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block/file-posix: Let post-EOF fallocate serialize

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The XFS kernel driver has a bug that may cause data corruption for qcow2
images as of qemu commit c8bb23cbdb.  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 <mreitz@redhat.com>
Message-id: 20191101152510.11719-4-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Max Reitz 2019-11-01 16:25:10 +01:00
parent c28107e9e5
commit 292d06b925
1 changed files with 36 additions and 0 deletions
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36
block/file-posix.c
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@ -2721,6 +2721,42 @@ 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,