xfs: don't mix reflink and DAX mode for now

Since we don't have a strategy for handling both DAX and reflink,
for now we'll just prohibit both being set at the same time.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 0726df8..54c27ed 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1055,6 +1055,10 @@
 	if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
 		return -EINVAL;
 
+	/* Don't share DAX file data for now. */
+	if (IS_DAX(inode_in) || IS_DAX(inode_out))
+		return -EINVAL;
+
 	/* Are we going all the way to the end? */
 	isize = i_size_read(inode_in);
 	if (isize == 0)