doc: add Python example
[lttng-ust.git] / libringbuffer / ring_buffer_backend.c
CommitLineData
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1/*
2 * ring_buffer_backend.c
3 *
e92f3e28 4 * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
852c2936 5 *
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6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; only
9 * version 2.1 of the License.
10 *
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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19 */
20
5ad63a16 21#define _GNU_SOURCE
14641deb 22#include <urcu/arch.h>
96e80018 23#include <limits.h>
14641deb 24
4318ae1b 25#include <lttng/ringbuffer-config.h>
2fed87ae 26#include "vatomic.h"
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27#include "backend.h"
28#include "frontend.h"
a6352fd4 29#include "smp.h"
431d5cf0 30#include "shm.h"
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31
32/**
33 * lib_ring_buffer_backend_allocate - allocate a channel buffer
34 * @config: ring buffer instance configuration
35 * @buf: the buffer struct
36 * @size: total size of the buffer
37 * @num_subbuf: number of subbuffers
38 * @extra_reader_sb: need extra subbuffer for reader
39 */
40static
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41int lib_ring_buffer_backend_allocate(const struct lttng_ust_lib_ring_buffer_config *config,
42 struct lttng_ust_lib_ring_buffer_backend *bufb,
852c2936 43 size_t size, size_t num_subbuf,
a6352fd4 44 int extra_reader_sb,
38fae1d3 45 struct lttng_ust_shm_handle *handle,
1d498196 46 struct shm_object *shmobj)
852c2936 47{
1d498196 48 struct channel_backend *chanb = &shmp(handle, bufb->chan)->backend;
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49 unsigned long subbuf_size, mmap_offset = 0;
50 unsigned long num_subbuf_alloc;
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51 unsigned long i;
52
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53 subbuf_size = chanb->subbuf_size;
54 num_subbuf_alloc = num_subbuf;
55
a6352fd4 56 if (extra_reader_sb)
852c2936 57 num_subbuf_alloc++;
852c2936 58
4cfec15c 59 align_shm(shmobj, __alignof__(struct lttng_ust_lib_ring_buffer_backend_pages_shmp));
1d498196 60 set_shmp(bufb->array, zalloc_shm(shmobj,
4cfec15c 61 sizeof(struct lttng_ust_lib_ring_buffer_backend_pages_shmp) * num_subbuf_alloc));
b5a3dfa5 62 if (caa_unlikely(!shmp(handle, bufb->array)))
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63 goto array_error;
64
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65 /*
66 * This is the largest element (the buffer pages) which needs to
67 * be aligned on PAGE_SIZE.
68 */
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69 align_shm(shmobj, PAGE_SIZE);
70 set_shmp(bufb->memory_map, zalloc_shm(shmobj,
a6352fd4 71 subbuf_size * num_subbuf_alloc));
b5a3dfa5 72 if (caa_unlikely(!shmp(handle, bufb->memory_map)))
a6352fd4 73 goto memory_map_error;
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74
75 /* Allocate backend pages array elements */
76 for (i = 0; i < num_subbuf_alloc; i++) {
4cfec15c 77 align_shm(shmobj, __alignof__(struct lttng_ust_lib_ring_buffer_backend_pages));
aead2025 78 set_shmp(shmp_index(handle, bufb->array, i)->shmp,
1d498196 79 zalloc_shm(shmobj,
4cfec15c 80 sizeof(struct lttng_ust_lib_ring_buffer_backend_pages)));
4746ae29 81 if (!shmp(handle, shmp_index(handle, bufb->array, i)->shmp))
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82 goto free_array;
83 }
84
85 /* Allocate write-side subbuffer table */
4cfec15c 86 align_shm(shmobj, __alignof__(struct lttng_ust_lib_ring_buffer_backend_subbuffer));
1d498196 87 set_shmp(bufb->buf_wsb, zalloc_shm(shmobj,
4cfec15c 88 sizeof(struct lttng_ust_lib_ring_buffer_backend_subbuffer)
1d498196 89 * num_subbuf));
b5a3dfa5 90 if (caa_unlikely(!shmp(handle, bufb->buf_wsb)))
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91 goto free_array;
92
93 for (i = 0; i < num_subbuf; i++)
4746ae29 94 shmp_index(handle, bufb->buf_wsb, i)->id = subbuffer_id(config, 0, 1, i);
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95
96 /* Assign read-side subbuffer table */
97 if (extra_reader_sb)
98 bufb->buf_rsb.id = subbuffer_id(config, 0, 1,
99 num_subbuf_alloc - 1);
100 else
101 bufb->buf_rsb.id = subbuffer_id(config, 0, 1, 0);
102
103 /* Assign pages to page index */
104 for (i = 0; i < num_subbuf_alloc; i++) {
