| 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 | |
| 19 | /* Ring buffer backend API presented to the frontend */ |
| 20 | |
| 21 | /* Ring buffer and channel backend create/free */ |
| 22 | |
| 23 | int lib_ring_buffer_backend_create(struct lib_ring_buffer_backend *bufb, |
| 24 | struct channel_backend *chan, int cpu); |
| 25 | void channel_backend_unregister_notifiers(struct channel_backend *chanb); |
| 26 | void lib_ring_buffer_backend_free(struct lib_ring_buffer_backend *bufb); |
| 27 | int channel_backend_init(struct channel_backend *chanb, |
| 28 | const char *name, |
| 29 | const struct lib_ring_buffer_config *config, |
| 30 | void *priv, size_t subbuf_size, |
| 31 | size_t num_subbuf); |
| 32 | void channel_backend_free(struct channel_backend *chanb); |
| 33 | |
| 34 | void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend *bufb); |
| 35 | void channel_backend_reset(struct channel_backend *chanb); |
| 36 | |
| 37 | int lib_ring_buffer_backend_init(void); |
| 38 | void lib_ring_buffer_backend_exit(void); |
| 39 | |
| 40 | extern void _lib_ring_buffer_write(struct lib_ring_buffer_backend *bufb, |
| 41 | size_t offset, const void *src, size_t len, |
| 42 | ssize_t pagecpy); |
| 43 | |
| 44 | /* |
| 45 | * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be |
| 46 | * exchanged atomically. |
| 47 | * |
| 48 | * Top half word, except lowest bit, belongs to "offset", which is used to keep |
| 49 | * to count the produced buffers. For overwrite mode, this provides the |
| 50 | * consumer with the capacity to read subbuffers in order, handling the |
| 51 | * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit |
| 52 | * systems) concurrently with a single execution of get_subbuf (between offset |
| 53 | * sampling and subbuffer ID exchange). |
| 54 | */ |
| 55 | |
| 56 | #define HALF_ULONG_BITS (BITS_PER_LONG >> 1) |
| 57 | |
| 58 | #define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1) |
| 59 | #define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT) |
| 60 | #define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1)) |
| 61 | /* |
| 62 | * Lowest bit of top word half belongs to noref. Used only for overwrite mode. |
| 63 | */ |
| 64 | #define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1) |
| 65 | #define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT) |
| 66 | #define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT |
| 67 | /* |
| 68 | * In overwrite mode: lowest half of word is used for index. |
| 69 | * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit. |
| 70 | * In producer-consumer mode: whole word used for index. |
| 71 | */ |
| 72 | #define SB_ID_INDEX_SHIFT 0 |
| 73 | #define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT) |
| 74 | #define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1) |
| 75 | |
| 76 | /* |
| 77 | * Construct the subbuffer id from offset, index and noref. Use only the index |
| 78 | * for producer-consumer mode (offset and noref are only used in overwrite |
| 79 | * mode). |
| 80 | */ |
| 81 | static inline |
| 82 | unsigned long subbuffer_id(const struct lib_ring_buffer_config *config, |
| 83 | unsigned long offset, unsigned long noref, |
| 84 | unsigned long index) |
| 85 | { |
| 86 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 87 | return (offset << SB_ID_OFFSET_SHIFT) |
| 88 | | (noref << SB_ID_NOREF_SHIFT) |
| 89 | | index; |
| 90 | else |
| 91 | return index; |
| 92 | } |
| 93 | |
| 94 | /* |
| 95 | * Compare offset with the offset contained within id. Return 1 if the offset |
| 96 | * bits are identical, else 0. |
| 97 | */ |
| 98 | static inline |
| 99 | int subbuffer_id_compare_offset(const struct lib_ring_buffer_config *config, |
| 100 | unsigned long id, unsigned long offset) |
| 101 | { |
| 102 | return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT); |
| 103 | } |
| 104 | |
