[Qemu-block] [PATCH v3] block/file-posix: do not fail on unlock bytes

[Vladimir Sementsov-Ogievskiy]

bdrv_replace_child() calls bdrv_check_perm() with error_abort on
loosening permissions. However file-locking operations may fail even
in this case, for example on NFS. And this leads to Qemu crash.

Let's avoid such errors. Note, that we ignore such things anyway on
permission update commit and abort.

Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
 block/file-posix.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/block/file-posix.c b/block/file-posix.c
index db4cccbe51..1cf4ee49eb 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -815,6 +815,18 @@ static int raw_handle_perm_lock(BlockDriverState *bs,
 
     switch (op) {
     case RAW_PL_PREPARE:
+        if ((s->perm | new_perm) == s->perm &&
+            (s->shared_perm & new_shared) == s->shared_perm)
+        {
+            /*
+             * We are going to unlock bytes, it should not fail. If it fail due
+             * to some fs-dependent permission-unrelated reasons (which occurs
+             * sometimes on NFS and leads to abort in bdrv_replace_child) we
+             * can't prevent such errors by any check here. And we ignore them
+             * anyway in ABORT and COMMIT.
+             */
+            return 0;
+        }
         ret = raw_apply_lock_bytes(s, s->fd, s->perm | new_perm,
                                    ~s->shared_perm | ~new_shared,
                                    false, errp);
-- 
2.18.0