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105 struct shm_ref ref;
106
107 ref.index = bufb->memory_map._ref.index;
108 ref.offset = bufb->memory_map._ref.offset;
109 ref.offset += i * subbuf_size;
110
4746ae29 111 set_shmp(shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->p,
1d498196 112 ref);
852c2936 113 if (config->output == RING_BUFFER_MMAP) {
4746ae29 114 shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->mmap_offset = mmap_offset;
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115 mmap_offset += subbuf_size;
116 }
117 }
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118 return 0;
119
120free_array:
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121 /* bufb->array[i] will be freed by shm teardown */
122memory_map_error:
123 /* bufb->array will be freed by shm teardown */
852c2936 124array_error:
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125 return -ENOMEM;
126}
127
4cfec15c 128int lib_ring_buffer_backend_create(struct lttng_ust_lib_ring_buffer_backend *bufb,
a6352fd4 129 struct channel_backend *chanb, int cpu,
38fae1d3 130 struct lttng_ust_shm_handle *handle,
1d498196 131 struct shm_object *shmobj)
852c2936 132{
4cfec15c 133 const struct lttng_ust_lib_ring_buffer_config *config = &chanb->config;
852c2936 134
1d498196 135 set_shmp(bufb->chan, handle->chan._ref);
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136 bufb->cpu = cpu;
137
138 return lib_ring_buffer_backend_allocate(config, bufb, chanb->buf_size,
139 chanb->num_subbuf,
a6352fd4 140 chanb->extra_reader_sb,
1d498196 141 handle, shmobj);
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142}
143
4cfec15c 144void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3 145 struct lttng_ust_shm_handle *handle)
852c2936 146{
1d498196 147 struct channel_backend *chanb = &shmp(handle, bufb->chan)->backend;
4cfec15c 148 const struct lttng_ust_lib_ring_buffer_config *config = &chanb->config;
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149 unsigned long num_subbuf_alloc;
150 unsigned int i;
151
152 num_subbuf_alloc = chanb->num_subbuf;
153 if (chanb->extra_reader_sb)
154 num_subbuf_alloc++;
155
156 for (i = 0; i < chanb->num_subbuf; i++)
4746ae29 157 shmp_index(handle, bufb->buf_wsb, i)->id = subbuffer_id(config, 0, 1, i);
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158 if (chanb->extra_reader_sb)
159 bufb->buf_rsb.id = subbuffer_id(config, 0, 1,
160 num_subbuf_alloc - 1);
161 else
162 bufb->buf_rsb.id = subbuffer_id(config, 0, 1, 0);
163
164 for (i = 0; i < num_subbuf_alloc; i++) {
165 /* Don't reset mmap_offset */
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166 v_set(config, &shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->records_commit, 0);
167 v_set(config, &shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->records_unread, 0);
168 shmp(handle, shmp_index(handle, bufb->array, i)->shmp)->data_size = 0;
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169 /* Don't reset backend page and virt addresses */
170 }
171 /* Don't reset num_pages_per_subbuf, cpu, allocated */
172 v_set(config, &bufb->records_read, 0);
173}
174
175/*
176 * The frontend is responsible for also calling ring_buffer_backend_reset for
177 * each buffer when calling channel_backend_reset.
178 */
179void channel_backend_reset(struct channel_backend *chanb)
180{
14641deb 181 struct channel *chan = caa_container_of(chanb, struct channel, backend);
4cfec15c 182 const struct lttng_ust_lib_ring_buffer_config *config = &chanb->config;
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183
184 /*
185 * Don't reset buf_size, subbuf_size, subbuf_size_order,
186 * num_subbuf_order, buf_size_order, extra_reader_sb, num_subbuf,
187 * priv, notifiers, config, cpumask and name.
188 */
189 chanb->start_tsc = config->cb.ring_buffer_clock_read(chan);
190}
191
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192/**
193 * channel_backend_init - initialize a channel backend
194 * @chanb: channel backend
195 * @name: channel name
196 * @config: client ring buffer configuration
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197 * @parent: dentry of parent directory, %NULL for root directory
198 * @subbuf_size: size of sub-buffers (> PAGE_SIZE, power of 2)
199 * @num_subbuf: number of sub-buffers (power of 2)
38fae1d3 200 * @lttng_ust_shm_handle: shared memory handle
5ea386c3 201 * @stream_fds: stream file descriptors.
