new helper: add_to_pipe()

single-buffer analogue of splice_to_pipe(); vmsplice_to_pipe() switched
to that, leaving splice_to_pipe() only for ->splice_read() instances
(and that only until they are converted as well).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/splice.h b/include/linux/splice.h
index da2751d..58b300f 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h
@@ -72,6 +72,8 @@
 				  struct splice_desc *, splice_actor *);
 extern ssize_t splice_to_pipe(struct pipe_inode_info *,
 			      struct splice_pipe_desc *);
+extern ssize_t add_to_pipe(struct pipe_inode_info *,
+			      struct pipe_buffer *);
 extern ssize_t splice_direct_to_actor(struct file *, struct splice_desc *,
 				      splice_direct_actor *);