pipe: merge anon_pipe_buf*_ops

All the op vectors are exactly the same, they are just used to encode
packet or nomerge behavior.  There already is a flag for the packet
behavior, so just add a new one to allow for merging.  Inverting it vs
the previous nomerge special casing actually allows for much nicer code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Christoph Hellwig

fs/pipe.c

@@ -231,48 +231,13 @@ void generic_pipe_buf_release(struct pipe_inode_info *pipe,
 }
 EXPORT_SYMBOL(generic_pipe_buf_release);
 
-/* New data written to a pipe may be appended to a buffer with this type. */
 static const struct pipe_buf_operations anon_pipe_buf_ops = {
 	.confirm = generic_pipe_buf_confirm,
 	.release = anon_pipe_buf_release,
 	.steal = anon_pipe_buf_steal,
 	.get = generic_pipe_buf_get,
 };
 
-static const struct pipe_buf_operations anon_pipe_buf_nomerge_ops = {
-	.confirm = generic_pipe_buf_confirm,
-	.release = anon_pipe_buf_release,
-	.steal = anon_pipe_buf_steal,
-	.get = generic_pipe_buf_get,
-};
-
-static const struct pipe_buf_operations packet_pipe_buf_ops = {
-	.confirm = generic_pipe_buf_confirm,
-	.release = anon_pipe_buf_release,
-	.steal = anon_pipe_buf_steal,
-	.get = generic_pipe_buf_get,
-};
-
-/**
- * pipe_buf_mark_unmergeable - mark a &struct pipe_buffer as unmergeable
- * @buf:	the buffer to mark
- *
- * Description:
- *	This function ensures that no future writes will be merged into the
- *	given &struct pipe_buffer. This is necessary when multiple pipe buffers
- *	share the same backing page.
- */
-void pipe_buf_mark_unmergeable(struct pipe_buffer *buf)
-{
-	if (buf->ops == &anon_pipe_buf_ops)
-		buf->ops = &anon_pipe_buf_nomerge_ops;
-}
-
-static bool pipe_buf_can_merge(struct pipe_buffer *buf)
-{
-	return buf->ops == &anon_pipe_buf_ops;
-}
-
 /* Done while waiting without holding the pipe lock - thus the READ_ONCE() */
 static inline bool pipe_readable(const struct pipe_inode_info *pipe)
 {
@@ -478,7 +443,8 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 		struct pipe_buffer *buf = &pipe->bufs[(head - 1) & mask];
 		int offset = buf->offset + buf->len;
 
-		if (pipe_buf_can_merge(buf) && offset + chars <= PAGE_SIZE) {
+		if ((buf->flags & PIPE_BUF_FLAG_CAN_MERGE) &&
+		    offset + chars <= PAGE_SIZE) {
 			ret = pipe_buf_confirm(pipe, buf);
 			if (ret)
 				goto out;
@@ -541,11 +507,10 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 			buf->ops = &anon_pipe_buf_ops;
 			buf->offset = 0;
 			buf->len = 0;
-			buf->flags = 0;
-			if (is_packetized(filp)) {
-				buf->ops = &packet_pipe_buf_ops;
+			if (is_packetized(filp))
 				buf->flags = PIPE_BUF_FLAG_PACKET;
-			}
+			else
+				buf->flags = PIPE_BUF_FLAG_CAN_MERGE;
 			pipe->tmp_page = NULL;
 
 			copied = copy_page_from_iter(page, 0, PAGE_SIZE, from);

fs/splice.c

@@ -1624,12 +1624,11 @@ static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
 			*obuf = *ibuf;
 
 			/*
-			 * Don't inherit the gift flag, we need to
+			 * Don't inherit the gift and merge flags, we need to
 			 * prevent multiple steals of this page.
 			 */
 			obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
-
-			pipe_buf_mark_unmergeable(obuf);
+			obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;
 
 			obuf->len = len;
 			ibuf->offset += len;
@@ -1717,12 +1716,11 @@ static int link_pipe(struct pipe_inode_info *ipipe,
 		*obuf = *ibuf;
 
 		/*
-		 * Don't inherit the gift flag, we need to
-		 * prevent multiple steals of this page.
+		 * Don't inherit the gift and merge flag, we need to prevent
+		 * multiple steals of this page.
 		 */
 		obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
-
-		pipe_buf_mark_unmergeable(obuf);
+		obuf->flags &= ~PIPE_BUF_FLAG_CAN_MERGE;
 
 		if (obuf->len > len)
 			obuf->len = len;

include/linux/pipe_fs_i.h

@@ -8,6 +8,7 @@
 #define PIPE_BUF_FLAG_ATOMIC	0x02	/* was atomically mapped */
 #define PIPE_BUF_FLAG_GIFT	0x04	/* page is a gift */
 #define PIPE_BUF_FLAG_PACKET	0x08	/* read() as a packet */
+#define PIPE_BUF_FLAG_CAN_MERGE	0x10	/* can merge buffers */
 
 /**
  *	struct pipe_buffer - a linux kernel pipe buffer
@@ -233,7 +234,6 @@ int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_nosteal(struct pipe_inode_info *, struct pipe_buffer *);
 void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
-void pipe_buf_mark_unmergeable(struct pipe_buffer *buf);
 
 extern const struct pipe_buf_operations nosteal_pipe_buf_ops;