lib/ringbuffer/backend_internal.h

   1 #ifndef _LINUX_RING_BUFFER_BACKEND_INTERNAL_H
   2 #define _LINUX_RING_BUFFER_BACKEND_INTERNAL_H
   3
   4 /*
   5  * linux/ringbuffer/backend_internal.h
   6  *
   7  * Copyright (C) 2008-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * Ring buffer backend (internal helpers).
  10  *
  11  * Dual LGPL v2.1/GPL v2 license.
  12  */
  13
  14 #include "../../wrapper/ringbuffer/config.h"
  15 #include "../../wrapper/ringbuffer/backend_types.h"
  16 #include "../../wrapper/ringbuffer/frontend_types.h"
  17 #include <linux/string.h>
  18 #include <linux/uaccess.h>
  19
  20 /* Ring buffer backend API presented to the frontend */
  21
  22 /* Ring buffer and channel backend create/free */
  23
  24 int lib_ring_buffer_backend_create(struct lib_ring_buffer_backend *bufb,
  25                                    struct channel_backend *chan, int cpu);
  26 void channel_backend_unregister_notifiers(struct channel_backend *chanb);
  27 void lib_ring_buffer_backend_free(struct lib_ring_buffer_backend *bufb);
  28 int channel_backend_init(struct channel_backend *chanb,
  29                          const char *name,
  30                          const struct lib_ring_buffer_config *config,
  31                          void *priv, size_t subbuf_size,
  32                          size_t num_subbuf);
  33 void channel_backend_free(struct channel_backend *chanb);
  34
  35 void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend *bufb);
  36 void channel_backend_reset(struct channel_backend *chanb);
  37
  38 int lib_ring_buffer_backend_init(void);
  39 void lib_ring_buffer_backend_exit(void);
  40
  41 extern void _lib_ring_buffer_write(struct lib_ring_buffer_backend *bufb,
  42                                    size_t offset, const void *src, size_t len,
  43                                    ssize_t pagecpy);
  44 extern void _lib_ring_buffer_memset(struct lib_ring_buffer_backend *bufb,
  45                                     size_t offset, int c, size_t len,
  46                                     ssize_t pagecpy);
  47 extern void _lib_ring_buffer_copy_from_user(struct lib_ring_buffer_backend *bufb,
  48                                             size_t offset, const void *src,
  49                                             size_t len, ssize_t pagecpy);
  50
  51 /*
  52  * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
  53  * exchanged atomically.
  54  *
  55  * Top half word, except lowest bit, belongs to "offset", which is used to keep
  56  * to count the produced buffers.  For overwrite mode, this provides the
  57  * consumer with the capacity to read subbuffers in order, handling the
  58  * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
  59  * systems) concurrently with a single execution of get_subbuf (between offset
  60  * sampling and subbuffer ID exchange).
  61  */
  62
  63 #define HALF_ULONG_BITS         (BITS_PER_LONG >> 1)
  64
  65 #define SB_ID_OFFSET_SHIFT      (HALF_ULONG_BITS + 1)
  66 #define SB_ID_OFFSET_COUNT      (1UL << SB_ID_OFFSET_SHIFT)
  67 #define SB_ID_OFFSET_MASK       (~(SB_ID_OFFSET_COUNT - 1))
  68 /*
  69  * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
  70  */
  71 #define SB_ID_NOREF_SHIFT       (SB_ID_OFFSET_SHIFT - 1)
  72 #define SB_ID_NOREF_COUNT       (1UL << SB_ID_NOREF_SHIFT)
  73 #define SB_ID_NOREF_MASK        SB_ID_NOREF_COUNT
  74 /*
  75  * In overwrite mode: lowest half of word is used for index.
  76  * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
  77  * In producer-consumer mode: whole word used for index.
  78  */
  79 #define SB_ID_INDEX_SHIFT       0
  80 #define SB_ID_INDEX_COUNT       (1UL << SB_ID_INDEX_SHIFT)
  81 #define SB_ID_INDEX_MASK        (SB_ID_NOREF_COUNT - 1)
  82
  83 /*
  84  * Construct the subbuffer id from offset, index and noref. Use only the index
  85  * for producer-consumer mode (offset and noref are only used in overwrite
  86  * mode).
