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From:   David Howells <dhowells@redhat.com>
To:     netdev@vger.kernel.org
Cc:     David Howells <dhowells@redhat.com>,
        Jakub Kicinski <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
        David Ahern <dsahern@kernel.org>,
        Matthew Wilcox <willy@infradead.org>,
        Jens Axboe <axboe@kernel.dk>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Tom Herbert <tom@herbertland.com>,
        Tom Herbert <tom@quantonium.net>
Subject: [PATCH net-next 5/6] kcm: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage
Date:   Fri,  9 Jun 2023 11:02:20 +0100
Message-ID: <20230609100221.2620633-6-dhowells@redhat.com>
In-Reply-To: <20230609100221.2620633-1-dhowells@redhat.com>
References: <20230609100221.2620633-1-dhowells@redhat.com>
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When transmitting data, call down into the transport socket using sendmsg
with MSG_SPLICE_PAGES to indicate that content should be spliced rather
than using sendpage.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Tom Herbert <tom@herbertland.com>
cc: Tom Herbert <tom@quantonium.net>
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/kcm/kcmsock.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 7dee74430b59..3bcac1453f10 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -641,6 +641,10 @@ static int kcm_write_msgs(struct kcm_sock *kcm)
 
 		for (fragidx = 0; fragidx < skb_shinfo(skb)->nr_frags;
 		     fragidx++) {
+			struct bio_vec bvec;
+			struct msghdr msg = {
+				.msg_flags = MSG_DONTWAIT | MSG_SPLICE_PAGES,
+			};
 			skb_frag_t *frag;
 
 			frag_offset = 0;
@@ -651,11 +655,13 @@ static int kcm_write_msgs(struct kcm_sock *kcm)
 				goto out;
 			}
 
-			ret = kernel_sendpage(psock->sk->sk_socket,
-					      skb_frag_page(frag),
-					      skb_frag_off(frag) + frag_offset,
-					      skb_frag_size(frag) - frag_offset,
-					      MSG_DONTWAIT);
+			bvec_set_page(&bvec,
+				      skb_frag_page(frag),
+				      skb_frag_size(frag) - frag_offset,
+				      skb_frag_off(frag) + frag_offset);
+			iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1,
+				      bvec.bv_len);
+			ret = sock_sendmsg(psock->sk->sk_socket, &msg);
 			if (ret <= 0) {
 				if (ret == -EAGAIN) {
 					/* Save state to try again when there's