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block: ignore_bds_parents parameter for drain functions

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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>
This commit is contained in:
Kevin Wolf 2018-05-29 17:17:45 +02:00
parent c8ca33d06d
commit 6cd5c9d7b2
5 changed files with 78 additions and 44 deletions
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6
include/block/block_int.h
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@ -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);