[RFC PATCH 4/6] block.c: add subtree_drains where needed

[Emanuele Giuseppe Esposito]

Protect bdrv_replace_child_noperm, as it modifies the
graph by adding/removing elements to .children and .parents
list of a bs.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/block.c b/block.c
index 3c3c90704c..1aa9e51a98 100644
--- a/block.c
+++ b/block.c
@@ -2369,7 +2369,11 @@ static void bdrv_replace_child_abort(void *opaque)
      * So whether new_bs was NULL or not, we cannot pass s->childp here; and in
      * any case, there is no reason to pass it anyway.
      */
+    bdrv_subtree_drained_begin_unlocked(s->child->bs);
+    bdrv_subtree_drained_begin_unlocked(s->old_bs);
     bdrv_replace_child_noperm(&s->child, s->old_bs, true);
+    bdrv_subtree_drained_end_unlocked(s->old_bs);
+    bdrv_subtree_drained_end_unlocked(s->child->bs);
     /*
      * The child was pre-existing, so s->old_bs must be non-NULL, and
      * s->child thus must not have been freed
@@ -2427,13 +2431,20 @@ static void bdrv_replace_child_tran(BdrvChild **childp,
 
     if (new_bs) {
         bdrv_ref(new_bs);
+        bdrv_subtree_drained_begin_unlocked(new_bs);
     }
     /*
      * Pass free_empty_child=false, we will free the child (if
      * necessary) in bdrv_replace_child_commit() (if our
      * @free_empty_child parameter was true).
      */
+    bdrv_subtree_drained_begin_unlocked(s->old_bs);
     bdrv_replace_child_noperm(childp, new_bs, false);
+    bdrv_subtree_drained_end_unlocked(s->old_bs);
+
+    if (new_bs) {
+        bdrv_subtree_drained_end_unlocked(new_bs);
+    }
     /* old_bs reference is transparently moved from *childp to @s */
 }
 
@@ -2951,7 +2962,9 @@ static void bdrv_attach_child_common_abort(void *opaque)
      * need to keep it as an empty shell (after this function, it will
      * not be attached to any parent, and it will not have a .bs).
      */
+    bdrv_subtree_drained_begin_unlocked(bs);
     bdrv_replace_child_noperm(s->child, NULL, false);
+    bdrv_subtree_drained_end_unlocked(bs);
 
     if (bdrv_get_aio_context(bs) != s->old_child_ctx) {
         bdrv_try_set_aio_context(bs, s->old_child_ctx, &error_abort);
@@ -3051,7 +3064,10 @@ static int bdrv_attach_child_common(BlockDriverState 
*child_bs,
     }
 
     bdrv_ref(child_bs);
+
+    bdrv_subtree_drained_begin_unlocked(child_bs);
     bdrv_replace_child_noperm(&new_child, child_bs, true);
+    bdrv_subtree_drained_end_unlocked(child_bs);
     /* child_bs was non-NULL, so new_child must not have been freed */
     assert(new_child != NULL);
 
@@ -3114,8 +3130,16 @@ static void bdrv_detach_child(BdrvChild **childp)
     BlockDriverState *old_bs = (*childp)->bs;
 
     assert(qemu_in_main_thread());
+    if (old_bs) {
+        bdrv_subtree_drained_begin(old_bs);
+    }
+
     bdrv_replace_child_noperm(childp, NULL, true);
 
+    if (old_bs) {
+        bdrv_subtree_drained_end(old_bs);
+    }
+
     if (old_bs) {
         /*
          * Update permissions for old node. We're just taking a parent away, so
-- 
2.31.1