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e92f3e28 MD |
1 | #ifndef _LTTNG_RING_BUFFER_FRONTEND_API_H |
2 | #define _LTTNG_RING_BUFFER_FRONTEND_API_H | |
852c2936 MD |
3 | |
4 | /* | |
e92f3e28 | 5 | * libringbuffer/frontend_api.h |
852c2936 | 6 | * |
e92f3e28 MD |
7 | * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
8 | * | |
9 | * This library is free software; you can redistribute it and/or | |
10 | * modify it under the terms of the GNU Lesser General Public | |
11 | * License as published by the Free Software Foundation; only | |
12 | * version 2.1 of the License. | |
13 | * | |
14 | * This library is distributed in the hope that it will be useful, | |
15 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
17 | * Lesser General Public License for more details. | |
18 | * | |
19 | * You should have received a copy of the GNU Lesser General Public | |
20 | * License along with this library; if not, write to the Free Software | |
21 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA | |
852c2936 MD |
22 | * |
23 | * Ring Buffer Library Synchronization Header (buffer write API). | |
24 | * | |
25 | * Author: | |
e92f3e28 | 26 | * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
852c2936 | 27 | * |
e92f3e28 MD |
28 | * See ring_buffer_frontend.c for more information on wait-free |
29 | * algorithms. | |
30 | * See frontend.h for channel allocation and read-side API. | |
852c2936 MD |
31 | */ |
32 | ||
b4051ad8 FD |
33 | #include <stddef.h> |
34 | ||
9f3fdbc6 | 35 | #include <urcu/compiler.h> |
852c2936 | 36 | |
b4051ad8 FD |
37 | #include "frontend.h" |
38 | ||
852c2936 MD |
39 | /** |
40 | * lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit. | |
41 | * | |
36cb884c MD |
42 | * Keeps a ring buffer nesting count as supplementary safety net to |
43 | * ensure tracer client code will never trigger an endless recursion. | |
44 | * Returns the processor ID on success, -EPERM on failure (nesting count | |
45 | * too high). | |
852c2936 MD |
46 | * |
47 | * asm volatile and "memory" clobber prevent the compiler from moving | |
48 | * instructions out of the ring buffer nesting count. This is required to ensure | |
49 | * that probe side-effects which can cause recursion (e.g. unforeseen traps, | |
50 | * divisions by 0, ...) are triggered within the incremented nesting count | |
51 | * section. | |
52 | */ | |
53 | static inline | |
4cfec15c | 54 | int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config) |
852c2936 MD |
55 | { |
56 | int cpu, nesting; | |
57 | ||
2b2d6ff7 | 58 | cpu = lttng_ust_get_cpu(); |
8c90a710 | 59 | nesting = ++URCU_TLS(lib_ring_buffer_nesting); |
9f3fdbc6 | 60 | cmm_barrier(); |
852c2936 | 61 | |
b5a3dfa5 | 62 | if (caa_unlikely(nesting > 4)) { |
852c2936 | 63 | WARN_ON_ONCE(1); |
8c90a710 | 64 | URCU_TLS(lib_ring_buffer_nesting)--; |
852c2936 MD |
65 | return -EPERM; |
66 | } else | |
67 | return cpu; | |
68 | } | |
69 | ||
70 | /** | |
71 | * lib_ring_buffer_put_cpu - Follows ring buffer reserve/commit. | |
72 | */ | |
73 | static inline | |
4cfec15c | 74 | void lib_ring_buffer_put_cpu(const struct lttng_ust_lib_ring_buffer_config *config) |
852c2936 | 75 | { |
9f3fdbc6 | 76 | cmm_barrier(); |
8c90a710 | 77 | URCU_TLS(lib_ring_buffer_nesting)--; /* TLS */ |
852c2936 MD |
78 | } |
79 | ||
80 | /* | |
81 | * lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not | |
82 | * part of the API per se. | |
83 | * | |
84 | * returns 0 if reserve ok, or 1 if the slow path must be taken. | |
85 | */ | |
86 | static inline | |
4cfec15c MD |
87 | int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
88 | struct lttng_ust_lib_ring_buffer_ctx *ctx, | |
e56bb47c | 89 | void *client_ctx, |
852c2936 MD |
90 | unsigned long *o_begin, unsigned long *o_end, |
91 | unsigned long *o_old, size_t *before_hdr_pad) | |
92 | { | |
93 | struct channel *chan = ctx->chan; | |
4cfec15c | 94 | struct lttng_ust_lib_ring_buffer *buf = ctx->buf; |
852c2936 MD |
95 | *o_begin = v_read(config, &buf->offset); |
96 | *o_old = *o_begin; | |
97 | ||
98 | ctx->tsc = lib_ring_buffer_clock_read(chan); | |
99 | if ((int64_t) ctx->tsc == -EIO) | |
100 | return 1; | |
101 | ||
102 | /* | |
103 | * Prefetch cacheline for read because we have to read the previous | |
104 | * commit counter to increment it and commit seq value to compare it to | |
105 | * the commit counter. | |
106 | */ | |
9f3fdbc6 | 107 | //prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]); |
852c2936 MD |
108 | |
109 | if (last_tsc_overflow(config, buf, ctx->tsc)) | |
110 | ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC; | |
111 | ||
b5a3dfa5 | 112 | if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0)) |
852c2936 MD |
113 | return 1; |
114 | ||
115 | ctx->slot_size = record_header_size(config, chan, *o_begin, | |
e56bb47c | 116 | before_hdr_pad, ctx, client_ctx); |
852c2936 MD |
117 | ctx->slot_size += |
118 | lib_ring_buffer_align(*o_begin + ctx->slot_size, | |
119 | ctx->largest_align) + ctx->data_size; | |
b5a3dfa5 | 120 | if (caa_unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size) |
852c2936 MD |
121 | > chan->backend.subbuf_size)) |
122 | return 1; | |
123 | ||
124 | /* | |
125 | * Record fits in the current buffer and we are not on a switch | |
126 | * boundary. It's safe to write. | |
127 | */ | |
128 | *o_end = *o_begin + ctx->slot_size; | |
1ad21f70 MD |
129 | |
130 | if (caa_unlikely((subbuf_offset(*o_end, chan)) == 0)) | |
131 | /* | |
132 | * The offset_end will fall at the very beginning of the next | |
133 | * subbuffer. | |
134 | */ | |
135 | return 1; | |
136 | ||
852c2936 MD |
137 | return 0; |
138 | } | |
139 | ||
140 | /** | |
141 | * lib_ring_buffer_reserve - Reserve space in a ring buffer. | |
142 | * @config: ring buffer instance configuration. | |
143 | * @ctx: ring buffer context. (input and output) Must be already initialized. | |
144 | * | |
145 | * Atomic wait-free slot reservation. The reserved space starts at the context | |
146 | * "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc". | |
147 | * | |
148 | * Return : | |
149 | * 0 on success. | |
150 | * -EAGAIN if channel is disabled. | |
151 | * -ENOSPC if event size is too large for packet. | |
152 | * -ENOBUFS if there is currently not enough space in buffer for the event. | |
153 | * -EIO if data cannot be written into the buffer for any other reason. | |
154 | */ | |
155 | ||
156 | static inline | |
4cfec15c | 157 | int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
e56bb47c MD |
158 | struct lttng_ust_lib_ring_buffer_ctx *ctx, |
159 | void *client_ctx) | |
852c2936 MD |
160 | { |
161 | struct channel *chan = ctx->chan; | |
38fae1d3 | 162 | struct lttng_ust_shm_handle *handle = ctx->handle; |
4cfec15c | 163 | struct lttng_ust_lib_ring_buffer *buf; |
852c2936 MD |
164 | unsigned long o_begin, o_end, o_old; |
165 | size_t before_hdr_pad = 0; | |
166 | ||
f52a5702 | 167 | if (caa_unlikely(uatomic_read(&chan->record_disabled))) |
852c2936 MD |
168 | return -EAGAIN; |
169 | ||
170 | if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) | |
1d498196 | 171 | buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp); |
852c2936 | 172 | else |
1d498196 | 173 | buf = shmp(handle, chan->backend.buf[0].shmp); |
15500a1b MD |
174 | if (caa_unlikely(!buf)) |
175 | return -EIO; | |
f52a5702 | 176 | if (caa_unlikely(uatomic_read(&buf->record_disabled))) |
852c2936 MD |
177 | return -EAGAIN; |
178 | ctx->buf = buf; | |
179 | ||
180 | /* | |
181 | * Perform retryable operations. | |
182 | */ | |
e56bb47c | 183 | if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, client_ctx, &o_begin, |
852c2936 MD |
184 | &o_end, &o_old, &before_hdr_pad))) |
185 | goto slow_path; | |
186 | ||
b5a3dfa5 | 187 | if (caa_unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end) |
852c2936 MD |
188 | != o_old)) |
189 | goto slow_path; | |
190 | ||
191 | /* | |
192 | * Atomically update last_tsc. This update races against concurrent | |
193 | * atomic updates, but the race will always cause supplementary full TSC | |
194 | * record headers, never the opposite (missing a full TSC record header | |
