include/ringbuffer/backend_internal.h

   1 /* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only)
   2  *
   3  * ringbuffer/backend_internal.h
   4  *
   5  * Ring buffer backend (internal helpers).
   6  *
   7  * Copyright (C) 2008-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  */
   9
  10 #ifndef _LIB_RING_BUFFER_BACKEND_INTERNAL_H
  11 #define _LIB_RING_BUFFER_BACKEND_INTERNAL_H
  12
  13 #include <wrapper/compiler.h>
  14 #include <wrapper/inline_memcpy.h>
  15 #include <ringbuffer/config.h>
  16 #include <ringbuffer/backend_types.h>
  17 #include <ringbuffer/frontend_types.h>
  18 #include <linux/string.h>
  19 #include <linux/uaccess.h>
  20
  21 /* Ring buffer backend API presented to the frontend */
  22
  23 /* Ring buffer and channel backend create/free */
  24
  25 int lib_ring_buffer_backend_create(struct lttng_kernel_ring_buffer_backend *bufb,
  26                                    struct channel_backend *chan, int cpu);
  27 void channel_backend_unregister_notifiers(struct channel_backend *chanb);
  28 void lib_ring_buffer_backend_free(struct lttng_kernel_ring_buffer_backend *bufb);
  29 int channel_backend_init(struct channel_backend *chanb,
  30                          const char *name,
  31                          const struct lttng_kernel_ring_buffer_config *config,
  32                          void *priv, size_t subbuf_size,
  33                          size_t num_subbuf);
  34 void channel_backend_free(struct channel_backend *chanb);
  35
  36 void lib_ring_buffer_backend_reset(struct lttng_kernel_ring_buffer_backend *bufb);
  37 void channel_backend_reset(struct channel_backend *chanb);
  38
  39 int lib_ring_buffer_backend_init(void);
  40 void lib_ring_buffer_backend_exit(void);
  41
  42 extern void _lib_ring_buffer_write(struct lttng_kernel_ring_buffer_backend *bufb,
  43                                    size_t offset, const void *src, size_t len,
  44                                    size_t pagecpy);
  45 extern void _lib_ring_buffer_memset(struct lttng_kernel_ring_buffer_backend *bufb,
  46                                     size_t offset, int c, size_t len,
  47                                     size_t pagecpy);
  48 extern void _lib_ring_buffer_strcpy(struct lttng_kernel_ring_buffer_backend *bufb,
  49                                    size_t offset, const char *src, size_t len,
  50                                    size_t pagecpy, int pad);
  51 extern void _lib_ring_buffer_pstrcpy(struct lttng_kernel_ring_buffer_backend *bufb,
  52                                    size_t offset, const char *src, size_t len, int pad);
  53 extern void _lib_ring_buffer_copy_from_user_inatomic(struct lttng_kernel_ring_buffer_backend *bufb,
  54                                             size_t offset, const void *src,
  55                                             size_t len, size_t pagecpy);
  56 extern void _lib_ring_buffer_strcpy_from_user_inatomic(struct lttng_kernel_ring_buffer_backend *bufb,
  57                 size_t offset, const char __user *src, size_t len,
  58                 size_t pagecpy, int pad);
  59 extern void _lib_ring_buffer_pstrcpy_from_user_inatomic(struct lttng_kernel_ring_buffer_backend *bufb,
  60                                    size_t offset, const char __user *src, size_t len, int pad);
  61
  62 /*
  63  * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
  64  * exchanged atomically.
  65  *
  66  * Top half word, except lowest bit, belongs to "offset", which is used to keep
  67  * to count the produced buffers.  For overwrite mode, this provides the
  68  * consumer with the capacity to read subbuffers in order, handling the
  69  * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
  70  * systems) concurrently with a single execution of get_subbuf (between offset
  71  * sampling and subbuffer ID exchange).
  72  */
  73
  74 #define HALF_ULONG_BITS         (BITS_PER_LONG >> 1)
  75
  76 #define SB_ID_OFFSET_SHIFT      (HALF_ULONG_BITS + 1)
  77 #define SB_ID_OFFSET_COUNT      (1UL << SB_ID_OFFSET_SHIFT)
  78 #define SB_ID_OFFSET_MASK       (~(SB_ID_OFFSET_COUNT - 1))
  79 /*
  80  * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
  81  */
  82 #define SB_ID_NOREF_SHIFT       (SB_ID_OFFSET_SHIFT - 1)
  83 #define SB_ID_NOREF_COUNT       (1UL << SB_ID_NOREF_SHIFT)
  84 #define SB_ID_NOREF_MASK        SB_ID_NOREF_COUNT
  85 /*
  86  * In overwrite mode: lowest half of word is used for index.
