| 1 | #ifndef _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H |
| 2 | #define _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H |
| 3 | |
| 4 | /* |
| 5 | * libringbuffer/backend_internal.h |
| 6 | * |
| 7 | * Ring buffer backend (internal helpers). |
| 8 | * |
| 9 | * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 10 | * |
| 11 | * This library is free software; you can redistribute it and/or |
| 12 | * modify it under the terms of the GNU Lesser General Public |
| 13 | * License as published by the Free Software Foundation; only |
| 14 | * version 2.1 of the License. |
| 15 | * |
| 16 | * This library is distributed in the hope that it will be useful, |
| 17 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 18 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 19 | * Lesser General Public License for more details. |
| 20 | * |
| 21 | * You should have received a copy of the GNU Lesser General Public |
| 22 | * License along with this library; if not, write to the Free Software |
| 23 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 24 | */ |
| 25 | |
| 26 | #include <unistd.h> |
| 27 | #include <urcu/compiler.h> |
| 28 | |
| 29 | #include <lttng/ringbuffer-config.h> |
| 30 | #include "backend_types.h" |
| 31 | #include "frontend_types.h" |
| 32 | #include "shm.h" |
| 33 | |
| 34 | /* Ring buffer backend API presented to the frontend */ |
| 35 | |
| 36 | /* Ring buffer and channel backend create/free */ |
| 37 | |
| 38 | int lib_ring_buffer_backend_create(struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 39 | struct channel_backend *chan, int cpu, |
| 40 | struct lttng_ust_shm_handle *handle, |
| 41 | struct shm_object *shmobj); |
| 42 | void channel_backend_unregister_notifiers(struct channel_backend *chanb); |
| 43 | void lib_ring_buffer_backend_free(struct lttng_ust_lib_ring_buffer_backend *bufb); |
| 44 | int channel_backend_init(struct channel_backend *chanb, |
| 45 | const char *name, |
| 46 | const struct lttng_ust_lib_ring_buffer_config *config, |
| 47 | size_t subbuf_size, |
| 48 | size_t num_subbuf, struct lttng_ust_shm_handle *handle); |
| 49 | void channel_backend_free(struct channel_backend *chanb, |
| 50 | struct lttng_ust_shm_handle *handle); |
| 51 | |
| 52 | void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 53 | struct lttng_ust_shm_handle *handle); |
| 54 | void channel_backend_reset(struct channel_backend *chanb); |
| 55 | |
| 56 | int lib_ring_buffer_backend_init(void); |
| 57 | void lib_ring_buffer_backend_exit(void); |
| 58 | |
| 59 | extern void _lib_ring_buffer_write(struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 60 | size_t offset, const void *src, size_t len, |
| 61 | ssize_t pagecpy); |
| 62 | |
| 63 | /* |
| 64 | * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be |
| 65 | * exchanged atomically. |
| 66 | * |
| 67 | * Top half word, except lowest bit, belongs to "offset", which is used to keep |
| 68 | * to count the produced buffers. For overwrite mode, this provides the |
| 69 | * consumer with the capacity to read subbuffers in order, handling the |
| 70 | * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit |
| 71 | * systems) concurrently with a single execution of get_subbuf (between offset |
| 72 | * sampling and subbuffer ID exchange). |
| 73 | */ |
| 74 | |
| 75 | #define HALF_ULONG_BITS (CAA_BITS_PER_LONG >> 1) |
| 76 | |
| 77 | #define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1) |
| 78 | #define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT) |
| 79 | #define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1)) |
| 80 | /* |
| 81 | * Lowest bit of top word half belongs to noref. Used only for overwrite mode. |
| 82 | */ |
| 83 | #define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1) |
| 84 | #define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT) |
| 85 | #define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT |
| 86 | /* |
| 87 | * In overwrite mode: lowest half of word is used for index. |
| 88 | * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit. |
| 89 | * In producer-consumer mode: whole word used for index. |
| 90 | */ |
| 91 | #define SB_ID_INDEX_SHIFT 0 |
| 92 | #define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT) |
| 93 | #define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1) |
| 94 | |
| 95 | /* |
| 96 | * Construct the subbuffer id from offset, index and noref. Use only the index |
| 97 | * for producer-consumer mode (offset and noref are only used in overwrite |
| 98 | * mode). |
| 99 | */ |
| 100 | static inline |
| 101 | unsigned long subbuffer_id(const struct lttng_ust_lib_ring_buffer_config *config, |
| 102 | unsigned long offset, unsigned long noref, |
| 103 | unsigned long index) |
| 104 | { |
| 105 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 106 | return (offset << SB_ID_OFFSET_SHIFT) |
| 107 | | (noref << SB_ID_NOREF_SHIFT) |
| 108 | | index; |
| 109 | else |
| 110 | return index; |
| 111 | } |
| 112 | |
| 113 | /* |
| 114 | * Compare offset with the offset contained within id. Return 1 if the offset |
| 115 | * bits are identical, else 0. |
| 116 | */ |
| 117 | static inline |
| 118 | int subbuffer_id_compare_offset(const struct lttng_ust_lib_ring_buffer_config *config, |
| 119 | unsigned long id, unsigned long offset) |
| 120 | { |
| 121 | return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT); |
| 122 | } |
| 123 | |
| 124 | static inline |
| 125 | unsigned long subbuffer_id_get_index(const struct lttng_ust_lib_ring_buffer_config *config, |
| 126 | unsigned long id) |
| 127 | { |
| 128 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 129 | return id & SB_ID_INDEX_MASK; |
| 130 | else |
| 131 | return id; |
| 132 | } |
| 133 | |
| 134 | static inline |
| 135 | unsigned long subbuffer_id_is_noref(const struct lttng_ust_lib_ring_buffer_config *config, |
| 136 | unsigned long id) |
| 137 | { |
| 138 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 139 | return !!(id & SB_ID_NOREF_MASK); |
| 140 | else |
| 141 | return 1; |
| 142 | } |
| 143 | |
| 144 | /* |
| 145 | * Only used by reader on subbuffer ID it has exclusive access to. No volatile |
| 146 | * needed. |
| 147 | */ |
| 148 | static inline |
| 149 | void subbuffer_id_set_noref(const struct lttng_ust_lib_ring_buffer_config *config, |
| 150 | unsigned long *id) |
| 151 | { |
| 152 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 153 | *id |= SB_ID_NOREF_MASK; |
| 154 | } |
| 155 | |
| 156 | static inline |
| 157 | void subbuffer_id_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config, |
| 158 | unsigned long *id, unsigned long offset) |
| 159 | { |
| 160 | unsigned long tmp; |
| 161 | |
| 162 | if (config->mode == RING_BUFFER_OVERWRITE) { |
| 163 | tmp = *id; |
| 164 | tmp &= ~SB_ID_OFFSET_MASK; |
| 165 | tmp |= offset << SB_ID_OFFSET_SHIFT; |
| 166 | tmp |= SB_ID_NOREF_MASK; |
| 167 | /* Volatile store, read concurrently by readers. */ |
| 168 | CMM_ACCESS_ONCE(*id) = tmp; |
| 169 | } |
| 170 | } |
| 171 | |
| 172 | /* No volatile access, since already used locally */ |
| 173 | static inline |
| 174 | void subbuffer_id_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config, |
| 175 | unsigned long *id) |
| 176 | { |
| 177 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 178 | *id &= ~SB_ID_NOREF_MASK; |
| 179 | } |
| 180 | |
| 181 | /* |
| 182 | * For overwrite mode, cap the number of subbuffers per buffer to: |
| 183 | * 2^16 on 32-bit architectures |
| 184 | * 2^32 on 64-bit architectures |
| 185 | * This is required to fit in the index part of the ID. Return 0 on success, |
| 186 | * -EPERM on failure. |
| 187 | */ |
| 188 | static inline |
| 189 | int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config *config, |
| 190 | unsigned long num_subbuf) |
