109 lines
3.5 KiB
C
109 lines
3.5 KiB
C
/* gprs_codel.h
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*
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* This is an implementation of the CoDel algorithm based on the reference
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* pseudocode (see http://queue.acm.org/appendices/codel.html).
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* Instead of abstracting the queue itself, the following implementation
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* provides a time stamp based automaton. The main work is done by a single
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* decision function which updates the state and tells whether to pass or to
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* drop a packet after it has been taken from the queue.
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*
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* Copyright (C) 2015 by Sysmocom s.f.m.c. GmbH
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* Author: Jacob Erlbeck <jerlbeck@sysmocom.de>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*/
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#pragma once
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#include <time.h>
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/* Spec default values */
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#define GPRS_CODEL_DEFAULT_INTERVAL_MS 100
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#define GPRS_CODEL_DEFAULT_MAXPACKET 512
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#ifdef __cplusplus
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extern "C" {
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#endif
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struct gprs_codel {
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int dropping;
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unsigned count;
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struct timespec first_above_time;
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struct timespec drop_next;
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struct timespec target;
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struct timespec interval;
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unsigned maxpacket;
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};
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/*!
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* \brief Decide about packet drop and update CoDel state
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*
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* This function takes timing information and decides whether the packet in
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* question should be dropped in order to keep related queue in a 'good' state.
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* The function is meant to be called when the packet is dequeued.
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*
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* The CoDel state is updated by this function.
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*
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* \param state A pointer to the CoDel state of this queue
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* \param recv The time when the packet has entered the queue,
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* use NULL if dequeueing was not possible because the queue is
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* empty
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* \param now The current (dequeueing) time
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* \param bytes The number of bytes currently stored in the queue (-1 if
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* unknown)
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*
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* \return != 0 if the packet should be dropped, 0 otherwise
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*/
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int gprs_codel_control(struct gprs_codel *state, const struct timespec *recv,
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const struct timespec *now, int bytes);
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/*!
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* \brief Initialise CoDel state
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*
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* This function initialises the CoDel state object. It sets the interval time
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* to the default value (GPRS_CODEL_DEFAULT_INTERVAL_MS).
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*
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* \param state A pointer to the CoDel state of this queue
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*/
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void gprs_codel_init(struct gprs_codel *state);
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/*!
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* \brief Set interval time
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*
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* This function changes the interval time.
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* The target time is derived from the interval time as proposed in the spec
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* (5% of interval time).
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*
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* \param state A pointer to the CoDel state of this queue
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* \param interval_ms The initial interval in ms to be used (<= 0 selects the
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* default value)
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*/
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void gprs_codel_set_interval(struct gprs_codel *state, int interval_ms);
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/*!
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* \brief Set max packet size
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*
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* This function changes the maxpacket value. If no more than this number of
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* bytes are still stored in the queue, no dropping will be done.
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*
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* \param state A pointer to the CoDel state of this queue
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* \param maxpacket The value in bytes
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*/
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void gprs_codel_set_maxpacket(struct gprs_codel *state, int maxpacket);
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#ifdef __cplusplus
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}
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#endif
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