[deliverable/linux.git] / net / ipv4 / tcp_cong.c

/*
 * Pluggable 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 <linux/jhash.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;
}

/* Must be called with rcu lock held */
static const struct tcp_congestion_ops *__tcp_ca_find_autoload(const char *name)
{
	const struct tcp_congestion_ops *ca = tcp_ca_find(name);
#ifdef CONFIG_MODULES
	if (!ca && capable(CAP_NET_ADMIN)) {
		rcu_read_unlock();
		request_module("tcp_%s", name);
		rcu_read_lock();
		ca = tcp_ca_find(name);
	}
#endif
	return ca;
}

/* Simple linear search, not much in here. */
struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
{
	struct tcp_congestion_ops *e;

	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
		if (e->key == key)
			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;
	}

	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));

	spin_lock(&tcp_cong_list_lock);
	if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
		pr_notice("%s already registered or non-unique key\n",
			  ca->name);
		ret = -EEXIST;
	} else {
		list_add_tail_rcu(&ca->list, &tcp_cong_list);
		pr_debug("%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);

	/* Wait for outstanding readers to complete before the
	 * module gets removed entirely.
	 *
	 * A try_module_get() should fail by now as our module is
	 * in "going" state since no refs are held anymore and
	 * module_exit() handler being called.
	 */
	synchronize_rcu();
}
EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);

u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca)
{
	const struct tcp_congestion_ops *ca;
	u32 key = TCP_CA_UNSPEC;

	might_sleep();

	rcu_read_lock();
	ca = __tcp_ca_find_autoload(name);
	if (ca) {
		key = ca->key;
		*ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
	}
	rcu_read_unlock();

	return key;
}
EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);

char *tcp_ca_get_name_by_key(u32 key, char *buffer)
{
	const struct tcp_congestion_ops *ca;
	char *ret = NULL;

	rcu_read_lock();
	ca = tcp_ca_find_key(key);
	if (ca)
		ret = strncpy(buffer, ca->name,
			      TCP_CA_NAME_MAX);
	rcu_read_unlock();

	return ret;
}
EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);

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

	rcu_read_lock();
	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
		if (likely(try_module_get(ca->owner))) {
			icsk->icsk_ca_ops = ca;
			goto out;
		}
		/* Fallback to next available. The last really
		 * guaranteed fallback is Reno from this list.
		 */
	}
out:
	rcu_read_unlock();

	/* Clear out private data before diag gets it and
	 * the ca has not been initialized.
	 */
	if (ca->get_info)
		memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
	if (ca->flags & TCP_CONG_NEEDS_ECN)
		INET_ECN_xmit(sk);
	else
		INET_ECN_dontxmit(sk);
}

void tcp_init_congestion_control(struct sock *sk)
{
	const struct inet_connection_sock *icsk = inet_csk(sk);

	if (icsk->icsk_ca_ops->init)
		icsk->icsk_ca_ops->init(sk);
	if (tcp_ca_needs_ecn(sk))
		INET_ECN_xmit(sk);
	else
		INET_ECN_dontxmit(sk);
}

static void tcp_reinit_congestion_control(struct sock *sk,
					  const struct tcp_congestion_ops *ca)
{
	struct inet_connection_sock *icsk = inet_csk(sk);

	tcp_cleanup_congestion_control(sk);
	icsk->icsk_ca_ops = ca;
	icsk->icsk_ca_setsockopt = 1;

	if (sk->sk_state != TCP_CLOSE)
		tcp_init_congestion_control(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);
	const struct tcp_congestion_ops *ca;
	int err = 0;

	if (icsk->icsk_ca_dst_locked)
		return -EPERM;

	rcu_read_lock();
	ca = __tcp_ca_find_autoload(name);
	/* No change asking for existing value */
	if (ca == icsk->icsk_ca_ops) {
		icsk->icsk_ca_setsockopt = 1;
		goto out;
	}
	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_reinit_congestion_control(sk, ca);
 out:
	rcu_read_unlock();
	return err;
}

/* 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.
 */
u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
{
	u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);

	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),
 * for every packet that was ACKed.
 */
void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
{
	/* If credits accumulated at a higher w, apply them gently now. */
	if (tp->snd_cwnd_cnt >= w) {
		tp->snd_cwnd_cnt = 0;
		tp->snd_cwnd++;
	}

	tp->snd_cwnd_cnt += acked;
	if (tp->snd_cwnd_cnt >= w) {
		u32 delta = tp->snd_cwnd_cnt / w;

		tp->snd_cwnd_cnt -= delta * w;
		tp->snd_cwnd += delta;
	}
	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
}
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)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (!tcp_is_cwnd_limited(sk))
		return;