| 191 | { |
| 192 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 193 | return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0; |
| 194 | else |
| 195 | return 0; |
| 196 | } |
| 197 | |
| 198 | static inline |
| 199 | void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *config, |
| 200 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 201 | unsigned long idx, struct lttng_ust_shm_handle *handle) |
| 202 | { |
| 203 | unsigned long sb_bindex; |
| 204 | |
| 205 | sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id); |
| 206 | v_inc(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit); |
| 207 | } |
| 208 | |
| 209 | /* |
| 210 | * Reader has exclusive subbuffer access for record consumption. No need to |
| 211 | * perform the decrement atomically. |
| 212 | */ |
| 213 | static inline |
| 214 | void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config *config, |
| 215 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 216 | struct lttng_ust_shm_handle *handle) |
| 217 | { |
| 218 | unsigned long sb_bindex; |
| 219 | |
| 220 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id); |
| 221 | CHAN_WARN_ON(shmp(handle, bufb->chan), |
| 222 | !v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread)); |
| 223 | /* Non-atomic decrement protected by exclusive subbuffer access */ |
| 224 | _v_dec(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread); |
| 225 | v_inc(config, &bufb->records_read); |
| 226 | } |
| 227 | |
| 228 | static inline |
| 229 | unsigned long subbuffer_get_records_count( |
| 230 | const struct lttng_ust_lib_ring_buffer_config *config, |
| 231 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 232 | unsigned long idx, |
| 233 | struct lttng_ust_shm_handle *handle) |
| 234 | { |
| 235 | unsigned long sb_bindex; |
| 236 | |
| 237 | sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id); |
| 238 | return v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit); |
| 239 | } |
| 240 | |
| 241 | /* |
| 242 | * Must be executed at subbuffer delivery when the writer has _exclusive_ |
| 243 | * subbuffer access. See ring_buffer_check_deliver() for details. |
| 244 | * ring_buffer_get_records_count() must be called to get the records count |
| 245 | * before this function, because it resets the records_commit count. |
| 246 | */ |
| 247 | static inline |
| 248 | unsigned long subbuffer_count_records_overrun( |
| 249 | const struct lttng_ust_lib_ring_buffer_config *config, |
| 250 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 251 | unsigned long idx, |
| 252 | struct lttng_ust_shm_handle *handle) |
| 253 | { |
| 254 | struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages; |
| 255 | unsigned long overruns, sb_bindex; |
| 256 | |
| 257 | sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id); |
| 258 | pages = shmp_index(handle, bufb->array, sb_bindex); |
| 259 | overruns = v_read(config, &shmp(handle, pages->shmp)->records_unread); |
| 260 | v_set(config, &shmp(handle, pages->shmp)->records_unread, |
| 261 | v_read(config, &shmp(handle, pages->shmp)->records_commit)); |
| 262 | v_set(config, &shmp(handle, pages->shmp)->records_commit, 0); |
| 263 | |
| 264 | return overruns; |
| 265 | } |
| 266 | |
| 267 | static inline |
| 268 | void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config *config, |
| 269 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 270 | unsigned long idx, |
| 271 | unsigned long data_size, |
| 272 | struct lttng_ust_shm_handle *handle) |
| 273 | { |
| 274 | struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages; |
| 275 | unsigned long sb_bindex; |
| 276 | |
| 277 | sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id); |
| 278 | pages = shmp_index(handle, bufb->array, sb_bindex); |
| 279 | shmp(handle, pages->shmp)->data_size = data_size; |
| 280 | } |
| 281 | |
| 282 | static inline |
