[PATCH net-next v8 13/16] udp: Convert udp_sendpage() to use MSG_SPLICE_PAGES

[David Howells <dhowells@xxxxxxxxxx>]

Convert udp_sendpage() to use sendmsg() with MSG_SPLICE_PAGES rather than
directly splicing in the pages itself.

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

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx>
cc: David Ahern <dsahern@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
---

Notes:
    ver #6)
     - udp_sendpage() shouldn't lock the socket around udp_sendpage().
     - udp_sendpage() should only set MSG_MORE if MSG_SENDPAGE_NOTLAST is set.

 net/ipv4/udp.c | 51 ++++++--------------------------------------------
 1 file changed, 6 insertions(+), 45 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index aa32afd871ee..2879dc6d66ea 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1332,54 +1332,15 @@ EXPORT_SYMBOL(udp_sendmsg);
 int udp_sendpage(struct sock *sk, struct page *page, int offset,
 		 size_t size, int flags)
 {
-	struct inet_sock *inet = inet_sk(sk);
-	struct udp_sock *up = udp_sk(sk);
-	int ret;
+	struct bio_vec bvec;
+	struct msghdr msg = { .msg_flags = flags | MSG_SPLICE_PAGES };
 
 	if (flags & MSG_SENDPAGE_NOTLAST)
-		flags |= MSG_MORE;
-
-	if (!up->pending) {
-		struct msghdr msg = {	.msg_flags = flags|MSG_MORE };
-
-		/* Call udp_sendmsg to specify destination address which
-		 * sendpage interface can't pass.
-		 * This will succeed only when the socket is connected.
-		 */
-		ret = udp_sendmsg(sk, &msg, 0);
-		if (ret < 0)
-			return ret;
-	}
-
-	lock_sock(sk);
+		msg.msg_flags |= MSG_MORE;
 
-	if (unlikely(!up->pending)) {
-		release_sock(sk);
-
-		net_dbg_ratelimited("cork failed\n");
-		return -EINVAL;
-	}
-
-	ret = ip_append_page(sk, &inet->cork.fl.u.ip4,
-			     page, offset, size, flags);
-	if (ret == -EOPNOTSUPP) {
-		release_sock(sk);
-		return sock_no_sendpage(sk->sk_socket, page, offset,
-					size, flags);
-	}
-	if (ret < 0) {
-		udp_flush_pending_frames(sk);
-		goto out;
-	}
-
-	up->len += size;
-	if (!(READ_ONCE(up->corkflag) || (flags&MSG_MORE)))
-		ret = udp_push_pending_frames(sk);
-	if (!ret)
-		ret = size;
-out:
-	release_sock(sk);
-	return ret;
+	bvec_set_page(&bvec, page, size, offset);
+	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
+	return udp_sendmsg(sk, &msg, size);
 }
 
 #define UDP_SKB_IS_STATELESS 0x80000000