net/ipv4/tcp_cong.c - kernel/msm-4.9 - Gitiles

 /*
  * Plugable TCP congestion control support and newReno
  * congestion control.
  * Based on ideas from I/O scheduler support and Web100.
  *
  * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
  */

 #define pr_fmt(fmt) "TCP: " fmt

 #include <linux/module.h>
 #include <linux/mm.h>
 #include <linux/types.h>
 #include <linux/list.h>
 #include <linux/gfp.h>
 #include <net/tcp.h>

 static DEFINE_SPINLOCK(tcp_cong_list_lock);
 static LIST_HEAD(tcp_cong_list);

 /* Simple linear search, don't expect many entries! */
 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
 {
 	struct tcp_congestion_ops *e;

 	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
 		if (strcmp(e->name, name) == 0)
 			return e;
 	}

 	return NULL;
 }

 /*
  * Attach new congestion control algorithm to the list
  * of available options.
  */
 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
 {
 	int ret = 0;

 	/* all algorithms must implement ssthresh and cong_avoid ops */
 	if (!ca->ssthresh || !ca->cong_avoid) {
 		pr_err("%s does not implement required ops\n", ca->name);
 		return -EINVAL;
 	}

 	spin_lock(&tcp_cong_list_lock);
 	if (tcp_ca_find(ca->name)) {
 		pr_notice("%s already registered\n", ca->name);
 		ret = -EEXIST;
 	} else {
 		list_add_tail_rcu(&ca->list, &tcp_cong_list);
 		pr_info("%s registered\n", ca->name);
 	}
 	spin_unlock(&tcp_cong_list_lock);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);

 /*
  * Remove congestion control algorithm, called from
  * the module's remove function.  Module ref counts are used
  * to ensure that this can't be done till all sockets using
  * that method are closed.
  */
 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
 {
 	spin_lock(&tcp_cong_list_lock);
 	list_del_rcu(&ca->list);
 	spin_unlock(&tcp_cong_list_lock);
 }
 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);

 /* Assign choice of congestion control. */
 void tcp_init_congestion_control(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_congestion_ops *ca;

 	/* if no choice made yet assign the current value set as default */
 	if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
 		rcu_read_lock();
 		list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 			if (try_module_get(ca->owner)) {
 				icsk->icsk_ca_ops = ca;
 				break;
 			}

 			/* fallback to next available */
 		}
 		rcu_read_unlock();
 	}

 	if (icsk->icsk_ca_ops->init)
 		icsk->icsk_ca_ops->init(sk);
 }

 /* Manage refcounts on socket close. */
 void tcp_cleanup_congestion_control(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);

 	if (icsk->icsk_ca_ops->release)
 		icsk->icsk_ca_ops->release(sk);
 	module_put(icsk->icsk_ca_ops->owner);
 }

 /* Used by sysctl to change default congestion control */
 int tcp_set_default_congestion_control(const char *name)
 {
 	struct tcp_congestion_ops *ca;
 	int ret = -ENOENT;

 	spin_lock(&tcp_cong_list_lock);
 	ca = tcp_ca_find(name);
 #ifdef CONFIG_MODULES
 	if (!ca && capable(CAP_NET_ADMIN)) {
 		spin_unlock(&tcp_cong_list_lock);

 		request_module("tcp_%s", name);
 		spin_lock(&tcp_cong_list_lock);
 		ca = tcp_ca_find(name);
 	}
 #endif

 	if (ca) {
 		ca->flags |= TCP_CONG_NON_RESTRICTED;	/* default is always allowed */
 		list_move(&ca->list, &tcp_cong_list);
 		ret = 0;
 	}
 	spin_unlock(&tcp_cong_list_lock);

 	return ret;
 }

 /* Set default value from kernel configuration at bootup */
 static int __init tcp_congestion_default(void)
 {
 	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
 }
 late_initcall(tcp_congestion_default);


 /* Build string with list of available congestion control values */
 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
 {
 	struct tcp_congestion_ops *ca;
 	size_t offs = 0;

 	rcu_read_lock();
 	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 		offs += snprintf(buf + offs, maxlen - offs,
 				 "%s%s",
 				 offs == 0 ? "" : " ", ca->name);

 	}
 	rcu_read_unlock();
 }

 /* Get current default congestion control */
 void tcp_get_default_congestion_control(char *name)
 {
 	struct tcp_congestion_ops *ca;
 	/* We will always have reno... */
 	BUG_ON(list_empty(&tcp_cong_list));

 	rcu_read_lock();
 	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
 	strncpy(name, ca->name, TCP_CA_NAME_MAX);
 	rcu_read_unlock();
 }

 /* Built list of non-restricted congestion control values */
 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
 {
 	struct tcp_congestion_ops *ca;
 	size_t offs = 0;

 	*buf = '\0';
 	rcu_read_lock();
 	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 		if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
 			continue;
 		offs += snprintf(buf + offs, maxlen - offs,
 				 "%s%s",
 				 offs == 0 ? "" : " ", ca->name);

 	}
 	rcu_read_unlock();
 }

 /* Change list of non-restricted congestion control */
 int tcp_set_allowed_congestion_control(char *val)
 {
 	struct tcp_congestion_ops *ca;
 	char *saved_clone, *clone, *name;
 	int ret = 0;

 	saved_clone = clone = kstrdup(val, GFP_USER);
 	if (!clone)
 		return -ENOMEM;

 	spin_lock(&tcp_cong_list_lock);
 	/* pass 1 check for bad entries */
 	while ((name = strsep(&clone, " ")) && *name) {
 		ca = tcp_ca_find(name);
 		if (!ca) {
 			ret = -ENOENT;
 			goto out;
 		}
 	}

 	/* pass 2 clear old values */
 	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
 		ca->flags &= ~TCP_CONG_NON_RESTRICTED;

 	/* pass 3 mark as allowed */
 	while ((name = strsep(&val, " ")) && *name) {
 		ca = tcp_ca_find(name);
 		WARN_ON(!ca);
 		if (ca)
 			ca->flags |= TCP_CONG_NON_RESTRICTED;
 	}
 out:
 	spin_unlock(&tcp_cong_list_lock);
 	kfree(saved_clone);

 	return ret;
 }


 /* Change congestion control for socket */
 int tcp_set_congestion_control(struct sock *sk, const char *name)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_congestion_ops *ca;
 	int err = 0;

 	rcu_read_lock();
 	ca = tcp_ca_find(name);

 	/* no change asking for existing value */
 	if (ca == icsk->icsk_ca_ops)
 		goto out;

 #ifdef CONFIG_MODULES
 	/* not found attempt to autoload module */
 	if (!ca && capable(CAP_NET_ADMIN)) {
 		rcu_read_unlock();
 		request_module("tcp_%s", name);
 		rcu_read_lock();
 		ca = tcp_ca_find(name);
 	}
 #endif
 	if (!ca)
 		err = -ENOENT;

 	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
 		   ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
 		err = -EPERM;

 	else if (!try_module_get(ca->owner))
 		err = -EBUSY;

 	else {
 		tcp_cleanup_congestion_control(sk);
 		icsk->icsk_ca_ops = ca;

 		if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
 			icsk->icsk_ca_ops->init(sk);
 	}
  out:
 	rcu_read_unlock();
 	return err;
 }

 /* RFC2861 Check whether we are limited by application or congestion window
  * This is the inverse of cwnd check in tcp_tso_should_defer
  */
 bool tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	u32 left;

 	if (in_flight >= tp->snd_cwnd)
 		return true;

 	left = tp->snd_cwnd - in_flight;
 	if (sk_can_gso(sk) &&
 	    left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
 	    left * tp->mss_cache < sk->sk_gso_max_size &&
 	    left < sk->sk_gso_max_segs)
 		return true;
 	return left <= tcp_max_tso_deferred_mss(tp);
 }
 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);

 /* Slow start is used when congestion window is no greater than the slow start
  * threshold. We base on RFC2581 and also handle stretch ACKs properly.
  * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
  * something better;) a packet is only considered (s)acked in its entirety to
  * defend the ACK attacks described in the RFC. Slow start processes a stretch
  * ACK of degree N as if N acks of degree 1 are received back to back except
  * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
  * returns the leftover acks to adjust cwnd in congestion avoidance mode.
  */
 int tcp_slow_start(struct tcp_sock *tp, u32 acked)
 {
 	u32 cwnd = tp->snd_cwnd + acked;

 	if (cwnd > tp->snd_ssthresh)
 		cwnd = tp->snd_ssthresh + 1;
 	acked -= cwnd - tp->snd_cwnd;
 	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
 	return acked;
 }
 EXPORT_SYMBOL_GPL(tcp_slow_start);