| 283 | unsigned long subbuffer_get_read_data_size( |
| 284 | const struct lttng_ust_lib_ring_buffer_config *config, |
| 285 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 286 | struct lttng_ust_shm_handle *handle) |
| 287 | { |
| 288 | struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages; |
| 289 | unsigned long sb_bindex; |
| 290 | |
| 291 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id); |
| 292 | pages = shmp_index(handle, bufb->array, sb_bindex); |
| 293 | return shmp(handle, pages->shmp)->data_size; |
| 294 | } |
| 295 | |
| 296 | static inline |
| 297 | unsigned long subbuffer_get_data_size( |
| 298 | const struct lttng_ust_lib_ring_buffer_config *config, |
| 299 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 300 | unsigned long idx, |
| 301 | struct lttng_ust_shm_handle *handle) |
| 302 | { |
| 303 | struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages; |
| 304 | unsigned long sb_bindex; |
| 305 | |
| 306 | sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id); |
| 307 | pages = shmp_index(handle, bufb->array, sb_bindex); |
| 308 | return shmp(handle, pages->shmp)->data_size; |
| 309 | } |
| 310 | |
| 311 | /** |
| 312 | * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by |
| 313 | * writer. |
| 314 | */ |
| 315 | static inline |
| 316 | void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config, |
| 317 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 318 | unsigned long idx, |
| 319 | struct lttng_ust_shm_handle *handle) |
| 320 | { |
| 321 | unsigned long id, new_id; |
| 322 | |
| 323 | if (config->mode != RING_BUFFER_OVERWRITE) |
| 324 | return; |
| 325 | |
| 326 | /* |
| 327 | * Performing a volatile access to read the sb_pages, because we want to |
| 328 | * read a coherent version of the pointer and the associated noref flag. |
| 329 | */ |
| 330 | id = CMM_ACCESS_ONCE(shmp_index(handle, bufb->buf_wsb, idx)->id); |
| 331 | for (;;) { |
| 332 | /* This check is called on the fast path for each record. */ |
| 333 | if (caa_likely(!subbuffer_id_is_noref(config, id))) { |
| 334 | /* |
| 335 | * Store after load dependency ordering the writes to |
| 336 | * the subbuffer after load and test of the noref flag |
| 337 | * matches the memory barrier implied by the cmpxchg() |
| 338 | * in update_read_sb_index(). |
| 339 | */ |
| 340 | return; /* Already writing to this buffer */ |
| 341 | } |
| 342 | new_id = id; |
| 343 | subbuffer_id_clear_noref(config, &new_id); |
| 344 | new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, idx)->id, id, new_id); |
| 345 | if (caa_likely(new_id == id)) |
| 346 | break; |
| 347 | id = new_id; |
| 348 | } |
| 349 | } |
| 350 | |
| 351 | /** |
| 352 | * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset, |
| 353 | * called by writer. |
| 354 | */ |
| 355 | static inline |
| 356 | void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config, |
| 357 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 358 | unsigned long idx, unsigned long offset, |
| 359 | struct lttng_ust_shm_handle *handle) |
| 360 | { |
| 361 | if (config->mode != RING_BUFFER_OVERWRITE) |
| 362 | return; |
| 363 | |
| 364 | /* |
| 365 | * Because ring_buffer_set_noref() is only called by a single thread |
| 366 | * (the one which updated the cc_sb value), there are no concurrent |
| 367 | * updates to take care of: other writers have not updated cc_sb, so |
| 368 | * they cannot set the noref flag, and concurrent readers cannot modify |
| 369 | * the pointer because the noref flag is not set yet. |
| 370 | * The smp_wmb() in ring_buffer_commit() takes care of ordering writes |
| 371 | * to the subbuffer before this set noref operation. |
| 372 | * subbuffer_set_noref() uses a volatile store to deal with concurrent |
| 373 | * readers of the noref flag. |
| 374 | */ |
| 375 | CHAN_WARN_ON(shmp(handle, bufb->chan), |
| 376 | subbuffer_id_is_noref(config, shmp_index(handle, bufb->buf_wsb, idx)->id)); |
| 377 | /* |
| 378 | * Memory barrier that ensures counter stores are ordered before set |
| 379 | * noref and offset. |
| 380 | */ |
| 381 | cmm_smp_mb(); |
| 382 | subbuffer_id_set_noref_offset(config, &shmp_index(handle, bufb->buf_wsb, idx)->id, offset); |
| 383 | } |
| 384 | |
| 385 | /** |
| 386 | * update_read_sb_index - Read-side subbuffer index update. |
| 387 | */ |
| 388 | static inline |
| 389 | int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config *config, |
| 390 | struct lttng_ust_lib_ring_buffer_backend *bufb, |
| 391 | struct channel_backend *chanb, |
| 392 | unsigned long consumed_idx, |
| 393 | unsigned long consumed_count, |
| 394 | struct lttng_ust_shm_handle *handle) |
| 395 | { |
| 396 | unsigned long old_id, new_id; |
| 397 | |
| 398 | if (config->mode == RING_BUFFER_OVERWRITE) { |
| 399 | /* |
| 400 | * Exchange the target writer subbuffer with our own unused |
| 401 | * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the |
| 402 | * old_wpage, because the value read will be confirmed by the |
| 403 | * following cmpxchg(). |
| 404 | */ |
| 405 | old_id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id; |
| 406 | if (caa_unlikely(!subbuffer_id_is_noref(config, old_id))) |
| 407 | return -EAGAIN; |
| 408 | /* |
| 409 | * Make sure the offset count we are expecting matches the one |
| 410 | * indicated by the writer. |
| 411 | */ |
| 412 | if (caa_unlikely(!subbuffer_id_compare_offset(config, old_id, |
| 413 | consumed_count))) |
| 414 | return -EAGAIN; |
| 415 | CHAN_WARN_ON(shmp(handle, bufb->chan), |
| 416 | !subbuffer_id_is_noref(config, bufb->buf_rsb.id)); |
| 417 | subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id, |
| 418 | consumed_count); |
| 419 | new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, consumed_idx)->id, old_id, |
| 420 | bufb->buf_rsb.id); |
| 421 | if (caa_unlikely(old_id != new_id)) |
| 422 | return -EAGAIN; |
| 423 | bufb->buf_rsb.id = new_id; |
| 424 | } else { |
| 425 | /* No page exchange, use the writer page directly */ |
| 426 | bufb->buf_rsb.id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id; |
| 427 | } |
| 428 | return 0; |
| 429 | } |
| 430 | |
| 431 | #ifndef inline_memcpy |
| 432 | #define inline_memcpy(dest, src, n) memcpy(dest, src, n) |
| 433 | #endif |
| 434 | |
| 435 | /* |
| 436 | * Use the architecture-specific memcpy implementation for constant-sized |
| 437 | * inputs, but rely on an inline memcpy for length statically unknown. |
| 438 | * The function call to memcpy is just way too expensive for a fast path. |
| 439 | */ |
| 440 | #define lib_ring_buffer_do_copy(config, dest, src, len) \ |
| 441 | do { \ |
| 442 | size_t __len = (len); \ |
| 443 | if (__builtin_constant_p(len)) \ |
| 444 | memcpy(dest, src, __len); \ |
| 445 | else \ |
| 446 | inline_memcpy(dest, src, __len); \ |
| 447 | } while (0) |
| 448 | |
| 449 | /* arch-agnostic implementation */ |
| 450 | |
| 451 | static inline int lttng_ust_fls(unsigned int x) |
| 452 | { |
| 453 | int r = 32; |
| 454 | |
| 455 | if (!x) |
| 456 | return 0; |
| 457 | if (!(x & 0xFFFF0000U)) { |
| 458 | x <<= 16; |
| 459 | r -= 16; |
| 460 | } |
| 461 | if (!(x & 0xFF000000U)) { |
| 462 | x <<= 8; |
| 463 | r -= 8; |
| 464 | } |
| 465 | if (!(x & 0xF0000000U)) { |
| 466 | x <<= 4; |
| 467 | r -= 4; |
| 468 | } |
| 469 | if (!(x & 0xC0000000U)) { |
| 470 | x <<= 2; |
| 471 | r -= 2; |
| 472 | } |
| 473 | if (!(x & 0x80000000U)) { |
| 474 | x <<= 1; |
| 475 | r -= 1; |
| 476 | } |
| 477 | return r; |
| 478 | } |
| 479 | |
| 480 | static inline int get_count_order(unsigned int count) |
| 481 | { |
| 482 | int order; |
| 483 | |
| 484 | order = lttng_ust_fls(count) - 1; |
| 485 | if (count & (count - 1)) |
| 486 | order++; |
| 487 | return order; |
| 488 | } |
| 489 | |
| 490 | #endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */ |