iomap: mark ->iomap_end as optional

No need to implement it for read-only mappings.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>


diff --git a/fs/iomap.c b/fs/iomap.c
index d9d1f50..0342254 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -84,8 +84,11 @@
 	 * Now the data has been copied, commit the range we've copied.  This
 	 * should not fail unless the filesystem has had a fatal error.
 	 */
-	ret = ops->iomap_end(inode, pos, length, written > 0 ? written : 0,
-			flags, &iomap);
+	if (ops->iomap_end) {
+		ret = ops->iomap_end(inode, pos, length,
+				     written > 0 ? written : 0,
+				     flags, &iomap);
+	}
 
 	return written ? written : ret;
 }