,10 +1061,11 @@
 /*
  * Handle a read request in coroutine context
  */
-int coroutine_fn bdrv_co_preadv(BlockDriverState *bs,
+int coroutine_fn bdrv_co_preadv(BdrvChild *child,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags)
 {
+    BlockDriverState *bs = child->bs;
     BlockDriver *drv = bs->drv;
     BdrvTrackedRequest req;
 
@@ -1137,7 +1138,7 @@
         return -EINVAL;
     }
 
-    return bdrv_co_preadv(child->bs, sector_num << BDRV_SECTOR_BITS,
+    return bdrv_co_preadv(child, sector_num << BDRV_SECTOR_BITS,
                           nb_sectors << BDRV_SECTOR_BITS, qiov, flags);
 }
 
@@ -1406,10 +1407,11 @@
 /*
  * Handle a write request in coroutine context
  */
-int coroutine_fn bdrv_co_pwritev(BlockDriverState *bs,
+int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags)
 {
+    BlockDriverState *bs = child->bs;
     BdrvTrackedRequest req;
     uint64_t align = bs->bl.request_alignment;
     uint8_t *head_buf = NULL;
@@ -1543,7 +1545,7 @@
         return -EINVAL;
     }
 
-    return bdrv_co_pwritev(child->bs, sector_num << BDRV_SECTOR_BITS,
+    return bdrv_co_pwritev(child, sector_num << BDRV_SECTOR_BITS,
                            nb_sectors << BDRV_SECTOR_BITS, qiov, flags);
 }
 
@@ -1555,17 +1557,16 @@
     return bdrv_co_do_writev(child, sector_num, nb_sectors, qiov, 0);
 }
 
-int coroutine_fn bdrv_co_pwrite_zeroes(BlockDriverState *bs,
-                                       int64_t offset, int count,
-                                       BdrvRequestFlags flags)
+int coroutine_fn bdrv_co_pwrite_zeroes(BdrvChild *child, int64_t offset,
+                                       int count, BdrvRequestFlags flags)
 {
-    trace_bdrv_co_pwrite_zeroes(bs, offset, count, flags);
+    trace_bdrv_co_pwrite_zeroes(child->bs, offset, count, flags);
 
-    if (!(bs->open_flags & BDRV_O_UNMAP)) {
+    if (!(child->bs->open_flags & BDRV_O_UNMAP)) {
         flags &= ~BDRV_REQ_MAY_UNMAP;
     }
 
-    return bdrv_co_pwritev(bs, offset, count, NULL,
+    return bdrv_co_pwritev(child, offset, count, NULL,
                            BDRV_REQ_ZERO_WRITE | flags);
 }
 
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 6a3ad90..cf159f1 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -446,7 +446,7 @@
     }
 
     BLKDBG_EVENT(bs->file, BLKDBG_COW_WRITE);
-    ret = bdrv_co_pwritev(bs->file->bs, cluster_offset + offset_in_cluster,
+    ret = bdrv_co_pwritev(bs->file, cluster_offset + offset_in_cluster,
                           bytes, &qiov, 0);
     if (ret < 0) {
         goto out;
diff --git a/block/qcow2.c b/block/qcow2.c
index a289c12..8a2c568 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1443,7 +1443,7 @@
 
                     BLKDBG_EVENT(bs->file, BLKDBG_READ_BACKING_AIO);
                     qemu_co_mutex_unlock(&s->lock);
-                    ret = bdrv_co_preadv(bs->backing->bs, offset, n1,
+                    ret = bdrv_co_preadv(bs->backing, offset, n1,
                                          &local_qiov, 0);
                     qemu_co_mutex_lock(&s->lock);
 
@@ -1506,7 +1506,7 @@
 
             BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
             qemu_co_mutex_unlock(&s->lock);
-            ret = bdrv_co_preadv(bs->file->bs,
+            ret = bdrv_co_preadv(bs->file,
                                  cluster_offset + offset_in_cluster,
                                  cur_bytes, &hd_qiov, 0);
             qemu_co_mutex_lock(&s->lock);
@@ -1637,7 +1637,7 @@
         BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
         trace_qcow2_writev_data(qemu_coroutine_self(),
                                 cluster_offset + offset_in_cluster);
-        ret = bdrv_co_pwritev(bs->file->bs,
+        ret = bdrv_co_pwritev(bs->file,
                               cluster_offset + offset_in_cluster,
                               cur_bytes, &hd_qiov, 0);
         qemu_co_mutex_lock(&s->lock);
diff --git a/block/raw_bsd.c b/block/raw_bsd.c
index 90b296e..5f9dd29 100644
--- a/block/raw_bsd.c
+++ b/block/raw_bsd.c
@@ -105,7 +105,7 @@
     }
 
     BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
-    ret = bdrv_co_pwritev(bs->file->bs, sector_num * BDRV_SECTOR_SIZE,
+    ret = bdrv_co_pwritev(bs->file, sector_num * BDRV_SECTOR_SIZE,
                           nb_sectors * BDRV_SECTOR_SIZE, qiov, flags);
 
 fail:
@@ -131,7 +131,7 @@
                                              int64_t offset, int count,
                                              BdrvRequestFlags flags)
 {
-    return bdrv_co_pwrite_zeroes(bs->file->bs, offset, count, flags);
+    return bdrv_co_pwrite_zeroes(bs->file, offset, count, flags);
 }
 
 static int coroutine_fn raw_co_discard(BlockDriverState *bs,
diff --git a/block/vdi.c b/block/vdi.c
index a1a12d9..8a1cf97 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -597,7 +597,7 @@
             qemu_iovec_reset(&local_qiov);
             qemu_iovec_concat(&local_qiov, qiov, bytes_done, n_bytes);
 
