block: Allow graph changes in subtree drained section

We need to remember how many of the drain sections in which a node is
were recursive (i.e. subtree drain rather than node drain), so that they
can be correctly applied when children are added or removed during the
drained section.

With this change, it is safe to modify the graph even inside a
bdrv_subtree_drained_begin/end() section.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 5 insertions, 2 deletions

diff --git a/include/block/block.h b/include/block/block.h
index de9c5a2..9b12774 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -610,8 +610,6 @@ void bdrv_drained_begin(BlockDriverState *bs);
 /**
  * Like bdrv_drained_begin, but recursively begins a quiesced section for
  * exclusive access to all child nodes as well.
- *
- * Graph changes are not allowed during a subtree drain section.
  */
 void bdrv_subtree_drained_begin(BlockDriverState *bs);
 
diff --git a/include/block/block_int.h b/include/block/block_int.h
index e107163..29cafa4 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -717,6 +717,8 @@ struct BlockDriverState {
 
     /* Accessed with atomic ops.  */
     int quiesce_counter;
+    int recursive_quiesce_counter;
+
     unsigned int write_gen;               /* Current data generation */
 
     /* Protected by reqs_lock.  */
@@ -768,6 +770,9 @@ int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags);
 
+void bdrv_apply_subtree_drain(BdrvChild *child, BlockDriverState *new_parent);
+void bdrv_unapply_subtree_drain(BdrvChild *child, BlockDriverState *old_parent);
+
 int get_tmp_filename(char *filename, int size);
 BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
                             const char *filename);