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                                    size_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                                     size_t pagecpy);
  59 extern void _lib_ring_buffer_strcpy(struct lib_ring_buffer_backend *bufb,
  60                                    size_t offset, const char *src, size_t len,
  61                                    size_t pagecpy, int pad);
  62 extern void _lib_ring_buffer_copy_from_user_inatomic(struct lib_ring_buffer_backend *bufb,
  63                                             size_t offset, const void *src,
  64                                             size_t len, size_t pagecpy);
  65 extern void _lib_ring_buffer_strcpy_from_user_inatomic(struct lib_ring_buffer_backend *bufb,
  66                 size_t offset, const char __user *src, size_t len,
  67                 size_t pagecpy, int pad);
  68
  69 /*
  70  * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
  71  * exchanged atomically.
  72  *
  73  * Top half word, except lowest bit, belongs to "offset", which is used to keep
  74  * to count the produced buffers.  For overwrite mode, this provides the
  75  * consumer with the capacity to read subbuffers in order, handling the
  76  * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
  77  * systems) concurrently with a single execution of get_subbuf (between offset
  78  * sampling and subbuffer ID exchange).
  79  */
  80
  81 #define HALF_ULONG_BITS         (BITS_PER_LONG >> 1)
  82
  83 #define SB_ID_OFFSET_SHIFT      (HALF_ULONG_BITS + 1)
  84 #define SB_ID_OFFSET_COUNT      (1UL << SB_ID_OFFSET_SHIFT)
  85 #define SB_ID_OFFSET_MASK       (~(SB_ID_OFFSET_COUNT - 1))
  86 /*
  87  * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
  88  */
  89 #define SB_ID_NOREF_SHIFT       (SB_ID_OFFSET_SHIFT - 1)
  90 #define SB_ID_NOREF_COUNT       (1UL << SB_ID_NOREF_SHIFT)
  91 #define SB_ID_NOREF_MASK        SB_ID_NOREF_COUNT
  92 /*
  93  * In overwrite mode: lowest half of word is used for index.
  94  * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
  95  * In producer-consumer mode: whole word used for index.
  96  */
  97 #define SB_ID_INDEX_SHIFT       0
  98 #define SB_ID_INDEX_COUNT       (1UL << SB_ID_INDEX_SHIFT)
  99 #define SB_ID_INDEX_MASK        (SB_ID_NOREF_COUNT - 1)
 100
 101 /*
 102  * Construct the subbuffer id from offset, index and noref. Use only the index
 103  * for producer-consumer mode (offset and noref are only used in overwrite
 104  * mode).
 105  */
 106 static inline
 107 unsigned long subbuffer_id(const struct lib_ring_buffer_config *config,
 108                            unsigned long offset, unsigned long noref,
 109                            unsigned long index)
 110 {
 111         if (config->mode == RING_BUFFER_OVERWRITE)
 112                 return (offset << SB_ID_OFFSET_SHIFT)
 113                        | (noref << SB_ID_NOREF_SHIFT)
 114                        | index;
 115         else
 116                 return index;
 117 }
 118
 119 /*
 120  * Compare offset with the offset contained within id. Return 1 if the offset
 121  * bits are identical, else 0.
 122  */
 123 static inline
 124 int subbuffer_id_compare_offset(const struct lib_ring_buffer_config *config,
 125                                 unsigned long id, unsigned long offset)
 126 {
 127         return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT);
 128 }
 129
 130 static inline
 131 unsigned long subbuffer_id_get_index(const struct lib_ring_buffer_config *config,
 132                                      unsigned long id)
 133 {
 134         if (config->mode == RING_BUFFER_OVERWRITE)
 135                 return id & SB_ID_INDEX_MASK;
 136         else
 137                 return id;
 138 }
 139
 140 static inline
 141 unsigned long subbuffer_id_is_noref(const struct lib_ring_buffer_config *config,
 142                                     unsigned long id)
 143 {
 144         if (config->mode == RING_BUFFER_OVERWRITE)
 145                 return !!(id & SB_ID_NOREF_MASK);
 146         else
 147                 return 1;
 148 }
 149
 150 /*
 151  * Only used by reader on subbuffer ID it has exclusive access to. No volatile
 152  * needed.
