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852c2936 | 1 | /* |
c0c0989a | 2 | * SPDX-License-Identifier: LGPL-2.1-only |
852c2936 | 3 | * |
e92f3e28 MD |
4 | * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
5 | * | |
e92f3e28 MD |
6 | * See ring_buffer_frontend.c for more information on wait-free |
7 | * algorithms. | |
8 | * See frontend.h for channel allocation and read-side API. | |
852c2936 MD |
9 | */ |
10 | ||
c0c0989a MJ |
11 | #ifndef _LTTNG_RING_BUFFER_FRONTEND_API_H |
12 | #define _LTTNG_RING_BUFFER_FRONTEND_API_H | |
13 | ||
b4051ad8 FD |
14 | #include <stddef.h> |
15 | ||
9f3fdbc6 | 16 | #include <urcu/compiler.h> |
852c2936 | 17 | |
f73bcf5e | 18 | #include "common/getcpu.h" |
b4051ad8 FD |
19 | #include "frontend.h" |
20 | ||
852c2936 | 21 | /** |
7489fcb4 | 22 | * lib_ring_buffer_nesting_inc - Ring buffer recursive use protection. |
852c2936 | 23 | * |
7489fcb4 MD |
24 | * The rint buffer buffer nesting count is a safety net to ensure tracer |
25 | * client code will never trigger an endless recursion. | |
8936b6c0 MD |
26 | * Returns a nesting level >= 0 on success, -EPERM on failure (nesting |
27 | * count too high). | |
852c2936 | 28 | * |
742ac92a | 29 | * __asm__ __volatile__ and "memory" clobber prevent the compiler from moving |
852c2936 MD |
30 | * instructions out of the ring buffer nesting count. This is required to ensure |
31 | * that probe side-effects which can cause recursion (e.g. unforeseen traps, | |
32 | * divisions by 0, ...) are triggered within the incremented nesting count | |
33 | * section. | |
34 | */ | |
35 | static inline | |
2208d8b5 | 36 | int lib_ring_buffer_nesting_inc( |
b5457df5 | 37 | const struct lttng_ust_ring_buffer_config *config __attribute__((unused))) |
852c2936 | 38 | { |
7489fcb4 | 39 | int nesting; |
852c2936 | 40 | |
8c90a710 | 41 | nesting = ++URCU_TLS(lib_ring_buffer_nesting); |
9f3fdbc6 | 42 | cmm_barrier(); |
8936b6c0 | 43 | if (caa_unlikely(nesting >= LIB_RING_BUFFER_MAX_NESTING)) { |
852c2936 | 44 | WARN_ON_ONCE(1); |
8c90a710 | 45 | URCU_TLS(lib_ring_buffer_nesting)--; |
852c2936 | 46 | return -EPERM; |
7489fcb4 | 47 | } |
8936b6c0 MD |
48 | return nesting - 1; |
49 | } | |
50 | ||
51 | static inline | |
2208d8b5 | 52 | int lib_ring_buffer_nesting_count( |
b5457df5 | 53 | const struct lttng_ust_ring_buffer_config *config __attribute__((unused))) |
8936b6c0 MD |
54 | { |
55 | return URCU_TLS(lib_ring_buffer_nesting); | |
852c2936 MD |
56 | } |
57 | ||
852c2936 | 58 | static inline |
2208d8b5 | 59 | void lib_ring_buffer_nesting_dec( |
b5457df5 | 60 | const struct lttng_ust_ring_buffer_config *config __attribute__((unused))) |
852c2936 | 61 | { |
9f3fdbc6 | 62 | cmm_barrier(); |
8c90a710 | 63 | URCU_TLS(lib_ring_buffer_nesting)--; /* TLS */ |
852c2936 MD |
64 | } |
65 | ||
66 | /* | |
67 | * lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not | |
68 | * part of the API per se. | |
69 | * | |
70 | * returns 0 if reserve ok, or 1 if the slow path must be taken. | |
71 | */ | |
72 | static inline | |
b5457df5 MD |
73 | int lib_ring_buffer_try_reserve(const struct lttng_ust_ring_buffer_config *config, |
74 | struct lttng_ust_ring_buffer_ctx *ctx, | |
e56bb47c | 75 | void *client_ctx, |
852c2936 MD |
76 | unsigned long *o_begin, unsigned long *o_end, |
77 | unsigned long *o_old, size_t *before_hdr_pad) | |
78 | { | |
b5457df5 MD |
79 | struct lttng_ust_ring_buffer_ctx_private *ctx_private = ctx->priv; |
80 | struct lttng_ust_ring_buffer_channel *chan = ctx_private->chan; | |
81 | struct lttng_ust_ring_buffer *buf = ctx_private->buf; | |
852c2936 MD |
82 | *o_begin = v_read(config, &buf->offset); |
83 | *o_old = *o_begin; | |
84 | ||
373ea80a MD |
85 | ctx_private->timestamp = lib_ring_buffer_clock_read(chan); |
86 | if ((int64_t) ctx_private->timestamp == -EIO) | |
852c2936 MD |
87 | return 1; |
88 | ||
89 | /* | |
90 | * Prefetch cacheline for read because we have to read the previous | |
91 | * commit counter to increment it and commit seq value to compare it to | |
92 | * the commit counter. | |
93 | */ | |
9f3fdbc6 | 94 | //prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]); |
852c2936 | 95 | |
373ea80a MD |
96 | if (last_timestamp_overflow(config, buf, ctx_private->timestamp)) |
97 | ctx_private->rflags |= RING_BUFFER_RFLAG_FULL_TIMESTAMP; | |
852c2936 | 98 | |
b5a3dfa5 | 99 | if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0)) |
852c2936 MD |
100 | return 1; |
101 | ||
8936b6c0 | 102 | ctx_private->slot_size = record_header_size(config, chan, *o_begin, |
e56bb47c | 103 | before_hdr_pad, ctx, client_ctx); |
8936b6c0 | 104 | ctx_private->slot_size += |
b5457df5 | 105 | lttng_ust_ring_buffer_align(*o_begin + ctx_private->slot_size, |
852c2936 | 106 | ctx->largest_align) + ctx->data_size; |
8936b6c0 | 107 | if (caa_unlikely((subbuf_offset(*o_begin, chan) + ctx_private->slot_size) |
852c2936 MD |
108 | > chan->backend.subbuf_size)) |
109 | return 1; | |
110 | ||
111 | /* | |
112 | * Record fits in the current buffer and we are not on a switch | |
113 | * boundary. It's safe to write. | |
114 | */ | |
8936b6c0 | 115 | *o_end = *o_begin + ctx_private->slot_size; |
1ad21f70 MD |
116 | |
117 | if (caa_unlikely((subbuf_offset(*o_end, chan)) == 0)) | |
118 | /* | |
119 | * The offset_end will fall at the very beginning of the next | |
120 | * subbuffer. | |
121 | */ | |
122 | return 1; | |
123 | ||
852c2936 MD |
124 | return 0; |
125 | } | |
126 | ||
127 | /** | |
128 | * lib_ring_buffer_reserve - Reserve space in a ring buffer. | |
129 | * @config: ring buffer instance configuration. | |
130 | * @ctx: ring buffer context. (input and output) Must be already initialized. | |
131 | * | |
132 | * Atomic wait-free slot reservation. The reserved space starts at the context | |
373ea80a MD |
133 | * "pre_offset". Its length is "slot_size". The associated time-stamp is |
134 | * "timestamp". | |
852c2936 MD |
135 | * |
136 | * Return : | |
137 | * 0 on success. | |
138 | * -EAGAIN if channel is disabled. | |
139 | * -ENOSPC if event size is too large for packet. | |
140 | * -ENOBUFS if there is currently not enough space in buffer for the event. | |
141 | * -EIO if data cannot be written into the buffer for any other reason. | |
142 | */ | |
143 | ||
144 | static inline | |
b5457df5 MD |
145 | int lib_ring_buffer_reserve(const struct lttng_ust_ring_buffer_config *config, |
146 | struct lttng_ust_ring_buffer_ctx *ctx, | |
e56bb47c | 147 | void *client_ctx) |
852c2936 | 148 | { |
b5457df5 MD |
149 | struct lttng_ust_ring_buffer_ctx_private *ctx_private = ctx->priv; |
150 | struct lttng_ust_ring_buffer_channel *chan = ctx_private->chan; | |
8936b6c0 | 151 | struct lttng_ust_shm_handle *handle = chan->handle; |
b5457df5 | 152 | struct lttng_ust_ring_buffer *buf; |
852c2936 MD |
153 | unsigned long o_begin, o_end, o_old; |
154 | size_t before_hdr_pad = 0; | |
155 | ||
f52a5702 | 156 | if (caa_unlikely(uatomic_read(&chan->record_disabled))) |
852c2936 MD |
157 | return -EAGAIN; |
158 | ||
7489fcb4 | 159 | if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) { |
8936b6c0 MD |
160 | ctx_private->reserve_cpu = lttng_ust_get_cpu(); |
161 | buf = shmp(handle, chan->backend.buf[ctx_private->reserve_cpu].shmp); | |
7489fcb4 | 162 | } else { |
1d498196 | 163 | buf = shmp(handle, chan->backend.buf[0].shmp); |
7489fcb4 | 164 | } |
15500a1b MD |
165 | if (caa_unlikely(!buf)) |
166 | return -EIO; | |
f52a5702 | 167 | if (caa_unlikely(uatomic_read(&buf->record_disabled))) |
852c2936 | 168 | return -EAGAIN; |
8936b6c0 | 169 | ctx_private->buf = buf; |
852c2936 MD |
170 | |
171 | /* | |
172 | * Perform retryable operations. | |
173 | */ | |
e56bb47c | 174 | if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, client_ctx, &o_begin, |
852c2936 MD |
175 | &o_end, &o_old, &before_hdr_pad))) |
176 | goto slow_path; | |
177 | ||
8936b6c0 | 178 | if (caa_unlikely(v_cmpxchg(config, &buf->offset, o_old, o_end) |
852c2936 MD |
179 | != o_old)) |
180 | goto slow_path; | |
181 | ||
182 | /* | |
373ea80a MD |
183 | * Atomically update last_timestamp. This update races against concurrent |
184 | * atomic updates, but the race will always cause supplementary full | |
185 | * timestamp record headers, never the opposite (missing a full | |
186 | * timestamp record header when it would be needed). | |
852c2936 | 187 | */ |
373ea80a | 188 | save_last_timestamp(config, buf, ctx_private->timestamp); |
852c2936 MD |
189 | |
190 | /* | |
191 | * Push the reader if necessary | |
192 | */ | |
8936b6c0 | 193 | lib_ring_buffer_reserve_push_reader(buf, chan, o_end - 1); |
852c2936 MD |
194 | |
195 | /* | |
196 | * Clear noref flag for this subbuffer. | |
197 | */ | |
8936b6c0 | 198 | lib_ring_buffer_clear_noref(config, &buf->backend, |
1d498196 | 199 | subbuf_index(o_end - 1, chan), handle); |
852c2936 | 200 | |
8936b6c0 MD |
201 | ctx_private->pre_offset = o_begin; |
202 | ctx_private->buf_offset = o_begin + before_hdr_pad; | |
852c2936 MD |
203 | return 0; |
204 | slow_path: | |
e56bb47c | 205 | return lib_ring_buffer_reserve_slow(ctx, client_ctx); |
852c2936 MD |
206 | } |
207 | ||
208 | /** | |
209 | * lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer. | |
210 | * @config: ring buffer instance configuration. | |
211 | * @buf: buffer | |
212 | * @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH) | |
213 | * | |
214 | * This operation is completely reentrant : can be called while tracing is | |
215 | * active with absolutely no lock held. | |
216 | * | |
217 | * Note, however, that as a v_cmpxchg is used for some atomic operations and | |
218 | * requires to be executed locally for per-CPU buffers, this function must be | |
219 | * called from the CPU which owns the buffer for a ACTIVE flush, with preemption | |
220 | * disabled, for RING_BUFFER_SYNC_PER_CPU configuration. | |
221 | */ | |
222 | static inline | |
2208d8b5 | 223 | void lib_ring_buffer_switch( |
b5457df5 MD |
224 | const struct lttng_ust_ring_buffer_config *config __attribute__((unused)), |
225 | struct lttng_ust_ring_buffer *buf, enum switch_mode mode, | |
2208d8b5 | 226 | struct lttng_ust_shm_handle *handle) |
852c2936 | 227 | { |
1d498196 | 228 | lib_ring_buffer_switch_slow(buf, mode, handle); |
852c2936 MD |
229 | } |
230 | ||
231 | /* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */ | |
232 | ||
233 | /** | |
234 | * lib_ring_buffer_commit - Commit an record. | |
235 | * @config: ring buffer instance configuration. | |
236 | * @ctx: ring buffer context. (input arguments only) | |
237 | * | |
238 | * Atomic unordered slot commit. Increments the commit count in the | |
239 | * specified sub-buffer, and delivers it if necessary. | |
240 | */ | |
241 | static inline | |
b5457df5 MD |
242 | void lib_ring_buffer_commit(const struct lttng_ust_ring_buffer_config *config, |
243 | const struct lttng_ust_ring_buffer_ctx *ctx) | |
852c2936 | 244 | { |
b5457df5 MD |
245 | struct lttng_ust_ring_buffer_ctx_private *ctx_private = ctx->priv; |
246 | struct lttng_ust_ring_buffer_channel *chan = ctx_private->chan; | |
8936b6c0 | 247 | struct lttng_ust_shm_handle *handle = chan->handle; |
b5457df5 | 248 | struct lttng_ust_ring_buffer *buf = ctx_private->buf; |
8936b6c0 | 249 | unsigned long offset_end = ctx_private->buf_offset; |
852c2936 MD |
250 | unsigned long endidx = subbuf_index(offset_end - 1, chan); |
251 | unsigned long commit_count; | |
d2fe4771 MD |
252 | struct commit_counters_hot *cc_hot = shmp_index(handle, |
253 | buf->commit_hot, endidx); | |
852c2936 | 254 | |
15500a1b MD |
255 | if (caa_unlikely(!cc_hot)) |
256 | return; | |
257 | ||
852c2936 MD |
258 | /* |
259 | * Must count record before incrementing the commit count. | |
260 | */ | |
bee7cf75 | 261 | subbuffer_count_record(config, ctx); |
852c2936 MD |
262 | |
263 | /* | |
264 | * Order all writes to buffer before the commit count update that will | |
265 | * determine that the subbuffer is full. | |
266 | */ | |
9f3fdbc6 | 267 | cmm_smp_wmb(); |
852c2936 | 268 | |
8936b6c0 | 269 | v_add(config, ctx_private->slot_size, &cc_hot->cc); |
852c2936 MD |
270 | |
271 | /* | |
272 | * commit count read can race with concurrent OOO commit count updates. | |
273 | * This is only needed for lib_ring_buffer_check_deliver (for | |
274 | * non-polling delivery only) and for | |
275 | * lib_ring_buffer_write_commit_counter. The race can only cause the | |
276 | * counter to be read with the same value more than once, which could | |
277 | * cause : | |
278 | * - Multiple delivery for the same sub-buffer (which is handled | |
279 | * gracefully by the reader code) if the value is for a full | |
280 | * sub-buffer. It's important that we can never miss a sub-buffer | |
281 | * delivery. Re-reading the value after the v_add ensures this. | |
282 | * - Reading a commit_count with a higher value that what was actually | |
283 | * added to it for the lib_ring_buffer_write_commit_counter call | |
284 | * (again caused by a concurrent committer). It does not matter, | |
285 | * because this function is interested in the fact that the commit | |
286 | * count reaches back the reserve offset for a specific sub-buffer, | |
287 | * which is completely independent of the order. | |
288 | */ | |
d2fe4771 | 289 | commit_count = v_read(config, &cc_hot->cc); |
852c2936 MD |
290 | |
291 | lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1, | |
f27b0770 | 292 | commit_count, endidx, handle, ctx); |
852c2936 MD |
293 | /* |
294 | * Update used size at each commit. It's needed only for extracting | |
295 | * ring_buffer buffers from vmcore, after crash. | |
296 | */ | |
d2fe4771 MD |
297 | lib_ring_buffer_write_commit_counter(config, buf, chan, |
298 | offset_end, commit_count, handle, cc_hot); | |
852c2936 MD |
299 | } |
300 | ||
301 | /** | |
302 | * lib_ring_buffer_try_discard_reserve - Try discarding a record. | |
303 | * @config: ring buffer instance configuration. | |
304 | * @ctx: ring buffer context. (input arguments only) | |
305 | * | |
306 | * Only succeeds if no other record has been written after the record to | |
307 | * discard. If discard fails, the record must be committed to the buffer. | |
308 | * | |
309 | * Returns 0 upon success, -EPERM if the record cannot be discarded. | |
310 | */ | |
311 | static inline | |
b5457df5 MD |
312 | int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_ring_buffer_config *config, |
313 | const struct lttng_ust_ring_buffer_ctx *ctx) | |
852c2936 | 314 | { |
b5457df5 MD |
315 | struct lttng_ust_ring_buffer_ctx_private *ctx_private = ctx->priv; |
316 | struct lttng_ust_ring_buffer *buf = ctx_private->buf; | |
8936b6c0 | 317 | unsigned long end_offset = ctx_private->pre_offset + ctx_private->slot_size; |
852c2936 MD |
318 | |
319 | /* | |
320 | * We need to ensure that if the cmpxchg succeeds and discards the | |
373ea80a MD |
321 | * record, the next record will record a full timestamp, because it cannot |
322 | * rely on the last_timestamp associated with the discarded record to detect | |
323 | * overflows. The only way to ensure this is to set the last_timestamp to 0 | |
324 | * (assuming no 64-bit timestamp overflow), which forces to write a 64-bit | |
852c2936 MD |
325 | * timestamp in the next record. |
326 | * | |
373ea80a MD |
327 | * Note: if discard fails, we must leave the timestamp in the record header. |
328 | * It is needed to keep track of timestamp overflows for the following | |
852c2936 MD |
329 | * records. |
330 | */ | |
373ea80a | 331 | save_last_timestamp(config, buf, 0ULL); |
852c2936 | 332 | |
8936b6c0 | 333 | if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx_private->pre_offset) |
852c2936 MD |
334 | != end_offset)) |
335 | return -EPERM; | |
336 | else | |
337 | return 0; | |
338 | } | |
339 | ||
340 | static inline | |
2208d8b5 | 341 | void channel_record_disable( |
b5457df5 MD |
342 | const struct lttng_ust_ring_buffer_config *config __attribute__((unused)), |
343 | struct lttng_ust_ring_buffer_channel *chan) | |
852c2936 | 344 | { |
9f3fdbc6 | 345 | uatomic_inc(&chan->record_disabled); |
852c2936 MD |
346 | } |
347 | ||
348 | static inline | |
2208d8b5 | 349 | void channel_record_enable( |
b5457df5 MD |
350 | const struct lttng_ust_ring_buffer_config *config __attribute__((unused)), |
351 | struct lttng_ust_ring_buffer_channel *chan) | |
852c2936 | 352 | { |
9f3fdbc6 | 353 | uatomic_dec(&chan->record_disabled); |
852c2936 MD |
354 | } |
355 | ||
356 | static inline | |
2208d8b5 | 357 | void lib_ring_buffer_record_disable( |
b5457df5 MD |
358 | const struct lttng_ust_ring_buffer_config *config __attribute__((unused)), |
359 | struct lttng_ust_ring_buffer *buf) | |
852c2936 | 360 | { |
9f3fdbc6 | 361 | uatomic_inc(&buf->record_disabled); |
852c2936 MD |
362 | } |
363 | ||
364 | static inline | |
2208d8b5 | 365 | void lib_ring_buffer_record_enable( |
b5457df5 MD |
366 | const struct lttng_ust_ring_buffer_config *config __attribute__((unused)), |
367 | struct lttng_ust_ring_buffer *buf) | |
852c2936 | 368 | { |
9f3fdbc6 | 369 | uatomic_dec(&buf->record_disabled); |
852c2936 MD |
370 | } |
371 | ||
e92f3e28 | 372 | #endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */ |