[PATCH net-next v6 03/14] splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()

David Howells
2023-06-07T18:20:39Z

Replace generic_splice_sendpage() + splice_from_pipe + pipe_to_sendpage()
with a net-specific handler, splice_to_socket(), that calls sendmsg() with
MSG_SPLICE_PAGES set instead of calling ->sendpage().

MSG_MORE is used to indicate if the sendmsg() is expected to be followed
with more data.

This allows multiple pipe-buffer pages to be passed in a single call in a
BVEC iterator, allowing the processing to be pushed down to a loop in the
protocol driver. This helps pave the way for passing multipage folios down
too.

Protocols that haven't been converted to handle MSG_SPLICE_PAGES yet should
just ignore it and do a normal sendmsg() for now - although that may be a
bit slower as it may copy everything.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---

Notes:
ver #5)
- Preclear ret just in case len is 0.

fs/splice.c | 158 +++++++++++++++++++++++++++++++++--------
include/linux/fs.h | 2 -
include/linux/splice.h | 2 +
net/socket.c | 26 +------
4 files changed, 131 insertions(+), 57 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 3e06611d19ae..e337630aed64 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -33,6 +33,7 @@
#include <linux/fsnotify.h>
#include <linux/security.h>
#include <linux/gfp.h>
+#include <linux/net.h>
#include <linux/socket.h>
#include <linux/sched/signal.h>

@@ -448,30 +449,6 @@ const struct pipe_buf_operations nosteal_pipe_buf_ops = {
};
EXPORT_SYMBOL(nosteal_pipe_buf_ops);

-/*
- * 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)
-{
- struct file *file = sd->u.file;
- loff_t pos = sd->pos;
- int more;
-
- if (!likely(file->f_op->sendpage))
- return -EINVAL;
-
- more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
-
- if (sd->len < sd->total_len &&
- pipe_occupancy(pipe->head, pipe->tail) > 1)
- more |= MSG_SENDPAGE_NOTLAST;
-
- return file->f_op->sendpage(file, buf->page, buf->offset,
- sd->len, &pos, more);
-}
-
static void wakeup_pipe_writers(struct pipe_inode_info *pipe)
{
smp_mb();
@@ -652,7 +629,7 @@ 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.
*
*/
@@ -833,8 +810,9 @@ 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
@@ -846,13 +824,131 @@ 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);
-}
+ struct socket *sock = sock_from_file(out);
+ struct bio_vec bvec[16];
+ struct msghdr msg = {};
+ ssize_t ret = 0;
+ size_t spliced = 0;
+ bool need_wakeup = false;
+
+ pipe_lock(pipe);
+
+ while (len > 0) {
+ unsigned int head, tail, mask, bc = 0;
+ size_t remain = len;
+
+ /*
+ * Check for signal early to make process killable when there
+ * are always buffers available
+ */
+ ret = -ERESTARTSYS;
+ if (signal_pending(current))
+ break;

-EXPORT_SYMBOL(generic_splice_sendpage);
+ while (pipe_empty(pipe->head, pipe->tail)) {
+ ret = 0;
+ if (!pipe->writers)
+ goto out;
+
+ if (spliced)
+ goto out;
+
+ ret = -EAGAIN;
+ if (flags & SPLICE_F_NONBLOCK)
+ goto out;
+
+ ret = -ERESTARTSYS;
+ if (signal_pending(current))
+ goto out;
+
+ if (need_wakeup) {
+ wakeup_pipe_writers(pipe);
+ need_wakeup = false;
+ }
+
+ pipe_wait_readable(pipe);
+ }
+
+ head = pipe->head;
+ tail = pipe->tail;
+ mask = pipe->ring_size - 1;
+
+ while (!pipe_empty(head, tail)) {
+ struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+ size_t seg;
+
+ if (!buf->len) {
+ tail++;
+ continue;
+ }
+
+ seg = min_t(size_t, remain, buf->len);
+ seg = min_t(size_t, seg, PAGE_SIZE);
+
+ ret = pipe_buf_confirm(pipe, buf);
+ if (unlikely(ret)) {
+ if (ret == -ENODATA)
+ ret = 0;
+ break;
+ }
+
+ bvec_set_page(&bvec[bc++], buf->page, seg, buf->offset);
+ remain -= seg;
+ if (seg >= buf->len)
+ tail++;
+ if (bc >= ARRAY_SIZE(bvec))
+ break;
+ }
+
+ if (!bc)
+ break;
+
+ msg.msg_flags = MSG_SPLICE_PAGES;
+ if (flags & SPLICE_F_MORE)
+ msg.msg_flags |= MSG_MORE;
+ if (remain && pipe_occupancy(pipe->head, tail) > 0)
+ msg.msg_flags |= MSG_MORE;
+
+ iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, bvec, bc,
+ len - remain);
+ ret = sock_sendmsg(sock, &msg);
+ if (ret <= 0)
+ break;
+
+ spliced += ret;
+ len -= ret;
+ tail = pipe->tail;
+ while (ret > 0) {
+ struct pipe_buffer *buf = &pipe->bufs[tail & mask];
+ size_t seg = min_t(size_t, ret, buf->len);
+
+ buf->offset += seg;
+ buf->len -= seg;
+ ret -= seg;
+
+ if (!buf->len) {
+ pipe_buf_release(pipe, buf);
+ tail++;
+ }
+ }
+
+ if (tail != pipe->tail) {
+ pipe->tail = tail;
+ if (pipe->files)
+ need_wakeup = true;
+ }
+ }
+
+out:
+ pipe_unlock(pipe);
+ if (need_wakeup)
+ wakeup_pipe_writers(pipe);
+ return spliced ?: ret;
+}
+#endif

static int warn_unsupported(struct file *file, const char *op)
{
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 133f0640fb24..df92f4b3d122 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2759,8 +2759,6 @@ 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 a55179fd60fc..991ae318b6eb 100644
--- a/include/linux/splice.h
+++ b/include/linux/splice.h
@@ -84,6 +84,8 @@ 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 3df96e9ba4e2..c4d9104418c8 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,
};
@@ -1066,26 +1064,6 @@ 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)