| 105 | static inline |
| 106 | unsigned long subbuffer_id_get_index(const struct lib_ring_buffer_config *config, |
| 107 | unsigned long id) |
| 108 | { |
| 109 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 110 | return id & SB_ID_INDEX_MASK; |
| 111 | else |
| 112 | return id; |
| 113 | } |
| 114 | |
| 115 | static inline |
| 116 | unsigned long subbuffer_id_is_noref(const struct lib_ring_buffer_config *config, |
| 117 | unsigned long id) |
| 118 | { |
| 119 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 120 | return !!(id & SB_ID_NOREF_MASK); |
| 121 | else |
| 122 | return 1; |
| 123 | } |
| 124 | |
| 125 | /* |
| 126 | * Only used by reader on subbuffer ID it has exclusive access to. No volatile |
| 127 | * needed. |
| 128 | */ |
| 129 | static inline |
| 130 | void subbuffer_id_set_noref(const struct lib_ring_buffer_config *config, |
| 131 | unsigned long *id) |
| 132 | { |
| 133 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 134 | *id |= SB_ID_NOREF_MASK; |
| 135 | } |
| 136 | |
| 137 | static inline |
| 138 | void subbuffer_id_set_noref_offset(const struct lib_ring_buffer_config *config, |
| 139 | unsigned long *id, unsigned long offset) |
| 140 | { |
| 141 | unsigned long tmp; |
| 142 | |
| 143 | if (config->mode == RING_BUFFER_OVERWRITE) { |
| 144 | tmp = *id; |
| 145 | tmp &= ~SB_ID_OFFSET_MASK; |
| 146 | tmp |= offset << SB_ID_OFFSET_SHIFT; |
| 147 | tmp |= SB_ID_NOREF_MASK; |
| 148 | /* Volatile store, read concurrently by readers. */ |
| 149 | ACCESS_ONCE(*id) = tmp; |
| 150 | } |
| 151 | } |
| 152 | |
| 153 | /* No volatile access, since already used locally */ |
| 154 | static inline |
| 155 | void subbuffer_id_clear_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 | /* |
| 163 | * For overwrite mode, cap the number of subbuffers per buffer to: |
| 164 | * 2^16 on 32-bit architectures |
| 165 | * 2^32 on 64-bit architectures |
| 166 | * This is required to fit in the index part of the ID. Return 0 on success, |
| 167 | * -EPERM on failure. |
| 168 | */ |
| 169 | static inline |
| 170 | int subbuffer_id_check_index(const struct lib_ring_buffer_config *config, |
| 171 | unsigned long num_subbuf) |
| 172 | { |
| 173 | if (config->mode == RING_BUFFER_OVERWRITE) |
| 174 | return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0; |
| 175 | else |
| 176 | return 0; |
| 177 | } |
| 178 | |
| 179 | static inline |
| 180 | void subbuffer_count_record(const struct lib_ring_buffer_config *config, |
| 181 | struct lib_ring_buffer_backend *bufb, |
| 182 | unsigned long idx) |
| 183 | { |
| 184 | unsigned long sb_bindex; |
| 185 | |
| 186 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id); |
| 187 | v_inc(config, &bufb->array[sb_bindex]->records_commit); |
| 188 | } |
| 189 | |
| 190 | /* |
| 191 | * Reader has exclusive subbuffer access for record consumption. No need to |
| 192 | * perform the decrement atomically. |
| 193 | */ |
| 194 | static inline |
| 195 | void subbuffer_consume_record(const struct lib_ring_buffer_config *config, |
| 196 | struct lib_ring_buffer_backend *bufb) |
| 197 | { |
| 198 | unsigned long sb_bindex; |
| 199 | |
| 200 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id); |
| 201 | CHAN_WARN_ON(bufb->chan, |
| 202 | !v_read(config, &bufb->array[sb_bindex]->records_unread)); |
| 203 | /* Non-atomic decrement protected by exclusive subbuffer access */ |
| 204 | _v_dec(config, &bufb->array[sb_bindex]->records_unread); |
| 205 | v_inc(config, &bufb->records_read); |
| 206 | } |
| 207 | |
| 208 | static inline |
| 209 | unsigned long subbuffer_get_records_count( |
| 210 | const struct lib_ring_buffer_config *config, |
| 211 | struct lib_ring_buffer_backend *bufb, |
| 212 | unsigned long idx) |
| 213 | { |
| 214 | unsigned long sb_bindex; |
| 215 | |
| 216 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id); |
| 217 | return v_read(config, &bufb->array[sb_bindex]->records_commit); |
