From: Max Reitz Date: Fri, 1 Nov 2019 16:25:10 +0100 Subject: block/file-posix: Let post-EOF fallocate serialize Git-commit: 292d06b925b2787ee6f2430996b95651cae42fce The XFS kernel driver has a bug that may cause data corruption for qcow2 images as of qemu commit c8bb23cbdbe32f. We can work around it by treating post-EOF fallocates as serializing up until infinity (INT64_MAX in practice). Cc: qemu-stable@nongnu.org Signed-off-by: Max Reitz Message-id: 20191101152510.11719-4-mreitz@redhat.com Signed-off-by: Max Reitz Signed-off-by: Bruce Rogers --- block/file-posix.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index 992eb4a798b99fe02e93103028c6..c5df61b47735ee7e5201cebec46c 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -2623,6 +2623,42 @@ raw_do_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int bytes, RawPosixAIOData acb; ThreadPoolFunc *handler; +#ifdef CONFIG_FALLOCATE + if (offset + bytes > bs->total_sectors * BDRV_SECTOR_SIZE) { + BdrvTrackedRequest *req; + uint64_t end; + + /* + * This is a workaround for a bug in the Linux XFS driver, + * where writes submitted through the AIO interface will be + * discarded if they happen beyond a concurrently running + * fallocate() that increases the file length (i.e., both the + * write and the fallocate() happen beyond the EOF). + * + * To work around it, we extend the tracked request for this + * zero write until INT64_MAX (effectively infinity), and mark + * it as serializing. + * + * We have to enable this workaround for all filesystems and + * AIO modes (not just XFS with aio=native), because for + * remote filesystems we do not know the host configuration. + */ + + req = bdrv_co_get_self_request(bs); + assert(req); + assert(req->type == BDRV_TRACKED_WRITE); + assert(req->offset <= offset); + assert(req->offset + req->bytes >= offset + bytes); + + end = INT64_MAX & -(uint64_t)bs->bl.request_alignment; + req->bytes = end - req->offset; + req->overlap_bytes = req->bytes; + + bdrv_mark_request_serialising(req, bs->bl.request_alignment); + bdrv_wait_serialising_requests(req); + } +#endif + acb = (RawPosixAIOData) { .bs = bs, .aio_fildes = s->fd,