[mirror_ubuntu-artful-kernel.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 these */
	if (!ca->ssthresh || !ca->undo_cwnd ||
	    !(ca->cong_avoid || ca->cong_control)) {
		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();
	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);

	tcp_sk(sk)->prior_ssthresh = 0;
	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;
	memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));

	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. If load is false, then it is the
 * responsibility of the caller to call tcp_init_congestion_control or
 * tcp_reinit_congestion_control (if the current congestion control was
 * already initialized.
 */
int tcp_set_congestion_control(struct sock *sk, const char *name, bool load, bool reinit)
{
	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();
	if (!load)
		ca = tcp_ca_find(name);
	else
		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 (!load) {
		const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;

		if (try_module_get(ca->owner)) {
			if (reinit) {
				tcp_reinit_congestion_control(sk, ca);
			} else {
				icsk->icsk_ca_ops = ca;
				module_put(old_ca->owner);
			}
		} else {
			err = -EBUSY;
		}
	} 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);

u32 tcp_reno_undo_cwnd(struct sock *sk)
{
	const struct tcp_sock *tp = tcp_sk(sk);

	return max(tp->snd_cwnd, tp->snd_ssthresh << 1);
}
EXPORT_SYMBOL_GPL(tcp_reno_undo_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,
	.undo_cwnd	= tcp_reno_undo_cwnd,
};
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
e9799183 FW	71	/* all algorithms must implement these */
	72	if (!ca->ssthresh \|\| !ca->undo_cwnd \|\|
	73	!(ca->cong_avoid \|\| ca->cong_control)) {
afd46503	74	pr_err("%s does not implement required ops\n", ca->name);
317a76f9 SH	75	return -EINVAL;
	76	}
	77
c5c6a8ab DB	78	ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
c5c6a8ab DB	79
317a76f9	80	spin_lock(&tcp_cong_list_lock);
c5c6a8ab DB	81	if (ca->key == TCP_CA_UNSPEC \|\| tcp_ca_find_key(ca->key)) {
	82	pr_notice("%s already registered or non-unique key\n",
	83	ca->name);
317a76f9 SH	84	ret = -EEXIST;
317a76f9 SH	85	} else {
3d2573f7	86	list_add_tail_rcu(&ca->list, &tcp_cong_list);
db2855ae	87	pr_debug("%s registered\n", ca->name);
317a76f9 SH	88	}
	89	spin_unlock(&tcp_cong_list_lock);
	90
	91	return ret;
	92	}
	93	EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
	94
	95	/*
	96	* Remove congestion control algorithm, called from
	97	* the module's remove function. Module ref counts are used
	98	* to ensure that this can't be done till all sockets using
	99	* that method are closed.
	100	*/
	101	void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
	102	{
	103	spin_lock(&tcp_cong_list_lock);
	104	list_del_rcu(&ca->list);
	105	spin_unlock(&tcp_cong_list_lock);
c5c6a8ab DB	106
	107	/* Wait for outstanding readers to complete before the
	108	* module gets removed entirely.
	109	*
	110	* A try_module_get() should fail by now as our module is
	111	* in "going" state since no refs are held anymore and
	112	* module_exit() handler being called.
	113	*/
	114	synchronize_rcu();
317a76f9 SH	115	}
	116	EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
	117
c3a8d947	118	u32 tcp_ca_get_key_by_name(const char name, bool ecn_ca)
c5c6a8ab DB	119	{
c5c6a8ab DB	120	const struct tcp_congestion_ops *ca;
c3a8d947	121	u32 key = TCP_CA_UNSPEC;
c5c6a8ab DB	122
	123	might_sleep();
	124
	125	rcu_read_lock();
	126	ca = __tcp_ca_find_autoload(name);
c3a8d947 DB	127	if (ca) {
	128	key = ca->key;
	129	*ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
	130	}
c5c6a8ab DB	131	rcu_read_unlock();
	132
	133	return key;
	134	}
	135	EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
	136
	137	char tcp_ca_get_name_by_key(u32 key, char buffer)
	138	{
	139	const struct tcp_congestion_ops *ca;
	140	char *ret = NULL;
	141
	142	rcu_read_lock();
	143	ca = tcp_ca_find_key(key);
	144	if (ca)
	145	ret = strncpy(buffer, ca->name,
	146	TCP_CA_NAME_MAX);
	147	rcu_read_unlock();
	148
	149	return ret;
	150	}
	151	EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
	152
317a76f9	153	/* Assign choice of congestion control. */
55d8694f	154	void tcp_assign_congestion_control(struct sock *sk)
317a76f9	155	{
6687e988	156	struct inet_connection_sock *icsk = inet_csk(sk);
317a76f9 SH	157	struct tcp_congestion_ops *ca;
317a76f9 SH	158
55d8694f FW	159	rcu_read_lock();
	160	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	161	if (likely(try_module_get(ca->owner))) {
	162	icsk->icsk_ca_ops = ca;
	163	goto out;
317a76f9	164	}
55d8694f FW	165	/* Fallback to next available. The last really
	166	* guaranteed fallback is Reno from this list.
