Commit 900c499d authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Greg Kroah-Hartman

xfs: reject all unaligned direct writes to reflinked files

commit 54a4ef8a upstream.

We currently fall back from direct to buffered writes if we detect a
remaining shared extent in the iomap_begin callback.  But by the time
iomap_begin is called for the potentially unaligned end block we might
have already written most of the data to disk, which we'd now write
again using buffered I/O.  To avoid this reject all writes to reflinked
files before starting I/O so that we are guaranteed to only write the
data once.

The alternative would be to unshare the unaligned start and/or end block
before doing the I/O. I think that's doable, and will actually be
required to support reflinks on DAX file system.  But it will take a
little more time and I'd rather get rid of the double write ASAP.
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarBrian Foster <bfoster@redhat.com>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 17c17805
......@@ -527,6 +527,15 @@ xfs_file_dio_aio_write(
if ((iocb->ki_pos & mp->m_blockmask) ||
((iocb->ki_pos + count) & mp->m_blockmask)) {
unaligned_io = 1;
/*
* We can't properly handle unaligned direct I/O to reflink
* files yet, as we can't unshare a partial block.
*/
if (xfs_is_reflink_inode(ip)) {
trace_xfs_reflink_bounce_dio_write(ip, iocb->ki_pos, count);
return -EREMCHG;
}
iolock = XFS_IOLOCK_EXCL;
} else {
iolock = XFS_IOLOCK_SHARED;
......
......@@ -1026,17 +1026,7 @@ xfs_file_iomap_begin(
if (error)
goto out_unlock;
/*
* We're here because we're trying to do a directio write to a
* region that isn't aligned to a filesystem block. If the
* extent is shared, fall back to buffered mode to handle the
* RMW.
*/
if (!(flags & IOMAP_REPORT) && shared) {
trace_xfs_reflink_bounce_dio_write(ip, &imap);
error = -EREMCHG;
goto out_unlock;
}
ASSERT((flags & IOMAP_REPORT) || !shared);
}
if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) {
......
......@@ -3250,7 +3250,7 @@ DEFINE_INODE_IREC_EVENT(xfs_reflink_convert_cow);
DEFINE_RW_EVENT(xfs_reflink_reserve_cow);
DEFINE_RW_EVENT(xfs_reflink_allocate_cow_range);
DEFINE_INODE_IREC_EVENT(xfs_reflink_bounce_dio_write);
DEFINE_SIMPLE_IO_EVENT(xfs_reflink_bounce_dio_write);
DEFINE_IOMAP_EVENT(xfs_reflink_find_cow_mapping);
DEFINE_INODE_IREC_EVENT(xfs_reflink_trim_irec);
......
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