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1/*
2 * Pluggable TCP congestion control support and newReno
3 * congestion control.
4 * Based on ideas from I/O scheduler support and Web100.
5 *
6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
7 */
8
9#define pr_fmt(fmt) "TCP: " fmt
10
11#include <linux/module.h>
12#include <linux/mm.h>
13#include <linux/types.h>
14#include <linux/list.h>
15#include <linux/gfp.h>
16#include <linux/jhash.h>
17#include <net/tcp.h>
18
19static DEFINE_SPINLOCK(tcp_cong_list_lock);
20static LIST_HEAD(tcp_cong_list);
21
22/* Simple linear search, don't expect many entries! */
23static struct tcp_congestion_ops *tcp_ca_find(const char *name)
24{
25 struct tcp_congestion_ops *e;
26
27 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
28 if (strcmp(e->name, name) == 0)
29 return e;
30 }
31
32 return NULL;
33}
34
35/* Must be called with rcu lock held */
36static struct tcp_congestion_ops *tcp_ca_find_autoload(struct net *net,
37 const char *name)
38{
39 struct tcp_congestion_ops *ca = tcp_ca_find(name);
40
41#ifdef CONFIG_MODULES
42 if (!ca && capable(CAP_NET_ADMIN)) {
43 rcu_read_unlock();
44 request_module("tcp_%s", name);
45 rcu_read_lock();
46 ca = tcp_ca_find(name);
47 }
48#endif
49 return ca;
50}
51
52/* Simple linear search, not much in here. */
53struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
54{
55 struct tcp_congestion_ops *e;
56
57 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
58 if (e->key == key)
59 return e;
60 }
61
62 return NULL;
63}
64
65/*
66 * Attach new congestion control algorithm to the list
67 * of available options.
68 */
69int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
70{
71 int ret = 0;
72
73 /* all algorithms must implement these */
74 if (!ca->ssthresh || !ca->undo_cwnd ||
75 !(ca->cong_avoid || ca->cong_control)) {
76 pr_err("%s does not implement required ops\n", ca->name);
77 return -EINVAL;
78 }
79
80 ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
81
82 spin_lock(&tcp_cong_list_lock);
83 if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
84 pr_notice("%s already registered or non-unique key\n",
85 ca->name);
86 ret = -EEXIST;
87 } else {
88 list_add_tail_rcu(&ca->list, &tcp_cong_list);
89 pr_debug("%s registered\n", ca->name);
90 }
91 spin_unlock(&tcp_cong_list_lock);
92
93 return ret;
94}
95EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
96
97/*
98 * Remove congestion control algorithm, called from
99 * the module's remove function. Module ref counts are used
100 * to ensure that this can't be done till all sockets using
101 * that method are closed.
102 */
103void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
104{
105 spin_lock(&tcp_cong_list_lock);
106 list_del_rcu(&ca->list);
107 spin_unlock(&tcp_cong_list_lock);
108
109 /* Wait for outstanding readers to complete before the
110 * module gets removed entirely.
111 *
112 * A try_module_get() should fail by now as our module is
113 * in "going" state since no refs are held anymore and
114 * module_exit() handler being called.
115 */
116 synchronize_rcu();
117}
118EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
119
120u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
121{
122 const struct tcp_congestion_ops *ca;
123 u32 key = TCP_CA_UNSPEC;
124
125 might_sleep();
126
127 rcu_read_lock();
128 ca = tcp_ca_find_autoload(net, name);
129 if (ca) {
130 key = ca->key;
131 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
132 }
133 rcu_read_unlock();
134
135 return key;
136}
137EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
138
139char *tcp_ca_get_name_by_key(u32 key, char *buffer)
140{
141 const struct tcp_congestion_ops *ca;
142 char *ret = NULL;
143
144 rcu_read_lock();
145 ca = tcp_ca_find_key(key);
146 if (ca)
147 ret = strncpy(buffer, ca->name,
148 TCP_CA_NAME_MAX);
149 rcu_read_unlock();
150
151 return ret;
152}
153EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
154
155/* Assign choice of congestion control. */
156void tcp_assign_congestion_control(struct sock *sk)
157{
158 struct net *net = sock_net(sk);
159 struct inet_connection_sock *icsk = inet_csk(sk);
160 const struct tcp_congestion_ops *ca;
161
162 rcu_read_lock();
163 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
164 if (unlikely(!try_module_get(ca->owner)))
165 ca = &tcp_reno;
166 icsk->icsk_ca_ops = ca;
167 rcu_read_unlock();
168
169 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
170 if (ca->flags & TCP_CONG_NEEDS_ECN)
171 INET_ECN_xmit(sk);
172 else
173 INET_ECN_dontxmit(sk);
174}
175
176void tcp_init_congestion_control(struct sock *sk)
177{
178 const struct inet_connection_sock *icsk = inet_csk(sk);
179
180 tcp_sk(sk)->prior_ssthresh = 0;
181 if (icsk->icsk_ca_ops->init)
182 icsk->icsk_ca_ops->init(sk);
183 if (tcp_ca_needs_ecn(sk))
184 INET_ECN_xmit(sk);
185 else
186 INET_ECN_dontxmit(sk);
187}
188
189static void tcp_reinit_congestion_control(struct sock *sk,
190 const struct tcp_congestion_ops *ca)
191{
192 struct inet_connection_sock *icsk = inet_csk(sk);
193
194 tcp_cleanup_congestion_control(sk);
195 icsk->icsk_ca_ops = ca;
196 icsk->icsk_ca_setsockopt = 1;
197 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
198
199 if (sk->sk_state != TCP_CLOSE)
200 tcp_init_congestion_control(sk);
201}
202
203/* Manage refcounts on socket close. */
204void tcp_cleanup_congestion_control(struct sock *sk)
205{
206 struct inet_connection_sock *icsk = inet_csk(sk);
207
208 if (icsk->icsk_ca_ops->release)
209 icsk->icsk_ca_ops->release(sk);
210 module_put(icsk->icsk_ca_ops->owner);
211}
212
213/* Used by sysctl to change default congestion control */
214int tcp_set_default_congestion_control(struct net *net, const char *name)
215{
216 struct tcp_congestion_ops *ca;
217 const struct tcp_congestion_ops *prev;
218 int ret;
219
220 rcu_read_lock();
221 ca = tcp_ca_find_autoload(net, name);
222 if (!ca) {
223 ret = -ENOENT;
224 } else if (!try_module_get(ca->owner)) {
225 ret = -EBUSY;
226 } else {
227 prev = xchg(&net->ipv4.tcp_congestion_control, ca);
228 if (prev)
229 module_put(prev->owner);
230
231 ca->flags |= TCP_CONG_NON_RESTRICTED;
232 ret = 0;
233 }
234 rcu_read_unlock();
235
236 return ret;
237}
238
239/* Set default value from kernel configuration at bootup */
240static int __init tcp_congestion_default(void)
241{
242 return tcp_set_default_congestion_control(&init_net,
243 CONFIG_DEFAULT_TCP_CONG);
244}
245late_initcall(tcp_congestion_default);
246
247/* Build string with list of available congestion control values */
248void tcp_get_available_congestion_control(char *buf, size_t maxlen)
249{
250 struct tcp_congestion_ops *ca;
251 size_t offs = 0;
252
253 rcu_read_lock();
254 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
255 offs += snprintf(buf + offs, maxlen - offs,
256 "%s%s",
257 offs == 0 ? "" : " ", ca->name);
258 }
259 rcu_read_unlock();
260}
261
262/* Get current default congestion control */
263void tcp_get_default_congestion_control(struct net *net, char *name)
264{
265 const struct tcp_congestion_ops *ca;
266
267 rcu_read_lock();
268 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
269 strncpy(name, ca->name, TCP_CA_NAME_MAX);
270 rcu_read_unlock();
271}
272
273/* Built list of non-restricted congestion control values */
274void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
275{
276 struct tcp_congestion_ops *ca;
277 size_t offs = 0;
278
279 *buf = '\0';
280 rcu_read_lock();
281 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
282 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
283 continue;
284 offs += snprintf(buf + offs, maxlen - offs,
285 "%s%s",
286 offs == 0 ? "" : " ", ca->name);
287 }
288 rcu_read_unlock();
289}
290
291/* Change list of non-restricted congestion control */
292int tcp_set_allowed_congestion_control(char *val)
293{
294 struct tcp_congestion_ops *ca;
295 char *saved_clone, *clone, *name;
296 int ret = 0;
297
298 saved_clone = clone = kstrdup(val, GFP_USER);
299 if (!clone)
300 return -ENOMEM;
301
302 spin_lock(&tcp_cong_list_lock);
303 /* pass 1 check for bad entries */
304 while ((name = strsep(&clone, " ")) && *name) {
305 ca = tcp_ca_find(name);
306 if (!ca) {
307 ret = -ENOENT;
308 goto out;
309 }
310 }
311
312 /* pass 2 clear old values */
313 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
314 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
315
316 /* pass 3 mark as allowed */
317 while ((name = strsep(&val, " ")) && *name) {
318 ca = tcp_ca_find(name);
319 WARN_ON(!ca);
320 if (ca)
321 ca->flags |= TCP_CONG_NON_RESTRICTED;
322 }
323out:
324 spin_unlock(&tcp_cong_list_lock);
325 kfree(saved_clone);
326
327 return ret;
328}
329
330/* Change congestion control for socket. If load is false, then it is the
331 * responsibility of the caller to call tcp_init_congestion_control or
332 * tcp_reinit_congestion_control (if the current congestion control was
333 * already initialized.
334 */
335int tcp_set_congestion_control(struct sock *sk, const char *name, bool load, bool reinit)
336{
337 struct inet_connection_sock *icsk = inet_csk(sk);
338 const struct tcp_congestion_ops *ca;
339 int err = 0;
340
341 if (icsk->icsk_ca_dst_locked)
342 return -EPERM;
343
344 rcu_read_lock();
345 if (!load)
346 ca = tcp_ca_find(name);
347 else
348 ca = tcp_ca_find_autoload(sock_net(sk), name);
349
350 /* No change asking for existing value */
351 if (ca == icsk->icsk_ca_ops) {
352 icsk->icsk_ca_setsockopt = 1;
353 goto out;
354 }
355
356 if (!ca) {
357 err = -ENOENT;
358 } else if (!load) {
359 const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
360
361 if (try_module_get(ca->owner)) {
362 if (reinit) {
363 tcp_reinit_congestion_control(sk, ca);
364 } else {
365 icsk->icsk_ca_ops = ca;
366 module_put(old_ca->owner);
367 }
368 } else {
369 err = -EBUSY;
370 }
371 } else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
372 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))) {
373 err = -EPERM;
374 } else if (!try_module_get(ca->owner)) {
375 err = -EBUSY;
376 } else {
377 tcp_reinit_congestion_control(sk, ca);
378 }
379 out:
380 rcu_read_unlock();
381 return err;
382}
383
384/* Slow start is used when congestion window is no greater than the slow start
385 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
386 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
387 * something better;) a packet is only considered (s)acked in its entirety to
388 * defend the ACK attacks described in the RFC. Slow start processes a stretch
389 * ACK of degree N as if N acks of degree 1 are received back to back except
390 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
391 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
392 */
393u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
394{
395 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
396
397 acked -= cwnd - tp->snd_cwnd;
398 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
399
400 return acked;
401}
402EXPORT_SYMBOL_GPL(tcp_slow_start);
403
404/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
405 * for every packet that was ACKed.
406 */
407void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
408{
409 /* If credits accumulated at a higher w, apply them gently now. */
410 if (tp->snd_cwnd_cnt >= w) {
411 tp->snd_cwnd_cnt = 0;
412 tp->snd_cwnd++;
413 }
414
415 tp->snd_cwnd_cnt += acked;
416 if (tp->snd_cwnd_cnt >= w) {
417 u32 delta = tp->snd_cwnd_cnt / w;
418
419 tp->snd_cwnd_cnt -= delta * w;
420 tp->snd_cwnd += delta;
421 }
422 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
423}
424EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
425
426/*
427 * TCP Reno congestion control
428 * This is special case used for fallback as well.
429 */
430/* This is Jacobson's slow start and congestion avoidance.
431 * SIGCOMM '88, p. 328.
432 */
433void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
434{
435 struct tcp_sock *tp = tcp_sk(sk);
436
437 if (!tcp_is_cwnd_limited(sk))
438 return;
439
440 /* In "safe" area, increase. */
441 if (tcp_in_slow_start(tp)) {
442 acked = tcp_slow_start(tp, acked);
443 if (!acked)
444 return;
445 }
446 /* In dangerous area, increase slowly. */
447 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
448}
449EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
450
451/* Slow start threshold is half the congestion window (min 2) */
452u32 tcp_reno_ssthresh(struct sock *sk)
453{
454 const struct tcp_sock *tp = tcp_sk(sk);
455
456 return max(tp->snd_cwnd >> 1U, 2U);
457}
458EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
459
460u32 tcp_reno_undo_cwnd(struct sock *sk)
461{
462 const struct tcp_sock *tp = tcp_sk(sk);
463
464 return max(tp->snd_cwnd, tp->prior_cwnd);
465}
466EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
467
468struct tcp_congestion_ops tcp_reno = {
469 .flags = TCP_CONG_NON_RESTRICTED,
470 .name = "reno",
471 .owner = THIS_MODULE,
472 .ssthresh = tcp_reno_ssthresh,
473 .cong_avoid = tcp_reno_cong_avoid,
474 .undo_cwnd = tcp_reno_undo_cwnd,
475};
1/*
2 * Pluggable TCP congestion control support and newReno
3 * congestion control.
4 * Based on ideas from I/O scheduler support and Web100.
5 *
6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
7 */
8
9#define pr_fmt(fmt) "TCP: " fmt
10
11#include <linux/module.h>
12#include <linux/mm.h>
13#include <linux/types.h>
14#include <linux/list.h>
15#include <linux/gfp.h>
16#include <linux/jhash.h>
17#include <net/tcp.h>
18
19static DEFINE_SPINLOCK(tcp_cong_list_lock);
20static LIST_HEAD(tcp_cong_list);
21
22/* Simple linear search, don't expect many entries! */
23static struct tcp_congestion_ops *tcp_ca_find(const char *name)
24{
25 struct tcp_congestion_ops *e;
26
27 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
28 if (strcmp(e->name, name) == 0)
29 return e;
30 }
31
32 return NULL;
33}
34
35/* Must be called with rcu lock held */
36static 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. */
51struct 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
63/*
64 * Attach new congestion control algorithm to the list
65 * of available options.
66 */
67int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
68{
69 int ret = 0;
70
71 /* all algorithms must implement these */
72 if (!ca->ssthresh || !ca->undo_cwnd ||
73 !(ca->cong_avoid || ca->cong_control)) {
74 pr_err("%s does not implement required ops\n", ca->name);
75 return -EINVAL;
76 }
77
78 ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
79
80 spin_lock(&tcp_cong_list_lock);
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);
84 ret = -EEXIST;
85 } else {
86 list_add_tail_rcu(&ca->list, &tcp_cong_list);
87 pr_debug("%s registered\n", ca->name);
88 }
89 spin_unlock(&tcp_cong_list_lock);
90
91 return ret;
92}
93EXPORT_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 */
101void 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);
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();
115}
116EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
117
118u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca)
119{
120 const struct tcp_congestion_ops *ca;
121 u32 key = TCP_CA_UNSPEC;
122
123 might_sleep();
124
125 rcu_read_lock();
126 ca = __tcp_ca_find_autoload(name);
127 if (ca) {
128 key = ca->key;
129 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
130 }
131 rcu_read_unlock();
132
133 return key;
134}
135EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
136
137char *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}
151EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
152
153/* Assign choice of congestion control. */
154void tcp_assign_congestion_control(struct sock *sk)
155{
156 struct inet_connection_sock *icsk = inet_csk(sk);
157 struct tcp_congestion_ops *ca;
158
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;
164 }
165 /* Fallback to next available. The last really
166 * guaranteed fallback is Reno from this list.
167 */
168 }
169out:
170 rcu_read_unlock();
171
172 /* Clear out private data before diag gets it and
173 * the ca has not been initialized.
174 */
175 if (ca->get_info)
176 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
177 if (ca->flags & TCP_CONG_NEEDS_ECN)
178 INET_ECN_xmit(sk);
179 else
180 INET_ECN_dontxmit(sk);
181}
182
183void tcp_init_congestion_control(struct sock *sk)
184{
185 const struct inet_connection_sock *icsk = inet_csk(sk);
186
187 if (icsk->icsk_ca_ops->init)
188 icsk->icsk_ca_ops->init(sk);
189 if (tcp_ca_needs_ecn(sk))
190 INET_ECN_xmit(sk);
191 else
192 INET_ECN_dontxmit(sk);
193}
194
195static void tcp_reinit_congestion_control(struct sock *sk,
196 const struct tcp_congestion_ops *ca)
197{
198 struct inet_connection_sock *icsk = inet_csk(sk);
199
200 tcp_cleanup_congestion_control(sk);
201 icsk->icsk_ca_ops = ca;
202 icsk->icsk_ca_setsockopt = 1;
203
204 if (sk->sk_state != TCP_CLOSE) {
205 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
206 tcp_init_congestion_control(sk);
207 }
208}
209
210/* Manage refcounts on socket close. */
211void tcp_cleanup_congestion_control(struct sock *sk)
212{
213 struct inet_connection_sock *icsk = inet_csk(sk);
214
215 if (icsk->icsk_ca_ops->release)
216 icsk->icsk_ca_ops->release(sk);
217 module_put(icsk->icsk_ca_ops->owner);
218}
219
220/* Used by sysctl to change default congestion control */
221int tcp_set_default_congestion_control(const char *name)
222{
223 struct tcp_congestion_ops *ca;
224 int ret = -ENOENT;
225
226 spin_lock(&tcp_cong_list_lock);
227 ca = tcp_ca_find(name);
228#ifdef CONFIG_MODULES
229 if (!ca && capable(CAP_NET_ADMIN)) {
230 spin_unlock(&tcp_cong_list_lock);
231
232 request_module("tcp_%s", name);
233 spin_lock(&tcp_cong_list_lock);
234 ca = tcp_ca_find(name);
235 }
236#endif
237
238 if (ca) {
239 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
240 list_move(&ca->list, &tcp_cong_list);
241 ret = 0;
242 }
243 spin_unlock(&tcp_cong_list_lock);
244
245 return ret;
246}
247
248/* Set default value from kernel configuration at bootup */
249static int __init tcp_congestion_default(void)
250{
251 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
252}
253late_initcall(tcp_congestion_default);
254
255/* Build string with list of available congestion control values */
256void tcp_get_available_congestion_control(char *buf, size_t maxlen)
257{
258 struct tcp_congestion_ops *ca;
259 size_t offs = 0;
260
261 rcu_read_lock();
262 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
263 offs += snprintf(buf + offs, maxlen - offs,
264 "%s%s",
265 offs == 0 ? "" : " ", ca->name);
266 }
267 rcu_read_unlock();
268}
269
270/* Get current default congestion control */
271void tcp_get_default_congestion_control(char *name)
272{
273 struct tcp_congestion_ops *ca;
274 /* We will always have reno... */
275 BUG_ON(list_empty(&tcp_cong_list));
276
277 rcu_read_lock();
278 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
279 strncpy(name, ca->name, TCP_CA_NAME_MAX);
280 rcu_read_unlock();
281}
282
283/* Built list of non-restricted congestion control values */
284void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
285{
286 struct tcp_congestion_ops *ca;
287 size_t offs = 0;
288
289 *buf = '\0';
290 rcu_read_lock();
291 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
292 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
293 continue;
294 offs += snprintf(buf + offs, maxlen - offs,
295 "%s%s",
296 offs == 0 ? "" : " ", ca->name);
297 }
298 rcu_read_unlock();
299}
300
301/* Change list of non-restricted congestion control */
302int tcp_set_allowed_congestion_control(char *val)
303{
304 struct tcp_congestion_ops *ca;
305 char *saved_clone, *clone, *name;
306 int ret = 0;
307
308 saved_clone = clone = kstrdup(val, GFP_USER);
309 if (!clone)
310 return -ENOMEM;
311
312 spin_lock(&tcp_cong_list_lock);
313 /* pass 1 check for bad entries */
314 while ((name = strsep(&clone, " ")) && *name) {
315 ca = tcp_ca_find(name);
316 if (!ca) {
317 ret = -ENOENT;
318 goto out;
319 }
320 }
321
322 /* pass 2 clear old values */
323 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