| 218 | } |
| 219 | |
| 220 | /* |
| 221 | * Must be executed at subbuffer delivery when the writer has _exclusive_ |
| 222 | * subbuffer access. See ring_buffer_check_deliver() for details. |
| 223 | * ring_buffer_get_records_count() must be called to get the records count |
| 224 | * before this function, because it resets the records_commit count. |
| 225 | */ |
| 226 | static inline |
| 227 | unsigned long subbuffer_count_records_overrun( |
| 228 | const struct lib_ring_buffer_config *config, |
| 229 | struct lib_ring_buffer_backend *bufb, |
| 230 | unsigned long idx) |
| 231 | { |
| 232 | struct lib_ring_buffer_backend_pages *pages; |
| 233 | unsigned long overruns, sb_bindex; |
| 234 | |
| 235 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id); |
| 236 | pages = bufb->array[sb_bindex]; |
| 237 | overruns = v_read(config, &pages->records_unread); |
| 238 | v_set(config, &pages->records_unread, |
| 239 | v_read(config, &pages->records_commit)); |
| 240 | v_set(config, &pages->records_commit, 0); |
| 241 | |
| 242 | return overruns; |
| 243 | } |
| 244 | |
| 245 | static inline |
| 246 | void subbuffer_set_data_size(const struct lib_ring_buffer_config *config, |
| 247 | struct lib_ring_buffer_backend *bufb, |
| 248 | unsigned long idx, |
| 249 | unsigned long data_size) |
| 250 | { |
| 251 | struct lib_ring_buffer_backend_pages *pages; |
| 252 | unsigned long sb_bindex; |
| 253 | |
| 254 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id); |
| 255 | pages = bufb->array[sb_bindex]; |
| 256 | pages->data_size = data_size; |
| 257 | } |
| 258 | |
| 259 | static inline |
| 260 | unsigned long subbuffer_get_read_data_size( |
| 261 | const struct lib_ring_buffer_config *config, |
| 262 | struct lib_ring_buffer_backend *bufb) |
| 263 | { |
| 264 | struct lib_ring_buffer_backend_pages *pages; |
| 265 | unsigned long sb_bindex; |
| 266 | |
| 267 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id); |
| 268 | pages = bufb->array[sb_bindex]; |
| 269 | return pages->data_size; |
| 270 | } |
| 271 | |
| 272 | static inline |
| 273 | unsigned long subbuffer_get_data_size( |
| 274 | const struct lib_ring_buffer_config *config, |
| 275 | struct lib_ring_buffer_backend *bufb, |
| 276 | unsigned long idx) |
| 277 | { |
| 278 | struct lib_ring_buffer_backend_pages *pages; |
| 279 | unsigned long sb_bindex; |
| 280 | |
| 281 | sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id); |
| 282 | pages = bufb->array[sb_bindex]; |
| 283 | return pages->data_size; |
| 284 | } |
| 285 | |
| 286 | /** |
| 287 | * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by |
| 288 | * writer. |
| 289 | */ |
| 290 | static inline |
| 291 | void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config, |
| 292 | struct lib_ring_buffer_backend *bufb, |
| 293 | unsigned long idx) |
| 294 | { |
| 295 | unsigned long id, new_id; |
| 296 | |
| 297 | if (config->mode != RING_BUFFER_OVERWRITE) |
| 298 | return; |
| 299 | |
| 300 | /* |
| 301 | * Performing a volatile access to read the sb_pages, because we want to |
| 302 | * read a coherent version of the pointer and the associated noref flag. |
| 303 | */ |
| 304 | id = ACCESS_ONCE(bufb->buf_wsb[idx].id); |
| 305 | for (;;) { |
| 306 | /* This check is called on the fast path for each record. */ |
| 307 | if (likely(!subbuffer_id_is_noref(config, id))) { |
| 308 | /* |
| 309 | * Store after load dependency ordering the writes to |
| 310 | * the subbuffer after load and test of the noref flag |
| 311 | * matches the memory barrier implied by the cmpxchg() |
| 312 | * in update_read_sb_index(). |
| 313 | */ |
| 314 | return; /* Already writing to this buffer */ |
| 315 | } |
| 316 | new_id = id; |
| 317 | subbuffer_id_clear_noref(config, &new_id); |
| 318 | new_id = cmpxchg(&bufb->buf_wsb[idx].id, id, new_id); |
| 319 | if (likely(new_id == id)) |
| 320 | break; |
| 321 | id = new_id; |
| 322 | } |
| 323 | } |
| 324 | |
| 325 | /** |
| 326 | * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset, |
| 327 | * called by writer. |
| 328 | */ |
| 329 | static inline |
| 330 | void lib_ring_buffer_set_noref_offset(const struct lib_ring_buffer_config *config, |
| 331 | struct lib_ring_buffer_backend *bufb, |
| 332 | unsigned long idx, unsigned long offset) |
| 333 | { |
| 334 | if (config->mode != RING_BUFFER_OVERWRITE) |
| 335 | return; |
| 336 | |
| 337 | /* |
| 338 | * Because ring_buffer_set_noref() is only called by a single thread |
| 339 | * (the one which updated the cc_sb value), there are no concurrent |
| 340 | * updates to take care of: other writers have not updated cc_sb, so |
| 341 | * they cannot set the noref flag, and concurrent readers cannot modify |
| 342 | * the pointer because the noref flag is not set yet. |
| 343 | * The smp_wmb() in ring_buffer_commit() takes care of ordering writes |
| 344 | * to the subbuffer before this set noref operation. |
| 345 | * subbuffer_set_noref() uses a volatile store to deal with concurrent |
| 346 | * readers of the noref flag. |
| 347 | */ |
| 348 | CHAN_WARN_ON(bufb->chan, |
| 349 | subbuffer_id_is_noref(config, bufb->buf_wsb[idx].id)); |
| 350 | /* |
| 351 | * Memory barrier that ensures counter stores are ordered before set |
| 352 | * noref and offset. |
| 353 | */ |
| 354 | smp_mb(); |
| 355 | subbuffer_id_set_noref_offset(config, &bufb->buf_wsb[idx].id, offset); |
| 356 | } |
| 357 | |
| 358 | /** |
| 359 | * update_read_sb_index - Read-side subbuffer index update. |
| 360 | */ |
| 361 | static inline |
| 362 | int update_read_sb_index(const struct lib_ring_buffer_config *config, |
| 363 | struct lib_ring_buffer_backend *bufb, |
| 364 | struct channel_backend *chanb, |
| 365 | unsigned long consumed_idx, |
| 366 | unsigned long consumed_count) |
| 367 | { |
| 368 | unsigned long old_id, new_id; |
| 369 | |
| 370 | if (config->mode == RING_BUFFER_OVERWRITE) { |
| 371 | /* |
| 372 | * Exchange the target writer subbuffer with our own unused |
| 373 | * subbuffer. No need to use ACCESS_ONCE() here to read the |
| 374 | * old_wpage, because the value read will be confirmed by the |
| 375 | * following cmpxchg(). |
| 376 | */ |
| 377 | old_id = bufb->buf_wsb[consumed_idx].id; |
| 378 | if (unlikely(!subbuffer_id_is_noref(config, old_id))) |
| 379 | return -EAGAIN; |
| 380 | /* |
| 381 | * Make sure the offset count we are expecting matches the one |
| 382 | * indicated by the writer. |
| 383 | */ |
| 384 | if (unlikely(!subbuffer_id_compare_offset(config, old_id, |
| 385 | consumed_count))) |
| 386 | return -EAGAIN; |
| 387 | CHAN_WARN_ON(bufb->chan, |
| 388 | !subbuffer_id_is_noref(config, bufb->buf_rsb.id)); |
| 389 | subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id, |
| 390 | consumed_count); |
| 391 | new_id = cmpxchg(&bufb->buf_wsb[consumed_idx].id, old_id, |
| 392 | bufb->buf_rsb.id); |
| 393 | if (unlikely(old_id != new_id)) |
| 394 | return -EAGAIN; |
| 395 | bufb->buf_rsb.id = new_id; |
| 396 | } else { |
| 397 | /* No page exchange, use the writer page directly */ |
| 398 | bufb->buf_rsb.id = bufb->buf_wsb[consumed_idx].id; |
| 399 | } |
| 400 | return 0; |
| 401 | } |
| 402 | |
| 403 | /* |
| 404 | * Use the architecture-specific memcpy implementation for constant-sized |
| 405 | * inputs, but rely on an inline memcpy for length statically unknown. |
| 406 | * The function call to memcpy is just way too expensive for a fast path. |
| 407 | */ |
| 408 | #define lib_ring_buffer_do_copy(config, dest, src, len) \ |
| 409 | do { \ |
| 410 | size_t __len = (len); \ |
| 411 | if (__builtin_constant_p(len)) \ |
| 412 | memcpy(dest, src, __len); \ |
| 413 | else \ |
| 414 | inline_memcpy(dest, src, __len); \ |
| 415 | } while (0) |
| 416 | |
| 417 | #endif /* _LINUX_RING_BUFFER_BACKEND_INTERNAL_H */ |