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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 suport and Web100.
5 *
6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
7 */
8
9#include <linux/module.h>
10#include <linux/mm.h>
11#include <linux/types.h>
12#include <linux/list.h>
13#include <linux/gfp.h>
14#include <net/tcp.h>
15
16int sysctl_tcp_max_ssthresh = 0;
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 printk(KERN_ERR "TCP %s does not implement required ops\n",
45 ca->name);
46 return -EINVAL;
47 }
48
49 spin_lock(&tcp_cong_list_lock);
50 if (tcp_ca_find(ca->name)) {
51 printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
52 ret = -EEXIST;
53 } else {
54 list_add_tail_rcu(&ca->list, &tcp_cong_list);
55 printk(KERN_INFO "TCP %s registered\n", ca->name);
56 }
57 spin_unlock(&tcp_cong_list_lock);
58
59 return ret;
60}
61EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
62
63/*
64 * Remove congestion control algorithm, called from
65 * the module's remove function. Module ref counts are used
66 * to ensure that this can't be done till all sockets using
67 * that method are closed.
68 */
69void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
70{
71 spin_lock(&tcp_cong_list_lock);
72 list_del_rcu(&ca->list);
73 spin_unlock(&tcp_cong_list_lock);
74}
75EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
76
77/* Assign choice of congestion control. */
78void tcp_init_congestion_control(struct sock *sk)
79{
80 struct inet_connection_sock *icsk = inet_csk(sk);
81 struct tcp_congestion_ops *ca;
82
83 /* if no choice made yet assign the current value set as default */
84 if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
85 rcu_read_lock();
86 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
87 if (try_module_get(ca->owner)) {
88 icsk->icsk_ca_ops = ca;
89 break;
90 }
91
92 /* fallback to next available */
93 }
94 rcu_read_unlock();
95 }
96
97 if (icsk->icsk_ca_ops->init)
98 icsk->icsk_ca_ops->init(sk);
99}
100
101/* Manage refcounts on socket close. */
102void tcp_cleanup_congestion_control(struct sock *sk)
103{
104 struct inet_connection_sock *icsk = inet_csk(sk);
105
106 if (icsk->icsk_ca_ops->release)
107 icsk->icsk_ca_ops->release(sk);
108 module_put(icsk->icsk_ca_ops->owner);
109}
110
111/* Used by sysctl to change default congestion control */
112int tcp_set_default_congestion_control(const char *name)
113{
114 struct tcp_congestion_ops *ca;
115 int ret = -ENOENT;
116
117 spin_lock(&tcp_cong_list_lock);
118 ca = tcp_ca_find(name);
119#ifdef CONFIG_MODULES
120 if (!ca && capable(CAP_NET_ADMIN)) {
121 spin_unlock(&tcp_cong_list_lock);
122
123 request_module("tcp_%s", name);
124 spin_lock(&tcp_cong_list_lock);
125 ca = tcp_ca_find(name);
126 }
127#endif
128
129 if (ca) {
130 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
131 list_move(&ca->list, &tcp_cong_list);
132 ret = 0;
133 }
134 spin_unlock(&tcp_cong_list_lock);
135
136 return ret;
137}
138
139/* Set default value from kernel configuration at bootup */
140static int __init tcp_congestion_default(void)
141{
142 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
143}
144late_initcall(tcp_congestion_default);
145
146
147/* Build string with list of available congestion control values */
148void tcp_get_available_congestion_control(char *buf, size_t maxlen)
149{
150 struct tcp_congestion_ops *ca;
151 size_t offs = 0;
152
153 rcu_read_lock();
154 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
155 offs += snprintf(buf + offs, maxlen - offs,
156 "%s%s",
157 offs == 0 ? "" : " ", ca->name);
158
159 }
160 rcu_read_unlock();
161}
162
163/* Get current default congestion control */
164void tcp_get_default_congestion_control(char *name)
165{
166 struct tcp_congestion_ops *ca;
167 /* We will always have reno... */
168 BUG_ON(list_empty(&tcp_cong_list));
169
170 rcu_read_lock();
171 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
172 strncpy(name, ca->name, TCP_CA_NAME_MAX);
173 rcu_read_unlock();
174}
175
176/* Built list of non-restricted congestion control values */
177void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
178{
179 struct tcp_congestion_ops *ca;
180 size_t offs = 0;
181
182 *buf = '\0';
183 rcu_read_lock();
184 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
185 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
186 continue;
187 offs += snprintf(buf + offs, maxlen - offs,
188 "%s%s",
189 offs == 0 ? "" : " ", ca->name);
190
191 }
192 rcu_read_unlock();
193}
194
195/* Change list of non-restricted congestion control */
196int tcp_set_allowed_congestion_control(char *val)
197{
198 struct tcp_congestion_ops *ca;
199 char *saved_clone, *clone, *name;
200 int ret = 0;
201
202 saved_clone = clone = kstrdup(val, GFP_USER);
203 if (!clone)
204 return -ENOMEM;
205
206 spin_lock(&tcp_cong_list_lock);
207 /* pass 1 check for bad entries */
208 while ((name = strsep(&clone, " ")) && *name) {
209 ca = tcp_ca_find(name);
210 if (!ca) {
211 ret = -ENOENT;
212 goto out;
213 }
214 }
215
216 /* pass 2 clear old values */
217 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
218 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
219
220 /* pass 3 mark as allowed */
221 while ((name = strsep(&val, " ")) && *name) {
222 ca = tcp_ca_find(name);
223 WARN_ON(!ca);
224 if (ca)
225 ca->flags |= TCP_CONG_NON_RESTRICTED;
226 }
227out:
228 spin_unlock(&tcp_cong_list_lock);
229 kfree(saved_clone);
230
231 return ret;
232}
233
234
235/* Change congestion control for socket */
236int tcp_set_congestion_control(struct sock *sk, const char *name)
237{
238 struct inet_connection_sock *icsk = inet_csk(sk);
239 struct tcp_congestion_ops *ca;
240 int err = 0;
241
242 rcu_read_lock();
243 ca = tcp_ca_find(name);
244
245 /* no change asking for existing value */
246 if (ca == icsk->icsk_ca_ops)
247 goto out;
248
249#ifdef CONFIG_MODULES
250 /* not found attempt to autoload module */
251 if (!ca && capable(CAP_NET_ADMIN)) {
252 rcu_read_unlock();
253 request_module("tcp_%s", name);
254 rcu_read_lock();
255 ca = tcp_ca_find(name);
256 }
257#endif
258 if (!ca)
259 err = -ENOENT;
260
261 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(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 */
282int 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 1;
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->mss_cache < sk->sk_gso_max_size)
294 return 1;
295 return left <= tcp_max_burst(tp);
296}
297EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
298
299/*
300 * Slow start is used when congestion window is less than slow start
301 * threshold. This version implements the basic RFC2581 version
302 * and optionally supports:
303 * RFC3742 Limited Slow Start - growth limited to max_ssthresh
304 * RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
305 */
306void tcp_slow_start(struct tcp_sock *tp)
307{
308 int cnt; /* increase in packets */
309
310 /* RFC3465: ABC Slow start
311 * Increase only after a full MSS of bytes is acked
312 *
313 * TCP sender SHOULD increase cwnd by the number of
314 * previously unacknowledged bytes ACKed by each incoming
315 * acknowledgment, provided the increase is not more than L
316 */
317 if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
318 return;
319
320 if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
321 cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
322 else
323 cnt = tp->snd_cwnd; /* exponential increase */
324
325 /* RFC3465: ABC
326 * We MAY increase by 2 if discovered delayed ack
327 */
328 if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
329 cnt <<= 1;
330 tp->bytes_acked = 0;
331
332 tp->snd_cwnd_cnt += cnt;
333 while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
334 tp->snd_cwnd_cnt -= tp->snd_cwnd;
335 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
336 tp->snd_cwnd++;
337 }
338}
339EXPORT_SYMBOL_GPL(tcp_slow_start);
340
341/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
342void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
343{
344 if (tp->snd_cwnd_cnt >= w) {
345 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
346 tp->snd_cwnd++;
347 tp->snd_cwnd_cnt = 0;
348 } else {
349 tp->snd_cwnd_cnt++;
350 }
351}
352EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
353
354/*
355 * TCP Reno congestion control
356 * This is special case used for fallback as well.
357 */
358/* This is Jacobson's slow start and congestion avoidance.
359 * SIGCOMM '88, p. 328.
360 */
361void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
362{
363 struct tcp_sock *tp = tcp_sk(sk);
364
365 if (!tcp_is_cwnd_limited(sk, in_flight))
366 return;
367
368 /* In "safe" area, increase. */
369 if (tp->snd_cwnd <= tp->snd_ssthresh)
370 tcp_slow_start(tp);
371
372 /* In dangerous area, increase slowly. */
373 else if (sysctl_tcp_abc) {
374 /* RFC3465: Appropriate Byte Count
375 * increase once for each full cwnd acked
376 */
377 if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
378 tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
379 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
380 tp->snd_cwnd++;
381 }
382 } else {
383 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
384 }
385}
386EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
387
388/* Slow start threshold is half the congestion window (min 2) */
389u32 tcp_reno_ssthresh(struct sock *sk)
390{
391 const struct tcp_sock *tp = tcp_sk(sk);
392 return max(tp->snd_cwnd >> 1U, 2U);
393}
394EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
395
396/* Lower bound on congestion window with halving. */
397u32 tcp_reno_min_cwnd(const struct sock *sk)
398{
399 const struct tcp_sock *tp = tcp_sk(sk);
400 return tp->snd_ssthresh/2;
401}
402EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
403
404struct tcp_congestion_ops tcp_reno = {
405 .flags = TCP_CONG_NON_RESTRICTED,
406 .name = "reno",
407 .owner = THIS_MODULE,
408 .ssthresh = tcp_reno_ssthresh,
409 .cong_avoid = tcp_reno_cong_avoid,
410 .min_cwnd = tcp_reno_min_cwnd,
411};
412
413/* Initial congestion control used (until SYN)
414 * really reno under another name so we can tell difference
415 * during tcp_set_default_congestion_control
416 */
417struct tcp_congestion_ops tcp_init_congestion_ops = {
418 .name = "",
419 .owner = THIS_MODULE,
420 .ssthresh = tcp_reno_ssthresh,
421 .cong_avoid = tcp_reno_cong_avoid,
422 .min_cwnd = tcp_reno_min_cwnd,
423};
424EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);