libringbuffer/backend_internal.h

   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                          const int *stream_fds);
  50 void channel_backend_free(struct channel_backend *chanb,
  51                           struct lttng_ust_shm_handle *handle);
  52
  53 void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend *bufb,
  54                                    struct lttng_ust_shm_handle *handle);
  55 void channel_backend_reset(struct channel_backend *chanb);
  56
  57 int lib_ring_buffer_backend_init(void);
  58 void lib_ring_buffer_backend_exit(void);
  59
  60 extern void _lib_ring_buffer_write(struct lttng_ust_lib_ring_buffer_backend *bufb,
  61                                    size_t offset, const void *src, size_t len,
  62                                    ssize_t pagecpy);
  63
  64 /*
  65  * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
  66  * exchanged atomically.
  67  *
  68  * Top half word, except lowest bit, belongs to "offset", which is used to keep
  69  * to count the produced buffers.  For overwrite mode, this provides the
  70  * consumer with the capacity to read subbuffers in order, handling the
  71  * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
  72  * systems) concurrently with a single execution of get_subbuf (between offset
  73  * sampling and subbuffer ID exchange).
  74  */
  75
  76 #define HALF_ULONG_BITS         (CAA_BITS_PER_LONG >> 1)
  77
  78 #define SB_ID_OFFSET_SHIFT      (HALF_ULONG_BITS + 1)
  79 #define SB_ID_OFFSET_COUNT      (1UL << SB_ID_OFFSET_SHIFT)
  80 #define SB_ID_OFFSET_MASK       (~(SB_ID_OFFSET_COUNT - 1))
  81 /*
  82  * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
  83  */
  84 #define SB_ID_NOREF_SHIFT       (SB_ID_OFFSET_SHIFT - 1)
  85 #define SB_ID_NOREF_COUNT       (1UL << SB_ID_NOREF_SHIFT)
  86 #define SB_ID_NOREF_MASK        SB_ID_NOREF_COUNT
  87 /*
  88  * In overwrite mode: lowest half of word is used for index.
  89  * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
  90  * In producer-consumer mode: whole word used for index.
  91  */
  92 #define SB_ID_INDEX_SHIFT       0
  93 #define SB_ID_INDEX_COUNT       (1UL << SB_ID_INDEX_SHIFT)
  94 #define SB_ID_INDEX_MASK        (SB_ID_NOREF_COUNT - 1)
  95
  96 /*
  97  * Construct the subbuffer id from offset, index and noref. Use only the index
  98  * for producer-consumer mode (offset and noref are only used in overwrite
  99  * mode).
 100  */
 101 static inline
 102 unsigned long subbuffer_id(const struct lttng_ust_lib_ring_buffer_config *config,
 103                            unsigned long offset, unsigned long noref,
 104                            unsigned long index)
 105 {
 106         if (config->mode == RING_BUFFER_OVERWRITE)
 107                 return (offset << SB_ID_OFFSET_SHIFT)
 108                        | (noref << SB_ID_NOREF_SHIFT)
 109                        | index;
 110         else
 111                 return index;
 112 }
 113
 114 /*
 115  * Compare offset with the offset contained within id. Return 1 if the offset
 116  * bits are identical, else 0.
 117  */
 118 static inline
 119 int subbuffer_id_compare_offset(const struct lttng_ust_lib_ring_buffer_config *config,
 120                                 unsigned long id, unsigned long offset)
 121 {
 122         return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT);
 123 }
 124
 125 static inline
 126 unsigned long subbuffer_id_get_index(const struct lttng_ust_lib_ring_buffer_config *config,
 127                                      unsigned long id)
 128 {
 129         if (config->mode == RING_BUFFER_OVERWRITE)
 130                 return id & SB_ID_INDEX_MASK;
 131         else
 132                 return id;
 133 }
 134
 135 static inline
 136 unsigned long subbuffer_id_is_noref(const struct lttng_ust_lib_ring_buffer_config *config,
 137                                     unsigned long id)
 138 {
 139         if (config->mode == RING_BUFFER_OVERWRITE)
 140                 return !!(id & SB_ID_NOREF_MASK);
 141         else
 142                 return 1;
 143 }
 144
 145 /*
 146  * Only used by reader on subbuffer ID it has exclusive access to. No volatile
 147  * needed.
