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1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Pluggable TCP congestion control support and newReno
4 * congestion control.
5 * Based on ideas from I/O scheduler support and Web100.
6 *
7 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
8 */
9
10#define pr_fmt(fmt) "TCP: " fmt
11
12#include <linux/module.h>
13#include <linux/mm.h>
14#include <linux/types.h>
15#include <linux/list.h>
16#include <linux/gfp.h>
17#include <linux/jhash.h>
18#include <net/tcp.h>
19
20static DEFINE_SPINLOCK(tcp_cong_list_lock);
21static LIST_HEAD(tcp_cong_list);
22
23/* Simple linear search, don't expect many entries! */
24static struct tcp_congestion_ops *tcp_ca_find(const char *name)
25{
26 struct tcp_congestion_ops *e;
27
28 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
29 if (strcmp(e->name, name) == 0)
30 return e;
31 }
32
33 return NULL;
34}
35
36/* Must be called with rcu lock held */
37static struct tcp_congestion_ops *tcp_ca_find_autoload(struct net *net,
38 const char *name)
39{
40 struct tcp_congestion_ops *ca = tcp_ca_find(name);
41
42#ifdef CONFIG_MODULES
43 if (!ca && capable(CAP_NET_ADMIN)) {
44 rcu_read_unlock();
45 request_module("tcp_%s", name);
46 rcu_read_lock();
47 ca = tcp_ca_find(name);
48 }
49#endif
50 return ca;
51}
52
53/* Simple linear search, not much in here. */
54struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
55{
56 struct tcp_congestion_ops *e;
57
58 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
59 if (e->key == key)
60 return e;
61 }
62
63 return NULL;
64}
65
66/*
67 * Attach new congestion control algorithm to the list
68 * of available options.
69 */
70int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
71{
72 int ret = 0;
73
74 /* all algorithms must implement these */
75 if (!ca->ssthresh || !ca->undo_cwnd ||
76 !(ca->cong_avoid || ca->cong_control)) {
77 pr_err("%s does not implement required ops\n", ca->name);
78 return -EINVAL;
79 }
80
81 ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
82
83 spin_lock(&tcp_cong_list_lock);
84 if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
85 pr_notice("%s already registered or non-unique key\n",
86 ca->name);
87 ret = -EEXIST;
88 } else {
89 list_add_tail_rcu(&ca->list, &tcp_cong_list);
90 pr_debug("%s registered\n", ca->name);
91 }
92 spin_unlock(&tcp_cong_list_lock);
93
94 return ret;
95}
96EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
97
98/*
99 * Remove congestion control algorithm, called from
100 * the module's remove function. Module ref counts are used
101 * to ensure that this can't be done till all sockets using
102 * that method are closed.
103 */
104void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
105{
106 spin_lock(&tcp_cong_list_lock);
107 list_del_rcu(&ca->list);
108 spin_unlock(&tcp_cong_list_lock);
109
110 /* Wait for outstanding readers to complete before the
111 * module gets removed entirely.
112 *
113 * A try_module_get() should fail by now as our module is
114 * in "going" state since no refs are held anymore and
115 * module_exit() handler being called.
116 */
117 synchronize_rcu();
118}
119EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
120
121u32 tcp_ca_get_key_by_name(struct net *net, const char *name, bool *ecn_ca)
122{
123 const struct tcp_congestion_ops *ca;
124 u32 key = TCP_CA_UNSPEC;
125
126 might_sleep();
127
128 rcu_read_lock();
129 ca = tcp_ca_find_autoload(net, name);
130 if (ca) {
131 key = ca->key;
132 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
133 }
134 rcu_read_unlock();
135
136 return key;
137}
138EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
139
140char *tcp_ca_get_name_by_key(u32 key, char *buffer)
141{
142 const struct tcp_congestion_ops *ca;
143 char *ret = NULL;
144
145 rcu_read_lock();
146 ca = tcp_ca_find_key(key);
147 if (ca)
148 ret = strncpy(buffer, ca->name,
149 TCP_CA_NAME_MAX);
150 rcu_read_unlock();
151
152 return ret;
153}
154EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
155
156/* Assign choice of congestion control. */
157void tcp_assign_congestion_control(struct sock *sk)
158{
159 struct net *net = sock_net(sk);
160 struct inet_connection_sock *icsk = inet_csk(sk);
161 const struct tcp_congestion_ops *ca;
162
163 rcu_read_lock();
164 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
165 if (unlikely(!try_module_get(ca->owner)))
166 ca = &tcp_reno;
167 icsk->icsk_ca_ops = ca;
168 rcu_read_unlock();
169
170 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
171 if (ca->flags & TCP_CONG_NEEDS_ECN)
172 INET_ECN_xmit(sk);
173 else
174 INET_ECN_dontxmit(sk);
175}
176
177void tcp_init_congestion_control(struct sock *sk)
178{
179 const struct inet_connection_sock *icsk = inet_csk(sk);
180
181 tcp_sk(sk)->prior_ssthresh = 0;
182 if (icsk->icsk_ca_ops->init)
183 icsk->icsk_ca_ops->init(sk);
184 if (tcp_ca_needs_ecn(sk))
185 INET_ECN_xmit(sk);
186 else
187 INET_ECN_dontxmit(sk);
188}
189
190static void tcp_reinit_congestion_control(struct sock *sk,
191 const struct tcp_congestion_ops *ca)
192{
193 struct inet_connection_sock *icsk = inet_csk(sk);
194
195 tcp_cleanup_congestion_control(sk);
196 icsk->icsk_ca_ops = ca;
197 icsk->icsk_ca_setsockopt = 1;
198 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
199
200 if (sk->sk_state != TCP_CLOSE)
201 tcp_init_congestion_control(sk);
202}
203
204/* Manage refcounts on socket close. */
205void tcp_cleanup_congestion_control(struct sock *sk)
206{
207 struct inet_connection_sock *icsk = inet_csk(sk);
208
209 if (icsk->icsk_ca_ops->release)
210 icsk->icsk_ca_ops->release(sk);
211 module_put(icsk->icsk_ca_ops->owner);
212}
213
214/* Used by sysctl to change default congestion control */
215int tcp_set_default_congestion_control(struct net *net, const char *name)
216{
217 struct tcp_congestion_ops *ca;
218 const struct tcp_congestion_ops *prev;
219 int ret;
220
221 rcu_read_lock();
222 ca = tcp_ca_find_autoload(net, name);
223 if (!ca) {
224 ret = -ENOENT;
225 } else if (!try_module_get(ca->owner)) {
226 ret = -EBUSY;
227 } else {
228 prev = xchg(&net->ipv4.tcp_congestion_control, ca);
229 if (prev)
230 module_put(prev->owner);
231
232 ca->flags |= TCP_CONG_NON_RESTRICTED;
233 ret = 0;
234 }
235 rcu_read_unlock();
236
237 return ret;
238}
239
240/* Set default value from kernel configuration at bootup */
241static int __init tcp_congestion_default(void)
242{
243 return tcp_set_default_congestion_control(&init_net,
244 CONFIG_DEFAULT_TCP_CONG);
245}
246late_initcall(tcp_congestion_default);
247
248/* Build string with list of available congestion control values */
249void tcp_get_available_congestion_control(char *buf, size_t maxlen)
250{
251 struct tcp_congestion_ops *ca;
252 size_t offs = 0;
253
254 rcu_read_lock();
255 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
256 offs += snprintf(buf + offs, maxlen - offs,
257 "%s%s",
258 offs == 0 ? "" : " ", ca->name);
259 }
260 rcu_read_unlock();
261}
262
263/* Get current default congestion control */
264void tcp_get_default_congestion_control(struct net *net, char *name)
265{
266 const struct tcp_congestion_ops *ca;
267
268 rcu_read_lock();
269 ca = rcu_dereference(net->ipv4.tcp_congestion_control);
270 strncpy(name, ca->name, TCP_CA_NAME_MAX);
271 rcu_read_unlock();
272}
273
274/* Built list of non-restricted congestion control values */
275void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
276{
277 struct tcp_congestion_ops *ca;
278 size_t offs = 0;
279
280 *buf = '\0';
281 rcu_read_lock();
282 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
283 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
284 continue;
285 offs += snprintf(buf + offs, maxlen - offs,
286 "%s%s",
287 offs == 0 ? "" : " ", ca->name);
288 }
289 rcu_read_unlock();
290}
291
292/* Change list of non-restricted congestion control */
293int tcp_set_allowed_congestion_control(char *val)
294{
295 struct tcp_congestion_ops *ca;
296 char *saved_clone, *clone, *name;
297 int ret = 0;
298
299 saved_clone = clone = kstrdup(val, GFP_USER);
300 if (!clone)
301 return -ENOMEM;
302
303 spin_lock(&tcp_cong_list_lock);
304 /* pass 1 check for bad entries */
305 while ((name = strsep(&clone, " ")) && *name) {
306 ca = tcp_ca_find(name);
307 if (!ca) {
308 ret = -ENOENT;
309 goto out;
310 }
311 }
312
313 /* pass 2 clear old values */
314 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
315 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
316
317 /* pass 3 mark as allowed */
318 while ((name = strsep(&val, " ")) && *name) {
319 ca = tcp_ca_find(name);
320 WARN_ON(!ca);
321 if (ca)
322 ca->flags |= TCP_CONG_NON_RESTRICTED;
323 }
324out:
325 spin_unlock(&tcp_cong_list_lock);
326 kfree(saved_clone);
327
328 return ret;
329}
330
331/* Change congestion control for socket. If load is false, then it is the
332 * responsibility of the caller to call tcp_init_congestion_control or
333 * tcp_reinit_congestion_control (if the current congestion control was
334 * already initialized.
