[RFC PATCH 16/28] splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()

[David Howells]

Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage() to splice data from
a pipe to a socket.  This paves the way for passing in multiple pages at
once from a pipe and the handling of multipage folios.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
cc: Eric Dumazet <edumazet@xxxxxxxxxx>
cc: Jakub Kicinski <kuba@xxxxxxxxxx>
cc: Paolo Abeni <pabeni@xxxxxxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
cc: netdev@xxxxxxxxxxxxxxx
---
 fs/splice.c            | 42 +++++++++++++++++++++++-------------------
 include/linux/fs.h     |  2 --
 include/linux/splice.h |  2 ++
 net/socket.c           | 26 ++------------------------
 4 files changed, 27 insertions(+), 45 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index f46dd1fb367b..23ead122d631 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -32,6 +32,7 @@
 #include <linux/uio.h>
 #include <linux/security.h>
 #include <linux/gfp.h>
+#include <linux/net.h>
 #include <linux/socket.h>
 #include <linux/sched/signal.h>
 
@@ -410,29 +411,32 @@ const struct pipe_buf_operations nosteal_pipe_buf_ops = {
 };
 EXPORT_SYMBOL(nosteal_pipe_buf_ops);
 
+#ifdef CONFIG_NET
 /*
  * Send 'sd->len' bytes to socket from 'sd->file' at position 'sd->pos'
  * using sendpage(). Return the number of bytes sent.
  */
-static int pipe_to_sendpage(struct pipe_inode_info *pipe,
-			    struct pipe_buffer *buf, struct splice_desc *sd)
+static int pipe_to_sendmsg(struct pipe_inode_info *pipe,
+			   struct pipe_buffer *buf, struct splice_desc *sd)
 {
-	struct file *file = sd->u.file;
-	loff_t pos = sd->pos;
-	int more;
-
-	if (!likely(file->f_op->sendpage))
-		return -EINVAL;
+	struct socket *sock = sock_from_file(sd->u.file);
+	struct bio_vec bvec;
+	struct msghdr msg = {
+		.msg_flags = MSG_SPLICE_PAGES,
+	};
 
-	more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
+	if (sd->flags & SPLICE_F_MORE)
+		msg.msg_flags |= MSG_MORE;
 
 	if (sd->len < sd->total_len &&
 	    pipe_occupancy(pipe->head, pipe->tail) > 1)
-		more |= MSG_SENDPAGE_NOTLAST;
+		msg.msg_flags |= MSG_MORE;
 
-	return file->f_op->sendpage(file, buf->page, buf->offset,
-				    sd->len, &pos, more);
+	bvec_set_page(&bvec, buf->page, sd->len, buf->offset);
+	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, sd->len);
+	return sock_sendmsg(sock, &msg);
 }
+#endif
 
 static void wakeup_pipe_writers(struct pipe_inode_info *pipe)
 {
@@ -614,7 +618,7 @@ static void splice_from_pipe_end(struct pipe_inode_info *pipe, struct splice_des
  * Description:
  *    This function does little more than loop over the pipe and call
  *    @actor to do the actual moving of a single struct pipe_buffer to
- *    the desired destination. See pipe_to_file, pipe_to_sendpage, or
+ *    the desired destination. See pipe_to_file, pipe_to_sendmsg, or
  *    pipe_to_user.
  *
  */
@@ -795,8 +799,9 @@ iter_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 
 EXPORT_SYMBOL(iter_file_splice_write);
 