  87  */
  88 static inline
  89 unsigned long subbuffer_id(const struct lib_ring_buffer_config *config,
  90                            unsigned long offset, unsigned long noref,
  91                            unsigned long index)
  92 {
  93         if (config->mode == RING_BUFFER_OVERWRITE)
  94                 return (offset << SB_ID_OFFSET_SHIFT)
  95                        | (noref << SB_ID_NOREF_SHIFT)
  96                        | index;
  97         else
  98                 return index;
  99 }
 100
 101 /*
 102  * Compare offset with the offset contained within id. Return 1 if the offset
 103  * bits are identical, else 0.
 104  */
 105 static inline
 106 int subbuffer_id_compare_offset(const struct lib_ring_buffer_config *config,
 107                                 unsigned long id, unsigned long offset)
 108 {
 109         return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT);
 110 }
 111
 112 static inline
 113 unsigned long subbuffer_id_get_index(const struct lib_ring_buffer_config *config,
 114                                      unsigned long id)
 115 {
 116         if (config->mode == RING_BUFFER_OVERWRITE)
 117                 return id & SB_ID_INDEX_MASK;
 118         else
 119                 return id;
 120 }
 121
 122 static inline
 123 unsigned long subbuffer_id_is_noref(const struct lib_ring_buffer_config *config,
 124                                     unsigned long id)
 125 {
 126         if (config->mode == RING_BUFFER_OVERWRITE)
 127                 return !!(id & SB_ID_NOREF_MASK);
 128         else
 129                 return 1;
 130 }
 131
 132 /*
 133  * Only used by reader on subbuffer ID it has exclusive access to. No volatile
 134  * needed.
 135  */
 136 static inline
 137 void subbuffer_id_set_noref(const struct lib_ring_buffer_config *config,
 138                             unsigned long *id)
 139 {
 140         if (config->mode == RING_BUFFER_OVERWRITE)
 141                 *id |= SB_ID_NOREF_MASK;
 142 }
 143
 144 static inline
 145 void subbuffer_id_set_noref_offset(const struct lib_ring_buffer_config *config,
 146                                    unsigned long *id, unsigned long offset)
 147 {
 148         unsigned long tmp;
 149
 150         if (config->mode == RING_BUFFER_OVERWRITE) {
 151                 tmp = *id;
 152                 tmp &= ~SB_ID_OFFSET_MASK;
 153                 tmp |= offset << SB_ID_OFFSET_SHIFT;
 154                 tmp |= SB_ID_NOREF_MASK;
 155                 /* Volatile store, read concurrently by readers. */
 156                 ACCESS_ONCE(*id) = tmp;
 157         }
 158 }
 159
 160 /* No volatile access, since already used locally */
 161 static inline
 162 void subbuffer_id_clear_noref(const struct lib_ring_buffer_config *config,
 163                               unsigned long *id)
 164 {
 165         if (config->mode == RING_BUFFER_OVERWRITE)
 166                 *id &= ~SB_ID_NOREF_MASK;
 167 }
 168
 169 /*
 170  * For overwrite mode, cap the number of subbuffers per buffer to:
 171  * 2^16 on 32-bit architectures
 172  * 2^32 on 64-bit architectures
 173  * This is required to fit in the index part of the ID. Return 0 on success,
 174  * -EPERM on failure.
 175  */
 176 static inline
 177 int subbuffer_id_check_index(const struct lib_ring_buffer_config *config,
 178                              unsigned long num_subbuf)
 179 {
 180         if (config->mode == RING_BUFFER_OVERWRITE)
 181                 return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0;
 182         else
 183                 return 0;
 184 }
 185
 186 static inline
 187 void subbuffer_count_record(const struct lib_ring_buffer_config *config,
 188                             struct lib_ring_buffer_backend *bufb,
 189                             unsigned long idx)
 190 {
 191         unsigned long sb_bindex;
 192
 193         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 194         v_inc(config, &bufb->array[sb_bindex]->records_commit);
 195 }
 196
 197 /*
 198  * Reader has exclusive subbuffer access for record consumption. No need to
 199  * perform the decrement atomically.