324 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
325
326 /* pass 3 mark as allowed */
327 while ((name = strsep(&val, " ")) && *name) {
328 ca = tcp_ca_find(name);
329 WARN_ON(!ca);
330 if (ca)
331 ca->flags |= TCP_CONG_NON_RESTRICTED;
332 }
333out:
334 spin_unlock(&tcp_cong_list_lock);
335 kfree(saved_clone);
336
337 return ret;
338}
339
340/* Change congestion control for socket */
341int tcp_set_congestion_control(struct sock *sk, const char *name)
342{
343 struct inet_connection_sock *icsk = inet_csk(sk);
344 const struct tcp_congestion_ops *ca;
345 int err = 0;
346
347 if (icsk->icsk_ca_dst_locked)
348 return -EPERM;
349
350 rcu_read_lock();
351 ca = __tcp_ca_find_autoload(name);
352 /* No change asking for existing value */
353 if (ca == icsk->icsk_ca_ops) {
354 icsk->icsk_ca_setsockopt = 1;
355 goto out;
356 }
357 if (!ca)
358 err = -ENOENT;
359 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
360 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
361 err = -EPERM;
362 else if (!try_module_get(ca->owner))
363 err = -EBUSY;
364 else
365 tcp_reinit_congestion_control(sk, ca);
366 out:
367 rcu_read_unlock();
368 return err;
369}
370
371/* Slow start is used when congestion window is no greater than the slow start
372 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
373 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
374 * something better;) a packet is only considered (s)acked in its entirety to
375 * defend the ACK attacks described in the RFC. Slow start processes a stretch
376 * ACK of degree N as if N acks of degree 1 are received back to back except
377 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
378 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
379 */
380u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
381{
382 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
383
384 acked -= cwnd - tp->snd_cwnd;
385 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
386
387 return acked;
388}
389EXPORT_SYMBOL_GPL(tcp_slow_start);
390
391/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
392 * for every packet that was ACKed.
393 */
394void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
395{
396 /* If credits accumulated at a higher w, apply them gently now. */
397 if (tp->snd_cwnd_cnt >= w) {
398 tp->snd_cwnd_cnt = 0;
399 tp->snd_cwnd++;
400 }
401
402 tp->snd_cwnd_cnt += acked;
403 if (tp->snd_cwnd_cnt >= w) {
404 u32 delta = tp->snd_cwnd_cnt / w;
405
406 tp->snd_cwnd_cnt -= delta * w;
407 tp->snd_cwnd += delta;
408 }
409 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
410}
411EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
412
413/*
414 * TCP Reno congestion control
415 * This is special case used for fallback as well.
416 */
417/* This is Jacobson's slow start and congestion avoidance.
418 * SIGCOMM '88, p. 328.
419 */
420void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
421{
422 struct tcp_sock *tp = tcp_sk(sk);
423
424 if (!tcp_is_cwnd_limited(sk))
425 return;
426
427 /* In "safe" area, increase. */
428 if (tcp_in_slow_start(tp)) {
429 acked = tcp_slow_start(tp, acked);
430 if (!acked)
431 return;
432 }
433 /* In dangerous area, increase slowly. */
434 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
435}
436EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
437
438/* Slow start threshold is half the congestion window (min 2) */
439u32 tcp_reno_ssthresh(struct sock *sk)
440{
441 const struct tcp_sock *tp = tcp_sk(sk);
442
443 return max(tp->snd_cwnd >> 1U, 2U);
444}
445EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
446
447u32 tcp_reno_undo_cwnd(struct sock *sk)
448{
449 const struct tcp_sock *tp = tcp_sk(sk);
450
451 return max(tp->snd_cwnd, tp->snd_ssthresh << 1);
452}
453EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
454
455struct tcp_congestion_ops tcp_reno = {
456 .flags = TCP_CONG_NON_RESTRICTED,
457 .name = "reno",
458 .owner = THIS_MODULE,
459 .ssthresh = tcp_reno_ssthresh,
460 .cong_avoid = tcp_reno_cong_avoid,
461 .undo_cwnd = tcp_reno_undo_cwnd,
462};