block: ignore_bds_parents parameter for drain functions

In the future, bdrv_drained_all_begin/end() will drain all invidiual
nodes separately rather than whole subtrees. This means that we don't
want to propagate the drain to all parents any more: If the parent is a
BDS, it will already be drained separately. Recursing to all parents is
unnecessary work and would make it an O(n²) operation.

Prepare the drain function for the changed drain_all by adding an
ignore_bds_parents parameter to the internal implementation that
prevents the propagation of the drain to BDS parents. We still (have to)
propagate it to non-BDS parents like BlockBackends or Jobs because those
are not drained separately.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 1b811db8ec..1abfc26d76 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -577,6 +577,12 @@ struct BdrvChildRole {
      * points to. */
     bool stay_at_node;
 
+    /* If true, the parent is a BlockDriverState and bdrv_next_all_states()
+     * will return it. This information is used for drain_all, where every node
+     * will be drained separately, so the drain only needs to be propagated to
+     * non-BDS parents. */
+    bool parent_is_bds;
+
     void (*inherit_options)(int *child_flags, QDict *child_options,
                             int parent_flags, QDict *parent_options);