	/* In "safe" area, increase. */
	if (tcp_in_slow_start(tp)) {
		acked = tcp_slow_start(tp, acked);
		if (!acked)
			return;
	}
	/* In dangerous area, increase slowly. */
	tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
}
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);

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,
};
Commit	Line	Data
317a76f9	1	/*
b92022f3	2	* Pluggable TCP congestion control support and newReno
317a76f9	3	* congestion control.
02582e9b	4	* Based on ideas from I/O scheduler support and Web100.
317a76f9 SH	5	*
	6	* Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
	7	*/
	8
afd46503 JP	9	#define pr_fmt(fmt) "TCP: " fmt
afd46503 JP	10
317a76f9 SH	11	#include <linux/module.h>
	12	#include <linux/mm.h>
	13	#include <linux/types.h>
	14	#include <linux/list.h>
5a0e3ad6	15	#include <linux/gfp.h>
c5c6a8ab	16	#include <linux/jhash.h>
317a76f9 SH	17	#include <net/tcp.h>
	18
	19	static DEFINE_SPINLOCK(tcp_cong_list_lock);
	20	static LIST_HEAD(tcp_cong_list);
	21
	22	/* Simple linear search, don't expect many entries! */
	23	static struct tcp_congestion_ops tcp_ca_find(const char name)
	24	{
	25	struct tcp_congestion_ops *e;
	26
5f8ef48d	27	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
317a76f9 SH	28	if (strcmp(e->name, name) == 0)
	29	return e;
	30	}
	31
	32	return NULL;
	33	}
	34
c5c6a8ab DB	35	/* Must be called with rcu lock held */
	36	static const struct tcp_congestion_ops __tcp_ca_find_autoload(const char name)
	37	{
	38	const struct tcp_congestion_ops *ca = tcp_ca_find(name);
	39	#ifdef CONFIG_MODULES
	40	if (!ca && capable(CAP_NET_ADMIN)) {
	41	rcu_read_unlock();
	42	request_module("tcp_%s", name);
	43	rcu_read_lock();
	44	ca = tcp_ca_find(name);
	45	}
	46	#endif
	47	return ca;
	48	}
	49
	50	/* Simple linear search, not much in here. */
	51	struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
	52	{
	53	struct tcp_congestion_ops *e;
	54
	55	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
	56	if (e->key == key)
	57	return e;
	58	}
	59
	60	return NULL;
	61	}
	62
317a76f9	63	/*
d08df601	64	* Attach new congestion control algorithm to the list
317a76f9 SH	65	* of available options.
	66	*/
	67	int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
	68	{
	69	int ret = 0;
	70
	71	/* all algorithms must implement ssthresh and cong_avoid ops */
72dc5b92	72	if (!ca->ssthresh \|\| !ca->cong_avoid) {
afd46503	73	pr_err("%s does not implement required ops\n", ca->name);
317a76f9 SH	74	return -EINVAL;
	75	}
	76
c5c6a8ab DB	77	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
c5c6a8ab DB	78
317a76f9	79	spin_lock(&tcp_cong_list_lock);
c5c6a8ab DB	80	if (ca->key == TCP_CA_UNSPEC \|\| tcp_ca_find_key(ca->key)) {
	81	pr_notice("%s already registered or non-unique key\n",
	82	ca->name);
317a76f9 SH	83	ret = -EEXIST;
317a76f9 SH	84	} else {
3d2573f7	85	list_add_tail_rcu(&ca->list, &tcp_cong_list);
db2855ae	86	pr_debug("%s registered\n", ca->name);
317a76f9 SH	87	}
	88	spin_unlock(&tcp_cong_list_lock);
	89
	90	return ret;
	91	}
	92	EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
	93
	94	/*
	95	* Remove congestion control algorithm, called from
	96	* the module's remove function. Module ref counts are used
	97	* to ensure that this can't be done till all sockets using
	98	* that method are closed.
	99	*/
	100	void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
	101	{
	102	spin_lock(&tcp_cong_list_lock);
	103	list_del_rcu(&ca->list);
	104	spin_unlock(&tcp_cong_list_lock);
c5c6a8ab DB	105
	106	/* Wait for outstanding readers to complete before the
	107	* module gets removed entirely.
	108	*
	109	* A try_module_get() should fail by now as our module is
	110	* in "going" state since no refs are held anymore and
	111	* module_exit() handler being called.
	112	*/
	113	synchronize_rcu();
317a76f9 SH	114	}
	115	EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
	116
c3a8d947	117	u32 tcp_ca_get_key_by_name(const char name, bool ecn_ca)
c5c6a8ab DB	118	{
c5c6a8ab DB	119	const struct tcp_congestion_ops *ca;
c3a8d947	120	u32 key = TCP_CA_UNSPEC;
c5c6a8ab DB	121
	122	might_sleep();
	123
	124	rcu_read_lock();
	125	ca = __tcp_ca_find_autoload(name);
c3a8d947 DB	126	if (ca) {
	127	key = ca->key;
	128	*ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
	129	}
c5c6a8ab DB	130	rcu_read_unlock();
	131
	132	return key;
	133	}
	134	EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
	135
	136	char tcp_ca_get_name_by_key(u32 key, char buffer)
	137	{
	138	const struct tcp_congestion_ops *ca;
	139	char *ret = NULL;
	140
	141	rcu_read_lock();
	142	ca = tcp_ca_find_key(key);
	143	if (ca)
	144	ret = strncpy(buffer, ca->name,
	145	TCP_CA_NAME_MAX);
	146	rcu_read_unlock();
	147
	148	return ret;
	149	}
	150	EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
	151
317a76f9	152	/* Assign choice of congestion control. */
55d8694f	153	void tcp_assign_congestion_control(struct sock *sk)
317a76f9	154	{
6687e988	155	struct inet_connection_sock *icsk = inet_csk(sk);
317a76f9 SH	156	struct tcp_congestion_ops *ca;
317a76f9 SH	157
55d8694f FW	158	rcu_read_lock();
	159	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	160	if (likely(try_module_get(ca->owner))) {
	161	icsk->icsk_ca_ops = ca;
	162	goto out;
317a76f9	163	}
55d8694f FW	164	/* Fallback to next available. The last really
	165	* guaranteed fallback is Reno from this list.
	166	*/
317a76f9	167	}
55d8694f FW	168	out:
	169	rcu_read_unlock();
	170
	171	/* Clear out private data before diag gets it and
	172	* the ca has not been initialized.
	173	*/
	174	if (ca->get_info)
	175	memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
6ac705b1 ED	176	if (ca->flags & TCP_CONG_NEEDS_ECN)
	177	INET_ECN_xmit(sk);
	178	else
	179	INET_ECN_dontxmit(sk);
55d8694f FW	180	}
	181
	182	void tcp_init_congestion_control(struct sock *sk)
	183	{
	184	const struct inet_connection_sock *icsk = inet_csk(sk);
317a76f9	185
6687e988 ACM	186	if (icsk->icsk_ca_ops->init)
6687e988 ACM	187	icsk->icsk_ca_ops->init(sk);
6ac705b1 ED	188	if (tcp_ca_needs_ecn(sk))
	189	INET_ECN_xmit(sk);
	190	else
	191	INET_ECN_dontxmit(sk);
317a76f9 SH	192	}
317a76f9 SH	193
29ba4fff DB	194	static void tcp_reinit_congestion_control(struct sock *sk,
	195	const struct tcp_congestion_ops *ca)
	196	{
	197	struct inet_connection_sock *icsk = inet_csk(sk);
	198
	199	tcp_cleanup_congestion_control(sk);
	200	icsk->icsk_ca_ops = ca;
9f950415	201	icsk->icsk_ca_setsockopt = 1;
29ba4fff	202
6ac705b1 ED	203	if (sk->sk_state != TCP_CLOSE)
6ac705b1 ED	204	tcp_init_congestion_control(sk);
29ba4fff DB	205	}
29ba4fff DB	206
317a76f9	207	/* Manage refcounts on socket close. */
6687e988	208	void tcp_cleanup_congestion_control(struct sock *sk)
317a76f9	209	{
6687e988 ACM	210	struct inet_connection_sock *icsk = inet_csk(sk);
	211
	212	if (icsk->icsk_ca_ops->release)
	213	icsk->icsk_ca_ops->release(sk);
	214	module_put(icsk->icsk_ca_ops->owner);
317a76f9 SH	215	}
	216
	217	/* Used by sysctl to change default congestion control */
	218	int tcp_set_default_congestion_control(const char *name)
	219	{
	220	struct tcp_congestion_ops *ca;
	221	int ret = -ENOENT;
	222
	223	spin_lock(&tcp_cong_list_lock);
	224	ca = tcp_ca_find(name);
95a5afca	225	#ifdef CONFIG_MODULES
a8f80e8f	226	if (!ca && capable(CAP_NET_ADMIN)) {
317a76f9 SH	227	spin_unlock(&tcp_cong_list_lock);
	228
	229	request_module("tcp_%s", name);
	230	spin_lock(&tcp_cong_list_lock);
