[Qemu-devel] [PATCH RFC] file-posix: make lock_fd read-only

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

We do not reopen lock_fd on bdrv_reopen which leads to problems on
reopen image RO. So, lets make lock_fd be always RO.
This is correct, because qemu_lock_fd always called with exclusive=false
on lock_fd.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---

Hi all!

We've faced the following problem with our shared-storage migration
scheme. We make an external snapshot and need base image to be reopened
RO. However, bdrv_reopen reopens only .fd of BDRVRawState but not
.lock_fd. So, .lock_fd is left opened RW and this breaks the whole
thing.

The simple fix is here: let's just open lock_fd as RO always. This
looks fine for current code, as we never try to set write locks
(qemu_lock_fd always called with exclusive=false).

However it will not work if we are going to use write locks.


 block/file-posix.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 36ee89e940..5c52df9174 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -514,7 +514,8 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
 
     s->lock_fd = -1;
     if (s->use_lock) {
-        fd = qemu_open(filename, s->open_flags);
+        /* open it read-only, as we do not reopen it on bdrv_reopen */
+        fd = qemu_open(filename, (s->open_flags & ~BDRV_O_RDWR));
         if (fd < 0) {
             ret = -errno;
             error_setg_errno(errp, errno, "Could not open '%s' for locking",
-- 
2.11.1