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Commit 5d424d5a authored by John Heffner's avatar John Heffner Committed by David S. Miller
Browse files

[TCP]: MTU probing 

Implementation of packetization layer path mtu discovery for TCP, based on
the internet-draft currently found at
<http://www.ietf.org/internet-drafts/draft-ietf-pmtud-method-05.txt

>.

Signed-off-by: default avatarJohn Heffner <jheffner@psc.edu>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1d60290f

include/linux/sysctl.h

+2 −0
Original line number Diff line number Diff line
@@ -397,6 +397,8 @@ enum 
	NET_TCP_CONG_CONTROL=110,

	NET_TCP_ABC=111,

	NET_IPV4_IPFRAG_MAX_DIST=112,

 	NET_TCP_MTU_PROBING=113,

	NET_TCP_BASE_MSS=114,

};



enum {

include/net/inet_connection_sock.h

+13 −0
Original line number Diff line number Diff line
@@ -72,6 +72,7 @@ struct inet_connection_sock_af_ops { 
 * @icsk_probes_out:	   unanswered 0 window probes

 * @icsk_ext_hdr_len:	   Network protocol overhead (IP/IPv6 options)

 * @icsk_ack:		   Delayed ACK control data

 * @icsk_mtup;		   MTU probing control data

 */

struct inet_connection_sock {

	/* inet_sock has to be the first member! */
@@ -104,6 +105,18 @@ struct inet_connection_sock { 
		__u16		  last_seg_size; /* Size of last incoming segment	   */

		__u16		  rcv_mss;	 /* MSS used for delayed ACK decisions	   */ 

	} icsk_ack;

	struct {

		int		  enabled;



		/* Range of MTUs to search */

		int		  search_high;

		int		  search_low;



		/* Information on the current probe. */

		int		  probe_size;

		__u32		  probe_seq_start;

		__u32		  probe_seq_end;

	} icsk_mtup;

	u32			  icsk_ca_priv[16];

#define ICSK_CA_PRIV_SIZE	(16 * sizeof(u32))

};

include/net/tcp.h

+9 −0
Original line number Diff line number Diff line
@@ -60,6 +60,9 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo); 
/* Minimal RCV_MSS. */

#define TCP_MIN_RCVMSS		536U



/* The least MTU to use for probing */

#define TCP_BASE_MSS		512



/* After receiving this amount of duplicate ACKs fast retransmit starts. */

#define TCP_FASTRETRANS_THRESH 3
@@ -219,6 +222,8 @@ extern int sysctl_tcp_nometrics_save; 
extern int sysctl_tcp_moderate_rcvbuf;

extern int sysctl_tcp_tso_win_divisor;

extern int sysctl_tcp_abc;

extern int sysctl_tcp_mtu_probing;

extern int sysctl_tcp_base_mss;



extern atomic_t tcp_memory_allocated;

extern atomic_t tcp_sockets_allocated;
@@ -447,6 +452,10 @@ extern int tcp_read_sock(struct sock *sk, read_descriptor_t *desc, 


extern void tcp_initialize_rcv_mss(struct sock *sk);



extern int tcp_mtu_to_mss(struct sock *sk, int pmtu);

extern int tcp_mss_to_mtu(struct sock *sk, int mss);

extern void tcp_mtup_init(struct sock *sk);



static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)

{

	tp->pred_flags = htonl((tp->tcp_header_len << 26) |

net/ipv4/sysctl_net_ipv4.c

+16 −0
Original line number Diff line number Diff line
@@ -664,6 +664,22 @@ ctl_table ipv4_table[] = { 
		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

	},

	{

		.ctl_name	= NET_TCP_MTU_PROBING,

		.procname	= "tcp_mtu_probing",

		.data		= &sysctl_tcp_mtu_probing,

		.maxlen		= sizeof(int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

	},

	{

		.ctl_name	= NET_TCP_BASE_MSS,

		.procname	= "tcp_base_mss",

		.data		= &sysctl_tcp_base_mss,

		.maxlen		= sizeof(int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

	},



	{ .ctl_name = 0 }

};

net/ipv4/tcp_input.c

+49 −0
Original line number Diff line number Diff line
@@ -1891,6 +1891,34 @@ static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag) 
	}

}



static void tcp_mtup_probe_failed(struct sock *sk)

{

	struct inet_connection_sock *icsk = inet_csk(sk);



	icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;

	icsk->icsk_mtup.probe_size = 0;

}



static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct inet_connection_sock *icsk = inet_csk(sk);



	/* FIXME: breaks with very large cwnd */

	tp->prior_ssthresh = tcp_current_ssthresh(sk);

	tp->snd_cwnd = tp->snd_cwnd *

		       tcp_mss_to_mtu(sk, tp->mss_cache) /

		       icsk->icsk_mtup.probe_size;

	tp->snd_cwnd_cnt = 0;

	tp->snd_cwnd_stamp = tcp_time_stamp;

	tp->rcv_ssthresh = tcp_current_ssthresh(sk);



	icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;

	icsk->icsk_mtup.probe_size = 0;

	tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);

}





/* Process an event, which can update packets-in-flight not trivially.

 * Main goal of this function is to calculate new estimate for left_out,

 * taking into account both packets sitting in receiver's buffer and
@@ -2023,6 +2051,17 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una, 
			return;

		}



		/* MTU probe failure: don't reduce cwnd */

		if (icsk->icsk_ca_state < TCP_CA_CWR &&

		    icsk->icsk_mtup.probe_size &&

		    tp->snd_una == icsk->icsk_mtup.probe_seq_start) {

			tcp_mtup_probe_failed(sk);

			/* Restores the reduction we did in tcp_mtup_probe() */

			tp->snd_cwnd++;

			tcp_simple_retransmit(sk);

			return;

		}



		/* Otherwise enter Recovery state */



		if (IsReno(tp))
@@ -2243,6 +2282,13 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p) 
			tp->retrans_stamp = 0;

		}



		/* MTU probing checks */

		if (icsk->icsk_mtup.probe_size) {

			if (!after(icsk->icsk_mtup.probe_seq_end, TCP_SKB_CB(skb)->end_seq)) {

				tcp_mtup_probe_success(sk, skb);

			}

		}



		if (sacked) {

			if (sacked & TCPCB_RETRANS) {

				if(sacked & TCPCB_SACKED_RETRANS)
@@ -4101,6 +4147,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 
		if (tp->rx_opt.sack_ok && sysctl_tcp_fack)

			tp->rx_opt.sack_ok |= 2;



		tcp_mtup_init(sk);

		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);

		tcp_initialize_rcv_mss(sk);
@@ -4211,6 +4258,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, 
		if (tp->ecn_flags&TCP_ECN_OK)

			sock_set_flag(sk, SOCK_NO_LARGESEND);



		tcp_mtup_init(sk);

		tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);

		tcp_initialize_rcv_mss(sk);
@@ -4399,6 +4447,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 
				 */

				tp->lsndtime = tcp_time_stamp;



				tcp_mtup_init(sk);

				tcp_initialize_rcv_mss(sk);

				tcp_init_buffer_space(sk);

				tcp_fast_path_on(tp);