+#ifdef CONFIG_NET
 /**
- * generic_splice_sendpage - splice data from a pipe to a socket
+ * splice_to_socket - splice data from a pipe to a socket
  * @pipe:	pipe to splice from
  * @out:	socket to write to
  * @ppos:	position in @out
@@ -808,13 +813,12 @@ EXPORT_SYMBOL(iter_file_splice_write);
  *    is involved.
  *
  */
-ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe, struct file *out,
-				loff_t *ppos, size_t len, unsigned int flags)
+ssize_t splice_to_socket(struct pipe_inode_info *pipe, struct file *out,
+			 loff_t *ppos, size_t len, unsigned int flags)
 {
-	return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendpage);
+	return splice_from_pipe(pipe, out, ppos, len, flags, pipe_to_sendmsg);
 }
-
-EXPORT_SYMBOL(generic_splice_sendpage);
+#endif
 
 static int warn_unsupported(struct file *file, const char *op)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c85916e9f7db..f3ccc243851e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2740,8 +2740,6 @@ extern ssize_t generic_file_splice_read(struct file *, loff_t *,
 		struct pipe_inode_info *, size_t, unsigned int);
 extern ssize_t iter_file_splice_write(struct pipe_inode_info *,
 		struct file *, loff_t *, size_t, unsigned int);
-extern ssize_t generic_splice_sendpage(struct pipe_inode_info *pipe,
-		struct file *out, loff_t *, size_t len, unsigned int flags);
 extern long do_splice_direct(struct file *in, loff_t *ppos, struct file *out,
 		loff_t *opos, size_t len, unsigned int flags);
 
diff --git a/include/linux/splice.h b/include/linux/splice.h
index 8f052c3dae95..e6153feda86c 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h
@@ -87,6 +87,8 @@ extern long do_splice(struct file *in, loff_t *off_in,
 
 extern long do_tee(struct file *in, struct file *out, size_t len,
 		   unsigned int flags);
+extern ssize_t splice_to_socket(struct pipe_inode_info *pipe, struct file *out,
+				loff_t *ppos, size_t len, unsigned int flags);
 
 /*
  * for dynamic pipe sizing
diff --git a/net/socket.c b/net/socket.c
index 6bae8ce7059e..1b48a976b8cc 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -57,6 +57,7 @@
 #include <linux/mm.h>
 #include <linux/socket.h>
 #include <linux/file.h>
+#include <linux/splice.h>
 #include <linux/net.h>
 #include <linux/interrupt.h>
 #include <linux/thread_info.h>
@@ -126,8 +127,6 @@ static long compat_sock_ioctl(struct file *file,
 			      unsigned int cmd, unsigned long arg);
 #endif
 static int sock_fasync(int fd, struct file *filp, int on);
-static ssize_t sock_sendpage(struct file *file, struct page *page,
-			     int offset, size_t size, loff_t *ppos, int more);
 static ssize_t sock_splice_read(struct file *file, loff_t *ppos,
 				struct pipe_inode_info *pipe, size_t len,
 				unsigned int flags);
@@ -162,8 +161,7 @@ static const struct file_operations socket_file_ops = {
 	.mmap =		sock_mmap,
 	.release =	sock_close,
 	.fasync =	sock_fasync,
-	.sendpage =	sock_sendpage,
-	.splice_write = generic_splice_sendpage,
+	.splice_write = splice_to_socket,
 	.splice_read =	sock_splice_read,
 	.show_fdinfo =	sock_show_fdinfo,
 };
@@ -1062,26 +1060,6 @@ int kernel_recvmsg(struct socket *sock, struct msghdr *msg,
 }
 EXPORT_SYMBOL(kernel_recvmsg);
 
-static ssize_t sock_sendpage(struct file *file, struct page *page,
-			     int offset, size_t size, loff_t *ppos, int more)
-{
-	struct socket *sock;
-	int flags;
-	int ret;
-
-	sock = file->private_data;
-
-	flags = (file->f_flags & O_NONBLOCK) ? MSG_DONTWAIT : 0;
-	/* more is a combination of MSG_MORE and MSG_SENDPAGE_NOTLAST */
-	flags |= more;
-
-	ret = kernel_sendpage(sock, page, offset, size, flags);
-
-	if (trace_sock_send_length_enabled())
-		call_trace_sock_send_length(sock->sk, ret, 0);
-	return ret;
-}
-
 static ssize_t sock_splice_read(struct file *file, loff_t *ppos,
 				struct pipe_inode_info *pipe, size_t len,
 				unsigned int flags)