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_ioctl.c b/fs/xfs/xfs_ioctl.c
index c65d9ea..8b9f31c5 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1038,6 +1038,10 @@
 	if ((fa->fsx_xflags & FS_XFLAG_REALTIME) && xfs_is_reflink_inode(ip))
 		return -EINVAL;
 
+	/* Don't allow us to set DAX mode for a reflinked file for now. */
+	if ((fa->fsx_xflags & FS_XFLAG_DAX) && xfs_is_reflink_inode(ip))
+		return -EINVAL;
+
 	/*
 	 * Can't modify an immutable/append-only file unless
 	 * we have appropriate permission.