[RFC PATCH v2 28/48] splice: Reimplement splice_to_socket() to pass multiple bufs to sendmsg()

David Howells
2023-03-29T14:20:55Z

Reimplement splice_to_socket() so that it can pass multiple pipe buffer
pages to sendmsg() in a single go.

Signed-off-by: David Howells <dhowells@redhat.com>
---
fs/splice.c | 148 ++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 120 insertions(+), 28 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 23ead122d631..d5bc28b59720 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -411,33 +411,6 @@ 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_sendmsg(struct pipe_inode_info *pipe,
- struct pipe_buffer *buf, struct splice_desc *sd)
-{
- struct socket *sock = sock_from_file(sd->u.file);
- struct bio_vec bvec;
- struct msghdr msg = {
- .msg_flags = MSG_SPLICE_PAGES,
- };
-
- if (sd->flags & SPLICE_F_MORE)
- msg.msg_flags |= MSG_MORE;
-
- if (sd->len < sd->total_len &&
- pipe_occupancy(pipe->head, pipe->tail) > 1)
- msg.msg_flags |= MSG_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)
{
smp_mb();
@@ -816,7 +789,126 @@ EXPORT_SYMBOL(iter_file_splice_write);
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_sendmsg);
+ struct socket *sock = sock_from_file(out);
+ struct bio_vec bvec[16];
+ struct msghdr msg = {};
+ ssize_t ret;
+ 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;
+
+ 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 = 0;
+ if (flags & SPLICE_F_MORE)
+ msg.msg_flags = MSG_MORE;
+ if (remain && pipe_occupancy(pipe->head, tail) > 0)
+ msg.msg_flags = MSG_MORE;
+ msg.msg_flags |= MSG_SPLICE_PAGES;
+
+ 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