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[lttng-ust.git] / libringbuffer / backend_internal.h
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1#ifndef _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H
2#define _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H
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3
4/*
e92f3e28 5 * libringbuffer/backend_internal.h
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6 *
7 * Ring buffer backend (internal helpers).
8 *
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9 * Copyright (C) 2005-2012 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
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24 */
25
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26#include <unistd.h>
27#include <urcu/compiler.h>
28
4318ae1b 29#include <lttng/ringbuffer-config.h>
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30#include "backend_types.h"
31#include "frontend_types.h"
a6352fd4 32#include "shm.h"
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33
34/* Ring buffer backend API presented to the frontend */
35
36/* Ring buffer and channel backend create/free */
37
4cfec15c 38int lib_ring_buffer_backend_create(struct lttng_ust_lib_ring_buffer_backend *bufb,
a6352fd4 39 struct channel_backend *chan, int cpu,
38fae1d3 40 struct lttng_ust_shm_handle *handle,
1d498196 41 struct shm_object *shmobj);
852c2936 42void channel_backend_unregister_notifiers(struct channel_backend *chanb);
4cfec15c 43void lib_ring_buffer_backend_free(struct lttng_ust_lib_ring_buffer_backend *bufb);
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44int channel_backend_init(struct channel_backend *chanb,
45 const char *name,
4cfec15c 46 const struct lttng_ust_lib_ring_buffer_config *config,
a3f61e7f 47 size_t subbuf_size,
a9ff648c 48 size_t num_subbuf, struct lttng_ust_shm_handle *handle,
5ea386c3 49 const int *stream_fds);
1d498196 50void channel_backend_free(struct channel_backend *chanb,
38fae1d3 51 struct lttng_ust_shm_handle *handle);
852c2936 52
4cfec15c 53void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3 54 struct lttng_ust_shm_handle *handle);
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55void channel_backend_reset(struct channel_backend *chanb);
56
57int lib_ring_buffer_backend_init(void);
58void lib_ring_buffer_backend_exit(void);
59
4cfec15c 60extern void _lib_ring_buffer_write(struct lttng_ust_lib_ring_buffer_backend *bufb,
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61 size_t offset, const void *src, size_t len,
62 ssize_t pagecpy);
63
64/*
65 * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
66 * exchanged atomically.
67 *
68 * Top half word, except lowest bit, belongs to "offset", which is used to keep
69 * to count the produced buffers. For overwrite mode, this provides the
70 * consumer with the capacity to read subbuffers in order, handling the
71 * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
72 * systems) concurrently with a single execution of get_subbuf (between offset
73 * sampling and subbuffer ID exchange).
74 */
75
14641deb 76#define HALF_ULONG_BITS (CAA_BITS_PER_LONG >> 1)
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77
78#define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1)
79#define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT)
80#define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1))
81/*
82 * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
83 */
84#define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1)
85#define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT)
86#define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT
87/*
88 * In overwrite mode: lowest half of word is used for index.
89 * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
90 * In producer-consumer mode: whole word used for index.
91 */
92#define SB_ID_INDEX_SHIFT 0
93#define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT)
94#define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1)
95
96/*
97 * Construct the subbuffer id from offset, index and noref. Use only the index
98 * for producer-consumer mode (offset and noref are only used in overwrite
99 * mode).
100 */
101static inline
4cfec15c 102unsigned long subbuffer_id(const struct lttng_ust_lib_ring_buffer_config *config,
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103 unsigned long offset, unsigned long noref,
104 unsigned long index)
105{
106 if (config->mode == RING_BUFFER_OVERWRITE)
107 return (offset << SB_ID_OFFSET_SHIFT)
108 | (noref << SB_ID_NOREF_SHIFT)
109 | index;
110 else
111 return index;
112}
113
114/*
115 * Compare offset with the offset contained within id. Return 1 if the offset
116 * bits are identical, else 0.
