block-backend: Add .drained_poll callback

A bdrv_drain operation must ensure that all parents are quiesced, this
includes BlockBackends. Otherwise, callbacks called by requests that are
completed on the BDS layer, but not quite yet on the BlockBackend layer
could still create new requests.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/block/block-backend.c b/block/block-backend.c
index 14a1b7ac6a..4e7d08ac3a 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -121,6 +121,7 @@ static void blk_root_inherit_options(int *child_flags, QDict *child_options,
     abort();
 }
 static void blk_root_drained_begin(BdrvChild *child);
+static bool blk_root_drained_poll(BdrvChild *child);
 static void blk_root_drained_end(BdrvChild *child);
 
 static void blk_root_change_media(BdrvChild *child, bool load);
@@ -294,6 +295,7 @@ static const BdrvChildRole child_root = {
     .get_parent_desc    = blk_root_get_parent_desc,
 
     .drained_begin      = blk_root_drained_begin,
+    .drained_poll       = blk_root_drained_poll,
     .drained_end        = blk_root_drained_end,
 
     .activate           = blk_root_activate,
@@ -2189,6 +2191,13 @@ static void blk_root_drained_begin(BdrvChild *child)
     }
 }
 
+static bool blk_root_drained_poll(BdrvChild *child)
+{
+    BlockBackend *blk = child->opaque;
+    assert(blk->quiesce_counter);
+    return !!blk->in_flight;
+}
+
 static void blk_root_drained_end(BdrvChild *child)
 {
     BlockBackend *blk = child->opaque;