 148  */
 149 static inline
 150 void subbuffer_id_set_noref(const struct lttng_ust_lib_ring_buffer_config *config,
 151                             unsigned long *id)
 152 {
 153         if (config->mode == RING_BUFFER_OVERWRITE)
 154                 *id |= SB_ID_NOREF_MASK;
 155 }
 156
 157 static inline
 158 void subbuffer_id_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config,
 159                                    unsigned long *id, unsigned long offset)
 160 {
 161         unsigned long tmp;
 162
 163         if (config->mode == RING_BUFFER_OVERWRITE) {
 164                 tmp = *id;
 165                 tmp &= ~SB_ID_OFFSET_MASK;
 166                 tmp |= offset << SB_ID_OFFSET_SHIFT;
 167                 tmp |= SB_ID_NOREF_MASK;
 168                 /* Volatile store, read concurrently by readers. */
 169                 CMM_ACCESS_ONCE(*id) = tmp;
 170         }
 171 }
 172
 173 /* No volatile access, since already used locally */
 174 static inline
 175 void subbuffer_id_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config,
 176                               unsigned long *id)
 177 {
 178         if (config->mode == RING_BUFFER_OVERWRITE)
 179                 *id &= ~SB_ID_NOREF_MASK;
 180 }
 181
 182 /*
 183  * For overwrite mode, cap the number of subbuffers per buffer to:
 184  * 2^16 on 32-bit architectures
 185  * 2^32 on 64-bit architectures
 186  * This is required to fit in the index part of the ID. Return 0 on success,
 187  * -EPERM on failure.
 188  */
 189 static inline
 190 int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config *config,
 191                              unsigned long num_subbuf)
 192 {
 193         if (config->mode == RING_BUFFER_OVERWRITE)
 194                 return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0;
 195         else
 196                 return 0;
 197 }
 198
 199 /*
 200  * The ring buffer can count events recorded and overwritten per buffer,
 201  * but it is disabled by default due to its performance overhead.
 202  */
 203 #ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
 204 static inline
 205 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *config,
 206                             const struct lttng_ust_lib_ring_buffer_ctx *ctx,
 207                             struct lttng_ust_lib_ring_buffer_backend *bufb,
 208                             unsigned long idx, struct lttng_ust_shm_handle *handle)
 209 {
 210         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 211
 212         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 213         if (caa_unlikely(!backend_pages)) {
 214                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
 215                         return;
 216         }
 217         v_inc(config, &backend_pages->records_commit);
 218 }
 219 #else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
 220 static inline
 221 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *config,
 222                             const struct lttng_ust_lib_ring_buffer_ctx *ctx,
 223                             struct lttng_ust_lib_ring_buffer_backend *bufb,
 224                             unsigned long idx, struct lttng_ust_shm_handle *handle)
 225 {
 226 }
 227 #endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
 228
 229 /*
 230  * Reader has exclusive subbuffer access for record consumption. No need to
 231  * perform the decrement atomically.
 232  */
 233 static inline
 234 void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config *config,
 235                               struct lttng_ust_lib_ring_buffer_backend *bufb,
 236                               struct lttng_ust_shm_handle *handle)
 237 {
 238         unsigned long sb_bindex;
 239         struct channel *chan;
 240         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages_shmp;
 241         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 242
 243         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 244         chan = shmp(handle, bufb->chan);
 245         if (!chan)
 246                 return;
 247         pages_shmp = shmp_index(handle, bufb->array, sb_bindex);
 248         if (!pages_shmp)
 249                 return;
 250         backend_pages = shmp(handle, pages_shmp->shmp);
 251         if (!backend_pages)
 252                 return;
 253         CHAN_WARN_ON(chan, !v_read(config, &backend_pages->records_unread));
 254         /* Non-atomic decrement protected by exclusive subbuffer access */
 255         _v_dec(config, &backend_pages->records_unread);
 256         v_inc(config, &bufb->records_read);
 257 }
 258
 259 static inline
 260 unsigned long subbuffer_get_records_count(
 261                                 const struct lttng_ust_lib_ring_buffer_config *config,
 262                                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 263                                 unsigned long idx,
 264                                 struct lttng_ust_shm_handle *handle)
 265 {
 266         unsigned long sb_bindex;
 267         struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 268         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 269         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 270
 271         wsb = shmp_index(handle, bufb->buf_wsb, idx);
 272         if (!wsb)
 273                 return 0;
 274         sb_bindex = subbuffer_id_get_index(config, wsb->id);
 275         rpages = shmp_index(handle, bufb->array, sb_bindex);
 276         if (!rpages)
 277                 return 0;
 278         backend_pages = shmp(handle, rpages->shmp);
 279         if (!backend_pages)
 280                 return 0;
 281         return v_read(config, &backend_pages->records_commit);
 282 }
 283
 284 /*
 285  * Must be executed at subbuffer delivery when the writer has _exclusive_
 286  * subbuffer access. See lib_ring_buffer_check_deliver() for details.
