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