[v2,1/6] block: skip implicit nodes in snapshots, blockjobs

diff --git a/block.c b/block.c
index 3615a6809e..e35d546c08 100644
--- a/block.c
+++ b/block.c
@@ -4945,3 +4945,13 @@  bool bdrv_can_store_new_dirty_bitmap(BlockDriverState *bs, const char *name,
 
     return drv->bdrv_can_store_new_dirty_bitmap(bs, name, granularity, errp);
 }
+
+/* Get first explicit node down a bs chain. */
+BlockDriverState *bdrv_get_first_explicit(BlockDriverState *bs)
+{
+    while (bs && bs->drv && bs->implicit) {
+        bs = child_bs(bs);
+        assert(bs);
+    }
+    return bs;
+}
diff --git a/block/qapi.c b/block/qapi.c
index 7fa2437923..847b044d13 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -147,9 +147,8 @@  BlockDeviceInfo *bdrv_block_device_info(BlockBackend *blk,
 
         /* Skip automatically inserted nodes that the user isn't aware of for
          * query-block (blk != NULL), but not for query-named-block-nodes */
-        while (blk && bs0->drv && bs0->implicit) {
-            bs0 = backing_bs(bs0);
-            assert(bs0);
+        if (blk) {
+            bs0 = bdrv_get_first_explicit(bs0);
         }
     }
 
@@ -336,9 +335,7 @@  static void bdrv_query_info(BlockBackend *blk, BlockInfo **p_info,
     char *qdev;
 
     /* Skip automatically inserted nodes that the user isn't aware of */
-    while (bs && bs->drv && bs->implicit) {
-        bs = backing_bs(bs);
-    }
+    bs = bdrv_get_first_explicit(bs);
 
     info->device = g_strdup(blk_name(blk));
     info->type = g_strdup("unknown");
@@ -465,9 +462,8 @@  static BlockStats *bdrv_query_bds_stats(BlockDriverState *bs,
     /* Skip automatically inserted nodes that the user isn't aware of in
      * a BlockBackend-level command. Stay at the exact node for a node-level
      * command. */
-    while (blk_level && bs->drv && bs->implicit) {
-        bs = backing_bs(bs);
-        assert(bs);
+    if (blk_level) {
+        bs = bdrv_get_first_explicit(bs);
     }
 
     if (bdrv_get_node_name(bs)[0]) {
diff --git a/blockdev.c b/blockdev.c
index 23475abb72..fc7b65c3f0 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1300,6 +1300,10 @@  SnapshotInfo *qmp_blockdev_snapshot_delete_internal_sync(const char *device,
     if (!bs) {
         return NULL;
     }
+
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
@@ -1508,6 +1512,9 @@  static void internal_snapshot_prepare(BlkActionState *common,
         return;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     /* AioContext is released in .clean() */
     state->aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(state->aio_context);
@@ -1664,6 +1671,9 @@  static void external_snapshot_prepare(BlkActionState *common,
         return;
     }
 
+    /* Skip implicit filter nodes */
+    state->old_bs = bdrv_get_first_explicit(state->old_bs);
+
     /* Acquire AioContext now so any threads operating on old_bs stop */
     state->aio_context = bdrv_get_aio_context(state->old_bs);
     aio_context_acquire(state->aio_context);
@@ -1844,6 +1854,9 @@  static void drive_backup_prepare(BlkActionState *common, Error **errp)
         return;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     /* AioContext is released in .clean() */
     state->aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(state->aio_context);
@@ -1908,6 +1921,9 @@  static void blockdev_backup_prepare(BlkActionState *common, Error **errp)
         return;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     target = bdrv_lookup_bs(backup->target, backup->target, errp);
     if (!target) {
         return;
@@ -2988,6 +3004,9 @@  void qmp_block_stream(bool has_job_id, const char *job_id, const char *device,
         return;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
@@ -3095,6 +3114,9 @@  void qmp_block_commit(bool has_job_id, const char *job_id, const char *device,
         return;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
@@ -3209,6 +3231,9 @@  static BlockJob *do_drive_backup(DriveBackup *backup, BlockJobTxn *txn,
         return NULL;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
@@ -3484,6 +3509,9 @@  void qmp_drive_mirror(DriveMirror *arg, Error **errp)
         return;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
@@ -3638,6 +3666,9 @@  void qmp_blockdev_mirror(bool has_job_id, const char *job_id,
         return;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     target_bs = bdrv_lookup_bs(target, target, errp);
     if (!target_bs) {
         return;
@@ -3786,6 +3817,9 @@  void qmp_change_backing_file(const char *device,
         return;
     }
 
+    /* Skip implicit filter nodes */
+    bs = bdrv_get_first_explicit(bs);
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
 
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 7571c0aaaf..8353b83e86 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -699,6 +699,13 @@  static inline BlockDriverState *backing_bs(BlockDriverState *bs)
     return bs->backing ? bs->backing->bs : NULL;
 }
 
+static inline BlockDriverState *child_bs(BlockDriverState *bs)
+{
+    BdrvChild *child = QLIST_FIRST(&bs->children);
+    assert(child && !QLIST_NEXT(child, next));
+    return child->bs;
+}
+
 
 /* Essential block drivers which must always be statically linked into qemu, and
  * which therefore can be accessed without using bdrv_find_format() */
@@ -980,4 +987,6 @@  void bdrv_dec_in_flight(BlockDriverState *bs);
 
 void blockdev_close_all_bdrv_states(void);
 
+BlockDriverState *bdrv_get_first_explicit(BlockDriverState *bs);
+
 #endif /* BLOCK_INT_H */