lib/ringbuffer/backend_internal.h

   1 #ifndef _LIB_RING_BUFFER_BACKEND_INTERNAL_H
   2 #define _LIB_RING_BUFFER_BACKEND_INTERNAL_H
   3
   4 /*
   5  * lib/ringbuffer/backend_internal.h
   6  *
   7  * Ring buffer backend (internal helpers).
   8  *
   9  * Copyright (C) 2008-2012 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 "../../wrapper/ringbuffer/config.h"
  27 #include "../../wrapper/ringbuffer/backend_types.h"
  28 #include "../../wrapper/ringbuffer/frontend_types.h"
  29 #include <linux/string.h>
  30 #include <linux/uaccess.h>
  31
  32 /* Ring buffer backend API presented to the frontend */
  33
  34 /* Ring buffer and channel backend create/free */
  35
  36 int lib_ring_buffer_backend_create(struct lib_ring_buffer_backend *bufb,
  37                                    struct channel_backend *chan, int cpu);
  38 void channel_backend_unregister_notifiers(struct channel_backend *chanb);
  39 void lib_ring_buffer_backend_free(struct lib_ring_buffer_backend *bufb);
  40 int channel_backend_init(struct channel_backend *chanb,
  41                          const char *name,
  42                          const struct lib_ring_buffer_config *config,
  43                          void *priv, size_t subbuf_size,
  44                          size_t num_subbuf);
  45 void channel_backend_free(struct channel_backend *chanb);
  46
  47 void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend *bufb);
  48 void channel_backend_reset(struct channel_backend *chanb);
  49
  50 int lib_ring_buffer_backend_init(void);
  51 void lib_ring_buffer_backend_exit(void);
  52
  53 extern void _lib_ring_buffer_write(struct lib_ring_buffer_backend *bufb,
  54                                    size_t offset, const void *src, size_t len,
  55                                    ssize_t pagecpy);
  56 extern void _lib_ring_buffer_memset(struct lib_ring_buffer_backend *bufb,
  57                                     size_t offset, int c, size_t len,
  58                                     ssize_t pagecpy);
  59 extern void _lib_ring_buffer_copy_from_user_inatomic(struct lib_ring_buffer_backend *bufb,
  60                                             size_t offset, const void *src,
  61                                             size_t len, 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         (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 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 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 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 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 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 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                 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 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 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 lib_ring_buffer_config *config,
 200                             struct lib_ring_buffer_backend *bufb,
 201                             unsigned long idx)
 202 {
 203         unsigned long sb_bindex;
 204
 205         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 206         v_inc(config, &bufb->array[sb_bindex]->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 lib_ring_buffer_config *config,
 215                               struct lib_ring_buffer_backend *bufb)
 216 {
 217         unsigned long sb_bindex;
 218
 219         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 220         CHAN_WARN_ON(bufb->chan,
 221                      !v_read(config, &bufb->array[sb_bindex]->records_unread));
 222         /* Non-atomic decrement protected by exclusive subbuffer access */
 223         _v_dec(config, &bufb->array[sb_bindex]->records_unread);
 224         v_inc(config, &bufb->records_read);
 225 }
 226
 227 static inline
 228 unsigned long subbuffer_get_records_count(
 229                                 const struct lib_ring_buffer_config *config,
 230                                 struct lib_ring_buffer_backend *bufb,
 231                                 unsigned long idx)
 232 {
 233         unsigned long sb_bindex;
 234
 235         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 236         return v_read(config, &bufb->array[sb_bindex]->records_commit);
 237 }
 238
 239 /*
 240  * Must be executed at subbuffer delivery when the writer has _exclusive_
 241  * subbuffer access. See lib_ring_buffer_check_deliver() for details.
 242  * lib_ring_buffer_get_records_count() must be called to get the records
 243  * count before this function, because it resets the records_commit
 244  * count.