  87  * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
  88  * In producer-consumer mode: whole word used for index.
  89  */
  90 #define SB_ID_INDEX_SHIFT       0
  91 #define SB_ID_INDEX_COUNT       (1UL << SB_ID_INDEX_SHIFT)
  92 #define SB_ID_INDEX_MASK        (SB_ID_NOREF_COUNT - 1)
  93
  94 /*
  95  * Construct the subbuffer id from offset, index and noref. Use only the index
  96  * for producer-consumer mode (offset and noref are only used in overwrite
  97  * mode).
  98  */
  99 static inline
 100 unsigned long subbuffer_id(const struct lttng_kernel_ring_buffer_config *config,
 101                            unsigned long offset, unsigned long noref,
 102                            unsigned long index)
 103 {
 104         if (config->mode == RING_BUFFER_OVERWRITE)
 105                 return (offset << SB_ID_OFFSET_SHIFT)
 106                        | (noref << SB_ID_NOREF_SHIFT)
 107                        | index;
 108         else
 109                 return index;
 110 }
 111
 112 /*
 113  * Compare offset with the offset contained within id. Return 1 if the offset
 114  * bits are identical, else 0.
 115  */
 116 static inline
 117 int subbuffer_id_compare_offset(const struct lttng_kernel_ring_buffer_config *config,
 118                                 unsigned long id, unsigned long offset)
 119 {
 120         return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT);
 121 }
 122
 123 static inline
 124 unsigned long subbuffer_id_get_index(const struct lttng_kernel_ring_buffer_config *config,
 125                                      unsigned long id)
 126 {
 127         if (config->mode == RING_BUFFER_OVERWRITE)
 128                 return id & SB_ID_INDEX_MASK;
 129         else
 130                 return id;
 131 }
 132
 133 static inline
 134 unsigned long subbuffer_id_is_noref(const struct lttng_kernel_ring_buffer_config *config,
 135                                     unsigned long id)
 136 {
 137         if (config->mode == RING_BUFFER_OVERWRITE)
 138                 return !!(id & SB_ID_NOREF_MASK);
 139         else
 140                 return 1;
 141 }
 142
 143 /*
 144  * Only used by reader on subbuffer ID it has exclusive access to. No volatile
 145  * needed.
 146  */
 147 static inline
 148 void subbuffer_id_set_noref(const struct lttng_kernel_ring_buffer_config *config,
 149                             unsigned long *id)
 150 {
 151         if (config->mode == RING_BUFFER_OVERWRITE)
 152                 *id |= SB_ID_NOREF_MASK;
 153 }
 154
 155 static inline
 156 void subbuffer_id_set_noref_offset(const struct lttng_kernel_ring_buffer_config *config,
 157                                    unsigned long *id, unsigned long offset)
 158 {
 159         unsigned long tmp;
 160
 161         if (config->mode == RING_BUFFER_OVERWRITE) {
 162                 tmp = *id;
 163                 tmp &= ~SB_ID_OFFSET_MASK;
 164                 tmp |= offset << SB_ID_OFFSET_SHIFT;
 165                 tmp |= SB_ID_NOREF_MASK;
 166                 /* Volatile store, read concurrently by readers. */
 167                 WRITE_ONCE(*id, tmp);
 168         }
 169 }
 170
 171 /* No volatile access, since already used locally */
 172 static inline
 173 void subbuffer_id_clear_noref(const struct lttng_kernel_ring_buffer_config *config,
 174                               unsigned long *id)
 175 {
 176         if (config->mode == RING_BUFFER_OVERWRITE)
 177                 *id &= ~SB_ID_NOREF_MASK;
 178 }
 179
 180 /*
 181  * For overwrite mode, cap the number of subbuffers per buffer to:
 182  * 2^16 on 32-bit architectures
 183  * 2^32 on 64-bit architectures
 184  * This is required to fit in the index part of the ID. Return 0 on success,
 185  * -EPERM on failure.