 200  */
 201 static inline
 202 void subbuffer_consume_record(const struct lib_ring_buffer_config *config,
 203                               struct lib_ring_buffer_backend *bufb)
 204 {
 205         unsigned long sb_bindex;
 206
 207         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 208         CHAN_WARN_ON(bufb->chan,
 209                      !v_read(config, &bufb->array[sb_bindex]->records_unread));
 210         /* Non-atomic decrement protected by exclusive subbuffer access */
 211         _v_dec(config, &bufb->array[sb_bindex]->records_unread);
 212         v_inc(config, &bufb->records_read);
 213 }
 214
 215 static inline
 216 unsigned long subbuffer_get_records_count(
 217                                 const struct lib_ring_buffer_config *config,
 218                                 struct lib_ring_buffer_backend *bufb,
 219                                 unsigned long idx)
 220 {
 221         unsigned long sb_bindex;
 222
 223         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 224         return v_read(config, &bufb->array[sb_bindex]->records_commit);
 225 }
 226
 227 /*
 228  * Must be executed at subbuffer delivery when the writer has _exclusive_
 229  * subbuffer access. See ring_buffer_check_deliver() for details.
 230  * ring_buffer_get_records_count() must be called to get the records count
 231  * before this function, because it resets the records_commit count.
 232  */
 233 static inline
 234 unsigned long subbuffer_count_records_overrun(
 235                                 const struct lib_ring_buffer_config *config,
 236                                 struct lib_ring_buffer_backend *bufb,
 237                                 unsigned long idx)
 238 {
 239         struct lib_ring_buffer_backend_pages *pages;
 240         unsigned long overruns, sb_bindex;
 241
 242         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 243         pages = bufb->array[sb_bindex];
 244         overruns = v_read(config, &pages->records_unread);
 245         v_set(config, &pages->records_unread,
 246               v_read(config, &pages->records_commit));
 247         v_set(config, &pages->records_commit, 0);
 248
 249         return overruns;
 250 }
 251
 252 static inline
 253 void subbuffer_set_data_size(const struct lib_ring_buffer_config *config,
 254                              struct lib_ring_buffer_backend *bufb,
 255                              unsigned long idx,
 256                              unsigned long data_size)
 257 {
 258         struct lib_ring_buffer_backend_pages *pages;
 259         unsigned long sb_bindex;
 260
 261         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 262         pages = bufb->array[sb_bindex];
 263         pages->data_size = data_size;
 264 }
 265
 266 static inline
 267 unsigned long subbuffer_get_read_data_size(
 268                                 const struct lib_ring_buffer_config *config,
 269                                 struct lib_ring_buffer_backend *bufb)
 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_rsb.id);
 275         pages = bufb->array[sb_bindex];
 276         return pages->data_size;
 277 }
 278
 279 static inline
 280 unsigned long subbuffer_get_data_size(
 281                                 const struct lib_ring_buffer_config *config,
 282                                 struct lib_ring_buffer_backend *bufb,
 283                                 unsigned long idx)
 284 {
 285         struct lib_ring_buffer_backend_pages *pages;
 286         unsigned long sb_bindex;
 287
 288         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 289         pages = bufb->array[sb_bindex];
 290         return pages->data_size;
 291 }
 292
 293 /**
 294  * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
 295  *                               writer.
 296  */
 297 static inline
 298 void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config,
 299                                  struct lib_ring_buffer_backend *bufb,
 300                                  unsigned long idx)
 301 {
 302         unsigned long id, new_id;
 303
 304         if (config->mode != RING_BUFFER_OVERWRITE)
 305                 return;
 306
 307         /*
 308          * Performing a volatile access to read the sb_pages, because we want to
 309          * read a coherent version of the pointer and the associated noref flag.
 310          */
 311         id = ACCESS_ONCE(bufb->buf_wsb[idx].id);
 312         for (;;) {
 313                 /* This check is called on the fast path for each record. */
 314                 if (likely(!subbuffer_id_is_noref(config, id))) {
 315                         /*
 316                          * Store after load dependency ordering the writes to
 317                          * the subbuffer after load and test of the noref flag
 318                          * matches the memory barrier implied by the cmpxchg()
 319                          * in update_read_sb_index().
 320                          */
 321                         return; /* Already writing to this buffer */
 322                 }
 323                 new_id = id;
 324                 subbuffer_id_clear_noref(config, &new_id);
 325                 new_id = cmpxchg(&bufb->buf_wsb[idx].id, id, new_id);
 326                 if (likely(new_id == id))
 327                         break;
 328                 id = new_id;
 329         }
 330 }
 331
 332 /**
 333  * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
 334  *                                    called by writer.