117 */
118static inline
4cfec15c 119int subbuffer_id_compare_offset(const struct lttng_ust_lib_ring_buffer_config *config,
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120 unsigned long id, unsigned long offset)
121{
122 return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT);
123}
124
125static inline
4cfec15c 126unsigned long subbuffer_id_get_index(const struct lttng_ust_lib_ring_buffer_config *config,
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127 unsigned long id)
128{
129 if (config->mode == RING_BUFFER_OVERWRITE)
130 return id & SB_ID_INDEX_MASK;
131 else
132 return id;
133}
134
135static inline
4cfec15c 136unsigned long subbuffer_id_is_noref(const struct lttng_ust_lib_ring_buffer_config *config,
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137 unsigned long id)
138{
139 if (config->mode == RING_BUFFER_OVERWRITE)
140 return !!(id & SB_ID_NOREF_MASK);
141 else
142 return 1;
143}
144
145/*
146 * Only used by reader on subbuffer ID it has exclusive access to. No volatile
147 * needed.
148 */
149static inline
4cfec15c 150void subbuffer_id_set_noref(const struct lttng_ust_lib_ring_buffer_config *config,
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151 unsigned long *id)
152{
153 if (config->mode == RING_BUFFER_OVERWRITE)
154 *id |= SB_ID_NOREF_MASK;
155}
156
157static inline
4cfec15c 158void subbuffer_id_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config,
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159 unsigned long *id, unsigned long offset)
160{
161 unsigned long tmp;
162
163 if (config->mode == RING_BUFFER_OVERWRITE) {
164 tmp = *id;
165 tmp &= ~SB_ID_OFFSET_MASK;
166 tmp |= offset << SB_ID_OFFSET_SHIFT;
167 tmp |= SB_ID_NOREF_MASK;
168 /* Volatile store, read concurrently by readers. */
14641deb 169 CMM_ACCESS_ONCE(*id) = tmp;
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170 }
171}
172
173/* No volatile access, since already used locally */
174static inline
4cfec15c 175void subbuffer_id_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config,
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176 unsigned long *id)
177{
178 if (config->mode == RING_BUFFER_OVERWRITE)
179 *id &= ~SB_ID_NOREF_MASK;
180}
181
182/*
183 * For overwrite mode, cap the number of subbuffers per buffer to:
184 * 2^16 on 32-bit architectures
185 * 2^32 on 64-bit architectures
186 * This is required to fit in the index part of the ID. Return 0 on success,
187 * -EPERM on failure.
188 */
189static inline
4cfec15c 190int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config *config,
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191 unsigned long num_subbuf)
192{
193 if (config->mode == RING_BUFFER_OVERWRITE)
194 return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0;
195 else
196 return 0;
197}
198
199static inline
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200void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *config,
201 struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3 202 unsigned long idx, struct lttng_ust_shm_handle *handle)
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203{
204 unsigned long sb_bindex;
205
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206 sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
207 v_inc(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
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208}
209
210/*
211 * Reader has exclusive subbuffer access for record consumption. No need to
212 * perform the decrement atomically.
213 */
214static inline
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215void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config *config,
216 struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3 217 struct lttng_ust_shm_handle *handle)
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218{
219 unsigned long sb_bindex;
220
221 sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
1d498196 222 CHAN_WARN_ON(shmp(handle, bufb->chan),
4746ae29 223 !v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread));
852c2936 224 /* Non-atomic decrement protected by exclusive subbuffer access */
4746ae29 225 _v_dec(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread);
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226 v_inc(config, &bufb->records_read);
227}
228
229static inline
230unsigned long subbuffer_get_records_count(
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231 const struct lttng_ust_lib_ring_buffer_config *config,
232 struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196 233 unsigned long idx,
38fae1d3 234 struct lttng_ust_shm_handle *handle)
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235{
236 unsigned long sb_bindex;
237
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238 sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
239 return v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
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240}
241
242/*
243 * Must be executed at subbuffer delivery when the writer has _exclusive_
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244 * subbuffer access. See lib_ring_buffer_check_deliver() for details.
245 * lib_ring_buffer_get_records_count() must be called to get the records
246 * count before this function, because it resets the records_commit
247 * count.
