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block: add bdrv_graph_wrlock_drained() convenience wrapper

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Many write-locked sections are also drained sections. A new
bdrv_graph_wrunlock_drained() wrapper around bdrv_graph_wrunlock() is
introduced, which will begin a drained section first. A global
variable is used so bdrv_graph_wrunlock() knows if it also needs
to end such a drained section. Both the aio_poll call in
bdrv_graph_wrlock() and the aio_bh_poll() in bdrv_graph_wrunlock()
can re-enter a write-locked section. While for the latter, ending the
drain could be moved to before the call, the former requires that the
variable is a counter and not just a boolean.

Since the wrapper calls bdrv_drain_all_begin(), which must be called
with the graph unlocked, mark the wrapper as GRAPH_UNLOCKED too.

The switch to the new helpers was generated with the following
commands and then manually checked:
find . -name '*.c' -exec sed -i -z 's/bdrv_drain_all_begin();\n\s*bdrv_graph_wrlock();/bdrv_graph_wrlock_drained();/g' {} ';'
find . -name '*.c' -exec sed -i -z 's/bdrv_graph_wrunlock();\n\s*bdrv_drain_all_end();/bdrv_graph_wrunlock();/g' {} ';'

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20250530151125.955508-25-f.ebner@proxmox.com>
[kwolf: Removed redundant GRAPH_UNLOCKED]
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fiona Ebner 2025-05-30 17:11:01 +02:00 • committed by Kevin Wolf
parent 502f00c51a
commit 6b89e851fa
19 changed files with 90 additions and 141 deletions
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6
block/commit.c
View file

@ -392,8 +392,7 @@ void commit_start(const char *job_id, BlockDriverState *bs,
* this is the responsibility of the interface (i.e. whoever calls
* commit_start()).
*/
bdrv_drain_all_begin();
bdrv_graph_wrlock();
bdrv_graph_wrlock_drained();
s->base_overlay = bdrv_find_overlay(top, base);
assert(s->base_overlay);
@ -425,21 +424,18 @@ void commit_start(const char *job_id, BlockDriverState *bs,
iter_shared_perms, errp);
if (ret < 0) {
bdrv_graph_wrunlock();
bdrv_drain_all_end();
goto fail;
}
}
if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
bdrv_graph_wrunlock();
bdrv_drain_all_end();
goto fail;
}
s->chain_frozen = true;
ret = block_job_add_bdrv(&s->common, "base", base, 0, BLK_PERM_ALL, errp);
bdrv_graph_wrunlock();
bdrv_drain_all_end();
if (ret < 0) {
goto fail;