Commit bc88ad75 authored by Paul Sokolovsky's avatar Paul Sokolovsky Committed by Jukka Rissanen
Browse files

net: tcp: Handle storage of TCP send MSS 



MSS is Maximum Segment Size (data payload) of TCP. In SYN packets,
each side of the connection shares an MSS it wants to use (receive)
via the corresponding TCP option. If the option is not available,
the RFC mandates use of the value 536.

This patch handles storage of the send MSS (in the TCP structure,
in TCP backlog), with follow up patch handling actual parsing it
from the SYN TCP options.

Signed-off-by: default avatarPaul Sokolovsky <paul.sokolovsky@linaro.org>
parent 682a2074

subsys/net/ip/net_context.c

+9 −2
Original line number Diff line number Diff line
@@ -99,6 +99,7 @@ static struct tcp_backlog_entry { 
	u32_t recv_max_ack;

	u32_t send_seq;

	u32_t send_ack;

	u16_t send_mss;

	struct k_delayed_work ack_timer;

} tcp_backlog[CONFIG_NET_TCP_BACKLOG_SIZE];
@@ -174,7 +175,8 @@ static int tcp_backlog_find(struct net_pkt *pkt, int *empty_slot) 
	return -EADDRNOTAVAIL;

}



static int tcp_backlog_syn(struct net_pkt *pkt, struct net_context *context)

static int tcp_backlog_syn(struct net_pkt *pkt, struct net_context *context,

			   u16_t send_mss)

{

	int empty_slot = -1;

	int ret;
@@ -198,6 +200,7 @@ static int tcp_backlog_syn(struct net_pkt *pkt, struct net_context *context) 
	tcp_backlog[empty_slot].recv_max_ack = context->tcp->recv_max_ack;

	tcp_backlog[empty_slot].send_seq = context->tcp->send_seq;

	tcp_backlog[empty_slot].send_ack = context->tcp->send_ack;

	tcp_backlog[empty_slot].send_mss = send_mss;



	k_delayed_work_init(&tcp_backlog[empty_slot].ack_timer,

			    backlog_ack_timeout);
@@ -232,6 +235,7 @@ static int tcp_backlog_ack(struct net_pkt *pkt, struct net_context *context) 
	context->tcp->recv_max_ack = tcp_backlog[r].recv_max_ack;

	context->tcp->send_seq = tcp_backlog[r].send_seq + 1;

	context->tcp->send_ack = tcp_backlog[r].send_ack;

	context->tcp->send_mss = tcp_backlog[r].send_mss;



	k_delayed_work_cancel(&tcp_backlog[r].ack_timer);

	memset(&tcp_backlog[r], 0, sizeof(struct tcp_backlog_entry));
@@ -1610,6 +1614,7 @@ NET_CONN_CB(tcp_syn_rcvd) 
	 */

	if (NET_TCP_FLAGS(tcp_hdr) == NET_TCP_SYN) {

		int r;

		u16_t send_mss = NET_TCP_DEFAULT_MSS;



		net_tcp_print_recv_info("SYN", pkt, tcp_hdr->src_port);
@@ -1621,7 +1626,9 @@ NET_CONN_CB(tcp_syn_rcvd) 
			sys_get_be32(tcp_hdr->seq) + 1;

		context->tcp->recv_max_ack = context->tcp->send_seq + 1;



		r = tcp_backlog_syn(pkt, context);

		/* Get MSS from TCP options here*/



		r = tcp_backlog_syn(pkt, context, send_mss);

		if (r < 0) {

			if (r == -EADDRINUSE) {

				NET_DBG("TCP connection already exists");

subsys/net/ip/tcp.c

+1 −0
Original line number Diff line number Diff line
@@ -238,6 +238,7 @@ struct net_tcp *net_tcp_alloc(struct net_context *context) 
	tcp_context[i].send_seq = tcp_init_isn();

	tcp_context[i].recv_max_ack = tcp_context[i].send_seq + 1u;

	tcp_context[i].recv_wnd = min(NET_TCP_MAX_WIN, NET_TCP_BUF_MAX_LEN);

	tcp_context[i].send_mss = NET_TCP_DEFAULT_MSS;



	tcp_context[i].accept_cb = NULL;

subsys/net/ip/tcp.h

+13 −0
Original line number Diff line number Diff line
@@ -72,6 +72,11 @@ enum net_tcp_state { 


#define NET_TCP_FLAGS(hdr) (hdr->flags & NET_TCP_CTL)



/* RFC 1122 4.2.2.6 "If an MSS option is not received at connection

 * setup, TCP MUST assume a default send MSS of 536"

 */

#define NET_TCP_DEFAULT_MSS   536



/* TCP max window size */

#define NET_TCP_MAX_WIN   (4 * 1024)
@@ -148,7 +153,15 @@ struct net_tcp { 
	 */

	struct k_sem connect_wait;



	/**

	 * Current TCP receive window for our side

	 */

	u16_t recv_wnd;



	/**

	 * Send MSS for the peer

	 */

	u16_t send_mss;

};



static inline bool net_tcp_is_used(struct net_tcp *tcp)

CRA Git | Maintained and supported by SUSTech CRA and CCSE