 287  * lib_ring_buffer_get_records_count() must be called to get the records
 288  * count before this function, because it resets the records_commit
 289  * count.
 290  */
 291 static inline
 292 unsigned long subbuffer_count_records_overrun(
 293                                 const struct lttng_ust_lib_ring_buffer_config *config,
 294                                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 295                                 unsigned long idx,
 296                                 struct lttng_ust_shm_handle *handle)
 297 {
 298         unsigned long overruns, sb_bindex;
 299         struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 300         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 301         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 302
 303         wsb = shmp_index(handle, bufb->buf_wsb, idx);
 304         if (!wsb)
 305                 return 0;
 306         sb_bindex = subbuffer_id_get_index(config, wsb->id);
 307         rpages = shmp_index(handle, bufb->array, sb_bindex);
 308         if (!rpages)
 309                 return 0;
 310         backend_pages = shmp(handle, rpages->shmp);
 311         if (!backend_pages)
 312                 return 0;
 313         overruns = v_read(config, &backend_pages->records_unread);
 314         v_set(config, &backend_pages->records_unread,
 315               v_read(config, &backend_pages->records_commit));
 316         v_set(config, &backend_pages->records_commit, 0);
 317
 318         return overruns;
 319 }
 320
 321 static inline
 322 void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
 323                              struct lttng_ust_lib_ring_buffer_backend *bufb,
 324                              unsigned long idx,
 325                              unsigned long data_size,
 326                              struct lttng_ust_shm_handle *handle)
 327 {
 328         unsigned long sb_bindex;
 329         struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 330         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 331         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 332
 333         wsb = shmp_index(handle, bufb->buf_wsb, idx);
 334         if (!wsb)
 335                 return;
 336         sb_bindex = subbuffer_id_get_index(config, wsb->id);
 337         rpages = shmp_index(handle, bufb->array, sb_bindex);
 338         if (!rpages)
 339                 return;
 340         backend_pages = shmp(handle, rpages->shmp);
 341         if (!backend_pages)
 342                 return;
 343         backend_pages->data_size = data_size;
 344 }
 345
 346 static inline
 347 unsigned long subbuffer_get_read_data_size(
 348                                 const struct lttng_ust_lib_ring_buffer_config *config,
 349                                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 350                                 struct lttng_ust_shm_handle *handle)
 351 {
 352         unsigned long sb_bindex;
 353         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages_shmp;
 354         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 355
 356         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 357         pages_shmp = shmp_index(handle, bufb->array, sb_bindex);
 358         if (!pages_shmp)
 359                 return 0;
 360         backend_pages = shmp(handle, pages_shmp->shmp);
 361         if (!backend_pages)
 362                 return 0;
 363         return backend_pages->data_size;
 364 }
 365
 366 static inline
 367 unsigned long subbuffer_get_data_size(
 368                                 const struct lttng_ust_lib_ring_buffer_config *config,
 369                                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 370                                 unsigned long idx,
 371                                 struct lttng_ust_shm_handle *handle)
 372 {
 373         unsigned long sb_bindex;
 374         struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 375         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 376         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 377
 378         wsb = shmp_index(handle, bufb->buf_wsb, idx);
 379         if (!wsb)
 380                 return 0;
 381         sb_bindex = subbuffer_id_get_index(config, wsb->id);
 382         rpages = shmp_index(handle, bufb->array, sb_bindex);
 383         if (!rpages)
 384                 return 0;
 385         backend_pages = shmp(handle, rpages->shmp);
 386         if (!backend_pages)
 387                 return 0;
 388         return backend_pages->data_size;
 389 }
 390
 391 static inline
 392 void subbuffer_inc_packet_count(const struct lttng_ust_lib_ring_buffer_config *config,
 393                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 394                 unsigned long idx, struct lttng_ust_shm_handle *handle)
 395 {
 396         struct lttng_ust_lib_ring_buffer_backend_counts *counts;
 397
 398         counts = shmp_index(handle, bufb->buf_cnt, idx);
 399         if (!counts)
 400                 return;
 401         counts->seq_cnt++;
 402 }
 403
 404 /**
 405  * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
 406  *                               writer.
 407  */
 408 static inline
 409 void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config,
 410                                  struct lttng_ust_lib_ring_buffer_backend *bufb,
 411                                  unsigned long idx,
 412                                  struct lttng_ust_shm_handle *handle)
 413 {
 414         unsigned long id, new_id;
 415         struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 416
 417         if (config->mode != RING_BUFFER_OVERWRITE)
 418                 return;
 419
 420         /*
 421          * Performing a volatile access to read the sb_pages, because we want to
 422          * read a coherent version of the pointer and the associated noref flag.
 423          */
 424         wsb = shmp_index(handle, bufb->buf_wsb, idx);
 425         if (!wsb)
 426                 return;
 427         id = CMM_ACCESS_ONCE(wsb->id);
 428         for (;;) {
 429                 /* This check is called on the fast path for each record. */
 430                 if (caa_likely(!subbuffer_id_is_noref(config, id))) {
 431                         /*
 432                          * Store after load dependency ordering the writes to
 433                          * the subbuffer after load and test of the noref flag
 434                          * matches the memory barrier implied by the cmpxchg()
 435                          * in update_read_sb_index().
 436                          */
 437                         return; /* Already writing to this buffer */
 438                 }
 439                 new_id = id;
 440                 subbuffer_id_clear_noref(config, &new_id);
 441                 new_id = uatomic_cmpxchg(&wsb->id, id, new_id);
 442                 if (caa_likely(new_id == id))
 443                         break;
 444                 id = new_id;
 445         }
 446 }
 447
 448 /**
 449  * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
 450  *                                    called by writer.
 451  */
 452 static inline
 453 void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config,
 454                                       struct lttng_ust_lib_ring_buffer_backend *bufb,
 455                                       unsigned long idx, unsigned long offset,
 456                                       struct lttng_ust_shm_handle *handle)
 457 {
 458         struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 459         struct channel *chan;
 460
 461         if (config->mode != RING_BUFFER_OVERWRITE)
 462                 return;
 463
 464         wsb = shmp_index(handle, bufb->buf_wsb, idx);
 465         if (!wsb)
 466                 return;
 467         /*
 468          * Because ring_buffer_set_noref() is only called by a single thread
 469          * (the one which updated the cc_sb value), there are no concurrent
 470          * updates to take care of: other writers have not updated cc_sb, so
 471          * they cannot set the noref flag, and concurrent readers cannot modify
 472          * the pointer because the noref flag is not set yet.
 473          * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
 474          * to the subbuffer before this set noref operation.
 475          * subbuffer_set_noref() uses a volatile store to deal with concurrent
 476          * readers of the noref flag.
 477          */
 478         chan = shmp(handle, bufb->chan);
 479         if (!chan)
 480                 return;
 481         CHAN_WARN_ON(chan, subbuffer_id_is_noref(config, wsb->id));
 482         /*
 483          * Memory barrier that ensures counter stores are ordered before set
 484          * noref and offset.
 485          */
 486         cmm_smp_mb();
 487         subbuffer_id_set_noref_offset(config, &wsb->id, offset);
 488 }
 489
 490 /**
 491  * update_read_sb_index - Read-side subbuffer index update.
 492  */
 493 static inline
 494 int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config *config,
 495                          struct lttng_ust_lib_ring_buffer_backend *bufb,
 496                          struct channel_backend *chanb,
 497                          unsigned long consumed_idx,
 498                          unsigned long consumed_count,
 499                          struct lttng_ust_shm_handle *handle)
 500 {
 501         struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 502         unsigned long old_id, new_id;
 503
 504         wsb = shmp_index(handle, bufb->buf_wsb, consumed_idx);
 505         if (caa_unlikely(!wsb))
 506                 return -EPERM;
 507
 508         if (config->mode == RING_BUFFER_OVERWRITE) {
 509                 struct channel *chan;
 510
 511                 /*
 512                  * Exchange the target writer subbuffer with our own unused
 513                  * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
 514                  * old_wpage, because the value read will be confirmed by the
 515                  * following cmpxchg().
 516                  */
 517                 old_id = wsb->id;
 518                 if (caa_unlikely(!subbuffer_id_is_noref(config, old_id)))
 519                         return -EAGAIN;
 520                 /*
 521                  * Make sure the offset count we are expecting matches the one
 522                  * indicated by the writer.
 523                  */
 524                 if (caa_unlikely(!subbuffer_id_compare_offset(config, old_id,
 525                                                           consumed_count)))
 526                         return -EAGAIN;
 527                 chan = shmp(handle, bufb->chan);
 528                 if (caa_unlikely(!chan))
 529                         return -EPERM;
 530                 CHAN_WARN_ON(chan, !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
 531                 subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
 532                                               consumed_count);
 533                 new_id = uatomic_cmpxchg(&wsb->id, old_id, bufb->buf_rsb.id);
 534                 if (caa_unlikely(old_id != new_id))
 535                         return -EAGAIN;
 536                 bufb->buf_rsb.id = new_id;
 537         } else {
 538                 /* No page exchange, use the writer page directly */
 539                 bufb->buf_rsb.id = wsb->id;
 540         }
 541         return 0;
 542 }
 543
 544 #ifndef inline_memcpy
 545 #define inline_memcpy(dest, src, n)     memcpy(dest, src, n)
 546 #endif
 547
 548 /*
 549  * Use the architecture-specific memcpy implementation for constant-sized
 550  * inputs, but rely on an inline memcpy for length statically unknown.
 551  * The function call to memcpy is just way too expensive for a fast path.
 552  */
 553 #define lib_ring_buffer_do_copy(config, dest, src, len)         \
 554 do {                                                            \
 555         size_t __len = (len);                                   \
 556         if (__builtin_constant_p(len))                          \
 557                 memcpy(dest, src, __len);                       \
 558         else                                                    \
 559                 inline_memcpy(dest, src, __len);                \
 560 } while (0)
 561
 562 /*
 563  * write len bytes to dest with c
 564  */
 565 static inline
 566 void lib_ring_buffer_do_memset(char *dest, int c, unsigned long len)
 567 {
 568         unsigned long i;
 569
 570         for (i = 0; i < len; i++)
 571                 dest[i] = c;
 572 }
 573
 574 /* arch-agnostic implementation */
 575
 576 static inline int lttng_ust_fls(unsigned int x)
 577 {
 578         int r = 32;
 579
 580         if (!x)
 581                 return 0;
 582         if (!(x & 0xFFFF0000U)) {
 583                 x <<= 16;
 584                 r -= 16;
 585         }
 586         if (!(x & 0xFF000000U)) {
 587                 x <<= 8;
 588                 r -= 8;
 589         }
 590         if (!(x & 0xF0000000U)) {
 591                 x <<= 4;
 592                 r -= 4;
 593         }
 594         if (!(x & 0xC0000000U)) {
 595                 x <<= 2;
 596                 r -= 2;
 597         }
 598         if (!(x & 0x80000000U)) {
 599                 /* No need to bit shift on last operation */
 600                 r -= 1;
 601         }
 602         return r;
 603 }
 604
 605 static inline int get_count_order(unsigned int count)
 606 {
 607         int order;
 608
 609         order = lttng_ust_fls(count) - 1;
 610         if (count & (count - 1))
 611                 order++;
 612         return order;
 613 }
 614
 615 #endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */