retry.c File Reference

Retry timers. More...

#include <stddef.h>
#include <gpxe/timer.h>
#include <gpxe/list.h>
#include <gpxe/process.h>
#include <gpxe/init.h>
#include <gpxe/retry.h>

Go to the source code of this file.

Defines
#define	MIN_TIMEOUT   7
Functions
	FILE_LICENCE (GPL2_OR_LATER)
static	LIST_HEAD (timers)
	List of running timers.
void	start_timer (struct retry_timer *timer)
	Start timer.
void	start_timer_fixed (struct retry_timer *timer, unsigned long timeout)
	Start timer with a specified fixed timeout.
void	stop_timer (struct retry_timer *timer)
	Stop timer.
static void	timer_expired (struct retry_timer *timer)
	Handle expired timer.
static void	retry_step (struct process *process __unused)
	Single-step the retry timer list.
Variables
struct process retry_process	__permanent_process
	Retry timer process.

---

Detailed Description

Retry timers.

A retry timer is a binary exponential backoff timer. It can be used to build automatic retransmission into network protocols.

This implementation of the timer is designed to satisfy RFC 2988 and therefore be usable as a TCP retransmission timer.

Definition in file retry.c.

---

Define Documentation

#define MIN_TIMEOUT   7

Definition at line 45 of file retry.c.

Referenced by start_timer().

---

Function Documentation

FILE_LICENCE

(

GPL2_OR_LATER

)

static LIST_HEAD

(

timers

)

[static]

List of running timers.

void start_timer

(

struct retry_timer *

timer

)

Start timer.

Parameters:

timer

Retry timer

This starts the timer running with the current timeout value. If stop_timer() is not called before the timer expires, the timer will be stopped and the timer's callback function will be called.

Definition at line 59 of file retry.c.

References currticks(), DBG2, DEFAULT_MIN_TIMEOUT, retry_timer::list, list_add, MIN_TIMEOUT, retry_timer::min_timeout, retry_timer::running, retry_timer::start, and retry_timer::timeout.

Referenced by aoe_send_command(), dhcp_tx(), dns_send_packet(), ib_mi_timer_expired(), ipv4_reassemble(), slam_master_timer_expired(), slam_slave_timer_expired(), slam_socket_deliver(), start_timer_fixed(), tcp_rx(), tcp_xmit(), and tftp_send_packet().

                                               {
        if ( ! timer->running )
                list_add ( &timer->list, &timers );
        timer->start = currticks();
        timer->running = 1;

        /* 0 means "use default timeout" */
        if ( timer->min_timeout == 0 )
                timer->min_timeout = DEFAULT_MIN_TIMEOUT;
        /* We must never be less than MIN_TIMEOUT under any circumstances */
        if ( timer->min_timeout < MIN_TIMEOUT )
                timer->min_timeout = MIN_TIMEOUT;
        /* Honor user-specified minimum timeout */
        if ( timer->timeout < timer->min_timeout )
                timer->timeout = timer->min_timeout;

        DBG2 ( "Timer %p started at time %ld (expires at %ld)\n",
               timer, timer->start, ( timer->start + timer->timeout ) );
}

void start_timer_fixed	(	struct retry_timer *	timer,
		unsigned long	timeout
	)

Start timer with a specified fixed timeout.

Parameters:

	timer	Retry timer
	timeout	Timeout, in ticks

Definition at line 85 of file retry.c.

References DBG2, retry_timer::start, start_timer(), and retry_timer::timeout.

Referenced by slam_mc_socket_deliver(), slam_open(), and start_timer_nodelay().

                                                                            {
        start_timer ( timer );
        timer->timeout = timeout;
        DBG2 ( "Timer %p expiry time changed to %ld\n",
               timer, ( timer->start + timer->timeout ) );
}

void stop_timer

(

struct retry_timer *

timer

)

Stop timer.

Parameters:

timer

Retry timer

This stops the timer and updates the timer's timeout value.

Definition at line 99 of file retry.c.

References retry_timer::count, currticks(), DBG, DBG2, retry_timer::list, list_del, retry_timer::running, retry_timer::start, and retry_timer::timeout.

Referenced by aoe_detach(), aoe_done(), aoe_rx_ata(), dhcp_finished(), dhcp_set_state(), dns_done(), dns_xfer_deliver_raw(), ib_destroy_madx(), slam_finished(), slam_mc_socket_deliver(), slam_socket_deliver(), tcp_close(), tcp_rx_ack(), tftp_done(), and tftp_send_packet().

                                              {
        unsigned long old_timeout = timer->timeout;
        unsigned long now = currticks();
        unsigned long runtime;

        /* If timer was already stopped, do nothing */
        if ( ! timer->running )
                return;

        list_del ( &timer->list );
        runtime = ( now - timer->start );
        timer->running = 0;
        DBG2 ( "Timer %p stopped at time %ld (ran for %ld)\n",
               timer, now, runtime );

        /* Update timer.  Variables are:
         *
         *   r = round-trip time estimate (i.e. runtime)
         *   t = timeout value (i.e. timer->timeout)
         *   s = smoothed round-trip time
         *
         * By choice, we set t = 4s, i.e. allow for four times the
         * normal round-trip time to pass before retransmitting.
         *
         * We want to smooth according to s := ( 7 s + r ) / 8
         *
         * Since we don't actually store s, this reduces to
         * t := ( 7 t / 8 ) + ( r / 2 )
         *
         */
        if ( timer->count ) {
                timer->count--;
        } else {
                timer->timeout -= ( timer->timeout >> 3 );
                timer->timeout += ( runtime >> 1 );
                if ( timer->timeout != old_timeout ) {
                        DBG ( "Timer %p timeout updated to %ld\n",
                              timer, timer->timeout );
                }
        }
}

static void timer_expired

(

struct retry_timer *

timer

)

[static]

Handle expired timer.

Parameters:

timer

Retry timer

Definition at line 146 of file retry.c.

References assert, retry_timer::count, currticks(), DBG, DBG2, DEFAULT_MAX_TIMEOUT, retry_timer::expired, retry_timer::list, list_del, retry_timer::max_timeout, retry_timer::running, and retry_timer::timeout.

Referenced by retry_step().

                                                        {
        int fail;

        /* Stop timer without performing RTT calculations */
        DBG2 ( "Timer %p stopped at time %ld on expiry\n",
               timer, currticks() );
        assert ( timer->running );
        list_del ( &timer->list );
        timer->running = 0;
        timer->count++;

        /* Back off the timeout value */
        timer->timeout <<= 1;
        if ( timer->max_timeout == 0 ) /* 0 means "use default timeout" */
                timer->max_timeout = DEFAULT_MAX_TIMEOUT;
        if ( ( fail = ( timer->timeout > timer->max_timeout ) ) )
                timer->timeout = timer->max_timeout;
        DBG ( "Timer %p timeout backed off to %ld\n",
              timer, timer->timeout );

        /* Call expiry callback */
        timer->expired ( timer, fail ); 
}

static void retry_step

(

struct process *process

__unused

)

[static]

Single-step the retry timer list.

Parameters:

process

Retry timer process

Definition at line 175 of file retry.c.

References currticks(), retry_timer::list, list_for_each_entry_safe, retry_timer::start, retry_timer::timeout, and timer_expired().

                                                            {
        struct retry_timer *timer;
        struct retry_timer *tmp;
        unsigned long now = currticks();
        unsigned long used;

        list_for_each_entry_safe ( timer, tmp, &timers, list ) {
                used = ( now - timer->start );
                if ( used >= timer->timeout )
                        timer_expired ( timer );
        }
}

---

Variable Documentation

struct process retry_process __permanent_process

Initial value:

 {
        .list = LIST_HEAD_INIT ( retry_process.list ),
        .step = retry_step,
}

Retry timer process.

Definition at line 189 of file retry.c.