mptcp: add the outgoing MP_PRIO support

This patch added the outgoing MP_PRIO logic:

In mptcp_pm_nl_mp_prio_send_ack, find the related subflow and subsocket
according to the input parameter addr. Save the input priority value to
suflow's backup, then set subflow's send_mp_prio flag to true, and save
the input priority value to suflow's request_bkup. Finally, send out a
pure ACK on the related subsocket.

In mptcp_established_options_mp_prio, check whether the subflow's
send_mp_prio is set. If it is, this is the packet for sending MP_PRIO.
So save subflow->request_bkup value to mptcp_out_options's backup, and
change the option type to OPTION_MPTCP_PRIO.

In mptcp_write_options, clear the send_mp_prio flag and send out the
MP_PRIO suboption with mptcp_out_options's backup value.

Signed-off-by: Geliang Tang <geliangtang@gmail.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/options.c

@@ -679,6 +679,28 @@ static bool mptcp_established_options_rm_addr(struct sock *sk,
 	return true;
 }
 
+static bool mptcp_established_options_mp_prio(struct sock *sk,
+					      unsigned int *size,
+					      unsigned int remaining,
+					      struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	if (!subflow->send_mp_prio)
+		return false;
+
+	if (remaining < TCPOLEN_MPTCP_PRIO)
+		return false;
+
+	*size = TCPOLEN_MPTCP_PRIO;
+	opts->suboptions |= OPTION_MPTCP_PRIO;
+	opts->backup = subflow->request_bkup;
+
+	pr_debug("prio=%d", opts->backup);
+
+	return true;
+}
+
 bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 			       unsigned int *size, unsigned int remaining,
 			       struct mptcp_out_options *opts)
@@ -721,6 +743,12 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 		ret = true;
 	}
 
+	if (mptcp_established_options_mp_prio(sk, &opt_size, remaining, opts)) {
+		*size += opt_size;
+		remaining -= opt_size;
+		ret = true;
+	}
+
 	return ret;
 }
 
@@ -1168,6 +1196,18 @@ mp_capable_done:
 				      0, opts->rm_id);
 	}
 
+	if (OPTION_MPTCP_PRIO & opts->suboptions) {
+		const struct sock *ssk = (const struct sock *)tp;
+		struct mptcp_subflow_context *subflow;
+
+		subflow = mptcp_subflow_ctx(ssk);
+		subflow->send_mp_prio = 0;
+
+		*ptr++ = mptcp_option(MPTCPOPT_MP_PRIO,
+				      TCPOLEN_MPTCP_PRIO,
+				      opts->backup, TCPOPT_NOP);
+	}
+
 	if (OPTION_MPTCP_MPJ_SYN & opts->suboptions) {
 		*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
 				      TCPOLEN_MPTCP_MPJ_SYN,

net/mptcp/pm_netlink.c

@@ -442,6 +442,39 @@ void mptcp_pm_nl_add_addr_send_ack(struct mptcp_sock *msk)
 	}
 }
 
+int mptcp_pm_nl_mp_prio_send_ack(struct mptcp_sock *msk,
+				 struct mptcp_addr_info *addr,
+				 u8 bkup)
+{
+	struct mptcp_subflow_context *subflow;
+
+	pr_debug("bkup=%d", bkup);
+
+	mptcp_for_each_subflow(msk, subflow) {
+		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+		struct mptcp_addr_info local;
+
+		local_address((struct sock_common *)ssk, &local);
+		if (!addresses_equal(&local, addr, addr->port))
+			continue;
+
+		subflow->backup = bkup;
+		subflow->send_mp_prio = 1;
+		subflow->request_bkup = bkup;
+
+		spin_unlock_bh(&msk->pm.lock);
+		pr_debug("send ack for mp_prio");
+		lock_sock(ssk);
+		tcp_send_ack(ssk);
+		release_sock(ssk);
+		spin_lock_bh(&msk->pm.lock);
+
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
 void mptcp_pm_nl_rm_addr_received(struct mptcp_sock *msk)
 {
 	struct mptcp_subflow_context *subflow, *tmp;

net/mptcp/protocol.h

@@ -24,6 +24,7 @@
 #define OPTION_MPTCP_ADD_ADDR6	BIT(7)
 #define OPTION_MPTCP_RM_ADDR	BIT(8)
 #define OPTION_MPTCP_FASTCLOSE	BIT(9)
+#define OPTION_MPTCP_PRIO	BIT(10)
 
 /* MPTCP option subtypes */
 #define MPTCPOPT_MP_CAPABLE	0
@@ -59,6 +60,7 @@
 #define TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT	24
 #define TCPOLEN_MPTCP_PORT_LEN		4
 #define TCPOLEN_MPTCP_RM_ADDR_BASE	4
+#define TCPOLEN_MPTCP_PRIO		4
 #define TCPOLEN_MPTCP_FASTCLOSE		12
 
 /* MPTCP MP_JOIN flags */
@@ -396,6 +398,7 @@ struct mptcp_subflow_context {
 		map_valid : 1,
 		mpc_map : 1,
 		backup : 1,
+		send_mp_prio : 1,
 		rx_eof : 1,
 		can_ack : 1,        /* only after processing the remote a key */
 		disposable : 1;	    /* ctx can be free at ulp release time */
@@ -550,6 +553,9 @@ void mptcp_pm_add_addr_received(struct mptcp_sock *msk,
 				const struct mptcp_addr_info *addr);
 void mptcp_pm_add_addr_send_ack(struct mptcp_sock *msk);
 void mptcp_pm_rm_addr_received(struct mptcp_sock *msk, u8 rm_id);
+int mptcp_pm_nl_mp_prio_send_ack(struct mptcp_sock *msk,
+				 struct mptcp_addr_info *addr,
+				 u8 bkup);
 void mptcp_pm_free_anno_list(struct mptcp_sock *msk);
 struct mptcp_pm_add_entry *
 mptcp_pm_del_add_timer(struct mptcp_sock *msk,