mptcp: Support for IP_TOS for MPTCP setsockopt()

SOL_IP provides a way to configure network layer attributes in a
socket. This patch adds support for IP_TOS for setsockopt(.. ,SOL_IP, ..)

Support for SOL_IP is added in mptcp_setsockopt() and IP_TOS is handled in
a private function. The idea here is to take in the value passed for IP_TOS
and set it to the current subflow, open subflows as well new subflows that
might be created after the initial call to setsockopt(). This sync is done
using sync_socket_options(.., ssk) and setting the value of tos using
__ip_sock_set_tos(ssk,..).

The patch has been tested using the packetdrill script here -
https://github.com/multipath-tcp/mptcp_net-next/issues/220#issuecomment-947863717

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/220Signed-off-by: Poorva Sonparote <psonparo@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/sockopt.c

@@ -598,6 +598,42 @@ static int mptcp_setsockopt_sol_tcp_congestion(struct mptcp_sock *msk, sockptr_t
 	return ret;
 }
 
+static int mptcp_setsockopt_v4_set_tos(struct mptcp_sock *msk, int optname,
+				       sockptr_t optval, unsigned int optlen)
+{
+	struct mptcp_subflow_context *subflow;
+	struct sock *sk = (struct sock *)msk;
+	int err, val;
+
+	err = ip_setsockopt(sk, SOL_IP, optname, optval, optlen);
+
+	if (err != 0)
+		return err;
+
+	lock_sock(sk);
+	sockopt_seq_inc(msk);
+	val = inet_sk(sk)->tos;
+	mptcp_for_each_subflow(msk, subflow) {
+		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+
+		__ip_sock_set_tos(ssk, val);
+	}
+	release_sock(sk);
+
+	return err;
+}
+
+static int mptcp_setsockopt_v4(struct mptcp_sock *msk, int optname,
+			       sockptr_t optval, unsigned int optlen)
+{
+	switch (optname) {
+	case IP_TOS:
+		return mptcp_setsockopt_v4_set_tos(msk, optname, optval, optlen);
+	}
+
+	return -EOPNOTSUPP;
+}
+
 static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 				    sockptr_t optval, unsigned int optlen)
 {
@@ -637,6 +673,9 @@ int mptcp_setsockopt(struct sock *sk, int level, int optname,
 	if (ssk)
 		return tcp_setsockopt(ssk, level, optname, optval, optlen);
 
+	if (level == SOL_IP)
+		return mptcp_setsockopt_v4(msk, optname, optval, optlen);
+
 	if (level == SOL_IPV6)
 		return mptcp_setsockopt_v6(msk, optname, optval, optlen);
 
@@ -1003,6 +1042,7 @@ static void sync_socket_options(struct mptcp_sock *msk, struct sock *ssk)
 	ssk->sk_priority = sk->sk_priority;
 	ssk->sk_bound_dev_if = sk->sk_bound_dev_if;
 	ssk->sk_incoming_cpu = sk->sk_incoming_cpu;
+	__ip_sock_set_tos(ssk, inet_sk(sk)->tos);
 
 	if (sk->sk_userlocks & tx_rx_locks) {
 		ssk->sk_userlocks |= sk->sk_userlocks & tx_rx_locks;