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
20 #include "libbpf.h"
21 #include "libbpf_internal.h"
22 #include "bpf.h"
23
24 struct ring {
25 ring_buffer_sample_fn sample_cb;
26 void *ctx;
27 void *data;
28 unsigned long *consumer_pos;
29 unsigned long *producer_pos;
30 unsigned long mask;
31 int map_fd;
32 };
33
34 struct ring_buffer {
35 struct epoll_event *events;
36 struct ring *rings;
37 size_t page_size;
38 int epoll_fd;
39 int ring_cnt;
40 };
41
ringbuf_unmap_ring(struct ring_buffer * rb,struct ring * r)42 static void ringbuf_unmap_ring(struct ring_buffer *rb, struct ring *r)
43 {
44 if (r->consumer_pos) {
45 munmap(r->consumer_pos, rb->page_size);
46 r->consumer_pos = NULL;
47 }
48 if (r->producer_pos) {
49 munmap(r->producer_pos, rb->page_size + 2 * (r->mask + 1));
50 r->producer_pos = NULL;
51 }
52 }
53
54 /* Add extra RINGBUF maps to this ring buffer manager */
ring_buffer__add(struct ring_buffer * rb,int map_fd,ring_buffer_sample_fn sample_cb,void * ctx)55 int ring_buffer__add(struct ring_buffer *rb, int map_fd,
56 ring_buffer_sample_fn sample_cb, void *ctx)
57 {
58 struct bpf_map_info info;
59 __u32 len = sizeof(info);
60 struct epoll_event *e;
61 struct ring *r;
62 void *tmp;
63 int err;
64
65 memset(&info, 0, sizeof(info));
66
67 err = bpf_obj_get_info_by_fd(map_fd, &info, &len);
68 if (err) {
69 err = -errno;
70 pr_warn("ringbuf: failed to get map info for fd=%d: %d\n",
71 map_fd, err);
72 return libbpf_err(err);
73 }
74
75 if (info.type != BPF_MAP_TYPE_RINGBUF) {
76 pr_warn("ringbuf: map fd=%d is not BPF_MAP_TYPE_RINGBUF\n",
77 map_fd);
78 return libbpf_err(-EINVAL);
79 }
80
81 tmp = libbpf_reallocarray(rb->rings, rb->ring_cnt + 1, sizeof(*rb->rings));
82 if (!tmp)
83 return libbpf_err(-ENOMEM);
84 rb->rings = tmp;
85
86 tmp = libbpf_reallocarray(rb->events, rb->ring_cnt + 1, sizeof(*rb->events));
87 if (!tmp)
88 return libbpf_err(-ENOMEM);
89 rb->events = tmp;
90
91 r = &rb->rings[rb->ring_cnt];
92 memset(r, 0, sizeof(*r));
93
94 r->map_fd = map_fd;
95 r->sample_cb = sample_cb;
96 r->ctx = ctx;
97 r->mask = info.max_entries - 1;
98
99 /* Map writable consumer page */
100 tmp = mmap(NULL, rb->page_size, PROT_READ | PROT_WRITE, MAP_SHARED,
101 map_fd, 0);
102 if (tmp == MAP_FAILED) {
103 err = -errno;
104 pr_warn("ringbuf: failed to mmap consumer page for map fd=%d: %d\n",
105 map_fd, err);
106 return libbpf_err(err);
107 }
108 r->consumer_pos = tmp;
109
110 /* Map read-only producer page and data pages. We map twice as big
111 * data size to allow simple reading of samples that wrap around the
112 * end of a ring buffer. See kernel implementation for details.
113 * */
114 tmp = mmap(NULL, rb->page_size + 2 * info.max_entries, PROT_READ,
115 MAP_SHARED, map_fd, rb->page_size);
116 if (tmp == MAP_FAILED) {
117 err = -errno;
118 ringbuf_unmap_ring(rb, r);
119 pr_warn("ringbuf: failed to mmap data pages for map fd=%d: %d\n",
120 map_fd, err);
121 return libbpf_err(err);
122 }
123 r->producer_pos = tmp;
124 r->data = tmp + rb->page_size;
125
126 e = &rb->events[rb->ring_cnt];
127 memset(e, 0, sizeof(*e));
128
129 e->events = EPOLLIN;
130 e->data.fd = rb->ring_cnt;
131 if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, e) < 0) {
132 err = -errno;
133 ringbuf_unmap_ring(rb, r);
134 pr_warn("ringbuf: failed to epoll add map fd=%d: %d\n",
135 map_fd, err);
136 return libbpf_err(err);
137 }
138
139 rb->ring_cnt++;
140 return 0;
141 }
142
ring_buffer__free(struct ring_buffer * rb)143 void ring_buffer__free(struct ring_buffer *rb)
144 {
145 int i;
146
147 if (!rb)
148 return;
149
150 for (i = 0; i < rb->ring_cnt; ++i)
151 ringbuf_unmap_ring(rb, &rb->rings[i]);
152 if (rb->epoll_fd >= 0)
153 close(rb->epoll_fd);
154
155 free(rb->events);
156 free(rb->rings);
157 free(rb);
158 }
159
160 struct ring_buffer *
ring_buffer__new(int map_fd,ring_buffer_sample_fn sample_cb,void * ctx,const struct ring_buffer_opts * opts)161 ring_buffer__new(int map_fd, ring_buffer_sample_fn sample_cb, void *ctx,
162 const struct ring_buffer_opts *opts)
163 {
164 struct ring_buffer *rb;
165 int err;
166
167 if (!OPTS_VALID(opts, ring_buffer_opts))
168 return errno = EINVAL, NULL;
169
170 rb = calloc(1, sizeof(*rb));
171 if (!rb)
172 return errno = ENOMEM, NULL;
173
174 rb->page_size = getpagesize();
175
176 rb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
177 if (rb->epoll_fd < 0) {
178 err = -errno;
179 pr_warn("ringbuf: failed to create epoll instance: %d\n", err);
180 goto err_out;
181 }
182
183 err = ring_buffer__add(rb, map_fd, sample_cb, ctx);
184 if (err)
185 goto err_out;
186
187 return rb;
188
189 err_out:
190 ring_buffer__free(rb);
191 return errno = -err, NULL;
192 }
193
roundup_len(__u32 len)194 static inline int roundup_len(__u32 len)
195 {
196 /* clear out top 2 bits (discard and busy, if set) */
197 len <<= 2;
198 len >>= 2;
199 /* add length prefix */
200 len += BPF_RINGBUF_HDR_SZ;
201 /* round up to 8 byte alignment */
202 return (len + 7) / 8 * 8;
203 }
204
ringbuf_process_ring(struct ring * r)205 static int64_t ringbuf_process_ring(struct ring* r)
206 {
207 int *len_ptr, len, err;
208 /* 64-bit to avoid overflow in case of extreme application behavior */
209 int64_t cnt = 0;
210 unsigned long cons_pos, prod_pos;
211 bool got_new_data;
212 void *sample;
213
214 cons_pos = smp_load_acquire(r->consumer_pos);
215 do {
216 got_new_data = false;
217 prod_pos = smp_load_acquire(r->producer_pos);
218 while (cons_pos < prod_pos) {
219 len_ptr = r->data + (cons_pos & r->mask);
220 len = smp_load_acquire(len_ptr);
221
222 /* sample not committed yet, bail out for now */
223 if (len & BPF_RINGBUF_BUSY_BIT)
224 goto done;
225
226 got_new_data = true;
227 cons_pos += roundup_len(len);
228
229 if ((len & BPF_RINGBUF_DISCARD_BIT) == 0) {
230 sample = (void *)len_ptr + BPF_RINGBUF_HDR_SZ;
231 err = r->sample_cb(r->ctx, sample, len);
232 if (err < 0) {
233 /* update consumer pos and bail out */
234 smp_store_release(r->consumer_pos,
235 cons_pos);
236 return err;
237 }
238 cnt++;
239 }
240
241 smp_store_release(r->consumer_pos, cons_pos);
242 }
243 } while (got_new_data);
244 done:
245 return cnt;
246 }
247
248 /* Consume available ring buffer(s) data without event polling.
249 * Returns number of records consumed across all registered ring buffers (or
250 * INT_MAX, whichever is less), or negative number if any of the callbacks
251 * return error.
252 */
ring_buffer__consume(struct ring_buffer * rb)253 int ring_buffer__consume(struct ring_buffer *rb)
254 {
255 int64_t err, res = 0;
256 int i;
257
258 for (i = 0; i < rb->ring_cnt; i++) {
259 struct ring *ring = &rb->rings[i];
260
261 err = ringbuf_process_ring(ring);
262 if (err < 0)
263 return libbpf_err(err);
264 res += err;
265 }
266 if (res > INT_MAX)
267 return INT_MAX;
268 return res;
269 }
270
271 /* Poll for available data and consume records, if any are available.
272 * Returns number of records consumed (or INT_MAX, whichever is less), or
273 * negative number, if any of the registered callbacks returned error.
274 */
ring_buffer__poll(struct ring_buffer * rb,int timeout_ms)275 int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
276 {
277 int i, cnt;
278 int64_t err, res = 0;
279
280 cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms);
281 if (cnt < 0)
282 return libbpf_err(-errno);
283
284 for (i = 0; i < cnt; i++) {
285 __u32 ring_id = rb->events[i].data.fd;
286 struct ring *ring = &rb->rings[ring_id];
287
288 err = ringbuf_process_ring(ring);
289 if (err < 0)
290 return libbpf_err(err);
291 res += err;
292 }
293 if (res > INT_MAX)
294 return INT_MAX;
295 return res;
296 }
297
298 /* Get an fd that can be used to sleep until data is available in the ring(s) */
ring_buffer__epoll_fd(const struct ring_buffer * rb)299 int ring_buffer__epoll_fd(const struct ring_buffer *rb)
300 {
301 return rb->epoll_fd;
302 }
303