	167	*/
317a76f9	168	}
55d8694f FW	169	out:
55d8694f FW	170	rcu_read_unlock();
c1201444	171	memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
55d8694f	172
6ac705b1 ED	173	if (ca->flags & TCP_CONG_NEEDS_ECN)
	174	INET_ECN_xmit(sk);
	175	else
	176	INET_ECN_dontxmit(sk);
55d8694f FW	177	}
	178
	179	void tcp_init_congestion_control(struct sock *sk)
	180	{
	181	const struct inet_connection_sock *icsk = inet_csk(sk);
317a76f9	182
44abafc4	183	tcp_sk(sk)->prior_ssthresh = 0;
6687e988 ACM	184	if (icsk->icsk_ca_ops->init)
6687e988 ACM	185	icsk->icsk_ca_ops->init(sk);
6ac705b1 ED	186	if (tcp_ca_needs_ecn(sk))
	187	INET_ECN_xmit(sk);
	188	else
	189	INET_ECN_dontxmit(sk);
317a76f9 SH	190	}
317a76f9 SH	191
ebfa00c5 SD	192	static void tcp_reinit_congestion_control(struct sock *sk,
ebfa00c5 SD	193	const struct tcp_congestion_ops *ca)
29ba4fff DB	194	{
	195	struct inet_connection_sock *icsk = inet_csk(sk);
	196
	197	tcp_cleanup_congestion_control(sk);
	198	icsk->icsk_ca_ops = ca;
9f950415	199	icsk->icsk_ca_setsockopt = 1;
c1201444	200	memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
29ba4fff	201
c1201444	202	if (sk->sk_state != TCP_CLOSE)
6ac705b1	203	tcp_init_congestion_control(sk);
29ba4fff DB	204	}
29ba4fff DB	205
317a76f9	206	/* Manage refcounts on socket close. */
6687e988	207	void tcp_cleanup_congestion_control(struct sock *sk)
317a76f9	208	{
6687e988 ACM	209	struct inet_connection_sock *icsk = inet_csk(sk);
	210
	211	if (icsk->icsk_ca_ops->release)
	212	icsk->icsk_ca_ops->release(sk);
	213	module_put(icsk->icsk_ca_ops->owner);
317a76f9 SH	214	}
	215
	216	/* Used by sysctl to change default congestion control */
	217	int tcp_set_default_congestion_control(const char *name)
	218	{
	219	struct tcp_congestion_ops *ca;
	220	int ret = -ENOENT;
	221
	222	spin_lock(&tcp_cong_list_lock);
	223	ca = tcp_ca_find(name);
95a5afca	224	#ifdef CONFIG_MODULES
a8f80e8f	225	if (!ca && capable(CAP_NET_ADMIN)) {
317a76f9 SH	226	spin_unlock(&tcp_cong_list_lock);
	227
	228	request_module("tcp_%s", name);
	229	spin_lock(&tcp_cong_list_lock);
	230	ca = tcp_ca_find(name);
	231	}
	232	#endif
	233
	234	if (ca) {
164891aa	235	ca->flags \|= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
317a76f9 SH	236	list_move(&ca->list, &tcp_cong_list);
	237	ret = 0;
	238	}
	239	spin_unlock(&tcp_cong_list_lock);
	240
	241	return ret;
	242	}
	243
b1736a71 SH	244	/* Set default value from kernel configuration at bootup */
	245	static int __init tcp_congestion_default(void)
	246	{
	247	return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
	248	}
	249	late_initcall(tcp_congestion_default);
	250
3ff825b2 SH	251	/* Build string with list of available congestion control values */
	252	void tcp_get_available_congestion_control(char *buf, size_t maxlen)
	253	{
	254	struct tcp_congestion_ops *ca;
	255	size_t offs = 0;
	256
	257	rcu_read_lock();
	258	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
	259	offs += snprintf(buf + offs, maxlen - offs,
	260	"%s%s",
	261	offs == 0 ? "" : " ", ca->name);
3ff825b2 SH	262	}
	263	rcu_read_unlock();
	264	}
	265
317a76f9 SH	266	/* Get current default congestion control */
	267	void tcp_get_default_congestion_control(char *name)
	268	{
	269	struct tcp_congestion_ops *ca;
	270	/* We will always have reno... */
	271	BUG_ON(list_empty(&tcp_cong_list));
	272
	273	rcu_read_lock();
	274	ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
	275	strncpy(name, ca->name, TCP_CA_NAME_MAX);
	276	rcu_read_unlock();
	277	}
	278
ce7bc3bf SH	279	/* Built list of non-restricted congestion control values */
