[PATCH v6 6/7] xfs: Validate atomic writes

[John Garry <john.g.garry@oracle.com>]

Validate that an atomic write adheres to length/offset rules. Currently
we can only write a single FS block.

For an IOCB with IOCB_ATOMIC set to get as far as xfs_file_dio_write(),
FMODE_CAN_ATOMIC_WRITE will need to be set for the file; for this,
ATOMICWRITES flags would also need to be set for the inode.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 fs/xfs/xfs_file.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 412b1d71b52b..fa6a44b88ecc 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -688,6 +688,13 @@ xfs_file_dio_write(
 	struct xfs_buftarg      *target = xfs_inode_buftarg(ip);
 	size_t			count = iov_iter_count(from);
 
+	if (iocb->ki_flags & IOCB_ATOMIC) {
+		if (count != ip->i_mount->m_sb.sb_blocksize)
+			return -EINVAL;
+		if (!generic_atomic_write_valid(iocb, from))
+			return -EINVAL;
+	}
+
 	/* direct I/O must be aligned to device logical sector size */
 	if ((iocb->ki_pos | count) & target->bt_logical_sectormask)
 		return -EINVAL;
-- 
2.31.1