195 | * when it would be needed). | |
196 | */ | |
197 | save_last_tsc(config, ctx->buf, ctx->tsc); | |
198 | ||
199 | /* | |
200 | * Push the reader if necessary | |
201 | */ | |
202 | lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1); | |
203 | ||
204 | /* | |
205 | * Clear noref flag for this subbuffer. | |
206 | */ | |
207 | lib_ring_buffer_clear_noref(config, &ctx->buf->backend, | |
1d498196 | 208 | subbuf_index(o_end - 1, chan), handle); |
852c2936 MD |
209 | |
210 | ctx->pre_offset = o_begin; | |
211 | ctx->buf_offset = o_begin + before_hdr_pad; | |
212 | return 0; | |
213 | slow_path: | |
e56bb47c | 214 | return lib_ring_buffer_reserve_slow(ctx, client_ctx); |
852c2936 MD |
215 | } |
216 | ||
217 | /** | |
218 | * lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer. | |
219 | * @config: ring buffer instance configuration. | |
220 | * @buf: buffer | |
221 | * @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH) | |
222 | * | |
223 | * This operation is completely reentrant : can be called while tracing is | |
224 | * active with absolutely no lock held. | |
225 | * | |
226 | * Note, however, that as a v_cmpxchg is used for some atomic operations and | |
227 | * requires to be executed locally for per-CPU buffers, this function must be | |
228 | * called from the CPU which owns the buffer for a ACTIVE flush, with preemption | |
229 | * disabled, for RING_BUFFER_SYNC_PER_CPU configuration. | |
230 | */ | |
231 | static inline | |
4cfec15c MD |
232 | void lib_ring_buffer_switch(const struct lttng_ust_lib_ring_buffer_config *config, |
233 | struct lttng_ust_lib_ring_buffer *buf, enum switch_mode mode, | |
38fae1d3 | 234 | struct lttng_ust_shm_handle *handle) |
852c2936 | 235 | { |
1d498196 | 236 | lib_ring_buffer_switch_slow(buf, mode, handle); |
852c2936 MD |
237 | } |
238 | ||
239 | /* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */ | |
240 | ||
241 | /** | |
242 | * lib_ring_buffer_commit - Commit an record. | |
243 | * @config: ring buffer instance configuration. | |
244 | * @ctx: ring buffer context. (input arguments only) | |
245 | * | |
246 | * Atomic unordered slot commit. Increments the commit count in the | |
247 | * specified sub-buffer, and delivers it if necessary. | |
248 | */ | |
249 | static inline | |
4cfec15c MD |
250 | void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *config, |
251 | const struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 MD |
252 | { |
253 | struct channel *chan = ctx->chan; | |
38fae1d3 | 254 | struct lttng_ust_shm_handle *handle = ctx->handle; |
4cfec15c | 255 | struct lttng_ust_lib_ring_buffer *buf = ctx->buf; |
852c2936 MD |
256 | unsigned long offset_end = ctx->buf_offset; |
257 | unsigned long endidx = subbuf_index(offset_end - 1, chan); | |
258 | unsigned long commit_count; | |
d2fe4771 MD |
259 | struct commit_counters_hot *cc_hot = shmp_index(handle, |
260 | buf->commit_hot, endidx); | |
852c2936 | 261 | |
15500a1b MD |
262 | if (caa_unlikely(!cc_hot)) |
263 | return; | |
264 | ||
852c2936 MD |
265 | /* |
266 | * Must count record before incrementing the commit count. | |
267 | */ | |
15500a1b | 268 | subbuffer_count_record(config, ctx, &buf->backend, endidx, handle); |
852c2936 MD |
269 | |
270 | /* | |
271 | * Order all writes to buffer before the commit count update that will | |
272 | * determine that the subbuffer is full. | |
273 | */ | |
9f3fdbc6 | 274 | cmm_smp_wmb(); |
852c2936 | 275 | |
d2fe4771 | 276 | v_add(config, ctx->slot_size, &cc_hot->cc); |
852c2936 MD |
277 | |
278 | /* | |
279 | * commit count read can race with concurrent OOO commit count updates. | |
280 | * This is only needed for lib_ring_buffer_check_deliver (for | |
281 | * non-polling delivery only) and for | |
282 | * lib_ring_buffer_write_commit_counter. The race can only cause the | |
283 | * counter to be read with the same value more than once, which could | |
284 | * cause : | |
285 | * - Multiple delivery for the same sub-buffer (which is handled | |
286 | * gracefully by the reader code) if the value is for a full | |
