/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2007-2008
 *	Swinburne University of Technology, Melbourne, Australia.
 * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
 * Copyright (c) 2010 The FreeBSD Foundation
 * All rights reserved.
 *
 * This software was developed at the Centre for Advanced Internet
 * Architectures, Swinburne University of Technology, by Lawrence Stewart and
 * James Healy, made possible in part by a grant from the Cisco University
 * Research Program Fund at Community Foundation Silicon Valley.
 *
 * Portions of this software were developed at the Centre for Advanced
 * Internet Architectures, Swinburne University of Technology, Melbourne,
 * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * This software was first released in 2007 by James Healy and Lawrence Stewart
 * whilst working on the NewTCP research project at Swinburne University of
 * Technology's Centre for Advanced Internet Architectures, Melbourne,
 * Australia, which was made possible in part by a grant from the Cisco
 * University Research Program Fund at Community Foundation Silicon Valley.
 * More details are available at:
 *   http://caia.swin.edu.au/urp/newtcp/
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: releng/12.0/sys/netinet/cc/cc.c 331214 2018-03-19 16:37:47Z lstewart $");

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/libkern.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/mutex.h>
#include <sys/queue.h>
#include <sys/rwlock.h>
#include <sys/sbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/sysctl.h>

#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_pcb.h>
#include <netinet/tcp.h>
#include <netinet/tcp_var.h>
#include <netinet/cc/cc.h>

#include <netinet/cc/cc_module.h>

/*
 * List of available cc algorithms on the current system. First element
 * is used as the system default CC algorithm.
 */
struct cc_head cc_list = STAILQ_HEAD_INITIALIZER(cc_list);

/* Protects the cc_list TAILQ. */
struct rwlock cc_list_lock;

VNET_DEFINE(struct cc_algo *, default_cc_ptr) = &newreno_cc_algo;

/*
 * Sysctl handler to show and change the default CC algorithm.
 */
static int
cc_default_algo(SYSCTL_HANDLER_ARGS)
{
	char default_cc[TCP_CA_NAME_MAX];
	struct cc_algo *funcs;
	int error;

	/* Get the current default: */
	CC_LIST_RLOCK();
	strlcpy(default_cc, CC_DEFAULT()->name, sizeof(default_cc));
	CC_LIST_RUNLOCK();

	error = sysctl_handle_string(oidp, default_cc, sizeof(default_cc), req);

	/* Check for error or no change */
	if (error != 0 || req->newptr == NULL)
		goto done;

	error = ESRCH;

	/* Find algo with specified name and set it to default. */
	CC_LIST_RLOCK();
	STAILQ_FOREACH(funcs, &cc_list, entries) {
		if (strncmp(default_cc, funcs->name, sizeof(default_cc)))
			continue;
		V_default_cc_ptr = funcs;
		error = 0;
		break;
	}
	CC_LIST_RUNLOCK();
done:
	return (error);
}

/*
 * Sysctl handler to display the list of available CC algorithms.
 */
static int
cc_list_available(SYSCTL_HANDLER_ARGS)
{
	struct cc_algo *algo;
	struct sbuf *s;
	int err, first, nalgos;

	err = nalgos = 0;
	first = 1;

	CC_LIST_RLOCK();
	STAILQ_FOREACH(algo, &cc_list, entries) {
		nalgos++;
	}
	CC_LIST_RUNLOCK();

	s = sbuf_new(NULL, NULL, nalgos * TCP_CA_NAME_MAX, SBUF_FIXEDLEN);

	if (s == NULL)
		return (ENOMEM);

	/*
	 * It is theoretically possible for the CC list to have grown in size
	 * since the call to sbuf_new() and therefore for the sbuf to be too
	 * small. If this were to happen (incredibly unlikely), the sbuf will
	 * reach an overflow condition, sbuf_printf() will return an error and
	 * the sysctl will fail gracefully.
	 */
	CC_LIST_RLOCK();
	STAILQ_FOREACH(algo, &cc_list, entries) {
		err = sbuf_printf(s, first ? "%s" : ", %s", algo->name);
		if (err) {
			/* Sbuf overflow condition. */
			err = EOVERFLOW;
			break;
		}
		first = 0;
	}
	CC_LIST_RUNLOCK();

	if (!err) {
		sbuf_finish(s);
		err = sysctl_handle_string(oidp, sbuf_data(s), 0, req);
	}

	sbuf_delete(s);
	return (err);
}

/*
 * Reset the default CC algo to NewReno for any netstack which is using the algo
 * that is about to go away as its default.
 */
static void
cc_checkreset_default(struct cc_algo *remove_cc)
{
	VNET_ITERATOR_DECL(vnet_iter);

	CC_LIST_LOCK_ASSERT();

	VNET_LIST_RLOCK_NOSLEEP();
	VNET_FOREACH(vnet_iter) {
		CURVNET_SET(vnet_iter);
		if (strncmp(CC_DEFAULT()->name, remove_cc->name,
		    TCP_CA_NAME_MAX) == 0)
			V_default_cc_ptr = &newreno_cc_algo;
		CURVNET_RESTORE();
	}
	VNET_LIST_RUNLOCK_NOSLEEP();
}

/*
 * Initialise CC subsystem on system boot.
 */
static void
cc_init(void)
{
	CC_LIST_LOCK_INIT();
	STAILQ_INIT(&cc_list);
}

/*
 * Returns non-zero on success, 0 on failure.
 */
int
cc_deregister_algo(struct cc_algo *remove_cc)
{
	struct cc_algo *funcs, *tmpfuncs;
	int err;

	err = ENOENT;

	/* Never allow newreno to be deregistered. */
	if (&newreno_cc_algo == remove_cc)
		return (EPERM);

	/* Remove algo from cc_list so that new connections can't use it. */
	CC_LIST_WLOCK();
	STAILQ_FOREACH_SAFE(funcs, &cc_list, entries, tmpfuncs) {
		if (funcs == remove_cc) {
			cc_checkreset_default(remove_cc);
			STAILQ_REMOVE(&cc_list, funcs, cc_algo, entries);
			err = 0;
			break;
		}
	}
	CC_LIST_WUNLOCK();

	if (!err)
		/*
		 * XXXLAS:
		 * - We may need to handle non-zero return values in future.
		 * - If we add CC framework support for protocols other than
		 *   TCP, we may want a more generic way to handle this step.
		 */
		tcp_ccalgounload(remove_cc);

	return (err);
}

/*
 * Returns 0 on success, non-zero on failure.
 */
int
cc_register_algo(struct cc_algo *add_cc)
{
	struct cc_algo *funcs;
	int err;

	err = 0;

	/*
	 * Iterate over list of registered CC algorithms and make sure
	 * we're not trying to add a duplicate.
	 */
	CC_LIST_WLOCK();
	STAILQ_FOREACH(funcs, &cc_list, entries) {
		if (funcs == add_cc || strncmp(funcs->name, add_cc->name,
		    TCP_CA_NAME_MAX) == 0)
			err = EEXIST;
	}

	if (!err)
		STAILQ_INSERT_TAIL(&cc_list, add_cc, entries);

	CC_LIST_WUNLOCK();

	return (err);
}

/*
 * Handles kld related events. Returns 0 on success, non-zero on failure.
 */
int
cc_modevent(module_t mod, int event_type, void *data)
{
	struct cc_algo *algo;
	int err;

	err = 0;
	algo = (struct cc_algo *)data;

	switch(event_type) {
	case MOD_LOAD:
		if (algo->mod_init != NULL)
			err = algo->mod_init();
		if (!err)
			err = cc_register_algo(algo);
		break;

	case MOD_QUIESCE:
	case MOD_SHUTDOWN:
	case MOD_UNLOAD:
		err = cc_deregister_algo(algo);
		if (!err && algo->mod_destroy != NULL)
			algo->mod_destroy();
		if (err == ENOENT)
			err = 0;
		break;

	default:
		err = EINVAL;
		break;
	}

	return (err);
}

SYSINIT(cc, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_FIRST, cc_init, NULL);

/* Declare sysctl tree and populate it. */
SYSCTL_NODE(_net_inet_tcp, OID_AUTO, cc, CTLFLAG_RW, NULL,
    "Congestion control related settings");

SYSCTL_PROC(_net_inet_tcp_cc, OID_AUTO, algorithm,
    CTLFLAG_VNET | CTLTYPE_STRING | CTLFLAG_RW,
    NULL, 0, cc_default_algo, "A", "Default congestion control algorithm");

SYSCTL_PROC(_net_inet_tcp_cc, OID_AUTO, available, CTLTYPE_STRING|CTLFLAG_RD,
    NULL, 0, cc_list_available, "A",
    "List available congestion control algorithms");

VNET_DEFINE(int, cc_do_abe) = 0;
SYSCTL_INT(_net_inet_tcp_cc, OID_AUTO, abe, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(cc_do_abe), 0,
    "Enable draft-ietf-tcpm-alternativebackoff-ecn (TCP Alternative Backoff with ECN)");

VNET_DEFINE(int, cc_abe_frlossreduce) = 0;
SYSCTL_INT(_net_inet_tcp_cc, OID_AUTO, abe_frlossreduce, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(cc_abe_frlossreduce), 0,
    "Apply standard beta instead of ABE-beta during ECN-signalled congestion "
    "recovery episodes if loss also needs to be repaired");
