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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 | ||
4931a13e | 33 | #include "frontend.h" |
9f3fdbc6 MD |
34 | #include <urcu-bp.h> |
35 | #include <urcu/compiler.h> | |
852c2936 MD |
36 | |
37 | /** | |
38 | * lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit. | |
39 | * | |
9f3fdbc6 MD |
40 | * Grabs RCU read-side lock and keeps a ring buffer nesting count as |
41 | * supplementary safety net to ensure tracer client code will never | |
42 | * trigger an endless recursion. Returns the processor ID on success, | |
43 | * -EPERM on failure (nesting count too high). | |
852c2936 MD |
44 | * |
45 | * asm volatile and "memory" clobber prevent the compiler from moving | |
46 | * instructions out of the ring buffer nesting count. This is required to ensure | |
47 | * that probe side-effects which can cause recursion (e.g. unforeseen traps, | |
48 | * divisions by 0, ...) are triggered within the incremented nesting count | |
49 | * section. | |
50 | */ | |
51 | static inline | |
4cfec15c | 52 | int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config) |
852c2936 MD |
53 | { |
54 | int cpu, nesting; | |
55 | ||
9f3fdbc6 | 56 | rcu_read_lock(); |
2b2d6ff7 | 57 | cpu = lttng_ust_get_cpu(); |
8c90a710 | 58 | nesting = ++URCU_TLS(lib_ring_buffer_nesting); |
9f3fdbc6 | 59 | cmm_barrier(); |
852c2936 | 60 | |
b5a3dfa5 | 61 | if (caa_unlikely(nesting > 4)) { |
852c2936 | 62 | WARN_ON_ONCE(1); |
8c90a710 | 63 | URCU_TLS(lib_ring_buffer_nesting)--; |
9f3fdbc6 | 64 | rcu_read_unlock(); |
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 */ |
9f3fdbc6 | 78 | rcu_read_unlock(); |
852c2936 MD |
79 | } |
80 | ||
81 | /* | |
82 | * lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not | |
83 | * part of the API per se. | |
84 | * | |
85 | * returns 0 if reserve ok, or 1 if the slow path must be taken. | |
86 | */ | |
87 | static inline | |
4cfec15c MD |
88 | int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
89 | struct lttng_ust_lib_ring_buffer_ctx *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, | |
116 | before_hdr_pad, ctx); | |
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; | |
852c2936 MD |
129 | return 0; |
130 | } | |
131 | ||
132 | /** | |
133 | * lib_ring_buffer_reserve - Reserve space in a ring buffer. | |
134 | * @config: ring buffer instance configuration. | |
135 | * @ctx: ring buffer context. (input and output) Must be already initialized. | |
136 | * | |
137 | * Atomic wait-free slot reservation. The reserved space starts at the context | |
138 | * "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc". | |
139 | * | |
140 | * Return : | |
141 | * 0 on success. | |
142 | * -EAGAIN if channel is disabled. | |
143 | * -ENOSPC if event size is too large for packet. | |
144 | * -ENOBUFS if there is currently not enough space in buffer for the event. | |
145 | * -EIO if data cannot be written into the buffer for any other reason. | |
146 | */ | |
147 | ||
148 | static inline | |
4cfec15c MD |
149 | int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
150 | struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 MD |
151 | { |
152 | struct channel *chan = ctx->chan; | |
38fae1d3 | 153 | struct lttng_ust_shm_handle *handle = ctx->handle; |
4cfec15c | 154 | struct lttng_ust_lib_ring_buffer *buf; |
852c2936 MD |
155 | unsigned long o_begin, o_end, o_old; |
156 | size_t before_hdr_pad = 0; | |
157 | ||
9f3fdbc6 | 158 | if (uatomic_read(&chan->record_disabled)) |
852c2936 MD |
159 | return -EAGAIN; |
160 | ||
161 | if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) | |
1d498196 | 162 | buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp); |
852c2936 | 163 | else |
1d498196 | 164 | buf = shmp(handle, chan->backend.buf[0].shmp); |
9f3fdbc6 | 165 | if (uatomic_read(&buf->record_disabled)) |
852c2936 MD |
166 | return -EAGAIN; |
167 | ctx->buf = buf; | |
168 | ||
169 | /* | |
170 | * Perform retryable operations. | |
171 | */ | |
b5a3dfa5 | 172 | if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, &o_begin, |
852c2936 MD |
173 | &o_end, &o_old, &before_hdr_pad))) |
174 | goto slow_path; | |
175 | ||
b5a3dfa5 | 176 | if (caa_unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end) |
852c2936 MD |
177 | != o_old)) |
178 | goto slow_path; | |
179 | ||
180 | /* | |
181 | * Atomically update last_tsc. This update races against concurrent | |
182 | * atomic updates, but the race will always cause supplementary full TSC | |
183 | * record headers, never the opposite (missing a full TSC record header | |
184 | * when it would be needed). | |
185 | */ | |
186 | save_last_tsc(config, ctx->buf, ctx->tsc); | |
187 | ||
188 | /* | |
189 | * Push the reader if necessary | |
190 | */ | |
191 | lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1); | |
192 | ||
193 | /* | |
194 | * Clear noref flag for this subbuffer. | |
195 | */ | |
196 | lib_ring_buffer_clear_noref(config, &ctx->buf->backend, | |
1d498196 | 197 | subbuf_index(o_end - 1, chan), handle); |
852c2936 MD |
198 | |
199 | ctx->pre_offset = o_begin; | |
200 | ctx->buf_offset = o_begin + before_hdr_pad; | |
201 | return 0; | |
202 | slow_path: | |
203 | return lib_ring_buffer_reserve_slow(ctx); | |
204 | } | |
205 | ||
206 | /** | |
207 | * lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer. | |
208 | * @config: ring buffer instance configuration. | |
209 | * @buf: buffer | |
210 | * @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH) | |
211 | * | |
212 | * This operation is completely reentrant : can be called while tracing is | |
213 | * active with absolutely no lock held. | |
214 | * | |
215 | * Note, however, that as a v_cmpxchg is used for some atomic operations and | |
216 | * requires to be executed locally for per-CPU buffers, this function must be | |
217 | * called from the CPU which owns the buffer for a ACTIVE flush, with preemption | |
218 | * disabled, for RING_BUFFER_SYNC_PER_CPU configuration. | |
219 | */ | |
220 | static inline | |
4cfec15c MD |
221 | void lib_ring_buffer_switch(const struct lttng_ust_lib_ring_buffer_config *config, |
222 | struct lttng_ust_lib_ring_buffer *buf, enum switch_mode mode, | |
38fae1d3 | 223 | struct lttng_ust_shm_handle *handle) |
852c2936 | 224 | { |
1d498196 | 225 | lib_ring_buffer_switch_slow(buf, mode, handle); |
852c2936 MD |
226 | } |
227 | ||
228 | /* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */ | |
229 | ||
230 | /** | |
231 | * lib_ring_buffer_commit - Commit an record. | |
232 | * @config: ring buffer instance configuration. | |
233 | * @ctx: ring buffer context. (input arguments only) | |
234 | * | |
235 | * Atomic unordered slot commit. Increments the commit count in the | |
236 | * specified sub-buffer, and delivers it if necessary. | |
237 | */ | |
238 | static inline | |
4cfec15c MD |
239 | void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *config, |
240 | const struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 MD |
241 | { |
242 | struct channel *chan = ctx->chan; | |
38fae1d3 | 243 | struct lttng_ust_shm_handle *handle = ctx->handle; |
4cfec15c | 244 | struct lttng_ust_lib_ring_buffer *buf = ctx->buf; |
852c2936 MD |
245 | unsigned long offset_end = ctx->buf_offset; |
246 | unsigned long endidx = subbuf_index(offset_end - 1, chan); | |
247 | unsigned long commit_count; | |
248 | ||
249 | /* | |
250 | * Must count record before incrementing the commit count. | |
251 | */ | |
1d498196 | 252 | subbuffer_count_record(config, &buf->backend, endidx, handle); |
852c2936 MD |
253 | |
254 | /* | |
255 | * Order all writes to buffer before the commit count update that will | |
256 | * determine that the subbuffer is full. | |
257 | */ | |
9f3fdbc6 | 258 | cmm_smp_wmb(); |
852c2936 | 259 | |
4746ae29 | 260 | v_add(config, ctx->slot_size, &shmp_index(handle, buf->commit_hot, endidx)->cc); |
852c2936 MD |
261 | |
262 | /* | |
263 | * commit count read can race with concurrent OOO commit count updates. | |
264 | * This is only needed for lib_ring_buffer_check_deliver (for | |
265 | * non-polling delivery only) and for | |
266 | * lib_ring_buffer_write_commit_counter. The race can only cause the | |
267 | * counter to be read with the same value more than once, which could | |
268 | * cause : | |
269 | * - Multiple delivery for the same sub-buffer (which is handled | |
270 | * gracefully by the reader code) if the value is for a full | |
271 | * sub-buffer. It's important that we can never miss a sub-buffer | |
272 | * delivery. Re-reading the value after the v_add ensures this. | |
273 | * - Reading a commit_count with a higher value that what was actually | |
274 | * added to it for the lib_ring_buffer_write_commit_counter call | |
275 | * (again caused by a concurrent committer). It does not matter, | |
276 | * because this function is interested in the fact that the commit | |
277 | * count reaches back the reserve offset for a specific sub-buffer, | |
278 | * which is completely independent of the order. | |
279 | */ | |
4746ae29 | 280 | commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, endidx)->cc); |
852c2936 MD |
281 | |
282 | lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1, | |
1d498196 | 283 | commit_count, endidx, handle); |
852c2936 MD |
284 | /* |
285 | * Update used size at each commit. It's needed only for extracting | |
286 | * ring_buffer buffers from vmcore, after crash. | |
287 | */ | |
288 | lib_ring_buffer_write_commit_counter(config, buf, chan, endidx, | |
289 | ctx->buf_offset, commit_count, | |
1d498196 | 290 | ctx->slot_size, handle); |
852c2936 MD |
291 | } |
292 | ||
293 | /** | |
294 | * lib_ring_buffer_try_discard_reserve - Try discarding a record. | |
295 | * @config: ring buffer instance configuration. | |
296 | * @ctx: ring buffer context. (input arguments only) | |
297 | * | |
298 | * Only succeeds if no other record has been written after the record to | |
299 | * discard. If discard fails, the record must be committed to the buffer. | |
300 | * | |
301 | * Returns 0 upon success, -EPERM if the record cannot be discarded. | |
302 | */ | |
303 | static inline | |
4cfec15c MD |
304 | int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_lib_ring_buffer_config *config, |
305 | const struct lttng_ust_lib_ring_buffer_ctx *ctx) | |
852c2936 | 306 | { |
4cfec15c | 307 | struct lttng_ust_lib_ring_buffer *buf = ctx->buf; |
852c2936 MD |
308 | unsigned long end_offset = ctx->pre_offset + ctx->slot_size; |
309 | ||
310 | /* | |
311 | * We need to ensure that if the cmpxchg succeeds and discards the | |
312 | * record, the next record will record a full TSC, because it cannot | |
313 | * rely on the last_tsc associated with the discarded record to detect | |
314 | * overflows. The only way to ensure this is to set the last_tsc to 0 | |
315 | * (assuming no 64-bit TSC overflow), which forces to write a 64-bit | |
316 | * timestamp in the next record. | |
317 | * | |
318 | * Note: if discard fails, we must leave the TSC in the record header. | |
319 | * It is needed to keep track of TSC overflows for the following | |
320 | * records. | |
321 | */ | |
322 | save_last_tsc(config, buf, 0ULL); | |
323 | ||
b5a3dfa5 | 324 | if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset) |
852c2936 MD |
325 | != end_offset)) |
326 | return -EPERM; | |
327 | else | |
328 | return 0; | |
329 | } | |
330 | ||
331 | static inline | |
4cfec15c | 332 | void channel_record_disable(const struct lttng_ust_lib_ring_buffer_config *config, |
852c2936 MD |
333 | struct channel *chan) |
334 | { | |
9f3fdbc6 | 335 | uatomic_inc(&chan->record_disabled); |
852c2936 MD |
336 | } |
337 | ||
338 | static inline | |
4cfec15c | 339 | void channel_record_enable(const struct lttng_ust_lib_ring_buffer_config *config, |
852c2936 MD |
340 | struct channel *chan) |
341 | { | |
9f3fdbc6 | 342 | uatomic_dec(&chan->record_disabled); |
852c2936 MD |
343 | } |
344 | ||
345 | static inline | |
4cfec15c MD |
346 | void lib_ring_buffer_record_disable(const struct lttng_ust_lib_ring_buffer_config *config, |
347 | struct lttng_ust_lib_ring_buffer *buf) | |
852c2936 | 348 | { |
9f3fdbc6 | 349 | uatomic_inc(&buf->record_disabled); |
852c2936 MD |
350 | } |
351 | ||
352 | static inline | |
4cfec15c MD |
353 | void lib_ring_buffer_record_enable(const struct lttng_ust_lib_ring_buffer_config *config, |
354 | struct lttng_ust_lib_ring_buffer *buf) | |
852c2936 | 355 | { |
9f3fdbc6 | 356 | uatomic_dec(&buf->record_disabled); |
852c2936 MD |
357 | } |
358 | ||
e92f3e28 | 359 | #endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */ |