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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 * Plugable 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 <net/tcp.h>
17
18static DEFINE_SPINLOCK(tcp_cong_list_lock);
19static LIST_HEAD(tcp_cong_list);
20
21/* Simple linear search, don't expect many entries! */
22static struct tcp_congestion_ops *tcp_ca_find(const char *name)
23{
24 struct tcp_congestion_ops *e;
25
26 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
27 if (strcmp(e->name, name) == 0)
28 return e;
29 }
30
31 return NULL;
32}
33
34/*
35 * Attach new congestion control algorithm to the list
36 * of available options.
37 */
38int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
39{
40 int ret = 0;
41
42 /* all algorithms must implement ssthresh and cong_avoid ops */
43 if (!ca->ssthresh || !ca->cong_avoid) {
44 pr_err("%s does not implement required ops\n", ca->name);
45 return -EINVAL;
46 }
47
48 spin_lock(&tcp_cong_list_lock);
49 if (tcp_ca_find(ca->name)) {
50 pr_notice("%s already registered\n", ca->name);
51 ret = -EEXIST;
52 } else {
53 list_add_tail_rcu(&ca->list, &tcp_cong_list);
54 pr_info("%s registered\n", ca->name);
55 }
56 spin_unlock(&tcp_cong_list_lock);
57
58 return ret;
59}
60EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
61
62/*
63 * Remove congestion control algorithm, called from
64 * the module's remove function. Module ref counts are used
65 * to ensure that this can't be done till all sockets using
66 * that method are closed.
67 */
68void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
69{
70 spin_lock(&tcp_cong_list_lock);
71 list_del_rcu(&ca->list);
72 spin_unlock(&tcp_cong_list_lock);
73}
74EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
75
76/* Assign choice of congestion control. */
77void tcp_init_congestion_control(struct sock *sk)
78{
79 struct inet_connection_sock *icsk = inet_csk(sk);
80 struct tcp_congestion_ops *ca;
81
82 /* if no choice made yet assign the current value set as default */
83 if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
84 rcu_read_lock();
85 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
86 if (try_module_get(ca->owner)) {
87 icsk->icsk_ca_ops = ca;
88 break;
89 }
90
91 /* fallback to next available */
92 }
93 rcu_read_unlock();
94 }
95
96 if (icsk->icsk_ca_ops->init)
97 icsk->icsk_ca_ops->init(sk);
98}
99
100/* Manage refcounts on socket close. */
101void tcp_cleanup_congestion_control(struct sock *sk)
102{
103 struct inet_connection_sock *icsk = inet_csk(sk);
104
105 if (icsk->icsk_ca_ops->release)
106 icsk->icsk_ca_ops->release(sk);
107 module_put(icsk->icsk_ca_ops->owner);
108}
109
110/* Used by sysctl to change default congestion control */
111int tcp_set_default_congestion_control(const char *name)
112{
113 struct tcp_congestion_ops *ca;
114 int ret = -ENOENT;
115
116 spin_lock(&tcp_cong_list_lock);
117 ca = tcp_ca_find(name);
118#ifdef CONFIG_MODULES
119 if (!ca && capable(CAP_NET_ADMIN)) {
120 spin_unlock(&tcp_cong_list_lock);
121
122 request_module("tcp_%s", name);
123 spin_lock(&tcp_cong_list_lock);
124 ca = tcp_ca_find(name);
125 }
126#endif
127
128 if (ca) {
129 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
130 list_move(&ca->list, &tcp_cong_list);
131 ret = 0;
132 }
133 spin_unlock(&tcp_cong_list_lock);
134
135 return ret;
136}
137
138/* Set default value from kernel configuration at bootup */
139static int __init tcp_congestion_default(void)
140{
141 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
142}
143late_initcall(tcp_congestion_default);
144
145
146/* Build string with list of available congestion control values */
147void tcp_get_available_congestion_control(char *buf, size_t maxlen)
148{
149 struct tcp_congestion_ops *ca;
150 size_t offs = 0;
151
152 rcu_read_lock();
153 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
154 offs += snprintf(buf + offs, maxlen - offs,
155 "%s%s",
156 offs == 0 ? "" : " ", ca->name);
157
158 }
159 rcu_read_unlock();
160}
161
162/* Get current default congestion control */
163void tcp_get_default_congestion_control(char *name)
164{
165 struct tcp_congestion_ops *ca;
166 /* We will always have reno... */
167 BUG_ON(list_empty(&tcp_cong_list));
168
169 rcu_read_lock();
170 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
171 strncpy(name, ca->name, TCP_CA_NAME_MAX);
172 rcu_read_unlock();
173}
174
175/* Built list of non-restricted congestion control values */
176void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
177{
178 struct tcp_congestion_ops *ca;
179 size_t offs = 0;
180
181 *buf = '\0';
182 rcu_read_lock();
183 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
184 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
185 continue;
186 offs += snprintf(buf + offs, maxlen - offs,
187 "%s%s",
188 offs == 0 ? "" : " ", ca->name);
189
190 }
191 rcu_read_unlock();
192}
193
194/* Change list of non-restricted congestion control */
195int tcp_set_allowed_congestion_control(char *val)
196{
197 struct tcp_congestion_ops *ca;
198 char *saved_clone, *clone, *name;
199 int ret = 0;
200
201 saved_clone = clone = kstrdup(val, GFP_USER);
202 if (!clone)
203 return -ENOMEM;
204
