[PATCH v3 43/55] net: Use sendmsg(MSG_SPLICE_PAGES) not sendpage in skb_send_sock()

David Howells
2023-03-31T16:18:01Z

Use sendmsg() with MSG_SPLICE_PAGES rather than sendpage in
skb_send_sock(). This causes pages to be spliced from the source iterator
if possible (the iterator must be ITER_BVEC and the pages must be
spliceable).

This allows ->sendpage() to be replaced by something that can handle
multiple multipage folios in a single transaction.

Note that this could perhaps be improved to fill out a bvec array with all
the frags and then make a single sendmsg call, possibly sticking the header
on the front also.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Jens Axboe <axboe@kernel.dk>
cc: Matthew Wilcox <willy@infradead.org>
cc: netdev@vger.kernel.org
---
net/core/skbuff.c | 49 ++++++++++++++++++++++++++---------------------
1 file changed, 27 insertions(+), 22 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0506e4cf1ed9..3693b3526d33 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2919,32 +2919,32 @@ int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
}
EXPORT_SYMBOL_GPL(skb_splice_bits);

-static int sendmsg_unlocked(struct sock *sk, struct msghdr *msg,
- struct kvec *vec, size_t num, size_t size)
+static int sendmsg_locked(struct sock *sk, struct msghdr *msg)
{
struct socket *sock = sk->sk_socket;
+ size_t size = msg_data_left(msg);

if (!sock)
return -EINVAL;
- return kernel_sendmsg(sock, msg, vec, num, size);
+
+ if (!sock->ops->sendmsg_locked)
+ return sock_no_sendmsg_locked(sk, msg, size);
+
+ return sock->ops->sendmsg_locked(sk, msg, size);
}

-static int sendpage_unlocked(struct sock *sk, struct page *page, int offset,
- size_t size, int flags)
+static int sendmsg_unlocked(struct sock *sk, struct msghdr *msg)
{
struct socket *sock = sk->sk_socket;

if (!sock)
return -EINVAL;
- return kernel_sendpage(sock, page, offset, size, flags);
+ return sock_sendmsg(sock, msg);
}

-typedef int (*sendmsg_func)(struct sock *sk, struct msghdr *msg,
- struct kvec *vec, size_t num, size_t size);
-typedef int (*sendpage_func)(struct sock *sk, struct page *page, int offset,
- size_t size, int flags);
+typedef int (*sendmsg_func)(struct sock *sk, struct msghdr *msg);
static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
- int len, sendmsg_func sendmsg, sendpage_func sendpage)
+ int len, sendmsg_func sendmsg)
{
unsigned int orig_len = len;
struct sk_buff *head = skb;
@@ -2964,8 +2964,9 @@ static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
memset(&msg, 0, sizeof(msg));
msg.msg_flags = MSG_DONTWAIT;

- ret = INDIRECT_CALL_2(sendmsg, kernel_sendmsg_locked,
- sendmsg_unlocked, sk, &msg, &kv, 1, slen);
+ iov_iter_kvec(&msg.msg_iter, ITER_SOURCE, &kv, 1, slen);
+ ret = INDIRECT_CALL_2(sendmsg, sendmsg_locked,
+ sendmsg_unlocked, sk, &msg);
if (ret <= 0)
goto error;

@@ -2996,11 +2997,17 @@ static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
slen = min_t(size_t, len, skb_frag_size(frag) - offset);

while (slen) {
- ret = INDIRECT_CALL_2(sendpage, kernel_sendpage_locked,
- sendpage_unlocked, sk,
- skb_frag_page(frag),
- skb_frag_off(frag) + offset,
- slen, MSG_DONTWAIT);
+ struct bio_vec bvec;
+ struct msghdr msg = {
+ .msg_flags = MSG_SPLICE_PAGES | MSG_DONTWAIT,
+ };
+
+ bvec_set_page(&bvec, skb_frag_page(frag), slen,
+ skb_frag_off(frag) + offset);
+ iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, slen);
+
+ ret = INDIRECT_CALL_2(sendmsg, sendmsg_locked,
+ sendmsg_unlocked, sk, &msg);
if (ret <= 0)
goto error;

@@ -3037,16 +3044,14 @@ static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
int len)
{
- return __skb_send_sock(sk, skb, offset, len, kernel_sendmsg_locked,
- kernel_sendpage_locked);
+ return __skb_send_sock(sk, skb, offset, len, sendmsg_locked);
}
EXPORT_SYMBOL_GPL(skb_send_sock_locked);

/* Send skb data on a socket. Socket must be unlocked. */
int skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset, int len)
{
- return __skb_send_sock(sk, skb, offset, len, sendmsg_unlocked,
- sendpage_unlocked);
+ return __skb_send_sock(sk, skb, offset, len, sendmsg_unlocked);
}

/**