netdev - [PATCH net-next v8 15/16] af_unix: Support MSG_SPLICE

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Date: Thu, 18 May 2023 12:34:52 +0100
From: David Howells <dhowells@...hat.com>
To: netdev@...r.kernel.org
Cc: David Howells <dhowells@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	David Ahern <dsahern@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	Jens Axboe <axboe@...nel.dk>,
	Jeff Layton <jlayton@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	Chuck Lever III <chuck.lever@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Kuniyuki Iwashima <kuniyu@...zon.com>
Subject: [PATCH net-next v8 15/16] af_unix: Support MSG_SPLICE_PAGES

Make AF_UNIX sendmsg() support MSG_SPLICE_PAGES, splicing in pages from the
source iterator if possible and copying the data in otherwise.

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

Signed-off-by: David Howells <dhowells@...hat.com>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: Kuniyuki Iwashima <kuniyu@...zon.com>
cc: Jens Axboe <axboe@...nel.dk>
cc: Matthew Wilcox <willy@...radead.org>
cc: netdev@...r.kernel.org
---

Notes:
    ver #6)
     - Use common helper.

 net/unix/af_unix.c | 49 +++++++++++++++++++++++++++++++---------------
 1 file changed, 33 insertions(+), 16 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index dd55506b4632..976bc1c5e11b 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2200,19 +2200,25 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 	while (sent < len) {
 		size = len - sent;
 
-		/* Keep two messages in the pipe so it schedules better */
-		size = min_t(int, size, (sk->sk_sndbuf >> 1) - 64);
+		if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES)) {
+			skb = sock_alloc_send_pskb(sk, 0, 0,
+						   msg->msg_flags & MSG_DONTWAIT,
+						   &err, 0);
+		} else {
+			/* Keep two messages in the pipe so it schedules better */
+			size = min_t(int, size, (sk->sk_sndbuf >> 1) - 64);
 
-		/* allow fallback to order-0 allocations */
-		size = min_t(int, size, SKB_MAX_HEAD(0) + UNIX_SKB_FRAGS_SZ);
+			/* allow fallback to order-0 allocations */
+			size = min_t(int, size, SKB_MAX_HEAD(0) + UNIX_SKB_FRAGS_SZ);
 
-		data_len = max_t(int, 0, size - SKB_MAX_HEAD(0));
+			data_len = max_t(int, 0, size - SKB_MAX_HEAD(0));
 
-		data_len = min_t(size_t, size, PAGE_ALIGN(data_len));
+			data_len = min_t(size_t, size, PAGE_ALIGN(data_len));
 
-		skb = sock_alloc_send_pskb(sk, size - data_len, data_len,
-					   msg->msg_flags & MSG_DONTWAIT, &err,
-					   get_order(UNIX_SKB_FRAGS_SZ));
+			skb = sock_alloc_send_pskb(sk, size - data_len, data_len,
+						   msg->msg_flags & MSG_DONTWAIT, &err,
+						   get_order(UNIX_SKB_FRAGS_SZ));
+		}
 		if (!skb)
 			goto out_err;
 
@@ -2224,13 +2230,24 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 		}
 		fds_sent = true;
 
-		skb_put(skb, size - data_len);
-		skb->data_len = data_len;
-		skb->len = size;
-		err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
-		if (err) {
-			kfree_skb(skb);
-			goto out_err;
+		if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES)) {
+			err = skb_splice_from_iter(skb, &msg->msg_iter, size,
+						   sk->sk_allocation);
+			if (err < 0) {
+				kfree_skb(skb);
+				goto out_err;
+			}
+			size = err;
+			refcount_add(size, &sk->sk_wmem_alloc);
+		} else {
+			skb_put(skb, size - data_len);
+			skb->data_len = data_len;
+			skb->len = size;
+			err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
+			if (err) {
+				kfree_skb(skb);
+				goto out_err;
+			}
 		}
 
 		unix_state_lock(other);