205 spin_lock(&tcp_cong_list_lock);
206 /* pass 1 check for bad entries */
207 while ((name = strsep(&clone, " ")) && *name) {
208 ca = tcp_ca_find(name);
209 if (!ca) {
210 ret = -ENOENT;
211 goto out;
212 }
213 }
214
215 /* pass 2 clear old values */
216 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
217 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
218
219 /* pass 3 mark as allowed */
220 while ((name = strsep(&val, " ")) && *name) {
221 ca = tcp_ca_find(name);
222 WARN_ON(!ca);
223 if (ca)
224 ca->flags |= TCP_CONG_NON_RESTRICTED;
225 }
226out:
227 spin_unlock(&tcp_cong_list_lock);
228 kfree(saved_clone);
229
230 return ret;
231}
232
233
234/* Change congestion control for socket */
235int tcp_set_congestion_control(struct sock *sk, const char *name)
236{
237 struct inet_connection_sock *icsk = inet_csk(sk);
238 struct tcp_congestion_ops *ca;
239 int err = 0;
240
241 rcu_read_lock();
242 ca = tcp_ca_find(name);
243
244 /* no change asking for existing value */
245 if (ca == icsk->icsk_ca_ops)
246 goto out;
247
248#ifdef CONFIG_MODULES
249 /* not found attempt to autoload module */
250 if (!ca && capable(CAP_NET_ADMIN)) {
251 rcu_read_unlock();
252 request_module("tcp_%s", name);
253 rcu_read_lock();
254 ca = tcp_ca_find(name);
255 }
256#endif
257 if (!ca)
258 err = -ENOENT;
259
260 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
261 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
262 err = -EPERM;
263
264 else if (!try_module_get(ca->owner))
265 err = -EBUSY;
266
267 else {
268 tcp_cleanup_congestion_control(sk);
269 icsk->icsk_ca_ops = ca;
270
271 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
272 icsk->icsk_ca_ops->init(sk);
273 }
274 out:
275 rcu_read_unlock();
276 return err;
277}
278
279/* RFC2861 Check whether we are limited by application or congestion window
280 * This is the inverse of cwnd check in tcp_tso_should_defer
281 */
282bool tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
283{
284 const struct tcp_sock *tp = tcp_sk(sk);
285 u32 left;
286
287 if (in_flight >= tp->snd_cwnd)
288 return true;
289
290 left = tp->snd_cwnd - in_flight;
291 if (sk_can_gso(sk) &&
292 left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
293 left < tp->xmit_size_goal_segs)
294 return true;
295 return left <= tcp_max_tso_deferred_mss(tp);
296}
297EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
298
299/* Slow start is used when congestion window is no greater than the slow start
300 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
301 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
302 * something better;) a packet is only considered (s)acked in its entirety to
303 * defend the ACK attacks described in the RFC. Slow start processes a stretch
304 * ACK of degree N as if N acks of degree 1 are received back to back except
305 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
306 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
307 */
308int tcp_slow_start(struct tcp_sock *tp, u32 acked)
309{
310 u32 cwnd = tp->snd_cwnd + acked;
311
312 if (cwnd > tp->snd_ssthresh)
313 cwnd = tp->snd_ssthresh + 1;
314 acked -= cwnd - tp->snd_cwnd;
315 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
316 return acked;
317}
318EXPORT_SYMBOL_GPL(tcp_slow_start);
319
320/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
321void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
322{
323 if (tp->snd_cwnd_cnt >= w) {
324 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
325 tp->snd_cwnd++;
326 tp->snd_cwnd_cnt = 0;
327 } else {
328 tp->snd_cwnd_cnt++;
329 }
330}
331EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
332
333/*
334 * TCP Reno congestion control
335 * This is special case used for fallback as well.
336 */
337/* This is Jacobson's slow start and congestion avoidance.
338 * SIGCOMM '88, p. 328.
339 */
340void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked, u32 in_flight)
341{
342 struct tcp_sock *tp = tcp_sk(sk);
343
344 if (!tcp_is_cwnd_limited(sk, in_flight))
345 return;
346
347 /* In "safe" area, increase. */
348 if (tp->snd_cwnd <= tp->snd_ssthresh)
349 tcp_slow_start(tp, acked);
350 /* In dangerous area, increase slowly. */
351 else
352 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
353}
354EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
355
356/* Slow start threshold is half the congestion window (min 2) */
357u32 tcp_reno_ssthresh(struct sock *sk)
358{
359 const struct tcp_sock *tp = tcp_sk(sk);
360 return max(tp->snd_cwnd >> 1U, 2U);
361}
362EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
363
364struct tcp_congestion_ops tcp_reno = {
365 .flags = TCP_CONG_NON_RESTRICTED,
366 .name = "reno",
367 .owner = THIS_MODULE,
368 .ssthresh = tcp_reno_ssthresh,
369 .cong_avoid = tcp_reno_cong_avoid,
370};
371
372/* Initial congestion control used (until SYN)
373 * really reno under another name so we can tell difference
374 * during tcp_set_default_congestion_control
375 */
376struct tcp_congestion_ops tcp_init_congestion_ops = {
377 .name = "",
378 .owner = THIS_MODULE,
379 .ssthresh = tcp_reno_ssthresh,
380 .cong_avoid = tcp_reno_cong_avoid,
381};
382EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);