 245  */
 246 static inline
 247 unsigned long subbuffer_count_records_overrun(
 248                                 const struct lib_ring_buffer_config *config,
 249                                 struct lib_ring_buffer_backend *bufb,
 250                                 unsigned long idx)
 251 {
 252         struct lib_ring_buffer_backend_pages *pages;
 253         unsigned long overruns, sb_bindex;
 254
 255         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 256         pages = bufb->array[sb_bindex];
 257         overruns = v_read(config, &pages->records_unread);
 258         v_set(config, &pages->records_unread,
 259               v_read(config, &pages->records_commit));
 260         v_set(config, &pages->records_commit, 0);
 261
 262         return overruns;
 263 }
 264
 265 static inline
 266 void subbuffer_set_data_size(const struct lib_ring_buffer_config *config,
 267                              struct lib_ring_buffer_backend *bufb,
 268                              unsigned long idx,
 269                              unsigned long data_size)
 270 {
 271         struct lib_ring_buffer_backend_pages *pages;
 272         unsigned long sb_bindex;
 273
 274         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 275         pages = bufb->array[sb_bindex];
 276         pages->data_size = data_size;
 277 }
 278
 279 static inline
 280 unsigned long subbuffer_get_read_data_size(
 281                                 const struct lib_ring_buffer_config *config,
 282                                 struct lib_ring_buffer_backend *bufb)
 283 {
 284         struct lib_ring_buffer_backend_pages *pages;
 285         unsigned long sb_bindex;
 286
 287         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 288         pages = bufb->array[sb_bindex];
 289         return pages->data_size;
 290 }
 291
 292 static inline
 293 unsigned long subbuffer_get_data_size(
 294                                 const struct lib_ring_buffer_config *config,
 295                                 struct lib_ring_buffer_backend *bufb,
 296                                 unsigned long idx)
 297 {
 298         struct lib_ring_buffer_backend_pages *pages;
 299         unsigned long sb_bindex;
 300
 301         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 302         pages = bufb->array[sb_bindex];
 303         return pages->data_size;
 304 }
 305
 306 /**
 307  * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
 308  *                               writer.
 309  */
 310 static inline
 311 void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config,
 312                                  struct lib_ring_buffer_backend *bufb,
 313                                  unsigned long idx)
 314 {
 315         unsigned long id, new_id;
 316
 317         if (config->mode != RING_BUFFER_OVERWRITE)
 318                 return;
 319
 320         /*
 321          * Performing a volatile access to read the sb_pages, because we want to
 322          * read a coherent version of the pointer and the associated noref flag.
 323          */
 324         id = ACCESS_ONCE(bufb->buf_wsb[idx].id);
 325         for (;;) {
 326                 /* This check is called on the fast path for each record. */
 327                 if (likely(!subbuffer_id_is_noref(config, id))) {
 328                         /*
 329                          * Store after load dependency ordering the writes to
 330                          * the subbuffer after load and test of the noref flag
 331                          * matches the memory barrier implied by the cmpxchg()
 332                          * in update_read_sb_index().
 333                          */
 334                         return; /* Already writing to this buffer */
 335                 }
 336                 new_id = id;
 337                 subbuffer_id_clear_noref(config, &new_id);
 338                 new_id = cmpxchg(&bufb->buf_wsb[idx].id, id, new_id);
 339                 if (likely(new_id == id))
 340                         break;
 341                 id = new_id;
 342         }
 343 }
 344
 345 /**
 346  * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
 347  *                                    called by writer.
 348  */
 349 static inline
 350 void lib_ring_buffer_set_noref_offset(const struct lib_ring_buffer_config *config,
 351                                       struct lib_ring_buffer_backend *bufb,
 352                                       unsigned long idx, unsigned long offset)
 353 {
 354         if (config->mode != RING_BUFFER_OVERWRITE)
 355                 return;
 356
 357         /*
 358          * Because ring_buffer_set_noref() is only called by a single thread
 359          * (the one which updated the cc_sb value), there are no concurrent
 360          * updates to take care of: other writers have not updated cc_sb, so
 361          * they cannot set the noref flag, and concurrent readers cannot modify
 362          * the pointer because the noref flag is not set yet.