 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
 {
 	if (tp->snd_cwnd_cnt >= w) {
 		if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 			tp->snd_cwnd++;
 		tp->snd_cwnd_cnt = 0;
 	} else {
 		tp->snd_cwnd_cnt++;
 	}
 }
 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);

 /*
  * TCP Reno congestion control
  * This is special case used for fallback as well.
  */
 /* This is Jacobson's slow start and congestion avoidance.
  * SIGCOMM '88, p. 328.
  */
 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked, u32 in_flight)
 {
 	struct tcp_sock *tp = tcp_sk(sk);

 	if (!tcp_is_cwnd_limited(sk, in_flight))
 		return;

 	/* In "safe" area, increase. */
 	if (tp->snd_cwnd <= tp->snd_ssthresh)
 		tcp_slow_start(tp, acked);
 	/* In dangerous area, increase slowly. */
 	else
 		tcp_cong_avoid_ai(tp, tp->snd_cwnd);
 }
 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);

 /* Slow start threshold is half the congestion window (min 2) */
 u32 tcp_reno_ssthresh(struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	return max(tp->snd_cwnd >> 1U, 2U);
 }
 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);

 /* Lower bound on congestion window with halving. */
 u32 tcp_reno_min_cwnd(const struct sock *sk)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	return tp->snd_ssthresh/2;
 }
 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);

 struct tcp_congestion_ops tcp_reno = {
 	.flags		= TCP_CONG_NON_RESTRICTED,
 	.name		= "reno",
 	.owner		= THIS_MODULE,
 	.ssthresh	= tcp_reno_ssthresh,
 	.cong_avoid	= tcp_reno_cong_avoid,
 	.min_cwnd	= tcp_reno_min_cwnd,
 };

 /* Initial congestion control used (until SYN)
  * really reno under another name so we can tell difference
  * during tcp_set_default_congestion_control
  */
 struct tcp_congestion_ops tcp_init_congestion_ops  = {
 	.name		= "",
 	.owner		= THIS_MODULE,
 	.ssthresh	= tcp_reno_ssthresh,
 	.cong_avoid	= tcp_reno_cong_avoid,
 	.min_cwnd	= tcp_reno_min_cwnd,
 };
 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);
	/*
	* Plugable TCP congestion control support and newReno
	* congestion control.
	* Based on ideas from I/O scheduler support and Web100.
	*
	* Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
	*/

	#define pr_fmt(fmt) "TCP: " fmt

	#include <linux/module.h>
	#include <linux/mm.h>
	#include <linux/types.h>
	#include <linux/list.h>
	#include <linux/gfp.h>
	#include <net/tcp.h>

	static DEFINE_SPINLOCK(tcp_cong_list_lock);
	static LIST_HEAD(tcp_cong_list);

	/* Simple linear search, don't expect many entries! */
	static struct tcp_congestion_ops tcp_ca_find(const char name)
	{
	struct tcp_congestion_ops *e;

	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
	if (strcmp(e->name, name) == 0)
	return e;
	}

	return NULL;
	}

	/*
	* Attach new congestion control algorithm to the list
	* of available options.
	*/
	int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
	{
	int ret = 0;

	/* all algorithms must implement ssthresh and cong_avoid ops */
	if (!ca->ssthresh \|\| !ca->cong_avoid) {
	pr_err("%s does not implement required ops\n", ca->name);
	return -EINVAL;
	}

	spin_lock(&tcp_cong_list_lock);
	if (tcp_ca_find(ca->name)) {
	pr_notice("%s already registered\n", ca->name);
	ret = -EEXIST;
	} else {
	list_add_tail_rcu(&ca->list, &tcp_cong_list);
	pr_info("%s registered\n", ca->name);
	}
	spin_unlock(&tcp_cong_list_lock);

	return ret;
	}
	EXPORT_SYMBOL_GPL(tcp_register_congestion_control);

	/*
	* Remove congestion control algorithm, called from
	* the module's remove function. Module ref counts are used
	* to ensure that this can't be done till all sockets using
	* that method are closed.
	*/
	void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
	{
	spin_lock(&tcp_cong_list_lock);
	list_del_rcu(&ca->list);
	spin_unlock(&tcp_cong_list_lock);
	}
	EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);

	/* Assign choice of congestion control. */
	void tcp_init_congestion_control(struct sock *sk)
	{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_congestion_ops *ca;

	/* if no choice made yet assign the current value set as default */
	if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
	rcu_read_lock();
	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	if (try_module_get(ca->owner)) {
	icsk->icsk_ca_ops = ca;
	break;
	}

