block: add bdrv_graph_wrlock_drained() convenience wrapper

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>

1 files changed, 2 insertions, 8 deletions

diff --git a/blockjob.c b/blockjob.c
index e68181a35b..db7c3a69a0 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -198,8 +198,7 @@ void block_job_remove_all_bdrv(BlockJob *job)
      * one to make sure that such a concurrent access does not attempt
      * to process an already freed BdrvChild.
      */
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     while (job->nodes) {
         GSList *l = job->nodes;
         BdrvChild *c = l->data;
@@ -212,7 +211,6 @@ void block_job_remove_all_bdrv(BlockJob *job)
         g_slist_free_1(l);
     }
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 }
 
 bool block_job_has_bdrv(BlockJob *job, BlockDriverState *bs)
@@ -498,8 +496,7 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
     int ret;
     GLOBAL_STATE_CODE();
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
 
     if (job_id == NULL && !(flags & JOB_INTERNAL)) {
         job_id = bdrv_get_device_name(bs);
@@ -509,7 +506,6 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
                      flags, cb, opaque, errp);
     if (job == NULL) {
         bdrv_graph_wrunlock();
-        bdrv_drain_all_end();
         return NULL;
     }
 
@@ -548,12 +544,10 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
     }
 
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
     return job;
 
 fail:
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
     job_early_fail(&job->job);
     return NULL;
 }