335 */
336int tcp_set_congestion_control(struct sock *sk, const char *name, bool load,
337 bool reinit, bool cap_net_admin)
338{
339 struct inet_connection_sock *icsk = inet_csk(sk);
340 const struct tcp_congestion_ops *ca;
341 int err = 0;
342
343 if (icsk->icsk_ca_dst_locked)
344 return -EPERM;
345
346 rcu_read_lock();
347 if (!load)
348 ca = tcp_ca_find(name);
349 else
350 ca = tcp_ca_find_autoload(sock_net(sk), name);
351
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
358 if (!ca) {
359 err = -ENOENT;
360 } else if (!load) {
361 const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
362
363 if (try_module_get(ca->owner)) {
364 if (reinit) {
365 tcp_reinit_congestion_control(sk, ca);
366 } else {
367 icsk->icsk_ca_ops = ca;
368 module_put(old_ca->owner);
369 }
370 } else {
371 err = -EBUSY;
372 }
373 } else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || cap_net_admin)) {
374 err = -EPERM;
375 } else if (!try_module_get(ca->owner)) {
376 err = -EBUSY;
377 } else {
378 tcp_reinit_congestion_control(sk, ca);
379 }
380 out:
381 rcu_read_unlock();
382 return err;
383}
384
385/* Slow start is used when congestion window is no greater than the slow start
386 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
387 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
388 * something better;) a packet is only considered (s)acked in its entirety to
389 * defend the ACK attacks described in the RFC. Slow start processes a stretch
390 * ACK of degree N as if N acks of degree 1 are received back to back except
391 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
392 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
393 */
394u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
395{
396 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
397
398 acked -= cwnd - tp->snd_cwnd;
399 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
400
401 return acked;
402}
403EXPORT_SYMBOL_GPL(tcp_slow_start);
404
405/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
406 * for every packet that was ACKed.
407 */
408void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
409{
410 /* If credits accumulated at a higher w, apply them gently now. */
411 if (tp->snd_cwnd_cnt >= w) {
412 tp->snd_cwnd_cnt = 0;
413 tp->snd_cwnd++;
414 }
415
416 tp->snd_cwnd_cnt += acked;
417 if (tp->snd_cwnd_cnt >= w) {
418 u32 delta = tp->snd_cwnd_cnt / w;
419
420 tp->snd_cwnd_cnt -= delta * w;
421 tp->snd_cwnd += delta;
422 }
423 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
424}
425EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
426
427/*
428 * TCP Reno congestion control
429 * This is special case used for fallback as well.
430 */
431/* This is Jacobson's slow start and congestion avoidance.
432 * SIGCOMM '88, p. 328.
433 */
434void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
435{
436 struct tcp_sock *tp = tcp_sk(sk);
437
438 if (!tcp_is_cwnd_limited(sk))
439 return;
440
441 /* In "safe" area, increase. */
442 if (tcp_in_slow_start(tp)) {
443 acked = tcp_slow_start(tp, acked);
444 if (!acked)
445 return;
446 }
447 /* In dangerous area, increase slowly. */
448 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
449}
450EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
451
452/* Slow start threshold is half the congestion window (min 2) */
453u32 tcp_reno_ssthresh(struct sock *sk)
454{
455 const struct tcp_sock *tp = tcp_sk(sk);
456
457 return max(tp->snd_cwnd >> 1U, 2U);
458}
459EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
460
461u32 tcp_reno_undo_cwnd(struct sock *sk)
462{
463 const struct tcp_sock *tp = tcp_sk(sk);
464
465 return max(tp->snd_cwnd, tp->prior_cwnd);
466}
467EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
468
469struct tcp_congestion_ops tcp_reno = {
470 .flags = TCP_CONG_NON_RESTRICTED,
471 .name = "reno",
472 .owner = THIS_MODULE,
473 .ssthresh = tcp_reno_ssthresh,
474 .cong_avoid = tcp_reno_cong_avoid,
475 .undo_cwnd = tcp_reno_undo_cwnd,
476};
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};