	231	ca = tcp_ca_find(name);
	232	}
	233	#endif
	234
	235	if (ca) {
164891aa	236	ca->flags \|= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
317a76f9 SH	237	list_move(&ca->list, &tcp_cong_list);
	238	ret = 0;
	239	}
	240	spin_unlock(&tcp_cong_list_lock);
	241
	242	return ret;
	243	}
	244
b1736a71 SH	245	/* Set default value from kernel configuration at bootup */
	246	static int __init tcp_congestion_default(void)
	247	{
	248	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
	249	}
	250	late_initcall(tcp_congestion_default);
	251
3ff825b2 SH	252	/* Build string with list of available congestion control values */
	253	void tcp_get_available_congestion_control(char *buf, size_t maxlen)
	254	{
	255	struct tcp_congestion_ops *ca;
	256	size_t offs = 0;
	257
	258	rcu_read_lock();
	259	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	260	offs += snprintf(buf + offs, maxlen - offs,
	261	"%s%s",
	262	offs == 0 ? "" : " ", ca->name);
3ff825b2 SH	263	}
	264	rcu_read_unlock();
	265	}
	266
317a76f9 SH	267	/* Get current default congestion control */
	268	void tcp_get_default_congestion_control(char *name)
	269	{
	270	struct tcp_congestion_ops *ca;
	271	/* We will always have reno... */
	272	BUG_ON(list_empty(&tcp_cong_list));
	273
	274	rcu_read_lock();
	275	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
	276	strncpy(name, ca->name, TCP_CA_NAME_MAX);
	277	rcu_read_unlock();
	278	}
	279
ce7bc3bf SH	280	/* Built list of non-restricted congestion control values */
	281	void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
	282	{
	283	struct tcp_congestion_ops *ca;
	284	size_t offs = 0;
	285
	286	*buf = '\0';
	287	rcu_read_lock();
	288	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
164891aa	289	if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
ce7bc3bf SH	290	continue;
	291	offs += snprintf(buf + offs, maxlen - offs,
	292	"%s%s",
	293	offs == 0 ? "" : " ", ca->name);
ce7bc3bf SH	294	}
	295	rcu_read_unlock();
	296	}
	297
	298	/* Change list of non-restricted congestion control */
	299	int tcp_set_allowed_congestion_control(char *val)
	300	{
	301	struct tcp_congestion_ops *ca;
c34186ed	302	char saved_clone, clone, *name;
ce7bc3bf SH	303	int ret = 0;
ce7bc3bf SH	304
c34186ed	305	saved_clone = clone = kstrdup(val, GFP_USER);
ce7bc3bf SH	306	if (!clone)
	307	return -ENOMEM;
	308
	309	spin_lock(&tcp_cong_list_lock);
	310	/* pass 1 check for bad entries */
	311	while ((name = strsep(&clone, " ")) && *name) {
	312	ca = tcp_ca_find(name);
	313	if (!ca) {
	314	ret = -ENOENT;
	315	goto out;
	316	}
	317	}
	318
164891aa	319	/* pass 2 clear old values */
ce7bc3bf	320	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
164891aa	321	ca->flags &= ~TCP_CONG_NON_RESTRICTED;
ce7bc3bf SH	322
	323	/* pass 3 mark as allowed */
	324	while ((name = strsep(&val, " ")) && *name) {
	325	ca = tcp_ca_find(name);
	326	WARN_ON(!ca);
	327	if (ca)
164891aa	328	ca->flags \|= TCP_CONG_NON_RESTRICTED;
ce7bc3bf SH	329	}
	330	out:
	331	spin_unlock(&tcp_cong_list_lock);
c34186ed	332	kfree(saved_clone);
ce7bc3bf SH	333
	334	return ret;
	335	}
	336
5f8ef48d	337	/* Change congestion control for socket */
6687e988	338	int tcp_set_congestion_control(struct sock sk, const char name)
5f8ef48d	339	{
6687e988	340	struct inet_connection_sock *icsk = inet_csk(sk);
c5c6a8ab	341	const struct tcp_congestion_ops *ca;
5f8ef48d SH	342	int err = 0;
5f8ef48d SH	343
c5c6a8ab DB	344	if (icsk->icsk_ca_dst_locked)
c5c6a8ab DB	345	return -EPERM;
4d4d3d1e	346
c5c6a8ab DB	347	rcu_read_lock();
	348	ca = __tcp_ca_find_autoload(name);
	349	/* No change asking for existing value */
9f950415 NC	350	if (ca == icsk->icsk_ca_ops) {
9f950415 NC	351	icsk->icsk_ca_setsockopt = 1;
5f8ef48d	352	goto out;
9f950415	353	}
5f8ef48d SH	354	if (!ca)
5f8ef48d SH	355	err = -ENOENT;
52e804c6 EB	356	else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) \|\|
52e804c6 EB	357	ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
ce7bc3bf	358	err = -EPERM;
5f8ef48d SH	359	else if (!try_module_get(ca->owner))
5f8ef48d SH	360	err = -EBUSY;
29ba4fff DB	361	else
29ba4fff DB	362	tcp_reinit_congestion_control(sk, ca);
5f8ef48d SH	363	out:
	364	rcu_read_unlock();
	365	return err;
	366	}
	367
9f9843a7 YC	368	/* Slow start is used when congestion window is no greater than the slow start
	369	* threshold. We base on RFC2581 and also handle stretch ACKs properly.
	370	* We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
	371	* something better;) a packet is only considered (s)acked in its entirety to
	372	* defend the ACK attacks described in the RFC. Slow start processes a stretch
	373	* ACK of degree N as if N acks of degree 1 are received back to back except
	374	* ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
	375	* returns the leftover acks to adjust cwnd in congestion avoidance mode.
40efc6fa	376	*/
e73ebb08	377	u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
40efc6fa	378	{
76174004	379	u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
a02ba041	380
e73ebb08	381	acked -= cwnd - tp->snd_cwnd;
9f9843a7	382	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
e73ebb08 NC	383
e73ebb08 NC	384	return acked;
40efc6fa SH	385	}
	386	EXPORT_SYMBOL_GPL(tcp_slow_start);
	387
814d488c NC	388	/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
	389	* for every packet that was ACKed.
	390	*/
e73ebb08	391	void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
758ce5c8	392	{
9949afa4 NC	393	/* If credits accumulated at a higher w, apply them gently now. */
	394	if (tp->snd_cwnd_cnt >= w) {
	395	tp->snd_cwnd_cnt = 0;
	396	tp->snd_cwnd++;
	397	}
	398
814d488c	399	tp->snd_cwnd_cnt += acked;
758ce5c8	400	if (tp->snd_cwnd_cnt >= w) {
814d488c NC	401	u32 delta = tp->snd_cwnd_cnt / w;
	402
	403	tp->snd_cwnd_cnt -= delta * w;
	404	tp->snd_cwnd += delta;
758ce5c8	405	}
814d488c	406	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
758ce5c8 IJ	407	}
	408	EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
	409
317a76f9 SH	410	/*
	411	* TCP Reno congestion control
	412	* This is special case used for fallback as well.
	413	*/
	414	/* This is Jacobson's slow start and congestion avoidance.
	415	* SIGCOMM '88, p. 328.
	416	*/
24901551	417	void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
317a76f9	418	{
6687e988 ACM	419	struct tcp_sock *tp = tcp_sk(sk);
6687e988 ACM	420
24901551	421	if (!tcp_is_cwnd_limited(sk))
317a76f9 SH	422	return;
317a76f9 SH	423
7faffa1c	424	/* In "safe" area, increase. */
071d5080	425	if (tcp_in_slow_start(tp)) {
c22bdca9 NC	426	acked = tcp_slow_start(tp, acked);
	427	if (!acked)
	428	return;
	429	}
e905a9ed	430	/* In dangerous area, increase slowly. */
c22bdca9	431	tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
317a76f9 SH	432	}
	433	EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
	434
	435	/* Slow start threshold is half the congestion window (min 2) */
6687e988	436	u32 tcp_reno_ssthresh(struct sock *sk)
317a76f9	437	{
6687e988	438	const struct tcp_sock *tp = tcp_sk(sk);
688d1945	439
317a76f9 SH	440	return max(tp->snd_cwnd >> 1U, 2U);
	441	}
	442	EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
	443
317a76f9	444	struct tcp_congestion_ops tcp_reno = {
164891aa	445	.flags = TCP_CONG_NON_RESTRICTED,
317a76f9 SH	446	.name = "reno",
	447	.owner = THIS_MODULE,
	448	.ssthresh = tcp_reno_ssthresh,
	449	.cong_avoid = tcp_reno_cong_avoid,
317a76f9	450	};