ipv4: add ip_sock_set_mtu_discover

Add a helper to directly set the IP_MTU_DISCOVER sockopt from kernel
space without going through a fake uaccess.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: David Howells <[e-mail]> [rxrpc bits]
Signed-off-by: David S. Miller <[e-mail]>

include/net/ip.h

···
 }
 
 void ip_sock_set_freebind(struct sock *sk);
+int ip_sock_set_mtu_discover(struct sock *sk, int val);
 void ip_sock_set_recverr(struct sock *sk);
 void ip_sock_set_tos(struct sock *sk, int val);
 

net/ipv4/ip_sockglue.c

···
 }
 EXPORT_SYMBOL(ip_sock_set_recverr);
 
+int ip_sock_set_mtu_discover(struct sock *sk, int val)
+{
+	if (val < IP_PMTUDISC_DONT || val > IP_PMTUDISC_OMIT)
+		return -EINVAL;
+	lock_sock(sk);
+	inet_sk(sk)->pmtudisc = val;
+	release_sock(sk);
+	return 0;
+}
+EXPORT_SYMBOL(ip_sock_set_mtu_discover);
+
 /*
  *	Socket option code for IP. This is the end of the line after any
  *	TCP,UDP etc options on an IP socket.

net/rxrpc/local_object.c

···
 		ip_sock_set_recverr(local->socket->sk);
 
 		/* we want to set the don't fragment bit */
-		opt = IP_PMTUDISC_DO;
-		ret = kernel_setsockopt(local->socket, SOL_IP, IP_MTU_DISCOVER,
-					(char *) &opt, sizeof(opt));
-		if (ret < 0) {
-			_debug("setsockopt failed");
-			goto error;
-		}
+		ip_sock_set_mtu_discover(local->socket->sk, IP_PMTUDISC_DO);
 
 		/* We want receive timestamps. */
 		sock_enable_timestamps(local->socket->sk);

net/rxrpc/output.c

···
 	struct kvec iov[2];
 	rxrpc_serial_t serial;
 	size_t len;
-	int ret, opt;
+	int ret;
 
 	_enter(",{%d}", skb->len);
 
···
 	switch (conn->params.local->srx.transport.family) {
 	case AF_INET6:
 	case AF_INET:
-		opt = IP_PMTUDISC_DONT;
-		kernel_setsockopt(conn->params.local->socket,
-				  SOL_IP, IP_MTU_DISCOVER,
-				  (char *)&opt, sizeof(opt));
+		ip_sock_set_mtu_discover(conn->params.local->socket->sk,
+				IP_PMTUDISC_DONT);
 		ret = kernel_sendmsg(conn->params.local->socket, &msg,
 				     iov, 2, len);
 		conn->params.peer->last_tx_at = ktime_get_seconds();
 
-		opt = IP_PMTUDISC_DO;
-		kernel_setsockopt(conn->params.local->socket,
-				  SOL_IP, IP_MTU_DISCOVER,
-				  (char *)&opt, sizeof(opt));
+		ip_sock_set_mtu_discover(conn->params.local->socket->sk,
+				IP_PMTUDISC_DO);
 		break;
 
 	default: