[Qemu-devel] [PATCH 3/3] block: acquire AioContext is qmp_query_blockstats()

[Stefan Hajnoczi <stefanha@redhat.com>]

Make query-blockstats safe for dataplane by acquiring the
BlockDriverState's AioContext.  This ensures that the dataplane IOThread
and the main loop's monitor code do not race.

Note the assumption that acquiring the drive's BDS AioContext also
protects ->file and ->backing_hd.  This assumption is made by other
aio_context_acquire() callers too.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/qapi.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/qapi.c b/block/qapi.c
index aeabaaf..f44f6b4 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -360,7 +360,11 @@ BlockStatsList *qmp_query_blockstats(Error **errp)
 
      while ((bs = bdrv_next(bs))) {
         BlockStatsList *info = g_malloc0(sizeof(*info));
+        AioContext *ctx = bdrv_get_aio_context(bs);
+
+        aio_context_acquire(ctx);
         info->value = bdrv_query_stats(bs);
+        aio_context_release(ctx);
 
         *p_next = info;
         p_next = &info->next;
-- 
1.9.3