Commit 54a4ef8a authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Darrick J. Wong
Browse files

xfs: reject all unaligned direct writes to reflinked files 



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>
parent 4dd2eb63

fs/xfs/xfs_file.c

+9 −0
Original line number Diff line number Diff line
@@ -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;

fs/xfs/xfs_iomap.c

+1 −11
Original line number Diff line number Diff line
@@ -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)) {

fs/xfs/xfs_trace.h

+1 −1
Original line number Diff line number Diff line
@@ -3249,7 +3249,7 @@ 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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