 153  */
 154 static inline
 155 void subbuffer_id_set_noref(const struct lib_ring_buffer_config *config,
 156                             unsigned long *id)
 157 {
 158         if (config->mode == RING_BUFFER_OVERWRITE)
 159                 *id |= SB_ID_NOREF_MASK;
 160 }
 161
 162 static inline
 163 void subbuffer_id_set_noref_offset(const struct lib_ring_buffer_config *config,
 164                                    unsigned long *id, unsigned long offset)
 165 {
 166         unsigned long tmp;
 167
 168         if (config->mode == RING_BUFFER_OVERWRITE) {
 169                 tmp = *id;
 170                 tmp &= ~SB_ID_OFFSET_MASK;
 171                 tmp |= offset << SB_ID_OFFSET_SHIFT;
 172                 tmp |= SB_ID_NOREF_MASK;
 173                 /* Volatile store, read concurrently by readers. */
 174                 ACCESS_ONCE(*id) = tmp;
 175         }
 176 }
 177
 178 /* No volatile access, since already used locally */
 179 static inline
 180 void subbuffer_id_clear_noref(const struct lib_ring_buffer_config *config,
 181                               unsigned long *id)
 182 {
 183         if (config->mode == RING_BUFFER_OVERWRITE)
 184                 *id &= ~SB_ID_NOREF_MASK;
 185 }
 186
 187 /*
 188  * For overwrite mode, cap the number of subbuffers per buffer to:
 189  * 2^16 on 32-bit architectures
 190  * 2^32 on 64-bit architectures
 191  * This is required to fit in the index part of the ID. Return 0 on success,
 192  * -EPERM on failure.
 193  */
 194 static inline
 195 int subbuffer_id_check_index(const struct lib_ring_buffer_config *config,
 196                              unsigned long num_subbuf)
 197 {
 198         if (config->mode == RING_BUFFER_OVERWRITE)
 199                 return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0;
 200         else
 201                 return 0;
 202 }
 203
 204 static inline
 205 void subbuffer_count_record(const struct lib_ring_buffer_config *config,
 206                             struct lib_ring_buffer_backend *bufb,
 207                             unsigned long idx)
 208 {
 209         unsigned long sb_bindex;
 210
 211         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 212         v_inc(config, &bufb->array[sb_bindex]->records_commit);
 213 }
 214
 215 /*
 216  * Reader has exclusive subbuffer access for record consumption. No need to
 217  * perform the decrement atomically.
 218  */
 219 static inline
 220 void subbuffer_consume_record(const struct lib_ring_buffer_config *config,
 221                               struct lib_ring_buffer_backend *bufb)
 222 {
 223         unsigned long sb_bindex;
 224
 225         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 226         CHAN_WARN_ON(bufb->chan,
 227                      !v_read(config, &bufb->array[sb_bindex]->records_unread));
 228         /* Non-atomic decrement protected by exclusive subbuffer access */
 229         _v_dec(config, &bufb->array[sb_bindex]->records_unread);
 230         v_inc(config, &bufb->records_read);
 231 }
 232
 233 static inline
 234 unsigned long subbuffer_get_records_count(
 235                                 const struct lib_ring_buffer_config *config,
 236                                 struct lib_ring_buffer_backend *bufb,
 237                                 unsigned long idx)
 238 {
 239         unsigned long sb_bindex;
 240
 241         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 242         return v_read(config, &bufb->array[sb_bindex]->records_commit);
 243 }
 244
 245 /*
 246  * Must be executed at subbuffer delivery when the writer has _exclusive_
 247  * subbuffer access. See lib_ring_buffer_check_deliver() for details.
 248  * lib_ring_buffer_get_records_count() must be called to get the records
 249  * count before this function, because it resets the records_commit
 250  * count.
 251  */
 252 static inline
 253 unsigned long subbuffer_count_records_overrun(
 254                                 const struct lib_ring_buffer_config *config,
 255                                 struct lib_ring_buffer_backend *bufb,
 256                                 unsigned long idx)
 257 {
 258         struct lib_ring_buffer_backend_pages *pages;
 259         unsigned long overruns, sb_bindex;
 260
 261         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 262         pages = bufb->array[sb_bindex];
 263         overruns = v_read(config, &pages->records_unread);
 264         v_set(config, &pages->records_unread,
 265               v_read(config, &pages->records_commit));
 266         v_set(config, &pages->records_commit, 0);
 267
 268         return overruns;
 269 }
 270
 271 static inline
 272 void subbuffer_set_data_size(const struct lib_ring_buffer_config *config,
 273                              struct lib_ring_buffer_backend *bufb,
 274                              unsigned long idx,
 275                              unsigned long data_size)
 276 {
 277         struct lib_ring_buffer_backend_pages *pages;
 278         unsigned long sb_bindex;
 279
 280         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 281         pages = bufb->array[sb_bindex];
 282         pages->data_size = data_size;
 283 }
 284
 285 static inline
 286 unsigned long subbuffer_get_read_data_size(
 287                                 const struct lib_ring_buffer_config *config,
 288                                 struct lib_ring_buffer_backend *bufb)
 289 {
 290         struct lib_ring_buffer_backend_pages *pages;
 291         unsigned long sb_bindex;
 292
 293         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 294         pages = bufb->array[sb_bindex];
 295         return pages->data_size;
 296 }
 297
 298 static inline
 299 unsigned long subbuffer_get_data_size(
 300                                 const struct lib_ring_buffer_config *config,
 301                                 struct lib_ring_buffer_backend *bufb,
 302                                 unsigned long idx)
 303 {
 304         struct lib_ring_buffer_backend_pages *pages;
 305         unsigned long sb_bindex;
 306
 307         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 308         pages = bufb->array[sb_bindex];
 309         return pages->data_size;
 310 }
 311
 312 /**
 313  * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
 314  *                               writer.
 315  */
 316 static inline
 317 void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config,
 318                                  struct lib_ring_buffer_backend *bufb,
 319                                  unsigned long idx)
 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 = ACCESS_ONCE(bufb->buf_wsb[idx].id);
 331         for (;;) {
 332                 /* This check is called on the fast path for each record. */
 333                 if (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 = cmpxchg(&bufb->buf_wsb[idx].id, id, new_id);
 345                 if (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 lib_ring_buffer_config *config,
 357                                       struct lib_ring_buffer_backend *bufb,
 358                                       unsigned long idx, unsigned long offset)
 359 {
 360         if (config->mode != RING_BUFFER_OVERWRITE)
 361                 return;
 362
 363         /*
 364          * Because ring_buffer_set_noref() is only called by a single thread
 365          * (the one which updated the cc_sb value), there are no concurrent
 366          * updates to take care of: other writers have not updated cc_sb, so
 367          * they cannot set the noref flag, and concurrent readers cannot modify
 368          * the pointer because the noref flag is not set yet.
 369          * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
 370          * to the subbuffer before this set noref operation.
 371          * subbuffer_set_noref() uses a volatile store to deal with concurrent
 372          * readers of the noref flag.
 373          */
 374         CHAN_WARN_ON(bufb->chan,
 375                      subbuffer_id_is_noref(config, bufb->buf_wsb[idx].id));
 376         /*
 377          * Memory barrier that ensures counter stores are ordered before set
 378          * noref and offset.
 379          */
 380         smp_mb();
 381         subbuffer_id_set_noref_offset(config, &bufb->buf_wsb[idx].id, offset);
 382 }
 383
 384 /**
 385  * update_read_sb_index - Read-side subbuffer index update.
 386  */
 387 static inline
 388 int update_read_sb_index(const struct lib_ring_buffer_config *config,
 389                          struct lib_ring_buffer_backend *bufb,
 390                          struct channel_backend *chanb,
 391                          unsigned long consumed_idx,
 392                          unsigned long consumed_count)
 393 {
 394         unsigned long old_id, new_id;
 395
 396         if (config->mode == RING_BUFFER_OVERWRITE) {
 397                 /*
 398                  * Exchange the target writer subbuffer with our own unused
 399                  * subbuffer. No need to use ACCESS_ONCE() here to read the
 400                  * old_wpage, because the value read will be confirmed by the
 401                  * following cmpxchg().
 402                  */
 403                 old_id = bufb->buf_wsb[consumed_idx].id;
 404                 if (unlikely(!subbuffer_id_is_noref(config, old_id)))
 405                         return -EAGAIN;
 406                 /*
 407                  * Make sure the offset count we are expecting matches the one
 408                  * indicated by the writer.
 409                  */
 410                 if (unlikely(!subbuffer_id_compare_offset(config, old_id,
 411                                                           consumed_count)))
 412                         return -EAGAIN;
 413                 CHAN_WARN_ON(bufb->chan,
 414                              !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
 415                 subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
 416                                               consumed_count);
 417                 new_id = cmpxchg(&bufb->buf_wsb[consumed_idx].id, old_id,
 418                                  bufb->buf_rsb.id);
 419                 if (unlikely(old_id != new_id))
 420                         return -EAGAIN;
 421                 bufb->buf_rsb.id = new_id;
 422         } else {
 423                 /* No page exchange, use the writer page directly */
 424                 bufb->buf_rsb.id = bufb->buf_wsb[consumed_idx].id;
 425         }
 426         return 0;
 427 }
 428
 429 /*
 430  * Use the architecture-specific memcpy implementation for constant-sized
 431  * inputs, but rely on an inline memcpy for length statically unknown.
 432  * The function call to memcpy is just way too expensive for a fast path.
 433  */
 434 #define lib_ring_buffer_do_copy(config, dest, src, len)         \
 435 do {                                                            \
 436         size_t __len = (len);                                   \
 437         if (__builtin_constant_p(len))                          \
 438                 memcpy(dest, src, __len);                       \
 439         else                                                    \
 440                 inline_memcpy(dest, src, __len);                \
 441 } while (0)
 442
 443 /*
 444  * We use __copy_from_user_inatomic to copy userspace data since we already
 445  * did the access_ok for the whole range.
 446  */
 447 static inline
 448 unsigned long lib_ring_buffer_do_copy_from_user_inatomic(void *dest,
 449                                                 const void __user *src,
 450                                                 unsigned long len)
 451 {
 452         return __copy_from_user_inatomic(dest, src, len);
 453 }
 454
 455 /*
 456  * write len bytes to dest with c
 457  */
 458 static inline
 459 void lib_ring_buffer_do_memset(char *dest, int c,
 460         unsigned long len)
 461 {
 462         unsigned long i;
 463
 464         for (i = 0; i < len; i++)
 465                 dest[i] = c;
 466 }
 467
 468 #endif /* _LIB_RING_BUFFER_BACKEND_INTERNAL_H */