[RFC PATCH 11/28] udp: Convert udp_sendpage() to use MSG_SPLICE_PAGES

[David Howells <dhowells@redhat.com>]

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@redhat.com>
cc: Willem de Bruijn <willemdebruijn.kernel@gmail.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/ipv4/udp.c | 50 +++++++++-----------------------------------------
 1 file changed, 9 insertions(+), 41 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index c605d171eb2d..097feb92e215 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1332,52 +1332,20 @@ 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);
+	struct bio_vec bvec;
+	struct msghdr msg = {
+		.msg_flags = flags | MSG_SPLICE_PAGES | MSG_MORE
+	};
 	int ret;
 
-	if (flags & MSG_SENDPAGE_NOTLAST)
-		flags |= MSG_MORE;
+	bvec_set_page(&bvec, page, size, offset);
+	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
 
-	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;
-	}
+	if (flags & MSG_SENDPAGE_NOTLAST)
+		msg.msg_flags |= MSG_MORE;
 
 	lock_sock(sk);
-
-	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:
+	ret = udp_sendmsg(sk, &msg, size);
 	release_sock(sk);
 	return ret;
 }