Commit 4712a792 authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

[DCCP]: Provide function for RTT sampling 



A recurring problem, in particular in the CCID code, is that RTT samples
from packets with timestamp echo and elapsed time options need to be taken.

This service is provided via a new function dccp_sample_rtt in this patch.
Furthermore, to protect against `insane' RTT samples, the sampled value
is bounded between 100 microseconds and 4 seconds - for which u32 is sufficient.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0c150efb

net/dccp/dccp.h

+8 −2
Original line number Diff line number Diff line
@@ -71,11 +71,15 @@ extern void dccp_time_wait(struct sock *sk, int state, int timeo); 
/* RFC 1122, 4.2.3.1 initial RTO value */

#define DCCP_TIMEOUT_INIT ((unsigned)(3 * HZ))



#define DCCP_RTO_MAX ((unsigned)(120 * HZ)) /* FIXME: using TCP value */



/* bounds for sampled RTT values from packet exchanges (in usec) */

#define DCCP_SANE_RTT_MIN	100

#define DCCP_SANE_RTT_MAX	(4 * USEC_PER_SEC)



/* Maximal interval between probes for local resources.  */

#define DCCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ / 2U))



#define DCCP_RTO_MAX ((unsigned)(120 * HZ)) /* FIXME: using TCP value */



/* sysctl variables for DCCP */

extern int  sysctl_dccp_request_retries;

extern int  sysctl_dccp_retries1;
@@ -292,6 +296,8 @@ extern int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, 
extern int	   dccp_send_reset(struct sock *sk, enum dccp_reset_codes code);

extern void	   dccp_send_close(struct sock *sk, const int active);

extern int	   dccp_invalid_packet(struct sk_buff *skb);

extern u32	   dccp_sample_rtt(struct sock *sk, struct timeval *t_recv,

						    struct timeval *t_history);



static inline int dccp_bad_service_code(const struct sock *sk,

					const __be32 service)

net/dccp/input.c

+40 −0
Original line number Diff line number Diff line
@@ -577,3 +577,43 @@ discard: 
}



EXPORT_SYMBOL_GPL(dccp_rcv_state_process);



/**

 * dccp_sample_rtt  -  Sample RTT from packet exchange

 *

 * @sk:     connected dccp_sock

 * @t_recv: receive timestamp of packet with timestamp echo

 * @t_hist: packet history timestamp or NULL

 */

u32 dccp_sample_rtt(struct sock *sk, struct timeval *t_recv,

				     struct timeval *t_hist)

{

	struct dccp_sock *dp = dccp_sk(sk);

	struct dccp_options_received *or = &dp->dccps_options_received;

	suseconds_t delta;



	if (t_hist == NULL) {

		if (!or->dccpor_timestamp_echo) {

			DCCP_WARN("packet without timestamp echo\n");

			return DCCP_SANE_RTT_MAX;

		}

		timeval_sub_usecs(t_recv, or->dccpor_timestamp_echo * 10);

		delta = timeval_usecs(t_recv);

	} else

		delta = timeval_delta(t_recv, t_hist);



	delta -= or->dccpor_elapsed_time * 10;		/* either set or 0 */



	if (unlikely(delta <= 0)) {

		DCCP_WARN("unusable RTT sample %ld, using min\n", (long)delta);

		return DCCP_SANE_RTT_MIN;

	}

	if (unlikely(delta - (suseconds_t)DCCP_SANE_RTT_MAX > 0)) {

		DCCP_WARN("RTT sample %ld too large, using max\n", (long)delta);

		return DCCP_SANE_RTT_MAX;

	}



	return delta;

}



EXPORT_SYMBOL_GPL(dccp_sample_rtt);

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