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 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 */ 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 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 -EINVAL; 79 } 80 81 tmp = libbpf_reallocarray(rb->rings, rb->ring_cnt + 1, sizeof(*rb->rings)); 82 if (!tmp) 83 return -ENOMEM; 84 rb->rings = tmp; 85 86 tmp = libbpf_reallocarray(rb->events, rb->ring_cnt + 1, sizeof(*rb->events)); 87 if (!tmp) 88 return -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 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 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 err; 137 } 138 139 rb->ring_cnt++; 140 return 0; 141 } 142 143 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 * 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 NULL; 169 170 rb = calloc(1, sizeof(*rb)); 171 if (!rb) 172 return 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 NULL; 192 } 193 194 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 } 204 205 static int ringbuf_process_ring(struct ring* r) 206 { 207 int *len_ptr, len, err, cnt = 0; 208 unsigned long cons_pos, prod_pos; 209 bool got_new_data; 210 void *sample; 211 212 cons_pos = smp_load_acquire(r->consumer_pos); 213 do { 214 got_new_data = false; 215 prod_pos = smp_load_acquire(r->producer_pos); 216 while (cons_pos < prod_pos) { 217 len_ptr = r->data + (cons_pos & r->mask); 218 len = smp_load_acquire(len_ptr); 219 220 /* sample not committed yet, bail out for now */ 221 if (len & BPF_RINGBUF_BUSY_BIT) 222 goto done; 223 224 got_new_data = true; 225 cons_pos += roundup_len(len); 226 227 if ((len & BPF_RINGBUF_DISCARD_BIT) == 0) { 228 sample = (void *)len_ptr + BPF_RINGBUF_HDR_SZ; 229 err = r->sample_cb(r->ctx, sample, len); 230 if (err) { 231 /* update consumer pos and bail out */ 232 smp_store_release(r->consumer_pos, 233 cons_pos); 234 return err; 235 } 236 cnt++; 237 } 238 239 smp_store_release(r->consumer_pos, cons_pos); 240 } 241 } while (got_new_data); 242 done: 243 return cnt; 244 } 245 246 /* Consume available ring buffer(s) data without event polling. 247 * Returns number of records consumed across all registered ring buffers, or 248 * negative number if any of the callbacks return error. 249 */ 250 int ring_buffer__consume(struct ring_buffer *rb) 251 { 252 int i, err, res = 0; 253 254 for (i = 0; i < rb->ring_cnt; i++) { 255 struct ring *ring = &rb->rings[i]; 256 257 err = ringbuf_process_ring(ring); 258 if (err < 0) 259 return err; 260 res += err; 261 } 262 return res; 263 } 264 265 /* Poll for available data and consume records, if any are available. 266 * Returns number of records consumed, or negative number, if any of the 267 * registered callbacks returned error. 268 */ 269 int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms) 270 { 271 int i, cnt, err, res = 0; 272 273 cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms); 274 for (i = 0; i < cnt; i++) { 275 __u32 ring_id = rb->events[i].data.fd; 276 struct ring *ring = &rb->rings[ring_id]; 277 278 err = ringbuf_process_ring(ring); 279 if (err < 0) 280 return err; 281 res += err; 282 } 283 return cnt < 0 ? -errno : res; 284 } 285 286 /* Get an fd that can be used to sleep until data is available in the ring(s) */ 287 int ring_buffer__epoll_fd(const struct ring_buffer *rb) 288 { 289 return rb->epoll_fd; 290 } 291