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202 *
203 * Returns channel pointer if successful, %NULL otherwise.
204 *
205 * Creates per-cpu channel buffers using the sizes and attributes
206 * specified. The created channel buffer files will be named
207 * name_0...name_N-1. File permissions will be %S_IRUSR.
208 *
209 * Called with CPU hotplug disabled.
210 */
211int channel_backend_init(struct channel_backend *chanb,
212 const char *name,
4cfec15c 213 const struct lttng_ust_lib_ring_buffer_config *config,
a3f61e7f 214 size_t subbuf_size, size_t num_subbuf,
a9ff648c 215 struct lttng_ust_shm_handle *handle,
5ea386c3 216 const int *stream_fds)
852c2936 217{
14641deb 218 struct channel *chan = caa_container_of(chanb, struct channel, backend);
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219 unsigned int i;
220 int ret;
6c1f7d8b 221 size_t shmsize = 0, num_subbuf_alloc;
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222
223 if (!name)
224 return -EPERM;
225
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226 /* Check that the subbuffer size is larger than a page. */
227 if (subbuf_size < PAGE_SIZE)
228 return -EINVAL;
229
230 /*
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231 * Make sure the number of subbuffers and subbuffer size are
232 * power of 2, and nonzero.
852c2936 233 */
12bcbbdb 234 if (!subbuf_size || (subbuf_size & (subbuf_size - 1)))
e52b0723 235 return -EINVAL;
12bcbbdb 236 if (!num_subbuf || (num_subbuf & (num_subbuf - 1)))
e52b0723 237 return -EINVAL;
3d8e9399
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238 /*
239 * Overwrite mode buffers require at least 2 subbuffers per
240 * buffer.
241 */
242 if (config->mode == RING_BUFFER_OVERWRITE && num_subbuf < 2)
243 return -EINVAL;
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244
245 ret = subbuffer_id_check_index(config, num_subbuf);
246 if (ret)
247 return ret;
248
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249 chanb->buf_size = num_subbuf * subbuf_size;
250 chanb->subbuf_size = subbuf_size;
251 chanb->buf_size_order = get_count_order(chanb->buf_size);
252 chanb->subbuf_size_order = get_count_order(subbuf_size);
253 chanb->num_subbuf_order = get_count_order(num_subbuf);
254 chanb->extra_reader_sb =
255 (config->mode == RING_BUFFER_OVERWRITE) ? 1 : 0;
256 chanb->num_subbuf = num_subbuf;
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257 strncpy(chanb->name, name, NAME_MAX);
258 chanb->name[NAME_MAX - 1] = '\0';
193183fb 259 memcpy(&chanb->config, config, sizeof(*config));
852c2936 260
1d498196 261 /* Per-cpu buffer size: control (prior to backend) */
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262 shmsize = offset_align(shmsize, __alignof__(struct lttng_ust_lib_ring_buffer));
263 shmsize += sizeof(struct lttng_ust_lib_ring_buffer);
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264
265 /* Per-cpu buffer size: backend */
266 /* num_subbuf + 1 is the worse case */
267 num_subbuf_alloc = num_subbuf + 1;
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268 shmsize += offset_align(shmsize, __alignof__(struct lttng_ust_lib_ring_buffer_backend_pages_shmp));
269 shmsize += sizeof(struct lttng_ust_lib_ring_buffer_backend_pages_shmp) * num_subbuf_alloc;
6c1f7d8b 270 shmsize += offset_align(shmsize, PAGE_SIZE);
1d498196 271 shmsize += subbuf_size * num_subbuf_alloc;
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272 shmsize += offset_align(shmsize, __alignof__(struct lttng_ust_lib_ring_buffer_backend_pages));
273 shmsize += sizeof(struct lttng_ust_lib_ring_buffer_backend_pages) * num_subbuf_alloc;
274 shmsize += offset_align(shmsize, __alignof__(struct lttng_ust_lib_ring_buffer_backend_subbuffer));
275 shmsize += sizeof(struct lttng_ust_lib_ring_buffer_backend_subbuffer) * num_subbuf;
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276 /* Per-cpu buffer size: control (after backend) */
277 shmsize += offset_align(shmsize, __alignof__(struct commit_counters_hot));
278 shmsize += sizeof(struct commit_counters_hot) * num_subbuf;
279 shmsize += offset_align(shmsize, __alignof__(struct commit_counters_cold));
280 shmsize += sizeof(struct commit_counters_cold) * num_subbuf;
281
852c2936 282 if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
4cfec15c 283 struct lttng_ust_lib_ring_buffer *buf;
852c2936 284 /*
a6352fd4 285 * We need to allocate for all possible cpus.
852c2936 286 */
852c2936 287 for_each_possible_cpu(i) {
1d498196 288 struct shm_object *shmobj;
5ea386c3 289
74d81a6c 290 shmobj = shm_object_table_alloc(handle->table, shmsize,
5ea386c3 291 SHM_OBJECT_SHM, stream_fds[i]);
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292 if (!shmobj)
293 goto end;
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294 align_shm(shmobj, __alignof__(struct lttng_ust_lib_ring_buffer));
295 set_shmp(chanb->buf[i].shmp, zalloc_shm(shmobj, sizeof(struct lttng_ust_lib_ring_buffer)));
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296 buf = shmp(handle, chanb->buf[i].shmp);
297 if (!buf)
298 goto end;
5d61a504 299 set_shmp(buf->self, chanb->buf[i].shmp._ref);
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300 ret = lib_ring_buffer_create(buf, chanb, i,
301 handle, shmobj);
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302 if (ret)
303 goto free_bufs; /* cpu hotplug locked */
304 }
852c2936 305 } else {
1d498196 306 struct shm_object *shmobj;
4cfec15c 307 struct lttng_ust_lib_ring_buffer *buf;
a6352fd4 308
74d81a6c 309 shmobj = shm_object_table_alloc(handle->table, shmsize,
5ea386c3 310 SHM_OBJECT_SHM, stream_fds[0]);
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311 if (!shmobj)
312 goto end;
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313 align_shm(shmobj, __alignof__(struct lttng_ust_lib_ring_buffer));
314 set_shmp(chanb->buf[0].shmp, zalloc_shm(shmobj, sizeof(struct lttng_ust_lib_ring_buffer)));
1d498196 315 buf = shmp(handle, chanb->buf[0].shmp);
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316 if (!buf)
317 goto end;
cb14bae9 318 set_shmp(buf->self, chanb->buf[0].shmp._ref);
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319 ret = lib_ring_buffer_create(buf, chanb, -1,
320 handle, shmobj);
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321 if (ret)
322 goto free_bufs;
323 }
324 chanb->start_tsc = config->cb.ring_buffer_clock_read(chan);
325
326 return 0;
327
328free_bufs:
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329 /* We only free the buffer data upon shm teardown */
330end:
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331 return -ENOMEM;
332}
333
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334/**
335 * channel_backend_free - destroy the channel
336 * @chan: the channel
337 *
338 * Destroy all channel buffers and frees the channel.
339 */
1d498196 340void channel_backend_free(struct channel_backend *chanb,
38fae1d3 341 struct lttng_ust_shm_handle *handle)
852c2936 342{
45e9e699 343 /* SHM teardown takes care of everything */
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344}
345
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346/**
347 * lib_ring_buffer_read - read data from ring_buffer_buffer.
348 * @bufb : buffer backend
349 * @offset : offset within the buffer
350 * @dest : destination address
351 * @len : length to copy to destination
352 *
353 * Should be protected by get_subbuf/put_subbuf.
354 * Returns the length copied.
355 */
4cfec15c 356size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend *bufb, size_t offset,
38fae1d3 357 void *dest, size_t len, struct lttng_ust_shm_handle *handle)
852c2936 358{
1d498196 359 struct channel_backend *chanb = &shmp(handle, bufb->chan)->backend;
4cfec15c 360 const struct lttng_ust_lib_ring_buffer_config *config = &chanb->config;
a6352fd4 361 ssize_t orig_len;
4cfec15c 362 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
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363 unsigned long sb_bindex, id;
364
365 orig_len = len;
366 offset &= chanb->buf_size - 1;
a6352fd4 367
b5a3dfa5 368 if (caa_unlikely(!len))
852c2936 369 return 0;
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370 id = bufb->buf_rsb.id;
371 sb_bindex = subbuffer_id_get_index(config, id);
4746ae29 372 rpages = shmp_index(handle, bufb->array, sb_bindex);
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373 /*
374 * Underlying layer should never ask for reads across
375 * subbuffers.
376 */
377 CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
378 CHAN_WARN_ON(chanb, config->mode == RING_BUFFER_OVERWRITE
379 && subbuffer_id_is_noref(config, id));
aead2025 380 memcpy(dest, shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & (chanb->subbuf_size - 1)), len);
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381 return orig_len;
382}
852c2936 383
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384/**
385 * lib_ring_buffer_read_cstr - read a C-style string from ring_buffer.
386 * @bufb : buffer backend
387 * @offset : offset within the buffer
388 * @dest : destination address
389 * @len : destination's length
390 *
0bf3c920 391 * Return string's length, or -EINVAL on error.
852c2936 392 * Should be protected by get_subbuf/put_subbuf.
0bf3c920 393 * Destination length should be at least 1 to hold '\0'.
852c2936 394 */
4cfec15c 395int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb, size_t offset,
38fae1d3 396 void *dest, size_t len, struct lttng_ust_shm_handle *handle)
852c2936 397{
1d498196 398 struct channel_backend *chanb = &shmp(handle, bufb->chan)->backend;
4cfec15c 399 const struct lttng_ust_lib_ring_buffer_config *config = &chanb->config;
a6352fd4 400 ssize_t string_len, orig_offset;
852c2936 401 char *str;
4cfec15c 402 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
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403 unsigned long sb_bindex, id;
404
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405 if (caa_unlikely(!len))
406 return -EINVAL;
852c2936 407 offset &= chanb->buf_size - 1;
852c2936 408 orig_offset = offset;
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409 id = bufb->buf_rsb.id;
410 sb_bindex = subbuffer_id_get_index(config, id);
4746ae29 411 rpages = shmp_index(handle, bufb->array, sb_bindex);
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412 /*
413 * Underlying layer should never ask for reads across
414 * subbuffers.
415 */
416 CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
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417 CHAN_WARN_ON(chanb, config->mode == RING_BUFFER_OVERWRITE
418 && subbuffer_id_is_noref(config, id));
aead2025 419 str = shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & (chanb->subbuf_size - 1));
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420 string_len = strnlen(str, len);
421 if (dest && len) {
422 memcpy(dest, str, string_len);
423 ((char *)dest)[0] = 0;
424 }
425 return offset - orig_offset;
852c2936 426}
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427
428/**
429 * lib_ring_buffer_read_offset_address - get address of a buffer location
430 * @bufb : buffer backend
431 * @offset : offset within the buffer.
432 *
433 * Return the address where a given offset is located (for read).
434 * Should be used to get the current subbuffer header pointer. Given we know
22b22ce9
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435 * it's never on a page boundary, it's safe to read/write directly
436 * from/to this address, as long as the read/write is never bigger than
437 * a page size.
852c2936 438 */
4cfec15c 439void *lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196 440 size_t offset,
38fae1d3 441 struct lttng_ust_shm_handle *handle)
852c2936 442{
4cfec15c 443 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
1d498196 444 struct channel_backend *chanb = &shmp(handle, bufb->chan)->backend;
4cfec15c 445 const struct lttng_ust_lib_ring_buffer_config *config = &chanb->config;
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446 unsigned long sb_bindex, id;
447
448 offset &= chanb->buf_size - 1;
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449 id = bufb->buf_rsb.id;
450 sb_bindex = subbuffer_id_get_index(config, id);
4746ae29 451 rpages = shmp_index(handle, bufb->array, sb_bindex);
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452 CHAN_WARN_ON(chanb, config->mode == RING_BUFFER_OVERWRITE
453 && subbuffer_id_is_noref(config, id));
aead2025 454 return shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & (chanb->subbuf_size - 1));
852c2936 455}
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456
457/**
458 * lib_ring_buffer_offset_address - get address of a location within the buffer
459 * @bufb : buffer backend
460 * @offset : offset within the buffer.
461 *
462 * Return the address where a given offset is located.
463 * Should be used to get the current subbuffer header pointer. Given we know
464 * it's always at the beginning of a page, it's safe to write directly to this
465 * address, as long as the write is never bigger than a page size.
466 */
4cfec15c 467void *lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196 468 size_t offset,
38fae1d3 469 struct lttng_ust_shm_handle *handle)
852c2936 470{
a6352fd4 471 size_t sbidx;
4cfec15c 472 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
1d498196 473 struct channel_backend *chanb = &shmp(handle, bufb->chan)->backend;
4cfec15c 474 const struct lttng_ust_lib_ring_buffer_config *config = &chanb->config;
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475 unsigned long sb_bindex, id;
476
477 offset &= chanb->buf_size - 1;
478 sbidx = offset >> chanb->subbuf_size_order;
4746ae29 479 id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
852c2936 480 sb_bindex = subbuffer_id_get_index(config, id);
4746ae29 481 rpages = shmp_index(handle, bufb->array, sb_bindex);
852c2936
MD
482 CHAN_WARN_ON(chanb, config->mode == RING_BUFFER_OVERWRITE
483 && subbuffer_id_is_noref(config, id));
aead2025 484 return shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & (chanb->subbuf_size - 1));
852c2936 485}
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