 335  */
 336 static inline
 337 void lib_ring_buffer_set_noref_offset(const struct lib_ring_buffer_config *config,
 338                                       struct lib_ring_buffer_backend *bufb,
 339                                       unsigned long idx, unsigned long offset)
 340 {
 341         if (config->mode != RING_BUFFER_OVERWRITE)
 342                 return;
 343
 344         /*
 345          * Because ring_buffer_set_noref() is only called by a single thread
 346          * (the one which updated the cc_sb value), there are no concurrent
 347          * updates to take care of: other writers have not updated cc_sb, so
 348          * they cannot set the noref flag, and concurrent readers cannot modify
 349          * the pointer because the noref flag is not set yet.
 350          * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
 351          * to the subbuffer before this set noref operation.
 352          * subbuffer_set_noref() uses a volatile store to deal with concurrent
 353          * readers of the noref flag.
 354          */
 355         CHAN_WARN_ON(bufb->chan,
 356                      subbuffer_id_is_noref(config, bufb->buf_wsb[idx].id));
 357         /*
 358          * Memory barrier that ensures counter stores are ordered before set
 359          * noref and offset.
 360          */
 361         smp_mb();
 362         subbuffer_id_set_noref_offset(config, &bufb->buf_wsb[idx].id, offset);
 363 }
 364
 365 /**
 366  * update_read_sb_index - Read-side subbuffer index update.
 367  */
 368 static inline
 369 int update_read_sb_index(const struct lib_ring_buffer_config *config,
 370                          struct lib_ring_buffer_backend *bufb,
 371                          struct channel_backend *chanb,
 372                          unsigned long consumed_idx,
 373                          unsigned long consumed_count)
 374 {
 375         unsigned long old_id, new_id;
 376
 377         if (config->mode == RING_BUFFER_OVERWRITE) {
 378                 /*
 379                  * Exchange the target writer subbuffer with our own unused
 380                  * subbuffer. No need to use ACCESS_ONCE() here to read the
 381                  * old_wpage, because the value read will be confirmed by the
 382                  * following cmpxchg().
 383                  */
 384                 old_id = bufb->buf_wsb[consumed_idx].id;
 385                 if (unlikely(!subbuffer_id_is_noref(config, old_id)))
 386                         return -EAGAIN;
 387                 /*
 388                  * Make sure the offset count we are expecting matches the one
 389                  * indicated by the writer.
 390                  */
 391                 if (unlikely(!subbuffer_id_compare_offset(config, old_id,
 392                                                           consumed_count)))
 393                         return -EAGAIN;
 394                 CHAN_WARN_ON(bufb->chan,
 395                              !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
 396                 subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
 397                                               consumed_count);
 398                 new_id = cmpxchg(&bufb->buf_wsb[consumed_idx].id, old_id,
 399                                  bufb->buf_rsb.id);
 400                 if (unlikely(old_id != new_id))
 401                         return -EAGAIN;
 402                 bufb->buf_rsb.id = new_id;
 403         } else {
 404                 /* No page exchange, use the writer page directly */
 405                 bufb->buf_rsb.id = bufb->buf_wsb[consumed_idx].id;
 406         }
 407         return 0;
 408 }
 409
 410 /*
 411  * Use the architecture-specific memcpy implementation for constant-sized
 412  * inputs, but rely on an inline memcpy for length statically unknown.
 413  * The function call to memcpy is just way too expensive for a fast path.
 414  */
 415 #define lib_ring_buffer_do_copy(config, dest, src, len)         \
 416 do {                                                            \
 417         size_t __len = (len);                                   \
 418         if (__builtin_constant_p(len))                          \
 419                 memcpy(dest, src, __len);                       \
 420         else                                                    \
 421                 inline_memcpy(dest, src, __len);                \
 422 } while (0)
 423
 424 /*
 425  * We use __copy_from_user to copy userspace data since we already
 426  * did the access_ok for the whole range.
 427  */
 428 static inline
 429 unsigned long lib_ring_buffer_do_copy_from_user(void *dest,
 430                                                 const void __user *src,
 431                                                 unsigned long len)
 432 {
 433         return __copy_from_user(dest, src, len);
 434 }
 435
 436 /*
 437  * write len bytes to dest with c
 438  */
 439 static inline
 440 void lib_ring_buffer_do_memset(char *dest, int c,
 441         unsigned long len)
 442 {
 443         unsigned long i;
 444
 445         for (i = 0; i < len; i++)
 446                 dest[i] = c;
 447 }
 448
 449 #endif /* _LINUX_RING_BUFFER_BACKEND_INTERNAL_H */