Subject: [PATCH RFC net-next 05/11] udp: add gso segment cmsg

From: Willem de Bruijn <[email-masked]>
Date: Tue, 17 Apr 2018 16:00:55 -0400

From: Willem de Bruijn <[email-masked]>

Allow specifying segment size in the send call.

The new control message performs the same function as socket option
UDP_SEGMENT while avoiding the extra system call.

Signed-off-by: Willem de Bruijn <[email-masked]>
---
 include/net/udp.h |  1 +
 net/ipv4/udp.c    | 43 +++++++++++++++++++++++++++++++++++++++++--
 net/ipv6/udp.c    |  5 ++++-
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/include/net/udp.h b/include/net/udp.h
index 741d888d0fdb..05990746810e 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -273,6 +273,7 @@ int udp_abort(struct sock *sk, int err);
 int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len);
 int udp_push_pending_frames(struct sock *sk);
 void udp_flush_pending_frames(struct sock *sk);
+int udp_cmsg_send(struct sock *sk, struct msghdr *msg, u16 *gso_size);
 void udp4_hwcsum(struct sk_buff *skb, __be32 src, __be32 dst);
 int udp_rcv(struct sk_buff *skb);
 int udp_ioctl(struct sock *sk, int cmd, unsigned long arg);
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 731772a69043..2bad61a05c5e 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -851,6 +851,42 @@ int udp_push_pending_frames(struct sock *sk)
 }
 EXPORT_SYMBOL(udp_push_pending_frames);
 
+static int __udp_cmsg_send(struct cmsghdr *cmsg, u16 *gso_size)
+{
+	switch (cmsg->cmsg_type) {
+	case UDP_SEGMENT:
+		if (cmsg->cmsg_len != CMSG_LEN(sizeof(__u16)))
+			return -EINVAL;
+		*gso_size = *(__u16 *)CMSG_DATA(cmsg);
+		return 0;
+	default:
+		return -EINVAL;
+	}
+}
+
+int udp_cmsg_send(struct sock *sk, struct msghdr *msg, u16 *gso_size)
+{
+	struct cmsghdr *cmsg;
+	bool need_ip = false;
+	int err;
+
+	for_each_cmsghdr(cmsg, msg) {
+		if (!CMSG_OK(msg, cmsg))
+			return -EINVAL;
+
+		if (cmsg->cmsg_level != SOL_UDP) {
+			need_ip = true;
+			continue;
+		}
+
+		err = __udp_cmsg_send(cmsg, gso_size);
+		if (err)
+			return err;
+	}
+
+	return need_ip;
+}
+
 int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 {
 	struct inet_sock *inet = inet_sk(sk);
@@ -939,8 +975,11 @@ int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	ipc.gso_size = up->gso_size;
 
 	if (msg->msg_controllen) {
-		err = ip_cmsg_send(sk, msg, &ipc, sk->sk_family == AF_INET6);
-		if (unlikely(err)) {
+		err = udp_cmsg_send(sk, msg, &ipc.gso_size);
+		if (err > 0)
+			err = ip_cmsg_send(sk, msg, &ipc,
+					   sk->sk_family == AF_INET6);
+		if (unlikely(err < 0)) {
 			kfree(ipc.opt);
 			return err;
 		}
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 16aee23b1e5f..c8b3289bdbd0 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1274,7 +1274,10 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		opt->tot_len = sizeof(*opt);
 		ipc6.opt = opt;
 
-		err = ip6_datagram_send_ctl(sock_net(sk), sk, msg, &fl6, &ipc6, &sockc);
+		err = udp_cmsg_send(sk, msg, &ipc6.gso_size);
+		if (err > 0)
+			err = ip6_datagram_send_ctl(sock_net(sk), sk, msg, &fl6,
+						    &ipc6, &sockc);
 		if (err < 0) {
 			fl6_sock_release(flowlabel);
 			return err;
-- 
2.17.0.484.g0c8726318c-goog