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 static inline
 200 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *config,
 201                             struct lttng_ust_lib_ring_buffer_backend *bufb,
 202                             unsigned long idx, struct lttng_ust_shm_handle *handle)
 203 {
 204         unsigned long sb_bindex;
 205
 206         sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
 207         v_inc(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
 208 }
 209
 210 /*
 211  * Reader has exclusive subbuffer access for record consumption. No need to
 212  * perform the decrement atomically.
 213  */
 214 static inline
 215 void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config *config,
 216                               struct lttng_ust_lib_ring_buffer_backend *bufb,
 217                               struct lttng_ust_shm_handle *handle)
 218 {
 219         unsigned long sb_bindex;
 220
 221         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 222         CHAN_WARN_ON(shmp(handle, bufb->chan),
 223                      !v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread));
 224         /* Non-atomic decrement protected by exclusive subbuffer access */
 225         _v_dec(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread);
 226         v_inc(config, &bufb->records_read);
 227 }
 228
 229 static inline
 230 unsigned long subbuffer_get_records_count(
 231                                 const struct lttng_ust_lib_ring_buffer_config *config,
 232                                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 233                                 unsigned long idx,
 234                                 struct lttng_ust_shm_handle *handle)
 235 {
 236         unsigned long sb_bindex;
 237
 238         sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
 239         return v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
 240 }
 241
 242 /*
 243  * Must be executed at subbuffer delivery when the writer has _exclusive_
 244  * subbuffer access. See lib_ring_buffer_check_deliver() for details.
 245  * lib_ring_buffer_get_records_count() must be called to get the records
 246  * count before this function, because it resets the records_commit
 247  * count.
 248  */
 249 static inline
 250 unsigned long subbuffer_count_records_overrun(
 251                                 const struct lttng_ust_lib_ring_buffer_config *config,
 252                                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 253                                 unsigned long idx,
 254                                 struct lttng_ust_shm_handle *handle)
 255 {
 256         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
 257         unsigned long overruns, sb_bindex;
 258
 259         sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
 260         pages = shmp_index(handle, bufb->array, sb_bindex);
 261         overruns = v_read(config, &shmp(handle, pages->shmp)->records_unread);
 262         v_set(config, &shmp(handle, pages->shmp)->records_unread,
 263               v_read(config, &shmp(handle, pages->shmp)->records_commit));
 264         v_set(config, &shmp(handle, pages->shmp)->records_commit, 0);
 265
 266         return overruns;
 267 }
 268
 269 static inline
 270 void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
 271                              struct lttng_ust_lib_ring_buffer_backend *bufb,
 272                              unsigned long idx,
 273                              unsigned long data_size,
 274                              struct lttng_ust_shm_handle *handle)
 275 {
 276         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
 277         unsigned long sb_bindex;
 278
 279         sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
 280         pages = shmp_index(handle, bufb->array, sb_bindex);
 281         shmp(handle, pages->shmp)->data_size = data_size;
 282 }
 283
 284 static inline
 285 unsigned long subbuffer_get_read_data_size(
 286                                 const struct lttng_ust_lib_ring_buffer_config *config,
 287                                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 288                                 struct lttng_ust_shm_handle *handle)
 289 {
 290         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
 291         unsigned long sb_bindex;
 292
 293         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 294         pages = shmp_index(handle, bufb->array, sb_bindex);
 295         return shmp(handle, pages->shmp)->data_size;
 296 }
 297
 298 static inline
 299 unsigned long subbuffer_get_data_size(
 300                                 const struct lttng_ust_lib_ring_buffer_config *config,
 301                                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 302                                 unsigned long idx,
 303                                 struct lttng_ust_shm_handle *handle)
 304 {
 305         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
 306         unsigned long sb_bindex;
 307
 308         sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
 309         pages = shmp_index(handle, bufb->array, sb_bindex);
 310         return shmp(handle, pages->shmp)->data_size;
 311 }
 312
 313 static inline
 314 void subbuffer_inc_packet_count(const struct lttng_ust_lib_ring_buffer_config *config,
 315                 struct lttng_ust_lib_ring_buffer_backend *bufb,
 316                 unsigned long idx, struct lttng_ust_shm_handle *handle)
 317 {
 318         shmp_index(handle, bufb->buf_cnt, idx)->seq_cnt++;
 319 }
 320
 321 /**
 322  * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
 323  *                               writer.
 324  */
 325 static inline
 326 void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config,
 327                                  struct lttng_ust_lib_ring_buffer_backend *bufb,
 328                                  unsigned long idx,
 329                                  struct lttng_ust_shm_handle *handle)
 330 {
 331         unsigned long id, new_id;
 332
 333         if (config->mode != RING_BUFFER_OVERWRITE)
 334                 return;
 335
 336         /*
 337          * Performing a volatile access to read the sb_pages, because we want to
 338          * read a coherent version of the pointer and the associated noref flag.
 339          */
 340         id = CMM_ACCESS_ONCE(shmp_index(handle, bufb->buf_wsb, idx)->id);
 341         for (;;) {
 342                 /* This check is called on the fast path for each record. */
 343                 if (caa_likely(!subbuffer_id_is_noref(config, id))) {
 344                         /*
 345                          * Store after load dependency ordering the writes to
 346                          * the subbuffer after load and test of the noref flag
 347                          * matches the memory barrier implied by the cmpxchg()
 348                          * in update_read_sb_index().
