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authorAlberto Garcia <berto@igalia.com>2015-10-28 15:43:49 +0200
committerKevin Wolf <kwolf@redhat.com>2015-11-11 16:25:47 +0100
commit3db2bd5508c86a1605258bc77c9672d93b5c350e (patch)
tree430d334eb2a56fe4b7063933fa0d641fb94fbdf0 /block
parent89e3a2d86d31212d09ca688193ccecb92c0c77b5 (diff)
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commit: reopen overlay_bs before base
'block-commit' needs write access to two different nodes of the chain: - 'base', because that's where the data is written to. - the overlay of 'top', because it needs to update the backing file string to point to 'base' after the operation. Both images have to be opened in read-write mode, and commit_start() takes care of reopening them if necessary. With the current implementation, however, when overlay_bs is reopened in read-write mode it has the side effect of making 'base' read-only again, eventually making 'block-commit' fail. This needs to be fixed in bdrv_reopen(), but until we get to that it can be worked around simply by swapping the order of base and overlay_bs in the reopen queue. In order to reproduce this bug, overlay_bs needs to be initially in read-only mode. That is: the 'top' parameter of 'block-commit' cannot be the active layer nor its immediate backing chain. Cc: qemu-stable@nongnu.org Signed-off-by: Alberto Garcia <berto@igalia.com> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'block')
-rw-r--r--block/commit.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/block/commit.c b/block/commit.c
index fdebe87..a5d02aa 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -236,14 +236,14 @@ void commit_start(BlockDriverState *bs, BlockDriverState *base,
orig_overlay_flags = bdrv_get_flags(overlay_bs);
/* convert base & overlay_bs to r/w, if necessary */
- if (!(orig_base_flags & BDRV_O_RDWR)) {
- reopen_queue = bdrv_reopen_queue(reopen_queue, base, NULL,
- orig_base_flags | BDRV_O_RDWR);
- }
if (!(orig_overlay_flags & BDRV_O_RDWR)) {
reopen_queue = bdrv_reopen_queue(reopen_queue, overlay_bs, NULL,
orig_overlay_flags | BDRV_O_RDWR);
}
+ if (!(orig_base_flags & BDRV_O_RDWR)) {
+ reopen_queue = bdrv_reopen_queue(reopen_queue, base, NULL,
+ orig_base_flags | BDRV_O_RDWR);
+ }
if (reopen_queue) {
bdrv_reopen_multiple(reopen_queue, &local_err);
if (local_err != NULL) {