 186  */
 187 static inline
 188 int subbuffer_id_check_index(const struct lttng_kernel_ring_buffer_config *config,
 189                              unsigned long num_subbuf)
 190 {
 191         if (config->mode == RING_BUFFER_OVERWRITE)
 192                 return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0;
 193         else
 194                 return 0;
 195 }
 196
 197 static inline
 198 void lib_ring_buffer_backend_get_pages(const struct lttng_kernel_ring_buffer_config *config,
 199                         struct lttng_kernel_ring_buffer_ctx *ctx,
 200                         struct lttng_kernel_ring_buffer_backend_pages **backend_pages)
 201 {
 202         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 203         struct channel_backend *chanb = &ctx->priv.chan->backend;
 204         size_t sbidx, offset = ctx->priv.buf_offset;
 205         unsigned long sb_bindex, id;
 206         struct lttng_kernel_ring_buffer_backend_pages *rpages;
 207
 208         offset &= chanb->buf_size - 1;
 209         sbidx = offset >> chanb->subbuf_size_order;
 210         id = bufb->buf_wsb[sbidx].id;
 211         sb_bindex = subbuffer_id_get_index(config, id);
 212         rpages = bufb->array[sb_bindex];
 213         CHAN_WARN_ON(ctx->priv.chan,
 214                      config->mode == RING_BUFFER_OVERWRITE
 215                      && subbuffer_id_is_noref(config, id));
 216         *backend_pages = rpages;
 217 }
 218
 219 /* Get backend pages from cache. */
 220 static inline
 221 struct lttng_kernel_ring_buffer_backend_pages *
 222         lib_ring_buffer_get_backend_pages_from_ctx(const struct lttng_kernel_ring_buffer_config *config,
 223                 struct lttng_kernel_ring_buffer_ctx *ctx)
 224 {
 225         return ctx->priv.backend_pages;
 226 }
 227
 228 /*
 229  * The ring buffer can count events recorded and overwritten per buffer,
 230  * but it is disabled by default due to its performance overhead.
 231  */
 232 #ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
 233 static inline
 234 void subbuffer_count_record(const struct lttng_kernel_ring_buffer_config *config,
 235                             struct lttng_kernel_ring_buffer_backend *bufb,
 236                             unsigned long idx)
 237 {
 238         unsigned long sb_bindex;
 239
 240         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 241         v_inc(config, &bufb->array[sb_bindex]->records_commit);
 242 }
 243
 244 /*
 245  * Reader has exclusive subbuffer access for record consumption. No need to
 246  * perform the decrement atomically.
 247  */
 248 static inline
 249 void subbuffer_consume_record(const struct lttng_kernel_ring_buffer_config *config,
 250                               struct lttng_kernel_ring_buffer_backend *bufb)
 251 {
 252         unsigned long sb_bindex;
 253
 254         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 255         CHAN_WARN_ON(bufb->chan,
 256                      !v_read(config, &bufb->array[sb_bindex]->records_unread));
 257         /* Non-atomic decrement protected by exclusive subbuffer access */
 258         _v_dec(config, &bufb->array[sb_bindex]->records_unread);
 259         v_inc(config, &bufb->records_read);
 260 }
 261 #else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
 262 static inline
 263 void subbuffer_count_record(const struct lttng_kernel_ring_buffer_config *config,
 264                             struct lttng_kernel_ring_buffer_backend *bufb,
 265                             unsigned long idx)
 266 {
 267 }
 268 static inline
 269 void subbuffer_consume_record(const struct lttng_kernel_ring_buffer_config *config,
 270                               struct lttng_kernel_ring_buffer_backend *bufb)
 271 {
 272 }
 273 #endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
 274
 275 static inline
 276 unsigned long subbuffer_get_records_count(
 277                                 const struct lttng_kernel_ring_buffer_config *config,
 278                                 struct lttng_kernel_ring_buffer_backend *bufb,
 279                                 unsigned long idx)
 280 {
 281         unsigned long sb_bindex;
 282
 283         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 284         return v_read(config, &bufb->array[sb_bindex]->records_commit);
 285 }
 286
 287 /*
 288  * Must be executed at subbuffer delivery when the writer has _exclusive_
 289  * subbuffer access. See lib_ring_buffer_check_deliver() for details.
 290  * lib_ring_buffer_get_records_count() must be called to get the records
 291  * count before this function, because it resets the records_commit
 292  * count.
 293  */
 294 static inline
 295 unsigned long subbuffer_count_records_overrun(
 296                                 const struct lttng_kernel_ring_buffer_config *config,
 297                                 struct lttng_kernel_ring_buffer_backend *bufb,
 298                                 unsigned long idx)
 299 {
 300         struct lttng_kernel_ring_buffer_backend_pages *pages;
 301         unsigned long overruns, sb_bindex;
 302
 303         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 304         pages = bufb->array[sb_bindex];
 305         overruns = v_read(config, &pages->records_unread);
 306         v_set(config, &pages->records_unread,
 307               v_read(config, &pages->records_commit));
 308         v_set(config, &pages->records_commit, 0);
 309
 310         return overruns;
 311 }
 312
 313 static inline
 314 void subbuffer_set_data_size(const struct lttng_kernel_ring_buffer_config *config,
 315                              struct lttng_kernel_ring_buffer_backend *bufb,
 316                              unsigned long idx,
 317                              unsigned long data_size)
 318 {
 319         struct lttng_kernel_ring_buffer_backend_pages *pages;
 320         unsigned long sb_bindex;
 321
 322         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 323         pages = bufb->array[sb_bindex];
 324         pages->data_size = data_size;
 325 }
 326
 327 static inline
 328 unsigned long subbuffer_get_read_data_size(
 329                                 const struct lttng_kernel_ring_buffer_config *config,
 330                                 struct lttng_kernel_ring_buffer_backend *bufb)
 331 {
 332         struct lttng_kernel_ring_buffer_backend_pages *pages;
 333         unsigned long sb_bindex;
 334
 335         sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 336         pages = bufb->array[sb_bindex];
 337         return pages->data_size;
 338 }
 339
 340 static inline
 341 unsigned long subbuffer_get_data_size(
 342                                 const struct lttng_kernel_ring_buffer_config *config,
 343                                 struct lttng_kernel_ring_buffer_backend *bufb,
 344                                 unsigned long idx)
 345 {
 346         struct lttng_kernel_ring_buffer_backend_pages *pages;
 347         unsigned long sb_bindex;
 348
 349         sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
 350         pages = bufb->array[sb_bindex];
 351         return pages->data_size;
 352 }
 353
 354 static inline
 355 void subbuffer_inc_packet_count(const struct lttng_kernel_ring_buffer_config *config,
 356                                 struct lttng_kernel_ring_buffer_backend *bufb,
 357                                 unsigned long idx)
 358 {
 359         bufb->buf_cnt[idx].seq_cnt++;
 360 }
 361
 362 /**
 363  * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
 364  *                               writer.
 365  */
 366 static inline
 367 void lib_ring_buffer_clear_noref(const struct lttng_kernel_ring_buffer_config *config,
 368                                  struct lttng_kernel_ring_buffer_backend *bufb,
 369                                  unsigned long idx)
 370 {
 371         unsigned long id, new_id;
 372
 373         if (config->mode != RING_BUFFER_OVERWRITE)
 374                 return;
 375
 376         /*
 377          * Performing a volatile access to read the sb_pages, because we want to
 378          * read a coherent version of the pointer and the associated noref flag.
 379          */
 380         id = LTTNG_READ_ONCE(bufb->buf_wsb[idx].id);
 381         for (;;) {
 382                 /* This check is called on the fast path for each record. */
 383                 if (likely(!subbuffer_id_is_noref(config, id))) {
 384                         /*
 385                          * Store after load dependency ordering the writes to
 386                          * the subbuffer after load and test of the noref flag
 387                          * matches the memory barrier implied by the cmpxchg()
 388                          * in update_read_sb_index().
 389                          */
 390                         return; /* Already writing to this buffer */
 391                 }
 392                 new_id = id;
 393                 subbuffer_id_clear_noref(config, &new_id);
 394                 new_id = cmpxchg(&bufb->buf_wsb[idx].id, id, new_id);
 395                 if (likely(new_id == id))
 396                         break;
 397                 id = new_id;
 398         }
 399 }
 400
 401 /**
 402  * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
 403  *                                    called by writer.
 404  */
 405 static inline
 406 void lib_ring_buffer_set_noref_offset(const struct lttng_kernel_ring_buffer_config *config,
 407                                       struct lttng_kernel_ring_buffer_backend *bufb,
 408                                       unsigned long idx, unsigned long offset)
 409 {
 410         if (config->mode != RING_BUFFER_OVERWRITE)
 411                 return;
 412
 413         /*
 414          * Because ring_buffer_set_noref() is only called by a single thread
 415          * (the one which updated the cc_sb value), there are no concurrent
 416          * updates to take care of: other writers have not updated cc_sb, so
 417          * they cannot set the noref flag, and concurrent readers cannot modify
 418          * the pointer because the noref flag is not set yet.
 419          * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
 420          * to the subbuffer before this set noref operation.
 421          * subbuffer_set_noref() uses a volatile store to deal with concurrent
 422          * readers of the noref flag.
 423          */
 424         CHAN_WARN_ON(bufb->chan,
 425                      subbuffer_id_is_noref(config, bufb->buf_wsb[idx].id));
 426         /*
 427          * Memory barrier that ensures counter stores are ordered before set
 428          * noref and offset.
 429          */
 430         smp_mb();
 431         subbuffer_id_set_noref_offset(config, &bufb->buf_wsb[idx].id, offset);
 432 }
 433
 434 /**
 435  * update_read_sb_index - Read-side subbuffer index update.
 436  */
 437 static inline
 438 int update_read_sb_index(const struct lttng_kernel_ring_buffer_config *config,
 439                          struct lttng_kernel_ring_buffer_backend *bufb,
 440                          struct channel_backend *chanb,
 441                          unsigned long consumed_idx,
 442                          unsigned long consumed_count)
 443 {
 444         unsigned long old_id, new_id;
 445
 446         if (config->mode == RING_BUFFER_OVERWRITE) {
 447                 /*
 448                  * Exchange the target writer subbuffer with our own unused
 449                  * subbuffer. No need to use READ_ONCE() here to read the
 450                  * old_wpage, because the value read will be confirmed by the
 451                  * following cmpxchg().
 452                  */
 453                 old_id = bufb->buf_wsb[consumed_idx].id;
 454                 if (unlikely(!subbuffer_id_is_noref(config, old_id)))
 455                         return -EAGAIN;
 456                 /*
 457                  * Make sure the offset count we are expecting matches the one
 458                  * indicated by the writer.
 459                  */
 460                 if (unlikely(!subbuffer_id_compare_offset(config, old_id,
 461                                                           consumed_count)))
 462                         return -EAGAIN;
 463                 CHAN_WARN_ON(bufb->chan,
 464                              !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
 465                 subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
 466                                               consumed_count);
 467                 new_id = cmpxchg(&bufb->buf_wsb[consumed_idx].id, old_id,
 468                                  bufb->buf_rsb.id);
 469                 if (unlikely(old_id != new_id))
 470                         return -EAGAIN;
 471                 bufb->buf_rsb.id = new_id;
 472         } else {
 473                 /* No page exchange, use the writer page directly */
 474                 bufb->buf_rsb.id = bufb->buf_wsb[consumed_idx].id;
 475         }
 476         return 0;
 477 }
 478
 479 static inline __attribute__((always_inline))
 480 void lttng_inline_memcpy(void *dest, const void *src,
 481                 unsigned long len)
 482 {
 483         switch (len) {
 484         case 1:
 485                 *(uint8_t *) dest = *(const uint8_t *) src;
 486                 break;
 487         case 2:
 488                 *(uint16_t *) dest = *(const uint16_t *) src;
 489                 break;
 490         case 4:
 491                 *(uint32_t *) dest = *(const uint32_t *) src;
 492                 break;
 493         case 8:
 494                 *(uint64_t *) dest = *(const uint64_t *) src;
 495                 break;
 496         default:
 497                 inline_memcpy(dest, src, len);
 498         }
 499 }
 500
 501 /*
 502  * Use the architecture-specific memcpy implementation for constant-sized
 503  * inputs, but rely on an inline memcpy for length statically unknown.
 504  * The function call to memcpy is just way too expensive for a fast path.
 505  */
 506 #define lib_ring_buffer_do_copy(config, dest, src, len)         \
 507 do {                                                            \
 508         size_t __len = (len);                                   \
 509         if (__builtin_constant_p(len))                          \
 510                 memcpy(dest, src, __len);                       \
 511         else                                                    \
 512                 lttng_inline_memcpy(dest, src, __len);          \
 513 } while (0)
 514
 515 /*
 516  * We use __copy_from_user_inatomic to copy userspace data since we already
 517  * did the access_ok for the whole range.
 518  *
 519  * Return 0 if OK, nonzero on error.
 520  */
 521 static inline
 522 unsigned long lib_ring_buffer_do_copy_from_user_inatomic(void *dest,
 523                                                 const void __user *src,
 524                                                 unsigned long len)
 525 {
 526         return __copy_from_user_inatomic(dest, src, len);
 527 }
 528
 529 /*
 530  * write len bytes to dest with c
 531  */
 532 static inline
 533 void lib_ring_buffer_do_memset(char *dest, int c,
 534         unsigned long len)
 535 {
 536         unsigned long i;
 537
 538         for (i = 0; i < len; i++)
 539                 dest[i] = c;
 540 }
 541
 542 #endif /* _LIB_RING_BUFFER_BACKEND_INTERNAL_H */