 349                          */
 350                         return; /* Already writing to this buffer */
 351                 }
 352                 new_id = id;
 353                 subbuffer_id_clear_noref(config, &new_id);
 354                 new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, idx)->id, id, new_id);
 355                 if (caa_likely(new_id == id))
 356                         break;
 357                 id = new_id;
 358         }
 359 }
 360
 361 /**
 362  * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
 363  *                                    called by writer.
 364  */
 365 static inline
 366 void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config,
 367                                       struct lttng_ust_lib_ring_buffer_backend *bufb,
 368                                       unsigned long idx, unsigned long offset,
 369                                       struct lttng_ust_shm_handle *handle)
 370 {
 371         if (config->mode != RING_BUFFER_OVERWRITE)
 372                 return;
 373
 374         /*
 375          * Because ring_buffer_set_noref() is only called by a single thread
 376          * (the one which updated the cc_sb value), there are no concurrent
 377          * updates to take care of: other writers have not updated cc_sb, so
 378          * they cannot set the noref flag, and concurrent readers cannot modify
 379          * the pointer because the noref flag is not set yet.
 380          * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
 381          * to the subbuffer before this set noref operation.
 382          * subbuffer_set_noref() uses a volatile store to deal with concurrent
 383          * readers of the noref flag.
 384          */
 385         CHAN_WARN_ON(shmp(handle, bufb->chan),
 386                      subbuffer_id_is_noref(config, shmp_index(handle, bufb->buf_wsb, idx)->id));
 387         /*
 388          * Memory barrier that ensures counter stores are ordered before set
 389          * noref and offset.
 390          */
 391         cmm_smp_mb();
 392         subbuffer_id_set_noref_offset(config, &shmp_index(handle, bufb->buf_wsb, idx)->id, offset);
 393 }
 394
 395 /**
 396  * update_read_sb_index - Read-side subbuffer index update.
 397  */
 398 static inline
 399 int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config *config,
 400                          struct lttng_ust_lib_ring_buffer_backend *bufb,
 401                          struct channel_backend *chanb,
 402                          unsigned long consumed_idx,
 403                          unsigned long consumed_count,
 404                          struct lttng_ust_shm_handle *handle)
 405 {
 406         unsigned long old_id, new_id;
 407
 408         if (config->mode == RING_BUFFER_OVERWRITE) {
 409                 /*
 410                  * Exchange the target writer subbuffer with our own unused
 411                  * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
 412                  * old_wpage, because the value read will be confirmed by the
 413                  * following cmpxchg().
 414                  */
 415                 old_id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id;
 416                 if (caa_unlikely(!subbuffer_id_is_noref(config, old_id)))
 417                         return -EAGAIN;
 418                 /*
 419                  * Make sure the offset count we are expecting matches the one
 420                  * indicated by the writer.
 421                  */
 422                 if (caa_unlikely(!subbuffer_id_compare_offset(config, old_id,
 423                                                           consumed_count)))
 424                         return -EAGAIN;
 425                 CHAN_WARN_ON(shmp(handle, bufb->chan),
 426                              !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
 427                 subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
 428                                               consumed_count);
 429                 new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, consumed_idx)->id, old_id,
 430                                  bufb->buf_rsb.id);
 431                 if (caa_unlikely(old_id != new_id))
 432                         return -EAGAIN;
 433                 bufb->buf_rsb.id = new_id;
 434         } else {
 435                 /* No page exchange, use the writer page directly */
 436                 bufb->buf_rsb.id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id;
 437         }
 438         return 0;
 439 }
 440
 441 #ifndef inline_memcpy
 442 #define inline_memcpy(dest, src, n)     memcpy(dest, src, n)
 443 #endif
 444
 445 /*
 446  * Use the architecture-specific memcpy implementation for constant-sized
 447  * inputs, but rely on an inline memcpy for length statically unknown.
 448  * The function call to memcpy is just way too expensive for a fast path.
 449  */
 450 #define lib_ring_buffer_do_copy(config, dest, src, len)         \
 451 do {                                                            \
 452         size_t __len = (len);                                   \
 453         if (__builtin_constant_p(len))                          \
 454                 memcpy(dest, src, __len);                       \
 455         else                                                    \
 456                 inline_memcpy(dest, src, __len);                \
 457 } while (0)
 458
 459 /*
 460  * write len bytes to dest with c
 461  */
 462 static inline
 463 void lib_ring_buffer_do_memset(char *dest, int c, unsigned long len)
 464 {
 465         unsigned long i;
 466
 467         for (i = 0; i < len; i++)
 468                 dest[i] = c;
 469 }
 470
 471 /* arch-agnostic implementation */
 472
 473 static inline int lttng_ust_fls(unsigned int x)
 474 {
 475         int r = 32;
 476
 477         if (!x)
 478                 return 0;
 479         if (!(x & 0xFFFF0000U)) {
 480                 x <<= 16;
 481                 r -= 16;
 482         }
 483         if (!(x & 0xFF000000U)) {
 484                 x <<= 8;
 485                 r -= 8;
 486         }
 487         if (!(x & 0xF0000000U)) {
 488                 x <<= 4;
 489                 r -= 4;
 490         }
 491         if (!(x & 0xC0000000U)) {
 492                 x <<= 2;
 493                 r -= 2;
 494         }
 495         if (!(x & 0x80000000U)) {
 496                 /* No need to bit shift on last operation */
 497                 r -= 1;
 498         }
 499         return r;
 500 }
 501
 502 static inline int get_count_order(unsigned int count)
 503 {
 504         int order;
 505
 506         order = lttng_ust_fls(count) - 1;
 507         if (count & (count - 1))
 508                 order++;
 509         return order;
 510 }
 511
 512 #endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */