[PATCH 05/43] xfs: refine the unaligned check for always COW inodes in xfs_file_dio_write

Christoph Hellwig
2025-02-06T06:45:25Z

For always COW inodes we also must check the alignment of each individual
iovec segment, as they could end up with different I/Os due to the way
bio_iov_iter_get_pages works, and we'd then overwrite an already written
block. The existing always_cow sysctl based code doesn't catch this
because nothing enforces that blocks aren't rewritten, but for zoned XFS
on sequential write required zones this is a hard error.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
---
fs/xfs/xfs_file.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 785f6bbf1406..d88a771d4c23 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -721,7 +721,16 @@ xfs_file_dio_write(
/* direct I/O must be aligned to device logical sector size */
if ((iocb->ki_pos | count) & target->bt_logical_sectormask)
return -EINVAL;
- if ((iocb->ki_pos | count) & ip->i_mount->m_blockmask)
+
+ /*
+ * For always COW inodes we also must check the alignment of each
+ * individual iovec segment, as they could end up with different
+ * I/Os due to the way bio_iov_iter_get_pages works, and we'd
+ * then overwrite an already written block.
+ */
+ if (((iocb->ki_pos | count) & ip->i_mount->m_blockmask) ||
+ (xfs_is_always_cow_inode(ip) &&
+ (iov_iter_alignment(from) & ip->i_mount->m_blockmask)))
return xfs_file_dio_write_unaligned(ip, iocb, from);
return xfs_file_dio_write_aligned(ip, iocb, from);
}
--
2.45.2