	/* fallback to next available */
	}
	rcu_read_unlock();
	}

	if (icsk->icsk_ca_ops->init)
	icsk->icsk_ca_ops->init(sk);
	}

	/* Manage refcounts on socket close. */
	void tcp_cleanup_congestion_control(struct sock *sk)
	{
	struct inet_connection_sock *icsk = inet_csk(sk);

	if (icsk->icsk_ca_ops->release)
	icsk->icsk_ca_ops->release(sk);
	module_put(icsk->icsk_ca_ops->owner);
	}

	/* Used by sysctl to change default congestion control */
	int tcp_set_default_congestion_control(const char *name)
	{
	struct tcp_congestion_ops *ca;
	int ret = -ENOENT;

	spin_lock(&tcp_cong_list_lock);
	ca = tcp_ca_find(name);
	#ifdef CONFIG_MODULES
	if (!ca && capable(CAP_NET_ADMIN)) {
	spin_unlock(&tcp_cong_list_lock);

	request_module("tcp_%s", name);
	spin_lock(&tcp_cong_list_lock);
	ca = tcp_ca_find(name);
	}
	#endif

	if (ca) {
	ca->flags \|= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
	list_move(&ca->list, &tcp_cong_list);
	ret = 0;
	}
	spin_unlock(&tcp_cong_list_lock);

	return ret;
	}

	/* Set default value from kernel configuration at bootup */
	static int __init tcp_congestion_default(void)
	{
	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
	}
	late_initcall(tcp_congestion_default);


	/* Build string with list of available congestion control values */
	void tcp_get_available_congestion_control(char *buf, size_t maxlen)
	{
	struct tcp_congestion_ops *ca;
	size_t offs = 0;

	rcu_read_lock();
	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	offs += snprintf(buf + offs, maxlen - offs,
	"%s%s",
	offs == 0 ? "" : " ", ca->name);

	}
	rcu_read_unlock();
	}

	/* Get current default congestion control */
	void tcp_get_default_congestion_control(char *name)
	{
	struct tcp_congestion_ops *ca;
	/* We will always have reno... */
	BUG_ON(list_empty(&tcp_cong_list));

	rcu_read_lock();
	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
	strncpy(name, ca->name, TCP_CA_NAME_MAX);
	rcu_read_unlock();
	}

	/* Built list of non-restricted congestion control values */
	void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
	{
	struct tcp_congestion_ops *ca;
	size_t offs = 0;

	*buf = '\0';
	rcu_read_lock();
	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
	continue;
	offs += snprintf(buf + offs, maxlen - offs,
	"%s%s",
	offs == 0 ? "" : " ", ca->name);

	}
	rcu_read_unlock();
	}

	/* Change list of non-restricted congestion control */
	int tcp_set_allowed_congestion_control(char *val)
	{
	struct tcp_congestion_ops *ca;
	char saved_clone, clone, *name;
	int ret = 0;

	saved_clone = clone = kstrdup(val, GFP_USER);
	if (!clone)
	return -ENOMEM;

	spin_lock(&tcp_cong_list_lock);
	/* pass 1 check for bad entries */
	while ((name = strsep(&clone, " ")) && *name) {
	ca = tcp_ca_find(name);
	if (!ca) {
	ret = -ENOENT;
	goto out;
	}
	}

	/* pass 2 clear old values */
	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
	ca->flags &= ~TCP_CONG_NON_RESTRICTED;

	/* pass 3 mark as allowed */
	while ((name = strsep(&val, " ")) && *name) {
	ca = tcp_ca_find(name);
	WARN_ON(!ca);
	if (ca)
	ca->flags \|= TCP_CONG_NON_RESTRICTED;
	}
	out:
	spin_unlock(&tcp_cong_list_lock);
	kfree(saved_clone);

	return ret;
	}


	/* Change congestion control for socket */
	int tcp_set_congestion_control(struct sock sk, const char name)
	{
	struct inet_connection_sock *icsk = inet_csk(sk);
	struct tcp_congestion_ops *ca;
	int err = 0;

	rcu_read_lock();
	ca = tcp_ca_find(name);

	/* no change asking for existing value */
	if (ca == icsk->icsk_ca_ops)
	goto out;

	#ifdef CONFIG_MODULES
	/* not found attempt to autoload module */
	if (!ca && capable(CAP_NET_ADMIN)) {
	rcu_read_unlock();
	request_module("tcp_%s", name);
	rcu_read_lock();
	ca = tcp_ca_find(name);
	}
	#endif
	if (!ca)
	err = -ENOENT;

	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) \|\|
	ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
	err = -EPERM;

	else if (!try_module_get(ca->owner))
	err = -EBUSY;

	else {
	tcp_cleanup_congestion_control(sk);
	icsk->icsk_ca_ops = ca;

	if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
	icsk->icsk_ca_ops->init(sk);
	}
	out:
	rcu_read_unlock();
	return err;
	}

	/* RFC2861 Check whether we are limited by application or congestion window
	* This is the inverse of cwnd check in tcp_tso_should_defer
	*/
	bool tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
	{
	const struct tcp_sock *tp = tcp_sk(sk);
	u32 left;

	if (in_flight >= tp->snd_cwnd)
	return true;

	left = tp->snd_cwnd - in_flight;
	if (sk_can_gso(sk) &&
	left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
	left * tp->mss_cache < sk->sk_gso_max_size &&
	left < sk->sk_gso_max_segs)
	return true;
	return left <= tcp_max_tso_deferred_mss(tp);
	}
	EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);

	/* Slow start is used when congestion window is no greater than the slow start
	* threshold. We base on RFC2581 and also handle stretch ACKs properly.
	* We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
	* something better;) a packet is only considered (s)acked in its entirety to
	* defend the ACK attacks described in the RFC. Slow start processes a stretch
	* ACK of degree N as if N acks of degree 1 are received back to back except
	* ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
	* returns the leftover acks to adjust cwnd in congestion avoidance mode.
	*/
	int tcp_slow_start(struct tcp_sock *tp, u32 acked)
	{
	u32 cwnd = tp->snd_cwnd + acked;

	if (cwnd > tp->snd_ssthresh)
	cwnd = tp->snd_ssthresh + 1;
	acked -= cwnd - tp->snd_cwnd;
	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
	return acked;
	}
	EXPORT_SYMBOL_GPL(tcp_slow_start);

	/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
	void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
	{
	if (tp->snd_cwnd_cnt >= w) {
	if (tp->snd_cwnd < tp->snd_cwnd_clamp)
	tp->snd_cwnd++;
	tp->snd_cwnd_cnt = 0;
	} else {
	tp->snd_cwnd_cnt++;
	}
	}
	EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);

	/*
	* TCP Reno congestion control
	* This is special case used for fallback as well.
	*/
	/* This is Jacobson's slow start and congestion avoidance.
	* SIGCOMM '88, p. 328.
	*/
	void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked, u32 in_flight)
	{
	struct tcp_sock *tp = tcp_sk(sk);

	if (!tcp_is_cwnd_limited(sk, in_flight))
	return;

	/* In "safe" area, increase. */
	if (tp->snd_cwnd <= tp->snd_ssthresh)
	tcp_slow_start(tp, acked);
	/* In dangerous area, increase slowly. */
	else
	tcp_cong_avoid_ai(tp, tp->snd_cwnd);
	}
	EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);

	/* Slow start threshold is half the congestion window (min 2) */
	u32 tcp_reno_ssthresh(struct sock *sk)
	{
	const struct tcp_sock *tp = tcp_sk(sk);
	return max(tp->snd_cwnd >> 1U, 2U);
	}
	EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);

	/* Lower bound on congestion window with halving. */
	u32 tcp_reno_min_cwnd(const struct sock *sk)
	{
	const struct tcp_sock *tp = tcp_sk(sk);
	return tp->snd_ssthresh/2;
	}
	EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);

	struct tcp_congestion_ops tcp_reno = {
	.flags = TCP_CONG_NON_RESTRICTED,
	.name = "reno",
	.owner = THIS_MODULE,
	.ssthresh = tcp_reno_ssthresh,
	.cong_avoid = tcp_reno_cong_avoid,
	.min_cwnd = tcp_reno_min_cwnd,
	};

	/* Initial congestion control used (until SYN)
	* really reno under another name so we can tell difference
	* during tcp_set_default_congestion_control
	*/
	struct tcp_congestion_ops tcp_init_congestion_ops = {
	.name = "",
	.owner = THIS_MODULE,
	.ssthresh = tcp_reno_ssthresh,
	.cong_avoid = tcp_reno_cong_avoid,
	.min_cwnd = tcp_reno_min_cwnd,
	};
	EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);