[PATCH net-next 05/10] udp: add gso segment cmsg

[Willem de Bruijn]

From: Willem de Bruijn <will...@google.com>

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 <will...@google.com>
---
 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 bda022c5480b..350bdafc462b 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -853,6 +853,42 @@ 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);
@@ -941,8 +977,11 @@ 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 86b7dd58d4b4..6acfdd3e442b 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1276,7 +1276,10 @@ 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;
-- 
2.17.0.441.gb46fe60e1d-goog