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248 */
249static inline
250unsigned long subbuffer_count_records_overrun(
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251 const struct lttng_ust_lib_ring_buffer_config *config,
252 struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196 253 unsigned long idx,
38fae1d3 254 struct lttng_ust_shm_handle *handle)
852c2936 255{
4cfec15c 256 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
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257 unsigned long overruns, sb_bindex;
258
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259 sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
260 pages = shmp_index(handle, bufb->array, sb_bindex);
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261 overruns = v_read(config, &shmp(handle, pages->shmp)->records_unread);
262 v_set(config, &shmp(handle, pages->shmp)->records_unread,
263 v_read(config, &shmp(handle, pages->shmp)->records_commit));
264 v_set(config, &shmp(handle, pages->shmp)->records_commit, 0);
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265
266 return overruns;
267}
268
269static inline
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270void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
271 struct lttng_ust_lib_ring_buffer_backend *bufb,
852c2936 272 unsigned long idx,
1d498196 273 unsigned long data_size,
38fae1d3 274 struct lttng_ust_shm_handle *handle)
852c2936 275{
4cfec15c 276 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
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277 unsigned long sb_bindex;
278
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279 sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
280 pages = shmp_index(handle, bufb->array, sb_bindex);
1d498196 281 shmp(handle, pages->shmp)->data_size = data_size;
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282}
283
284static inline
285unsigned long subbuffer_get_read_data_size(
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286 const struct lttng_ust_lib_ring_buffer_config *config,
287 struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3 288 struct lttng_ust_shm_handle *handle)
852c2936 289{
4cfec15c 290 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
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291 unsigned long sb_bindex;
292
293 sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
4746ae29 294 pages = shmp_index(handle, bufb->array, sb_bindex);
1d498196 295 return shmp(handle, pages->shmp)->data_size;
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296}
297
298static inline
299unsigned long subbuffer_get_data_size(
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300 const struct lttng_ust_lib_ring_buffer_config *config,
301 struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196 302 unsigned long idx,
38fae1d3 303 struct lttng_ust_shm_handle *handle)
852c2936 304{
4cfec15c 305 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
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306 unsigned long sb_bindex;
307
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308 sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
309 pages = shmp_index(handle, bufb->array, sb_bindex);
1d498196 310 return shmp(handle, pages->shmp)->data_size;
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311}
312
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313static inline
314void subbuffer_inc_packet_count(const struct lttng_ust_lib_ring_buffer_config *config,
315 struct lttng_ust_lib_ring_buffer_backend *bufb,
316 unsigned long idx, struct lttng_ust_shm_handle *handle)
317{
318 shmp_index(handle, bufb->buf_cnt, idx)->seq_cnt++;
319}
320
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321/**
322 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
323 * writer.
324 */
325static inline
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326void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config,
327 struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196 328 unsigned long idx,
38fae1d3 329 struct lttng_ust_shm_handle *handle)
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330{
331 unsigned long id, new_id;
332
333 if (config->mode != RING_BUFFER_OVERWRITE)
334 return;
335
336 /*
337 * Performing a volatile access to read the sb_pages, because we want to
338 * read a coherent version of the pointer and the associated noref flag.
339 */
4746ae29 340 id = CMM_ACCESS_ONCE(shmp_index(handle, bufb->buf_wsb, idx)->id);
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341 for (;;) {
342 /* This check is called on the fast path for each record. */
b5a3dfa5 343 if (caa_likely(!subbuffer_id_is_noref(config, id))) {
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344 /*
345 * Store after load dependency ordering the writes to
346 * the subbuffer after load and test of the noref flag
347 * matches the memory barrier implied by the cmpxchg()
348 * in update_read_sb_index().
349 */
350 return; /* Already writing to this buffer */
351 }
352 new_id = id;
353 subbuffer_id_clear_noref(config, &new_id);
4746ae29 354 new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, idx)->id, id, new_id);
b5a3dfa5 355 if (caa_likely(new_id == id))
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356 break;
357 id = new_id;
358 }
359}
360
361/**
362 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
363 * called by writer.
364 */
365static inline
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366void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config,
367 struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196 368 unsigned long idx, unsigned long offset,
38fae1d3 369 struct lttng_ust_shm_handle *handle)
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370{
371 if (config->mode != RING_BUFFER_OVERWRITE)
372 return;
373
374 /*
375 * Because ring_buffer_set_noref() is only called by a single thread
376 * (the one which updated the cc_sb value), there are no concurrent
377 * updates to take care of: other writers have not updated cc_sb, so
378 * they cannot set the noref flag, and concurrent readers cannot modify
379 * the pointer because the noref flag is not set yet.
380 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
381 * to the subbuffer before this set noref operation.
382 * subbuffer_set_noref() uses a volatile store to deal with concurrent
383 * readers of the noref flag.
384 */
1d498196 385 CHAN_WARN_ON(shmp(handle, bufb->chan),
4746ae29 386 subbuffer_id_is_noref(config, shmp_index(handle, bufb->buf_wsb, idx)->id));
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387 /*
388 * Memory barrier that ensures counter stores are ordered before set
389 * noref and offset.
390 */
14641deb 391 cmm_smp_mb();
4746ae29 392 subbuffer_id_set_noref_offset(config, &shmp_index(handle, bufb->buf_wsb, idx)->id, offset);
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393}
394
395/**
396 * update_read_sb_index - Read-side subbuffer index update.
397 */
398static inline
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399int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config *config,
400 struct lttng_ust_lib_ring_buffer_backend *bufb,
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401 struct channel_backend *chanb,
402 unsigned long consumed_idx,
1d498196 403 unsigned long consumed_count,
38fae1d3 404 struct lttng_ust_shm_handle *handle)
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405{
406 unsigned long old_id, new_id;
407
408 if (config->mode == RING_BUFFER_OVERWRITE) {
409 /*
410 * Exchange the target writer subbuffer with our own unused
14641deb 411 * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
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412 * old_wpage, because the value read will be confirmed by the
413 * following cmpxchg().
414 */
4746ae29 415 old_id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id;
b5a3dfa5 416 if (caa_unlikely(!subbuffer_id_is_noref(config, old_id)))
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417 return -EAGAIN;
418 /*
419 * Make sure the offset count we are expecting matches the one
420 * indicated by the writer.
421 */
b5a3dfa5 422 if (caa_unlikely(!subbuffer_id_compare_offset(config, old_id,
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423 consumed_count)))
424 return -EAGAIN;
1d498196 425 CHAN_WARN_ON(shmp(handle, bufb->chan),
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426 !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
427 subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
428 consumed_count);
4746ae29 429 new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, consumed_idx)->id, old_id,
852c2936 430 bufb->buf_rsb.id);
b5a3dfa5 431 if (caa_unlikely(old_id != new_id))
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432 return -EAGAIN;
433 bufb->buf_rsb.id = new_id;
434 } else {
435 /* No page exchange, use the writer page directly */
4746ae29 436 bufb->buf_rsb.id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id;
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437 }
438 return 0;
439}
440
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441#ifndef inline_memcpy
442#define inline_memcpy(dest, src, n) memcpy(dest, src, n)
443#endif
444
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445/*
446 * Use the architecture-specific memcpy implementation for constant-sized
447 * inputs, but rely on an inline memcpy for length statically unknown.
448 * The function call to memcpy is just way too expensive for a fast path.
449 */
450#define lib_ring_buffer_do_copy(config, dest, src, len) \
451do { \
452 size_t __len = (len); \
453 if (__builtin_constant_p(len)) \
454 memcpy(dest, src, __len); \
455 else \
456 inline_memcpy(dest, src, __len); \
457} while (0)
458
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459/*
460 * write len bytes to dest with c
461 */
462static inline
463void lib_ring_buffer_do_memset(char *dest, int c, unsigned long len)
464{
465 unsigned long i;
466
467 for (i = 0; i < len; i++)
468 dest[i] = c;
469}
470
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471/* arch-agnostic implementation */
472
bfd26582 473static inline int lttng_ust_fls(unsigned int x)
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474{
475 int r = 32;
476
477 if (!x)
478 return 0;
479 if (!(x & 0xFFFF0000U)) {
480 x <<= 16;
481 r -= 16;
482 }
483 if (!(x & 0xFF000000U)) {
484 x <<= 8;
485 r -= 8;
486 }
487 if (!(x & 0xF0000000U)) {
488 x <<= 4;
489 r -= 4;
490 }
491 if (!(x & 0xC0000000U)) {
492 x <<= 2;
493 r -= 2;
494 }
495 if (!(x & 0x80000000U)) {
e2bd33a5 496 /* No need to bit shift on last operation */
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497 r -= 1;
498 }
499 return r;
500}
501
502static inline int get_count_order(unsigned int count)
503{
504 int order;
505
bfd26582 506 order = lttng_ust_fls(count) - 1;
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507 if (count & (count - 1))
508 order++;
509 return order;
510}
511
e92f3e28 512#endif /* _LTTNG_RING_BUFFER_BACKEND_INTERNAL_H */
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