	280	void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
	281	{
	282	struct tcp_congestion_ops *ca;
	283	size_t offs = 0;
	284
	285	*buf = '\0';
	286	rcu_read_lock();
	287	list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
164891aa	288	if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
ce7bc3bf SH	289	continue;
	290	offs += snprintf(buf + offs, maxlen - offs,
	291	"%s%s",
	292	offs == 0 ? "" : " ", ca->name);
ce7bc3bf SH	293	}
	294	rcu_read_unlock();
	295	}
	296
	297	/* Change list of non-restricted congestion control */
	298	int tcp_set_allowed_congestion_control(char *val)
	299	{
	300	struct tcp_congestion_ops *ca;
c34186ed	301	char saved_clone, clone, *name;
ce7bc3bf SH	302	int ret = 0;
ce7bc3bf SH	303
c34186ed	304	saved_clone = clone = kstrdup(val, GFP_USER);
ce7bc3bf SH	305	if (!clone)
	306	return -ENOMEM;
	307
	308	spin_lock(&tcp_cong_list_lock);
	309	/* pass 1 check for bad entries */
	310	while ((name = strsep(&clone, " ")) && *name) {
	311	ca = tcp_ca_find(name);
	312	if (!ca) {
	313	ret = -ENOENT;
	314	goto out;
	315	}
	316	}
	317
164891aa	318	/* pass 2 clear old values */
ce7bc3bf	319	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
164891aa	320	ca->flags &= ~TCP_CONG_NON_RESTRICTED;
ce7bc3bf SH	321
	322	/* pass 3 mark as allowed */
	323	while ((name = strsep(&val, " ")) && *name) {
	324	ca = tcp_ca_find(name);
	325	WARN_ON(!ca);
	326	if (ca)
164891aa	327	ca->flags \|= TCP_CONG_NON_RESTRICTED;
ce7bc3bf SH	328	}
	329	out:
	330	spin_unlock(&tcp_cong_list_lock);
c34186ed	331	kfree(saved_clone);
ce7bc3bf SH	332
	333	return ret;
	334	}
	335
91b5b21c LB	336	/* Change congestion control for socket. If load is false, then it is the
	337	* responsibility of the caller to call tcp_init_congestion_control or
	338	* tcp_reinit_congestion_control (if the current congestion control was
	339	* already initialized.
	340	*/
ebfa00c5	341	int tcp_set_congestion_control(struct sock sk, const char name, bool load, bool reinit)
5f8ef48d	342	{
6687e988	343	struct inet_connection_sock *icsk = inet_csk(sk);
c5c6a8ab	344	const struct tcp_congestion_ops *ca;
5f8ef48d SH	345	int err = 0;
5f8ef48d SH	346
c5c6a8ab DB	347	if (icsk->icsk_ca_dst_locked)
c5c6a8ab DB	348	return -EPERM;
4d4d3d1e	349
c5c6a8ab	350	rcu_read_lock();
91b5b21c LB	351	if (!load)
	352	ca = tcp_ca_find(name);
	353	else
	354	ca = __tcp_ca_find_autoload(name);
c5c6a8ab	355	/* No change asking for existing value */
9f950415 NC	356	if (ca == icsk->icsk_ca_ops) {
9f950415 NC	357	icsk->icsk_ca_setsockopt = 1;
5f8ef48d	358	goto out;
9f950415	359	}
91b5b21c	360	if (!ca) {
5f8ef48d	361	err = -ENOENT;
91b5b21c	362	} else if (!load) {
ebfa00c5 SD	363	const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
	364
	365	if (try_module_get(ca->owner)) {
	366	if (reinit) {
	367	tcp_reinit_congestion_control(sk, ca);
	368	} else {
	369	icsk->icsk_ca_ops = ca;
	370	module_put(old_ca->owner);
	371	}
	372	} else {
91b5b21c	373	err = -EBUSY;
ebfa00c5	374	}
91b5b21c LB	375	} else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) \|\|
91b5b21c LB	376	ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))) {
ce7bc3bf	377	err = -EPERM;
91b5b21c	378	} else if (!try_module_get(ca->owner)) {
5f8ef48d	379	err = -EBUSY;
91b5b21c	380	} else {
29ba4fff	381	tcp_reinit_congestion_control(sk, ca);
91b5b21c	382	}
5f8ef48d SH	383	out:
	384	rcu_read_unlock();
	385	return err;
	386	}
	387
9f9843a7 YC	388	/* Slow start is used when congestion window is no greater than the slow start
	389	* threshold. We base on RFC2581 and also handle stretch ACKs properly.
	390	* We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
	391	* something better;) a packet is only considered (s)acked in its entirety to
	392	* defend the ACK attacks described in the RFC. Slow start processes a stretch
	393	* ACK of degree N as if N acks of degree 1 are received back to back except
	394	* ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
	395	* returns the leftover acks to adjust cwnd in congestion avoidance mode.
40efc6fa	396	*/
e73ebb08	397	u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
40efc6fa	398	{
76174004	399	u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
a02ba041	400
e73ebb08	401	acked -= cwnd - tp->snd_cwnd;
9f9843a7	402	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
e73ebb08 NC	403
e73ebb08 NC	404	return acked;
40efc6fa SH	405	}
	406	EXPORT_SYMBOL_GPL(tcp_slow_start);
	407
814d488c NC	408	/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
	409	* for every packet that was ACKed.
	410	*/
e73ebb08	411	void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
758ce5c8	412	{
9949afa4 NC	413	/* If credits accumulated at a higher w, apply them gently now. */
	414	if (tp->snd_cwnd_cnt >= w) {
	415	tp->snd_cwnd_cnt = 0;
	416	tp->snd_cwnd++;
	417	}
	418
814d488c	419	tp->snd_cwnd_cnt += acked;
758ce5c8	420	if (tp->snd_cwnd_cnt >= w) {
814d488c NC	421	u32 delta = tp->snd_cwnd_cnt / w;
	422
	423	tp->snd_cwnd_cnt -= delta * w;
	424	tp->snd_cwnd += delta;
758ce5c8	425	}
814d488c	426	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
758ce5c8 IJ	427	}
	428	EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
	429
317a76f9 SH	430	/*
	431	* TCP Reno congestion control
	432	* This is special case used for fallback as well.
	433	*/
	434	/* This is Jacobson's slow start and congestion avoidance.
	435	* SIGCOMM '88, p. 328.
	436	*/
24901551	437	void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
317a76f9	438	{
6687e988 ACM	439	struct tcp_sock *tp = tcp_sk(sk);
6687e988 ACM	440
24901551	441	if (!tcp_is_cwnd_limited(sk))
317a76f9 SH	442	return;
317a76f9 SH	443
7faffa1c	444	/* In "safe" area, increase. */
071d5080	445	if (tcp_in_slow_start(tp)) {
c22bdca9 NC	446	acked = tcp_slow_start(tp, acked);
	447	if (!acked)
	448	return;
	449	}
e905a9ed	450	/* In dangerous area, increase slowly. */
c22bdca9	451	tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
317a76f9 SH	452	}
	453	EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
	454
	455	/* Slow start threshold is half the congestion window (min 2) */
6687e988	456	u32 tcp_reno_ssthresh(struct sock *sk)
317a76f9	457	{
6687e988	458	const struct tcp_sock *tp = tcp_sk(sk);
688d1945	459
317a76f9 SH	460	return max(tp->snd_cwnd >> 1U, 2U);
	461	}
	462	EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
	463
e9799183 FW	464	u32 tcp_reno_undo_cwnd(struct sock *sk)
	465	{
	466	const struct tcp_sock *tp = tcp_sk(sk);
	467
	468	return max(tp->snd_cwnd, tp->snd_ssthresh << 1);
	469	}
	470	EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
	471
317a76f9	472	struct tcp_congestion_ops tcp_reno = {
164891aa	473	.flags = TCP_CONG_NON_RESTRICTED,
317a76f9 SH	474	.name = "reno",
	475	.owner = THIS_MODULE,
	476	.ssthresh = tcp_reno_ssthresh,
	477	.cong_avoid = tcp_reno_cong_avoid,
e9799183	478	.undo_cwnd = tcp_reno_undo_cwnd,
317a76f9	479	};