-            ret = bdrv_co_preadv(bs->file->bs, data_offset, n_bytes,
+            ret = bdrv_co_preadv(bs->file, data_offset, n_bytes,
                                  &local_qiov, 0);
         }
         logout("%u bytes read\n", n_bytes);
@@ -690,7 +690,7 @@
             qemu_iovec_reset(&local_qiov);
             qemu_iovec_concat(&local_qiov, qiov, bytes_done, n_bytes);
 
-            ret = bdrv_co_pwritev(bs->file->bs, data_offset, n_bytes,
+            ret = bdrv_co_pwritev(bs->file, data_offset, n_bytes,
                                   &local_qiov, 0);
         }
 
diff --git a/block/vmdk.c b/block/vmdk.c
index ae70b63..d73f431 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1369,7 +1369,7 @@
     }
 
     write_offset = cluster_offset + offset_in_cluster,
-    ret = bdrv_co_pwritev(extent->file->bs, write_offset, n_bytes,
+    ret = bdrv_co_pwritev(extent->file, write_offset, n_bytes,
                           &local_qiov, 0);
 
     write_end_sector = DIV_ROUND_UP(write_offset + n_bytes, BDRV_SECTOR_SIZE);
@@ -1407,7 +1407,7 @@
 
 
     if (!extent->compressed) {
-        ret = bdrv_co_preadv(extent->file->bs,
+        ret = bdrv_co_preadv(extent->file,
                              cluster_offset + offset_in_cluster, bytes,
                              qiov, 0);
         if (ret < 0) {
@@ -1497,7 +1497,7 @@
                 qemu_iovec_reset(&local_qiov);
                 qemu_iovec_concat(&local_qiov, qiov, bytes_done, n_bytes);
 
-                ret = bdrv_co_preadv(bs->backing->bs, offset, n_bytes,
+                ret = bdrv_co_preadv(bs->backing, offset, n_bytes,
                                      &local_qiov, 0);
                 if (ret < 0) {
                     goto fail;
diff --git a/block/vpc.c b/block/vpc.c
index dcb5312..43707ed 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -591,7 +591,7 @@
     QEMUIOVector local_qiov;
 
     if (be32_to_cpu(footer->type) == VHD_FIXED) {
-        return bdrv_co_preadv(bs->file->bs, offset, bytes, qiov, 0);
+        return bdrv_co_preadv(bs->file, offset, bytes, qiov, 0);
     }
 
     qemu_co_mutex_lock(&s->lock);
@@ -607,7 +607,7 @@
             qemu_iovec_reset(&local_qiov);
             qemu_iovec_concat(&local_qiov, qiov, bytes_done, n_bytes);
 
-            ret = bdrv_co_preadv(bs->file->bs, image_offset, n_bytes,
+            ret = bdrv_co_preadv(bs->file, image_offset, n_bytes,
                                  &local_qiov, 0);
             if (ret < 0) {
                 goto fail;
@@ -640,7 +640,7 @@
     QEMUIOVector local_qiov;
 
     if (be32_to_cpu(footer->type) == VHD_FIXED) {
-        return bdrv_co_pwritev(bs->file->bs, offset, bytes, qiov, 0);
+        return bdrv_co_pwritev(bs->file, offset, bytes, qiov, 0);
     }
 
     qemu_co_mutex_lock(&s->lock);
@@ -661,7 +661,7 @@
         qemu_iovec_reset(&local_qiov);
         qemu_iovec_concat(&local_qiov, qiov, bytes_done, n_bytes);
 
-        ret = bdrv_co_pwritev(bs->file->bs, image_offset, n_bytes,
+        ret = bdrv_co_pwritev(bs->file, image_offset, n_bytes,
                               &local_qiov, 0);
         if (ret < 0) {
             goto fail;
diff --git a/include/block/block.h b/include/block/block.h
index 4eaa1c1..616d8b9 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -249,8 +249,8 @@
  * function is not suitable for zeroing the entire image in a single request
  * because it may allocate memory for the entire region.
  */
-int coroutine_fn bdrv_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
-    int count, BdrvRequestFlags flags);
+int coroutine_fn bdrv_co_pwrite_zeroes(BdrvChild *child, int64_t offset,
+                                       int count, BdrvRequestFlags flags);
 BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
     const char *backing_file);
 int bdrv_get_backing_file_depth(BlockDriverState *bs);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 0432ba5..47b9aac 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -563,10 +563,10 @@
  */
 void bdrv_setup_io_funcs(BlockDriver *bdrv);
 
-int coroutine_fn bdrv_co_preadv(BlockDriverState *bs,
+int coroutine_fn bdrv_co_preadv(BdrvChild *child,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags);
-int coroutine_fn bdrv_co_pwritev(BlockDriverState *bs,
+int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags);