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 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 */