diff options
Diffstat (limited to 'contrib/syslinux-4.02/gpxe/src/net/retry.c')
| -rw-r--r-- | contrib/syslinux-4.02/gpxe/src/net/retry.c | 192 |
1 files changed, 192 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/gpxe/src/net/retry.c b/contrib/syslinux-4.02/gpxe/src/net/retry.c new file mode 100644 index 0000000..40f656f --- /dev/null +++ b/contrib/syslinux-4.02/gpxe/src/net/retry.c @@ -0,0 +1,192 @@ +/* + * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of the + * License, or any later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ + +FILE_LICENCE ( GPL2_OR_LATER ); + +#include <stddef.h> +#include <gpxe/timer.h> +#include <gpxe/list.h> +#include <gpxe/process.h> +#include <gpxe/init.h> +#include <gpxe/retry.h> + +/** @file + * + * 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. + * + * + */ + +/* The theoretical minimum that the algorithm in stop_timer() can + * adjust the timeout back down to is seven ticks, so set the minimum + * timeout to at least that value for the sake of consistency. + */ +#define MIN_TIMEOUT 7 + +/** List of running timers */ +static LIST_HEAD ( timers ); + +/** + * Start timer + * + * @v 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. + */ +void start_timer ( struct retry_timer *timer ) { + 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 ) ); +} + +/** + * Start timer with a specified fixed timeout + * + * @v timer Retry timer + * @v timeout Timeout, in ticks + */ +void start_timer_fixed ( struct retry_timer *timer, unsigned long timeout ) { + start_timer ( timer ); + timer->timeout = timeout; + DBG2 ( "Timer %p expiry time changed to %ld\n", + timer, ( timer->start + timer->timeout ) ); +} + +/** + * Stop timer + * + * @v timer Retry timer + * + * This stops the timer and updates the timer's timeout value. + */ +void stop_timer ( struct retry_timer *timer ) { + 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 ); + } + } +} + +/** + * Handle expired timer + * + * @v timer Retry timer + */ +static void timer_expired ( struct retry_timer *timer ) { + 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 ); +} + +/** + * Single-step the retry timer list + * + * @v process Retry timer process + */ +static void retry_step ( struct process *process __unused ) { + 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 ); + } +} + +/** Retry timer process */ +struct process retry_process __permanent_process = { + .list = LIST_HEAD_INIT ( retry_process.list ), + .step = retry_step, +}; |