1// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
2/*
3 * Ring buffer operations.
4 *
5 * Copyright (C) 2020 Facebook, Inc.
6 */
7#ifndef _GNU_SOURCE
8#define _GNU_SOURCE
9#endif
10#include <stdlib.h>
11#include <stdio.h>
12#include <errno.h>
13#include <unistd.h>
14#include <linux/err.h>
15#include <linux/bpf.h>
16#include <asm/barrier.h>
17#include <sys/mman.h>
18#include <sys/epoll.h>
19#include <time.h>
20
21#include "libbpf.h"
22#include "libbpf_internal.h"
23#include "bpf.h"
24
25struct ring {
26 ring_buffer_sample_fn sample_cb;
27 void *ctx;
28 void *data;
29 unsigned long *consumer_pos;
30 unsigned long *producer_pos;
31 unsigned long mask;
32 int map_fd;
33};
34
35struct ring_buffer {
36 struct epoll_event *events;
37 struct ring **rings;
38 size_t page_size;
39 int epoll_fd;
40 int ring_cnt;
41};
42
43struct user_ring_buffer {
44 struct epoll_event event;
45 unsigned long *consumer_pos;
46 unsigned long *producer_pos;
47 void *data;
48 unsigned long mask;
49 size_t page_size;
50 int map_fd;
51 int epoll_fd;
52};
53
54/* 8-byte ring buffer header structure */
55struct ringbuf_hdr {
56 __u32 len;
57 __u32 pad;
58};
59
60static void ringbuf_free_ring(struct ring_buffer *rb, struct ring *r)
61{
62 if (r->consumer_pos) {
63 munmap(r->consumer_pos, rb->page_size);
64 r->consumer_pos = NULL;
65 }
66 if (r->producer_pos) {
67 munmap(r->producer_pos, rb->page_size + 2 * (r->mask + 1));
68 r->producer_pos = NULL;
69 }
70
71 free(r);
72}
73
74/* Add extra RINGBUF maps to this ring buffer manager */
75int ring_buffer__add(struct ring_buffer *rb, int map_fd,
76 ring_buffer_sample_fn sample_cb, void *ctx)
77{
78 struct bpf_map_info info;
79 __u32 len = sizeof(info);
80 struct epoll_event *e;
81 struct ring *r;
82 __u64 mmap_sz;
83 void *tmp;
84 int err;
85
86 memset(&info, 0, sizeof(info));
87
88 err = bpf_map_get_info_by_fd(map_fd, info: &info, info_len: &len);
89 if (err) {
90 err = -errno;
91 pr_warn("ringbuf: failed to get map info for fd=%d: %d\n",
92 map_fd, err);
93 return libbpf_err(ret: err);
94 }
95
96 if (info.type != BPF_MAP_TYPE_RINGBUF) {
97 pr_warn("ringbuf: map fd=%d is not BPF_MAP_TYPE_RINGBUF\n",
98 map_fd);
99 return libbpf_err(ret: -EINVAL);
100 }
101
102 tmp = libbpf_reallocarray(ptr: rb->rings, nmemb: rb->ring_cnt + 1, size: sizeof(*rb->rings));
103 if (!tmp)
104 return libbpf_err(ret: -ENOMEM);
105 rb->rings = tmp;
106
107 tmp = libbpf_reallocarray(rb->events, rb->ring_cnt + 1, sizeof(*rb->events));
108 if (!tmp)
109 return libbpf_err(ret: -ENOMEM);
110 rb->events = tmp;
111
112 r = calloc(1, sizeof(*r));
113 if (!r)
114 return libbpf_err(ret: -ENOMEM);
115 rb->rings[rb->ring_cnt] = r;
116
117 r->map_fd = map_fd;
118 r->sample_cb = sample_cb;
119 r->ctx = ctx;
120 r->mask = info.max_entries - 1;
121
122 /* Map writable consumer page */
123 tmp = mmap(NULL, rb->page_size, PROT_READ | PROT_WRITE, MAP_SHARED, map_fd, 0);
124 if (tmp == MAP_FAILED) {
125 err = -errno;
126 pr_warn("ringbuf: failed to mmap consumer page for map fd=%d: %d\n",
127 map_fd, err);
128 goto err_out;
129 }
130 r->consumer_pos = tmp;
131
132 /* Map read-only producer page and data pages. We map twice as big
133 * data size to allow simple reading of samples that wrap around the
134 * end of a ring buffer. See kernel implementation for details.
135 */
136 mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
137 if (mmap_sz != (__u64)(size_t)mmap_sz) {
138 err = -E2BIG;
139 pr_warn("ringbuf: ring buffer size (%u) is too big\n", info.max_entries);
140 goto err_out;
141 }
142 tmp = mmap(NULL, (size_t)mmap_sz, PROT_READ, MAP_SHARED, map_fd, rb->page_size);
143 if (tmp == MAP_FAILED) {
144 err = -errno;
145 pr_warn("ringbuf: failed to mmap data pages for map fd=%d: %d\n",
146 map_fd, err);
147 goto err_out;
148 }
149 r->producer_pos = tmp;
150 r->data = tmp + rb->page_size;
151
152 e = &rb->events[rb->ring_cnt];
153 memset(e, 0, sizeof(*e));
154
155 e->events = EPOLLIN;
156 e->data.fd = rb->ring_cnt;
157 if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, e) < 0) {
158 err = -errno;
159 pr_warn("ringbuf: failed to epoll add map fd=%d: %d\n",
160 map_fd, err);
161 goto err_out;
162 }
163
164 rb->ring_cnt++;
165 return 0;
166
167err_out:
168 ringbuf_free_ring(rb, r);
169 return libbpf_err(ret: err);
170}
171
172void ring_buffer__free(struct ring_buffer *rb)
173{
174 int i;
175
176 if (!rb)
177 return;
178
179 for (i = 0; i < rb->ring_cnt; ++i)
180 ringbuf_free_ring(rb, r: rb->rings[i]);
181 if (rb->epoll_fd >= 0)
182 close(rb->epoll_fd);
183
184 free(rb->events);
185 free(rb->rings);
186 free(rb);
187}
188
189struct ring_buffer *
190ring_buffer__new(int map_fd, ring_buffer_sample_fn sample_cb, void *ctx,
191 const struct ring_buffer_opts *opts)
192{
193 struct ring_buffer *rb;
194 int err;
195
196 if (!OPTS_VALID(opts, ring_buffer_opts))
197 return errno = EINVAL, NULL;
198
199 rb = calloc(1, sizeof(*rb));
200 if (!rb)
201 return errno = ENOMEM, NULL;
202
203 rb->page_size = getpagesize();
204
205 rb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
206 if (rb->epoll_fd < 0) {
207 err = -errno;
208 pr_warn("ringbuf: failed to create epoll instance: %d\n", err);
209 goto err_out;
210 }
211
212 err = ring_buffer__add(rb, map_fd, sample_cb, ctx);
213 if (err)
214 goto err_out;
215
216 return rb;
217
218err_out:
219 ring_buffer__free(rb);
220 return errno = -err, NULL;
221}
222
223static inline int roundup_len(__u32 len)
224{
225 /* clear out top 2 bits (discard and busy, if set) */
226 len <<= 2;
227 len >>= 2;
228 /* add length prefix */
229 len += BPF_RINGBUF_HDR_SZ;
230 /* round up to 8 byte alignment */
231 return (len + 7) / 8 * 8;
232}
233
234static int64_t ringbuf_process_ring(struct ring *r)
235{
236 int *len_ptr, len, err;
237 /* 64-bit to avoid overflow in case of extreme application behavior */
238 int64_t cnt = 0;
239 unsigned long cons_pos, prod_pos;
240 bool got_new_data;
241 void *sample;
242
243 cons_pos = smp_load_acquire(r->consumer_pos);
244 do {
245 got_new_data = false;
246 prod_pos = smp_load_acquire(r->producer_pos);
247 while (cons_pos < prod_pos) {
248 len_ptr = r->data + (cons_pos & r->mask);
249 len = smp_load_acquire(len_ptr);
250
251 /* sample not committed yet, bail out for now */
252 if (len & BPF_RINGBUF_BUSY_BIT)
253 goto done;
254
255 got_new_data = true;
256 cons_pos += roundup_len(len);
257
258 if ((len & BPF_RINGBUF_DISCARD_BIT) == 0) {
259 sample = (void *)len_ptr + BPF_RINGBUF_HDR_SZ;
260 err = r->sample_cb(r->ctx, sample, len);
261 if (err < 0) {
262 /* update consumer pos and bail out */
263 smp_store_release(r->consumer_pos,
264 cons_pos);
265 return err;
266 }
267 cnt++;
268 }
269
270 smp_store_release(r->consumer_pos, cons_pos);
271 }
272 } while (got_new_data);
273done:
274 return cnt;
275}
276
277/* Consume available ring buffer(s) data without event polling.
278 * Returns number of records consumed across all registered ring buffers (or
279 * INT_MAX, whichever is less), or negative number if any of the callbacks
280 * return error.
281 */
282int ring_buffer__consume(struct ring_buffer *rb)
283{
284 int64_t err, res = 0;
285 int i;
286
287 for (i = 0; i < rb->ring_cnt; i++) {
288 struct ring *ring = rb->rings[i];
289
290 err = ringbuf_process_ring(r: ring);
291 if (err < 0)
292 return libbpf_err(ret: err);
293 res += err;
294 }
295 if (res > INT_MAX)
296 return INT_MAX;
297 return res;
298}
299
300/* Poll for available data and consume records, if any are available.
301 * Returns number of records consumed (or INT_MAX, whichever is less), or
302 * negative number, if any of the registered callbacks returned error.
303 */
304int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
305{
306 int i, cnt;
307 int64_t err, res = 0;
308
309 cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms);
310 if (cnt < 0)
311 return libbpf_err(ret: -errno);
312
313 for (i = 0; i < cnt; i++) {
314 __u32 ring_id = rb->events[i].data.fd;
315 struct ring *ring = rb->rings[ring_id];
316
317 err = ringbuf_process_ring(r: ring);
318 if (err < 0)
319 return libbpf_err(ret: err);
320 res += err;
321 }
322 if (res > INT_MAX)
323 return INT_MAX;
324 return res;
325}
326
327/* Get an fd that can be used to sleep until data is available in the ring(s) */
328int ring_buffer__epoll_fd(const struct ring_buffer *rb)
329{
330 return rb->epoll_fd;
331}
332
333struct ring *ring_buffer__ring(struct ring_buffer *rb, unsigned int idx)
334{
335 if (idx >= rb->ring_cnt)
336 return errno = ERANGE, NULL;
337
338 return rb->rings[idx];
339}
340
341unsigned long ring__consumer_pos(const struct ring *r)
342{
343 /* Synchronizes with smp_store_release() in ringbuf_process_ring(). */
344 return smp_load_acquire(r->consumer_pos);
345}
346
347unsigned long ring__producer_pos(const struct ring *r)
348{
349 /* Synchronizes with smp_store_release() in __bpf_ringbuf_reserve() in
350 * the kernel.
351 */
352 return smp_load_acquire(r->producer_pos);
353}
354
355size_t ring__avail_data_size(const struct ring *r)
356{
357 unsigned long cons_pos, prod_pos;
358
359 cons_pos = ring__consumer_pos(r);
360 prod_pos = ring__producer_pos(r);
361 return prod_pos - cons_pos;
362}
363
364size_t ring__size(const struct ring *r)
365{
366 return r->mask + 1;
367}
368
369int ring__map_fd(const struct ring *r)
370{
371 return r->map_fd;
372}
373
374int ring__consume(struct ring *r)
375{
376 int64_t res;
377
378 res = ringbuf_process_ring(r);
379 if (res < 0)
380 return libbpf_err(ret: res);
381
382 return res > INT_MAX ? INT_MAX : res;
383}
384
385static void user_ringbuf_unmap_ring(struct user_ring_buffer *rb)
386{
387 if (rb->consumer_pos) {
388 munmap(rb->consumer_pos, rb->page_size);
389 rb->consumer_pos = NULL;
390 }
391 if (rb->producer_pos) {
392 munmap(rb->producer_pos, rb->page_size + 2 * (rb->mask + 1));
393 rb->producer_pos = NULL;
394 }
395}
396
397void user_ring_buffer__free(struct user_ring_buffer *rb)
398{
399 if (!rb)
400 return;
401
402 user_ringbuf_unmap_ring(rb);
403
404 if (rb->epoll_fd >= 0)
405 close(rb->epoll_fd);
406
407 free(rb);
408}
409
410static int user_ringbuf_map(struct user_ring_buffer *rb, int map_fd)
411{
412 struct bpf_map_info info;
413 __u32 len = sizeof(info);
414 __u64 mmap_sz;
415 void *tmp;
416 struct epoll_event *rb_epoll;
417 int err;
418
419 memset(&info, 0, sizeof(info));
420
421 err = bpf_map_get_info_by_fd(map_fd, info: &info, info_len: &len);
422 if (err) {
423 err = -errno;
424 pr_warn("user ringbuf: failed to get map info for fd=%d: %d\n", map_fd, err);
425 return err;
426 }
427
428 if (info.type != BPF_MAP_TYPE_USER_RINGBUF) {
429 pr_warn("user ringbuf: map fd=%d is not BPF_MAP_TYPE_USER_RINGBUF\n", map_fd);
430 return -EINVAL;
431 }
432
433 rb->map_fd = map_fd;
434 rb->mask = info.max_entries - 1;
435
436 /* Map read-only consumer page */
437 tmp = mmap(NULL, rb->page_size, PROT_READ, MAP_SHARED, map_fd, 0);
438 if (tmp == MAP_FAILED) {
439 err = -errno;
440 pr_warn("user ringbuf: failed to mmap consumer page for map fd=%d: %d\n",
441 map_fd, err);
442 return err;
443 }
444 rb->consumer_pos = tmp;
445
446 /* Map read-write the producer page and data pages. We map the data
447 * region as twice the total size of the ring buffer to allow the
448 * simple reading and writing of samples that wrap around the end of
449 * the buffer. See the kernel implementation for details.
450 */
451 mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
452 if (mmap_sz != (__u64)(size_t)mmap_sz) {
453 pr_warn("user ringbuf: ring buf size (%u) is too big\n", info.max_entries);
454 return -E2BIG;
455 }
456 tmp = mmap(NULL, (size_t)mmap_sz, PROT_READ | PROT_WRITE, MAP_SHARED,
457 map_fd, rb->page_size);
458 if (tmp == MAP_FAILED) {
459 err = -errno;
460 pr_warn("user ringbuf: failed to mmap data pages for map fd=%d: %d\n",
461 map_fd, err);
462 return err;
463 }
464
465 rb->producer_pos = tmp;
466 rb->data = tmp + rb->page_size;
467
468 rb_epoll = &rb->event;
469 rb_epoll->events = EPOLLOUT;
470 if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, rb_epoll) < 0) {
471 err = -errno;
472 pr_warn("user ringbuf: failed to epoll add map fd=%d: %d\n", map_fd, err);
473 return err;
474 }
475
476 return 0;
477}
478
479struct user_ring_buffer *
480user_ring_buffer__new(int map_fd, const struct user_ring_buffer_opts *opts)
481{
482 struct user_ring_buffer *rb;
483 int err;
484
485 if (!OPTS_VALID(opts, user_ring_buffer_opts))
486 return errno = EINVAL, NULL;
487
488 rb = calloc(1, sizeof(*rb));
489 if (!rb)
490 return errno = ENOMEM, NULL;
491
492 rb->page_size = getpagesize();
493
494 rb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
495 if (rb->epoll_fd < 0) {
496 err = -errno;
497 pr_warn("user ringbuf: failed to create epoll instance: %d\n", err);
498 goto err_out;
499 }
500
501 err = user_ringbuf_map(rb, map_fd);
502 if (err)
503 goto err_out;
504
505 return rb;
506
507err_out:
508 user_ring_buffer__free(rb);
509 return errno = -err, NULL;
510}
511
512static void user_ringbuf_commit(struct user_ring_buffer *rb, void *sample, bool discard)
513{
514 __u32 new_len;
515 struct ringbuf_hdr *hdr;
516 uintptr_t hdr_offset;
517
518 hdr_offset = rb->mask + 1 + (sample - rb->data) - BPF_RINGBUF_HDR_SZ;
519 hdr = rb->data + (hdr_offset & rb->mask);
520
521 new_len = hdr->len & ~BPF_RINGBUF_BUSY_BIT;
522 if (discard)
523 new_len |= BPF_RINGBUF_DISCARD_BIT;
524
525 /* Synchronizes with smp_load_acquire() in __bpf_user_ringbuf_peek() in
526 * the kernel.
527 */
528 __atomic_exchange_n(&hdr->len, new_len, __ATOMIC_ACQ_REL);
529}
530
531void user_ring_buffer__discard(struct user_ring_buffer *rb, void *sample)
532{
533 user_ringbuf_commit(rb, sample, discard: true);
534}
535
536void user_ring_buffer__submit(struct user_ring_buffer *rb, void *sample)
537{
538 user_ringbuf_commit(rb, sample, discard: false);
539}
540
541void *user_ring_buffer__reserve(struct user_ring_buffer *rb, __u32 size)
542{
543 __u32 avail_size, total_size, max_size;
544 /* 64-bit to avoid overflow in case of extreme application behavior */
545 __u64 cons_pos, prod_pos;
546 struct ringbuf_hdr *hdr;
547
548 /* The top two bits are used as special flags */
549 if (size & (BPF_RINGBUF_BUSY_BIT | BPF_RINGBUF_DISCARD_BIT))
550 return errno = E2BIG, NULL;
551
552 /* Synchronizes with smp_store_release() in __bpf_user_ringbuf_peek() in
553 * the kernel.
554 */
555 cons_pos = smp_load_acquire(rb->consumer_pos);
556 /* Synchronizes with smp_store_release() in user_ringbuf_commit() */
557 prod_pos = smp_load_acquire(rb->producer_pos);
558
559 max_size = rb->mask + 1;
560 avail_size = max_size - (prod_pos - cons_pos);
561 /* Round up total size to a multiple of 8. */
562 total_size = (size + BPF_RINGBUF_HDR_SZ + 7) / 8 * 8;
563
564 if (total_size > max_size)
565 return errno = E2BIG, NULL;
566
567 if (avail_size < total_size)
568 return errno = ENOSPC, NULL;
569
570 hdr = rb->data + (prod_pos & rb->mask);
571 hdr->len = size | BPF_RINGBUF_BUSY_BIT;
572 hdr->pad = 0;
573
574 /* Synchronizes with smp_load_acquire() in __bpf_user_ringbuf_peek() in
575 * the kernel.
576 */
577 smp_store_release(rb->producer_pos, prod_pos + total_size);
578
579 return (void *)rb->data + ((prod_pos + BPF_RINGBUF_HDR_SZ) & rb->mask);
580}
581
582static __u64 ns_elapsed_timespec(const struct timespec *start, const struct timespec *end)
583{
584 __u64 start_ns, end_ns, ns_per_s = 1000000000;
585
586 start_ns = (__u64)start->tv_sec * ns_per_s + start->tv_nsec;
587 end_ns = (__u64)end->tv_sec * ns_per_s + end->tv_nsec;
588
589 return end_ns - start_ns;
590}
591
592void *user_ring_buffer__reserve_blocking(struct user_ring_buffer *rb, __u32 size, int timeout_ms)
593{
594 void *sample;
595 int err, ms_remaining = timeout_ms;
596 struct timespec start;
597
598 if (timeout_ms < 0 && timeout_ms != -1)
599 return errno = EINVAL, NULL;
600
601 if (timeout_ms != -1) {
602 err = clock_gettime(CLOCK_MONOTONIC, &start);
603 if (err)
604 return NULL;
605 }
606
607 do {
608 int cnt, ms_elapsed;
609 struct timespec curr;
610 __u64 ns_per_ms = 1000000;
611
612 sample = user_ring_buffer__reserve(rb, size);
613 if (sample)
614 return sample;
615 else if (errno != ENOSPC)
616 return NULL;
617
618 /* The kernel guarantees at least one event notification
619 * delivery whenever at least one sample is drained from the
620 * ring buffer in an invocation to bpf_ringbuf_drain(). Other
621 * additional events may be delivered at any time, but only one
622 * event is guaranteed per bpf_ringbuf_drain() invocation,
623 * provided that a sample is drained, and the BPF program did
624 * not pass BPF_RB_NO_WAKEUP to bpf_ringbuf_drain(). If
625 * BPF_RB_FORCE_WAKEUP is passed to bpf_ringbuf_drain(), a
626 * wakeup event will be delivered even if no samples are
627 * drained.
628 */
629 cnt = epoll_wait(rb->epoll_fd, &rb->event, 1, ms_remaining);
630 if (cnt < 0)
631 return NULL;
632
633 if (timeout_ms == -1)
634 continue;
635
636 err = clock_gettime(CLOCK_MONOTONIC, &curr);
637 if (err)
638 return NULL;
639
640 ms_elapsed = ns_elapsed_timespec(start: &start, end: &curr) / ns_per_ms;
641 ms_remaining = timeout_ms - ms_elapsed;
642 } while (ms_remaining > 0);
643
644 /* Try one more time to reserve a sample after the specified timeout has elapsed. */
645 return user_ring_buffer__reserve(rb, size);
646}
647

source code of linux/tools/lib/bpf/ringbuf.c