[Qemu-devel] [PATCH 02/12] migration: Don't lose errno across aio context changes

[Eric Blake <eblake@redhat.com>]

set_drity_tracking() was assuming that the errno value set by
bdrv_create_dirty_bitmap() would not be corrupted by either
blk_get_aio_context() or aio_context_release().  Rather than
audit whether this assumption is safe, rewrite the code to just
grab the value of errno sooner.

CC: qemu-stable@nongnu.org
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 migration/block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/migration/block.c b/migration/block.c
index 18d50ff..9a9c214 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -350,9 +350,9 @@ static int set_dirty_tracking(void)
         aio_context_acquire(blk_get_aio_context(bmds->blk));
         bmds->dirty_bitmap = bdrv_create_dirty_bitmap(blk_bs(bmds->blk),
                                                       BLOCK_SIZE, NULL, NULL);
+        ret = -errno;
         aio_context_release(blk_get_aio_context(bmds->blk));
         if (!bmds->dirty_bitmap) {
-            ret = -errno;
             goto fail;
         }
     }
-- 
2.9.3