 363          * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
 364          * to the subbuffer before this set noref operation.
 365          * subbuffer_set_noref() uses a volatile store to deal with concurrent
 366          * readers of the noref flag.
 367          */
 368         CHAN_WARN_ON(bufb->chan,
 369                      subbuffer_id_is_noref(config, bufb->buf_wsb[idx].id));
 370         /*
 371          * Memory barrier that ensures counter stores are ordered before set
 372          * noref and offset.
 373          */
 374         smp_mb();
 375         subbuffer_id_set_noref_offset(config, &bufb->buf_wsb[idx].id, offset);
 376 }
 377
 378 /**
 379  * update_read_sb_index - Read-side subbuffer index update.
 380  */
 381 static inline
 382 int update_read_sb_index(const struct lib_ring_buffer_config *config,
 383                          struct lib_ring_buffer_backend *bufb,
 384                          struct channel_backend *chanb,
 385                          unsigned long consumed_idx,
 386                          unsigned long consumed_count)
 387 {
 388         unsigned long old_id, new_id;
 389
 390         if (config->mode == RING_BUFFER_OVERWRITE) {
 391                 /*
 392                  * Exchange the target writer subbuffer with our own unused
 393                  * subbuffer. No need to use ACCESS_ONCE() here to read the
 394                  * old_wpage, because the value read will be confirmed by the
 395                  * following cmpxchg().
 396                  */
 397                 old_id = bufb->buf_wsb[consumed_idx].id;
 398                 if (unlikely(!subbuffer_id_is_noref(config, old_id)))
 399                         return -EAGAIN;
 400                 /*
 401                  * Make sure the offset count we are expecting matches the one
 402                  * indicated by the writer.
 403                  */
 404                 if (unlikely(!subbuffer_id_compare_offset(config, old_id,
 405                                                           consumed_count)))
 406                         return -EAGAIN;
 407                 CHAN_WARN_ON(bufb->chan,
 408                              !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
 409                 subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
 410                                               consumed_count);
 411                 new_id = cmpxchg(&bufb->buf_wsb[consumed_idx].id, old_id,
 412                                  bufb->buf_rsb.id);
 413                 if (unlikely(old_id != new_id))
 414                         return -EAGAIN;
 415                 bufb->buf_rsb.id = new_id;
 416         } else {
 417                 /* No page exchange, use the writer page directly */
 418                 bufb->buf_rsb.id = bufb->buf_wsb[consumed_idx].id;
 419         }
 420         return 0;
 421 }
 422
 423 /*
 424  * Use the architecture-specific memcpy implementation for constant-sized
 425  * inputs, but rely on an inline memcpy for length statically unknown.
 426  * The function call to memcpy is just way too expensive for a fast path.
 427  */
 428 #define lib_ring_buffer_do_copy(config, dest, src, len)         \
 429 do {                                                            \
 430         size_t __len = (len);                                   \
 431         if (__builtin_constant_p(len))                          \
 432                 memcpy(dest, src, __len);                       \
 433         else                                                    \
 434                 inline_memcpy(dest, src, __len);                \
 435 } while (0)
 436
 437 /*
 438  * We use __copy_from_user_inatomic to copy userspace data since we already
 439  * did the access_ok for the whole range.
 440  */
 441 static inline
 442 unsigned long lib_ring_buffer_do_copy_from_user_inatomic(void *dest,
 443                                                 const void __user *src,
 444                                                 unsigned long len)
 445 {
 446         return __copy_from_user_inatomic(dest, src, len);
 447 }
 448
 449 /*
 450  * write len bytes to dest with c
 451  */
 452 static inline
 453 void lib_ring_buffer_do_memset(char *dest, int c,
 454         unsigned long len)
 455 {
 456         unsigned long i;
 457
 458         for (i = 0; i < len; i++)
 459                 dest[i] = c;
 460 }
 461
 462 #endif /* _LIB_RING_BUFFER_BACKEND_INTERNAL_H */