block: introduce assert_bdrv_graph_writable

We want to be sure that the functions that write the child and
parent list of a bs are under BQL and drain.

BQL prevents from concurrent writings from the GS API, while
drains protect from I/O.

TODO: drains are missing in some functions using this assert.
Therefore a proper assertion will fail. Because adding drains
requires additional discussions, they will be added in future
series.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20220303151616.325444-15-eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/block.c b/block.c
index f2a7350548..fe05df471a 100644
--- a/block.c
+++ b/block.c
@@ -1420,6 +1420,7 @@ static void bdrv_child_cb_attach(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
 
+    assert_bdrv_graph_writable(bs);
     QLIST_INSERT_HEAD(&bs->children, child, next);
 
     if (child->role & BDRV_CHILD_COW) {
@@ -1439,6 +1440,7 @@ static void bdrv_child_cb_detach(BdrvChild *child)
 
     bdrv_unapply_subtree_drain(child, bs);
 
+    assert_bdrv_graph_writable(bs);
     QLIST_REMOVE(child, next);
 }
 
@@ -2829,6 +2831,7 @@ static void bdrv_replace_child_noperm(BdrvChild **childp,
         if (child->klass->detach) {
             child->klass->detach(child);
         }
+        assert_bdrv_graph_writable(old_bs);
         QLIST_REMOVE(child, next_parent);
     }
 
@@ -2838,6 +2841,7 @@ static void bdrv_replace_child_noperm(BdrvChild **childp,
     }
 
     if (new_bs) {
+        assert_bdrv_graph_writable(new_bs);
         QLIST_INSERT_HEAD(&new_bs->parents, child, next_parent);
 
         /*