qcow2_header_updated() is the final call during image close. This means after this point we will have no IO operations on this file descriptor. This assumption has been validated via 'strace' which clearly confirms that this is very final write and there is no sync after this point.
There is almost no problem when the image is residing in local filesystem except that we will have image check if the chage will not reach disk before powerloss, but with a network or distributed filesystem we come to trouble. The change could be in flight and we can miss this data on other node like during migration. The patch adds BDRV_REQ_FUA to the write request to do the trick. Signed-off-by: Denis V. Lunev <[email protected]> CC: Kevin Wolf <[email protected]> CC: Hanna Reitz <[email protected]> --- block/qcow2.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/qcow2.c b/block/qcow2.c index e29810d86a..abbc4e82ba 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -3252,7 +3252,7 @@ int qcow2_update_header(BlockDriverState *bs) } /* Write the new header */ - ret = bdrv_pwrite(bs->file, 0, s->cluster_size, header, 0); + ret = bdrv_pwrite(bs->file, 0, s->cluster_size, header, BDRV_REQ_FUA); if (ret < 0) { goto fail; } -- 2.51.0
