From 5bbf5ba693ac6dc323d6608740311c34b978e986 Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Mon, 6 Feb 2017 13:00:54 -0800 Subject: xfs: reject all unaligned direct writes to reflinked files commit 54a4ef8af4e0dc5c983d17fcb9cf5fd25666d94e 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: Christoph Hellwig Reviewed-by: Brian Foster Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong [slight changes in context due to the new direct I/O code in 4.10+] Signed-off-by: Greg Kroah-Hartman --- fs/xfs/xfs_file.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'fs/xfs/xfs_file.c') diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 780be7a7abe9..1209ad29e902 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -554,6 +554,15 @@ 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; -- cgit v1.2.3