287 | * sub-buffer. It's important that we can never miss a sub-buffer | |
288 | * delivery. Re-reading the value after the v_add ensures this. | |
289 | * - Reading a commit_count with a higher value that what was actually | |
290 | * added to it for the lib_ring_buffer_write_commit_counter call | |
291 | * (again caused by a concurrent committer). It does not matter, | |
292 | * because this function is interested in the fact that the commit | |
293 | * count reaches back the reserve offset for a specific sub-buffer, | |
294 | * which is completely independent of the order. | |
295 | */ | |
d2fe4771 | 296 | commit_count = v_read(config, &cc_hot->cc); |
852c2936 MD |
297 | |
298 | lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1, | |
1b7b0501 | 299 | commit_count, endidx, handle, ctx->tsc); |
852c2936 MD |
300 | /* |
301 | * Update used size at each commit. It's needed only for extracting | |
302 | * ring_buffer buffers from vmcore, after crash. | |
303 | */ | |
d2fe4771 MD |
304 | lib_ring_buffer_write_commit_counter(config, buf, chan, |
305 | offset_end, commit_count, handle, cc_hot); | |
852c2936 MD |
306 | } |
307 | ||
308 | /** | |
309 | * lib_ring_buffer_try_discard_reserve - Try discarding a record. | |
310 | * @config: ring buffer instance configuration. | |
311 | * @ctx: ring buffer context. (input arguments only) | |
312 | * | |
313 | * Only succeeds if no other record has been written after the record to | |
314 | * discard. If discard fails, the record must be committed to the buffer. | |
315 | * | |
316 | * Returns 0 upon success, -EPERM if the record cannot be discarded. | |
317 | */ | |
318 | static inline | |
4cfec15c MD |
319 | int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
320 | const struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 | 321 | { |
4cfec15c | 322 | struct lttng_ust_lib_ring_buffer *buf = ctx->buf; |
852c2936 MD |
323 | unsigned long end_offset = ctx->pre_offset + ctx->slot_size; |
324 | ||
325 | /* | |
326 | * We need to ensure that if the cmpxchg succeeds and discards the | |
327 | * record, the next record will record a full TSC, because it cannot | |
328 | * rely on the last_tsc associated with the discarded record to detect | |
329 | * overflows. The only way to ensure this is to set the last_tsc to 0 | |
330 | * (assuming no 64-bit TSC overflow), which forces to write a 64-bit | |
331 | * timestamp in the next record. | |
332 | * | |
333 | * Note: if discard fails, we must leave the TSC in the record header. | |
334 | * It is needed to keep track of TSC overflows for the following | |
335 | * records. | |
336 | */ | |
337 | save_last_tsc(config, buf, 0ULL); | |
338 | ||
b5a3dfa5 | 339 | if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset) |
852c2936 MD |
340 | != end_offset)) |
341 | return -EPERM; | |
342 | else | |
343 | return 0; | |
344 | } | |
345 | ||
346 | static inline | |
4cfec15c | 347 | void channel_record_disable(const struct lttng_ust_lib_ring_buffer_config *config, |
852c2936 MD |
348 | struct channel *chan) |
349 | { | |
9f3fdbc6 | 350 | uatomic_inc(&chan->record_disabled); |
852c2936 MD |
351 | } |
352 | ||
353 | static inline | |
4cfec15c | 354 | void channel_record_enable(const struct lttng_ust_lib_ring_buffer_config *config, |
852c2936 MD |
355 | struct channel *chan) |
356 | { | |
9f3fdbc6 | 357 | uatomic_dec(&chan->record_disabled); |
852c2936 MD |
358 | } |
359 | ||
360 | static inline | |
4cfec15c MD |
361 | void lib_ring_buffer_record_disable(const struct lttng_ust_lib_ring_buffer_config *config, |
362 | struct lttng_ust_lib_ring_buffer *buf) | |
852c2936 | 363 | { |
9f3fdbc6 | 364 | uatomic_inc(&buf->record_disabled); |
852c2936 MD |
365 | } |
366 | ||
367 | static inline | |
4cfec15c MD |
368 | void lib_ring_buffer_record_enable(const struct lttng_ust_lib_ring_buffer_config *config, |
369 | struct lttng_ust_lib_ring_buffer *buf) | |
852c2936 | 370 | { |
9f3fdbc6 | 371 | uatomic_dec(&buf->record_disabled); |
852c2936 MD |
372 | } |
373 | ||
e92f3e28 | 374 | #endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */ |