?  search:
summary | log | graphiclog1 | graphiclog2 | commit | commitdiff | tree | refs | edit | fork
blame | history | raw | HEAD
revert "ocfs2/dlm: use list_for_each_entry instead of list_for_each"
[linux-2.6/btrfs-unstable.git] / net / sched / sch_fq_codel.c
blob4c834e93dafbe27bea51435113552819f7496d5b
1 /*
2 * Fair Queue CoDel discipline
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version
7 * 2 of the License, or (at your option) any later version.
8 *
9 * Copyright (C) 2012,2015 Eric Dumazet <edumazet@google.com>
10 */
11
12 #include <linux/module.h>
13 #include <linux/types.h>
14 #include <linux/kernel.h>
15 #include <linux/jiffies.h>
16 #include <linux/string.h>
17 #include <linux/in.h>
18 #include <linux/errno.h>
19 #include <linux/init.h>
20 #include <linux/skbuff.h>
21 #include <linux/jhash.h>
22 #include <linux/slab.h>
23 #include <linux/vmalloc.h>
24 #include <net/netlink.h>
25 #include <net/pkt_sched.h>
26 #include <net/codel.h>
27
28 /* Fair Queue CoDel.
29 *
30 * Principles :
31 * Packets are classified (internal classifier or external) on flows.
32 * This is a Stochastic model (as we use a hash, several flows
33 * might be hashed on same slot)
34 * Each flow has a CoDel managed queue.
35 * Flows are linked onto two (Round Robin) lists,
36 * so that new flows have priority on old ones.
37 *
38 * For a given flow, packets are not reordered (CoDel uses a FIFO)
39 * head drops only.
40 * ECN capability is on by default.
41 * Low memory footprint (64 bytes per flow)
42 */
43
44 struct fq_codel_flow {
45 struct sk_buff *head;
46 struct sk_buff *tail;
47 struct list_head flowchain;
48 int deficit;
49 u32 dropped; /* number of drops (or ECN marks) on this flow */
50 struct codel_vars cvars;
51 }; /* please try to keep this structure <= 64 bytes */
52
53 struct fq_codel_sched_data {
54 struct tcf_proto __rcu *filter_list; /* optional external classifier */
55 struct fq_codel_flow *flows; /* Flows table [flows_cnt] */
56 u32 *backlogs; /* backlog table [flows_cnt] */
57 u32 flows_cnt; /* number of flows */
58 u32 perturbation; /* hash perturbation */
59 u32 quantum; /* psched_mtu(qdisc_dev(sch)); */
60 struct codel_params cparams;
61 struct codel_stats cstats;
62 u32 drop_overlimit;
63 u32 new_flow_count;
64
65 struct list_head new_flows; /* list of new flows */
66 struct list_head old_flows; /* list of old flows */
67 };
68
69 static unsigned int fq_codel_hash(const struct fq_codel_sched_data *q,
70 struct sk_buff *skb)
71 {
72 u32 hash = skb_get_hash_perturb(skb, q->perturbation);
73
74 return reciprocal_scale(hash, q->flows_cnt);
75 }
76
77 static unsigned int fq_codel_classify(struct sk_buff *skb, struct Qdisc *sch,
78 int *qerr)
79 {
80 struct fq_codel_sched_data *q = qdisc_priv(sch);
81 struct tcf_proto *filter;
82 struct tcf_result res;
83 int result;
84
85 if (TC_H_MAJ(skb->priority) == sch->handle &&
86 TC_H_MIN(skb->priority) > 0 &&
87 TC_H_MIN(skb->priority) <= q->flows_cnt)
88 return TC_H_MIN(skb->priority);
89
90 filter = rcu_dereference_bh(q->filter_list);
91 if (!filter)
92 return fq_codel_hash(q, skb) + 1;
93
94 *qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
95 result = tc_classify(skb, filter, &res, false);
96 if (result >= 0) {
97 #ifdef CONFIG_NET_CLS_ACT
98 switch (result) {
99 case TC_ACT_STOLEN:
100 case TC_ACT_QUEUED:
101 *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
102 case TC_ACT_SHOT:
103 return 0;
104 }
105 #endif
106 if (TC_H_MIN(res.classid) <= q->flows_cnt)
107 return TC_H_MIN(res.classid);
108 }
109 return 0;
110 }
111
112 /* helper functions : might be changed when/if skb use a standard list_head */
113
114 /* remove one skb from head of slot queue */
115 static inline struct sk_buff *dequeue_head(struct fq_codel_flow *flow)
116 {
117 struct sk_buff *skb = flow->head;
118
119 flow->head = skb->next;
120 skb->next = NULL;
121 return skb;
122 }
123
124 /* add skb to flow queue (tail add) */
125 static inline void flow_queue_add(struct fq_codel_flow *flow,
126 struct sk_buff *skb)
127 {
128 if (flow->head == NULL)
129 flow->head = skb;
130 else
131 flow->tail->next = skb;
132 flow->tail = skb;
133 skb->next = NULL;
134 }
135
136 static unsigned int fq_codel_drop(struct Qdisc *sch)
137 {
138 struct fq_codel_sched_data *q = qdisc_priv(sch);
139 struct sk_buff *skb;
140 unsigned int maxbacklog = 0, idx = 0, i, len;
141 struct fq_codel_flow *flow;
142
143 /* Queue is full! Find the fat flow and drop packet from it.
144 * This might sound expensive, but with 1024 flows, we scan
145 * 4KB of memory, and we dont need to handle a complex tree
146 * in fast path (packet queue/enqueue) with many cache misses.
147 */
148 for (i = 0; i < q->flows_cnt; i++) {
149 if (q->backlogs[i] > maxbacklog) {
150 maxbacklog = q->backlogs[i];
151 idx = i;
152 }
153 }
154 flow = &q->flows[idx];
155 skb = dequeue_head(flow);
156 len = qdisc_pkt_len(skb);
157 q->backlogs[idx] -= len;
158 sch->q.qlen--;
159 qdisc_qstats_drop(sch);
160 qdisc_qstats_backlog_dec(sch, skb);
161 kfree_skb(skb);
162 flow->dropped++;
163 return idx;
164 }
165
166 static unsigned int fq_codel_qdisc_drop(struct Qdisc *sch)
167 {
168 unsigned int prev_backlog;
169
170 prev_backlog = sch->qstats.backlog;
171 fq_codel_drop(sch);
172 return prev_backlog - sch->qstats.backlog;
173 }
174
175 static int fq_codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
176 {
177 struct fq_codel_sched_data *q = qdisc_priv(sch);
178 unsigned int idx;
179 struct fq_codel_flow *flow;
180 int uninitialized_var(ret);
181
182 idx = fq_codel_classify(skb, sch, &ret);
183 if (idx == 0) {
184 if (ret & __NET_XMIT_BYPASS)
185 qdisc_qstats_drop(sch);
186 kfree_skb(skb);
187 return ret;
188 }
189 idx--;
190
191 codel_set_enqueue_time(skb);
192 flow = &q->flows[idx];
193 flow_queue_add(flow, skb);
194 q->backlogs[idx] += qdisc_pkt_len(skb);
195 qdisc_qstats_backlog_inc(sch, skb);
196
197 if (list_empty(&flow->flowchain)) {
198 list_add_tail(&flow->flowchain, &q->new_flows);
199 q->new_flow_count++;
200 flow->deficit = q->quantum;
201 flow->dropped = 0;
202 }
203 if (++sch->q.qlen <= sch->limit)
204 return NET_XMIT_SUCCESS;
205
206 q->drop_overlimit++;
207 /* Return Congestion Notification only if we dropped a packet
208 * from this flow.
209 */
210 if (fq_codel_drop(sch) == idx)
211 return NET_XMIT_CN;
212
213 /* As we dropped a packet, better let upper stack know this */
214 qdisc_tree_decrease_qlen(sch, 1);
215 return NET_XMIT_SUCCESS;
216 }
217
218 /* This is the specific function called from codel_dequeue()
219 * to dequeue a packet from queue. Note: backlog is handled in
220 * codel, we dont need to reduce it here.
221 */
222 static struct sk_buff *dequeue(struct codel_vars *vars, struct Qdisc *sch)
223 {
224 struct fq_codel_sched_data *q = qdisc_priv(sch);
225 struct fq_codel_flow *flow;
226 struct sk_buff *skb = NULL;
227
228 flow = container_of(vars, struct fq_codel_flow, cvars);
229 if (flow->head) {
230 skb = dequeue_head(flow);
231 q->backlogs[flow - q->flows] -= qdisc_pkt_len(skb);
232 sch->q.qlen--;
233 }
234 return skb;
235 }
236
237 static struct sk_buff *fq_codel_dequeue(struct Qdisc *sch)
238 {
239 struct fq_codel_sched_data *q = qdisc_priv(sch);
240 struct sk_buff *skb;
241 struct fq_codel_flow *flow;
242 struct list_head *head;
243 u32 prev_drop_count, prev_ecn_mark;
244
245 begin:
246 head = &q->new_flows;
247 if (list_empty(head)) {
248 head = &q->old_flows;
249 if (list_empty(head))
250 return NULL;
251 }
252 flow = list_first_entry(head, struct fq_codel_flow, flowchain);
253
254 if (flow->deficit <= 0) {
255 flow->deficit += q->quantum;
256 list_move_tail(&flow->flowchain, &q->old_flows);
257 goto begin;
258 }
259
260 prev_drop_count = q->cstats.drop_count;
261 prev_ecn_mark = q->cstats.ecn_mark;
262
263 skb = codel_dequeue(sch, &q->cparams, &flow->cvars, &q->cstats,
264 dequeue);
265
266 flow->dropped += q->cstats.drop_count - prev_drop_count;
267 flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;
268
269 if (!skb) {
270 /* force a pass through old_flows to prevent starvation */
271 if ((head == &q->new_flows) && !list_empty(&q->old_flows))
272 list_move_tail(&flow->flowchain, &q->old_flows);
273 else
274 list_del_init(&flow->flowchain);
275 goto begin;
276 }
277 qdisc_bstats_update(sch, skb);
278 flow->deficit -= qdisc_pkt_len(skb);
279 /* We cant call qdisc_tree_decrease_qlen() if our qlen is 0,
280 * or HTB crashes. Defer it for next round.
281 */
282 if (q->cstats.drop_count && sch->q.qlen) {
283 qdisc_tree_decrease_qlen(sch, q->cstats.drop_count);
284 q->cstats.drop_count = 0;
285 }
286 return skb;
287 }
288
289 static void fq_codel_reset(struct Qdisc *sch)
290 {
291 struct fq_codel_sched_data *q = qdisc_priv(sch);
292 int i;
293
294 INIT_LIST_HEAD(&q->new_flows);
295 INIT_LIST_HEAD(&q->old_flows);
296 for (i = 0; i < q->flows_cnt; i++) {
297 struct fq_codel_flow *flow = q->flows + i;
298
299 while (flow->head) {
300 struct sk_buff *skb = dequeue_head(flow);
301
302 qdisc_qstats_backlog_dec(sch, skb);
303 kfree_skb(skb);
304 }
305
306 INIT_LIST_HEAD(&flow->flowchain);
307 codel_vars_init(&flow->cvars);
308 }
309 memset(q->backlogs, 0, q->flows_cnt * sizeof(u32));
310 sch->q.qlen = 0;
311 }
312
313 static const struct nla_policy fq_codel_policy[TCA_FQ_CODEL_MAX + 1] = {
314 [TCA_FQ_CODEL_TARGET] = { .type = NLA_U32 },
315 [TCA_FQ_CODEL_LIMIT] = { .type = NLA_U32 },
316 [TCA_FQ_CODEL_INTERVAL] = { .type = NLA_U32 },
317 [TCA_FQ_CODEL_ECN] = { .type = NLA_U32 },
318 [TCA_FQ_CODEL_FLOWS] = { .type = NLA_U32 },
319 [TCA_FQ_CODEL_QUANTUM] = { .type = NLA_U32 },
320 [TCA_FQ_CODEL_CE_THRESHOLD] = { .type = NLA_U32 },
321 };
322
323 static int fq_codel_change(struct Qdisc *sch, struct nlattr *opt)
324 {
325 struct fq_codel_sched_data *q = qdisc_priv(sch);
326 struct nlattr *tb[TCA_FQ_CODEL_MAX + 1];
327 int err;
328
329 if (!opt)
330 return -EINVAL;
331
332 err = nla_parse_nested(tb, TCA_FQ_CODEL_MAX, opt, fq_codel_policy);
333 if (err < 0)
334 return err;
335 if (tb[TCA_FQ_CODEL_FLOWS]) {
336 if (q->flows)
337 return -EINVAL;
338 q->flows_cnt = nla_get_u32(tb[TCA_FQ_CODEL_FLOWS]);
339 if (!q->flows_cnt ||
340 q->flows_cnt > 65536)
341 return -EINVAL;
342 }
343 sch_tree_lock(sch);
344
345 if (tb[TCA_FQ_CODEL_TARGET]) {
346 u64 target = nla_get_u32(tb[TCA_FQ_CODEL_TARGET]);
347
348 q->cparams.target = (target * NSEC_PER_USEC) >> CODEL_SHIFT;
349 }
350
351 if (tb[TCA_FQ_CODEL_CE_THRESHOLD]) {
352 u64 val = nla_get_u32(tb[TCA_FQ_CODEL_CE_THRESHOLD]);
353
354 q->cparams.ce_threshold = (val * NSEC_PER_USEC) >> CODEL_SHIFT;
355 }
356
357 if (tb[TCA_FQ_CODEL_INTERVAL]) {
358 u64 interval = nla_get_u32(tb[TCA_FQ_CODEL_INTERVAL]);
359
360 q->cparams.interval = (interval * NSEC_PER_USEC) >> CODEL_SHIFT;
361 }
362
363 if (tb[TCA_FQ_CODEL_LIMIT])
364 sch->limit = nla_get_u32(tb[TCA_FQ_CODEL_LIMIT]);
365
366 if (tb[TCA_FQ_CODEL_ECN])
367 q->cparams.ecn = !!nla_get_u32(tb[TCA_FQ_CODEL_ECN]);
368
369 if (tb[TCA_FQ_CODEL_QUANTUM])
370 q->quantum = max(256U, nla_get_u32(tb[TCA_FQ_CODEL_QUANTUM]));
371
372 while (sch->q.qlen > sch->limit) {
373 struct sk_buff *skb = fq_codel_dequeue(sch);
374
375 kfree_skb(skb);
376 q->cstats.drop_count++;
377 }
378 qdisc_tree_decrease_qlen(sch, q->cstats.drop_count);
379 q->cstats.drop_count = 0;
380
381 sch_tree_unlock(sch);
382 return 0;
383 }
384
385 static void *fq_codel_zalloc(size_t sz)
386 {
387 void *ptr = kzalloc(sz, GFP_KERNEL | __GFP_NOWARN);
388
389 if (!ptr)
390 ptr = vzalloc(sz);
391 return ptr;
392 }
393
394 static void fq_codel_free(void *addr)
395 {
396 kvfree(addr);
397 }
398
399 static void fq_codel_destroy(struct Qdisc *sch)
400 {
401 struct fq_codel_sched_data *q = qdisc_priv(sch);
402
403 tcf_destroy_chain(&q->filter_list);
404 fq_codel_free(q->backlogs);
405 fq_codel_free(q->flows);
406 }
407
408 static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt)
409 {
410 struct fq_codel_sched_data *q = qdisc_priv(sch);
411 int i;
412
413 sch->limit = 10*1024;
414 q->flows_cnt = 1024;
415 q->quantum = psched_mtu(qdisc_dev(sch));
416 q->perturbation = prandom_u32();
417 INIT_LIST_HEAD(&q->new_flows);
418 INIT_LIST_HEAD(&q->old_flows);
419 codel_params_init(&q->cparams, sch);
420 codel_stats_init(&q->cstats);
421 q->cparams.ecn = true;
422
423 if (opt) {
424 int err = fq_codel_change(sch, opt);
425 if (err)
426 return err;
427 }
428
429 if (!q->flows) {
430 q->flows = fq_codel_zalloc(q->flows_cnt *
431 sizeof(struct fq_codel_flow));
432 if (!q->flows)
433 return -ENOMEM;
434 q->backlogs = fq_codel_zalloc(q->flows_cnt * sizeof(u32));
435 if (!q->backlogs) {
436 fq_codel_free(q->flows);
437 return -ENOMEM;
438 }
439 for (i = 0; i < q->flows_cnt; i++) {
440 struct fq_codel_flow *flow = q->flows + i;
441
442 INIT_LIST_HEAD(&flow->flowchain);
443 codel_vars_init(&flow->cvars);
444 }
445 }
446 if (sch->limit >= 1)
447 sch->flags |= TCQ_F_CAN_BYPASS;
448 else
449 sch->flags &= ~TCQ_F_CAN_BYPASS;
450 return 0;
451 }
452
453 static int fq_codel_dump(struct Qdisc *sch, struct sk_buff *skb)
454 {
455 struct fq_codel_sched_data *q = qdisc_priv(sch);
456 struct nlattr *opts;
457
458 opts = nla_nest_start(skb, TCA_OPTIONS);
459 if (opts == NULL)
460 goto nla_put_failure;
461
462 if (nla_put_u32(skb, TCA_FQ_CODEL_TARGET,
463 codel_time_to_us(q->cparams.target)) ||
464 nla_put_u32(skb, TCA_FQ_CODEL_LIMIT,
465 sch->limit) ||
466 nla_put_u32(skb, TCA_FQ_CODEL_INTERVAL,
467 codel_time_to_us(q->cparams.interval)) ||
468 nla_put_u32(skb, TCA_FQ_CODEL_ECN,
469 q->cparams.ecn) ||
470 nla_put_u32(skb, TCA_FQ_CODEL_QUANTUM,
471 q->quantum) ||
472 nla_put_u32(skb, TCA_FQ_CODEL_FLOWS,
473 q->flows_cnt))
474 goto nla_put_failure;
475
476 if (q->cparams.ce_threshold != CODEL_DISABLED_THRESHOLD &&
477 nla_put_u32(skb, TCA_FQ_CODEL_CE_THRESHOLD,
478 codel_time_to_us(q->cparams.ce_threshold)))
479 goto nla_put_failure;
480
481 return nla_nest_end(skb, opts);
482
483 nla_put_failure:
484 return -1;
485 }
486
487 static int fq_codel_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
488 {
489 struct fq_codel_sched_data *q = qdisc_priv(sch);
490 struct tc_fq_codel_xstats st = {
491 .type = TCA_FQ_CODEL_XSTATS_QDISC,
492 };
493 struct list_head *pos;
494
495 st.qdisc_stats.maxpacket = q->cstats.maxpacket;
496 st.qdisc_stats.drop_overlimit = q->drop_overlimit;
497 st.qdisc_stats.ecn_mark = q->cstats.ecn_mark;
498 st.qdisc_stats.new_flow_count = q->new_flow_count;
499 st.qdisc_stats.ce_mark = q->cstats.ce_mark;
500
501 list_for_each(pos, &q->new_flows)
502 st.qdisc_stats.new_flows_len++;
503
504 list_for_each(pos, &q->old_flows)
505 st.qdisc_stats.old_flows_len++;
506
507 return gnet_stats_copy_app(d, &st, sizeof(st));
508 }
509
510 static struct Qdisc *fq_codel_leaf(struct Qdisc *sch, unsigned long arg)
511 {
512 return NULL;
513 }
514
515 static unsigned long fq_codel_get(struct Qdisc *sch, u32 classid)
516 {
517 return 0;
518 }
519
520 static unsigned long fq_codel_bind(struct Qdisc *sch, unsigned long parent,
521 u32 classid)
522 {
523 /* we cannot bypass queue discipline anymore */
524 sch->flags &= ~TCQ_F_CAN_BYPASS;
525 return 0;
526 }
527
528 static void fq_codel_put(struct Qdisc *q, unsigned long cl)
529 {
530 }
531
532 static struct tcf_proto __rcu **fq_codel_find_tcf(struct Qdisc *sch,
533 unsigned long cl)
534 {
535 struct fq_codel_sched_data *q = qdisc_priv(sch);
536
537 if (cl)
538 return NULL;
539 return &q->filter_list;
540 }
541
542 static int fq_codel_dump_class(struct Qdisc *sch, unsigned long cl,
543 struct sk_buff *skb, struct tcmsg *tcm)
544 {
545 tcm->tcm_handle |= TC_H_MIN(cl);
546 return 0;
547 }
548
549 static int fq_codel_dump_class_stats(struct Qdisc *sch, unsigned long cl,
550 struct gnet_dump *d)
551 {
552 struct fq_codel_sched_data *q = qdisc_priv(sch);
553 u32 idx = cl - 1;
554 struct gnet_stats_queue qs = { 0 };
555 struct tc_fq_codel_xstats xstats;
556
557 if (idx < q->flows_cnt) {
558 const struct fq_codel_flow *flow = &q->flows[idx];
559 const struct sk_buff *skb = flow->head;
560
561 memset(&xstats, 0, sizeof(xstats));
562 xstats.type = TCA_FQ_CODEL_XSTATS_CLASS;
563 xstats.class_stats.deficit = flow->deficit;
564 xstats.class_stats.ldelay =
565 codel_time_to_us(flow->cvars.ldelay);
566 xstats.class_stats.count = flow->cvars.count;
567 xstats.class_stats.lastcount = flow->cvars.lastcount;
568 xstats.class_stats.dropping = flow->cvars.dropping;
569 if (flow->cvars.dropping) {
570 codel_tdiff_t delta = flow->cvars.drop_next -
571 codel_get_time();
572
573 xstats.class_stats.drop_next = (delta >= 0) ?
574 codel_time_to_us(delta) :
575 -codel_time_to_us(-delta);
576 }
577 while (skb) {
578 qs.qlen++;
579 skb = skb->next;
580 }
581 qs.backlog = q->backlogs[idx];
582 qs.drops = flow->dropped;
583 }
584 if (gnet_stats_copy_queue(d, NULL, &qs, 0) < 0)
585 return -1;
586 if (idx < q->flows_cnt)
587 return gnet_stats_copy_app(d, &xstats, sizeof(xstats));
588 return 0;
589 }
590
591 static void fq_codel_walk(struct Qdisc *sch, struct qdisc_walker *arg)
592 {
593 struct fq_codel_sched_data *q = qdisc_priv(sch);
594 unsigned int i;
595
596 if (arg->stop)
597 return;
598
599 for (i = 0; i < q->flows_cnt; i++) {
600 if (list_empty(&q->flows[i].flowchain) ||
601 arg->count < arg->skip) {
602 arg->count++;
603 continue;
604 }
605 if (arg->fn(sch, i + 1, arg) < 0) {
606 arg->stop = 1;
607 break;
608 }
609 arg->count++;
610 }
611 }
612
613 static const struct Qdisc_class_ops fq_codel_class_ops = {
614 .leaf = fq_codel_leaf,
615 .get = fq_codel_get,
616 .put = fq_codel_put,
617 .tcf_chain = fq_codel_find_tcf,
618 .bind_tcf = fq_codel_bind,
619 .unbind_tcf = fq_codel_put,
620 .dump = fq_codel_dump_class,
621 .dump_stats = fq_codel_dump_class_stats,
622 .walk = fq_codel_walk,
623 };
624
625 static struct Qdisc_ops fq_codel_qdisc_ops __read_mostly = {
626 .cl_ops = &fq_codel_class_ops,
627 .id = "fq_codel",
628 .priv_size = sizeof(struct fq_codel_sched_data),
629 .enqueue = fq_codel_enqueue,
630 .dequeue = fq_codel_dequeue,
631 .peek = qdisc_peek_dequeued,
632 .drop = fq_codel_qdisc_drop,
633 .init = fq_codel_init,
634 .reset = fq_codel_reset,
635 .destroy = fq_codel_destroy,
636 .change = fq_codel_change,
637 .dump = fq_codel_dump,
638 .dump_stats = fq_codel_dump_stats,
639 .owner = THIS_MODULE,
640 };
641
642 static int __init fq_codel_module_init(void)
643 {
644 return register_qdisc(&fq_codel_qdisc_ops);
645 }
646
647 static void __exit fq_codel_module_exit(void)
648 {
649 unregister_qdisc(&fq_codel_qdisc_ops);
650 }
651
652 module_init(fq_codel_module_init)
653 module_exit(fq_codel_module_exit)
654 MODULE_AUTHOR("Eric Dumazet");
655 MODULE_LICENSE("GPL");
(deprecated) Btrfs devel tree