lttng-ring-buffer-client.h

   1 /*
   2  * lttng-ring-buffer-client.h
   3  *
   4  * LTTng lib ring buffer client template.
   5  *
   6  * Copyright (C) 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; only
  11  * version 2.1 of the License.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #include <linux/module.h>
  24 #include <linux/types.h>
  25 #include "lib/bitfield.h"
  26 #include "wrapper/vmalloc.h"    /* for wrapper_vmalloc_sync_all() */
  27 #include "wrapper/trace-clock.h"
  28 #include "lttng-events.h"
  29 #include "lttng-tracer.h"
  30 #include "wrapper/ringbuffer/frontend_types.h"
  31
  32 #define LTTNG_COMPACT_EVENT_BITS        5
  33 #define LTTNG_COMPACT_TSC_BITS          27
  34
  35 /*
  36  * Keep the natural field alignment for _each field_ within this structure if
  37  * you ever add/remove a field from this header. Packed attribute is not used
  38  * because gcc generates poor code on at least powerpc and mips. Don't ever
  39  * let gcc add padding between the structure elements.
  40  *
  41  * The guarantee we have with timestamps is that all the events in a
  42  * packet are included (inclusive) within the begin/end timestamps of
  43  * the packet. Another guarantee we have is that the "timestamp begin",
  44  * as well as the event timestamps, are monotonically increasing (never
  45  * decrease) when moving forward in a stream (physically). But this
  46  * guarantee does not apply to "timestamp end", because it is sampled at
  47  * commit time, which is not ordered with respect to space reservation.
  48  */
  49
  50 struct packet_header {
  51         /* Trace packet header */
  52         uint32_t magic;                 /*
  53                                          * Trace magic number.
  54                                          * contains endianness information.
  55                                          */
  56         uint8_t uuid[16];
  57         uint32_t stream_id;
  58
  59         struct {
  60                 /* Stream packet context */
  61                 uint64_t timestamp_begin;       /* Cycle count at subbuffer start */
  62                 uint64_t timestamp_end;         /* Cycle count at subbuffer end */
  63                 uint64_t content_size;          /* Size of data in subbuffer */
  64                 uint64_t packet_size;           /* Subbuffer size (include padding) */
  65                 unsigned long events_discarded; /*
  66                                                  * Events lost in this subbuffer since
  67                                                  * the beginning of the trace.
  68                                                  * (may overflow)
  69                                                  */
  70                 uint32_t cpu_id;                /* CPU id associated with stream */
  71                 uint8_t header_end;             /* End of header */
  72         } ctx;
  73 };
  74
  75
  76 static inline notrace u64 lib_ring_buffer_clock_read(struct channel *chan)
  77 {
  78         return trace_clock_read64();
  79 }
  80
  81 static inline
  82 size_t ctx_get_size(size_t offset, struct lttng_ctx *ctx)
  83 {
  84         int i;
  85         size_t orig_offset = offset;
  86
  87         if (likely(!ctx))
  88                 return 0;
  89         for (i = 0; i < ctx->nr_fields; i++)
  90                 offset += ctx->fields[i].get_size(offset);
  91         return offset - orig_offset;
  92 }
  93
  94 static inline
  95 void ctx_record(struct lib_ring_buffer_ctx *bufctx,
  96                 struct lttng_channel *chan,
  97                 struct lttng_ctx *ctx)
  98 {
  99         int i;
 100
 101         if (likely(!ctx))
 102                 return;
 103         for (i = 0; i < ctx->nr_fields; i++)
 104                 ctx->fields[i].record(&ctx->fields[i], bufctx, chan);
 105 }
 106
 107 /*
 108  * record_header_size - Calculate the header size and padding necessary.
 109  * @config: ring buffer instance configuration
 110  * @chan: channel
 111  * @offset: offset in the write buffer
 112  * @pre_header_padding: padding to add before the header (output)
 113  * @ctx: reservation context
 114  *
 115  * Returns the event header size (including padding).
 116  *
 117  * The payload must itself determine its own alignment from the biggest type it
 118  * contains.
 119  */
 120 static __inline__
 121 unsigned char record_header_size(const struct lib_ring_buffer_config *config,
 122                                  struct channel *chan, size_t offset,
 123                                  size_t *pre_header_padding,
 124                                  struct lib_ring_buffer_ctx *ctx)
 125 {
 126         struct lttng_channel *lttng_chan = channel_get_private(chan);
 127         struct lttng_event *event = ctx->priv;
 128         size_t orig_offset = offset;
 129         size_t padding;
 130
 131         switch (lttng_chan->header_type) {
 132         case 1: /* compact */
 133                 padding = lib_ring_buffer_align(offset, lttng_alignof(uint32_t));
 134                 offset += padding;
 135                 if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
 136                         offset += sizeof(uint32_t);     /* id and timestamp */
 137                 } else {
 138                         /* Minimum space taken by LTTNG_COMPACT_EVENT_BITS id */
 139                         offset += (LTTNG_COMPACT_EVENT_BITS + CHAR_BIT - 1) / CHAR_BIT;
 140                         /* Align extended struct on largest member */
 141                         offset += lib_ring_buffer_align(offset, lttng_alignof(uint64_t));
 142                         offset += sizeof(uint32_t);     /* id */
 143                         offset += lib_ring_buffer_align(offset, lttng_alignof(uint64_t));
 144                         offset += sizeof(uint64_t);     /* timestamp */
 145                 }
 146                 break;
 147         case 2: /* large */
 148                 padding = lib_ring_buffer_align(offset, lttng_alignof(uint16_t));
 149                 offset += padding;
 150                 offset += sizeof(uint16_t);
 151                 if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
 152                         offset += lib_ring_buffer_align(offset, lttng_alignof(uint32_t));
 153                         offset += sizeof(uint32_t);     /* timestamp */
 154                 } else {
 155                         /* Align extended struct on largest member */
 156                         offset += lib_ring_buffer_align(offset, lttng_alignof(uint64_t));
 157                         offset += sizeof(uint32_t);     /* id */
 158                         offset += lib_ring_buffer_align(offset, lttng_alignof(uint64_t));
 159                         offset += sizeof(uint64_t);     /* timestamp */
 160                 }
 161                 break;
 162         default:
 163                 padding = 0;
 164                 WARN_ON_ONCE(1);
 165         }
 166         offset += ctx_get_size(offset, event->ctx);
 167         offset += ctx_get_size(offset, lttng_chan->ctx);
 168
 169         *pre_header_padding = padding;
 170         return offset - orig_offset;
 171 }
 172
 173 #include "wrapper/ringbuffer/api.h"
 174
 175 static
 176 void lttng_write_event_header_slow(const struct lib_ring_buffer_config *config,
 177                                  struct lib_ring_buffer_ctx *ctx,
 178                                  uint32_t event_id);
 179
 180 /*
 181  * lttng_write_event_header
 182  *
 183  * Writes the event header to the offset (already aligned on 32-bits).
 184  *
 185  * @config: ring buffer instance configuration
 186  * @ctx: reservation context
 187  * @event_id: event ID
 188  */
 189 static __inline__
 190 void lttng_write_event_header(const struct lib_ring_buffer_config *config,
 191                             struct lib_ring_buffer_ctx *ctx,
 192                             uint32_t event_id)
 193 {
 194         struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
 195         struct lttng_event *event = ctx->priv;
 196
 197         if (unlikely(ctx->rflags))
 198                 goto slow_path;
 199
 200         switch (lttng_chan->header_type) {
 201         case 1: /* compact */
 202         {
 203                 uint32_t id_time = 0;
 204
 205                 bt_bitfield_write(&id_time, uint32_t,
 206                                 0,
 207                                 LTTNG_COMPACT_EVENT_BITS,
 208                                 event_id);
 209                 bt_bitfield_write(&id_time, uint32_t,
 210                                 LTTNG_COMPACT_EVENT_BITS,
 211                                 LTTNG_COMPACT_TSC_BITS,
 212                                 ctx->tsc);
 213                 lib_ring_buffer_write(config, ctx, &id_time, sizeof(id_time));
 214                 break;
 215         }
 216         case 2: /* large */
 217         {
 218                 uint32_t timestamp = (uint32_t) ctx->tsc;
 219                 uint16_t id = event_id;
 220
 221                 lib_ring_buffer_write(config, ctx, &id, sizeof(id));
 222                 lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint32_t));
 223                 lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
 224                 break;
 225         }
 226         default:
 227                 WARN_ON_ONCE(1);
 228         }
 229
 230         ctx_record(ctx, lttng_chan, lttng_chan->ctx);
 231         ctx_record(ctx, lttng_chan, event->ctx);
 232         lib_ring_buffer_align_ctx(ctx, ctx->largest_align);
 233
 234         return;
 235
 236 slow_path:
 237         lttng_write_event_header_slow(config, ctx, event_id);
 238 }
 239
 240 static
 241 void lttng_write_event_header_slow(const struct lib_ring_buffer_config *config,
 242                                  struct lib_ring_buffer_ctx *ctx,
 243                                  uint32_t event_id)
 244 {
 245         struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
 246         struct lttng_event *event = ctx->priv;
 247
 248         switch (lttng_chan->header_type) {
 249         case 1: /* compact */
 250                 if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
 251                         uint32_t id_time = 0;
 252
 253                         bt_bitfield_write(&id_time, uint32_t,
 254                                         0,
 255                                         LTTNG_COMPACT_EVENT_BITS,
 256                                         event_id);
 257                         bt_bitfield_write(&id_time, uint32_t,
 258                                         LTTNG_COMPACT_EVENT_BITS,
 259                                         LTTNG_COMPACT_TSC_BITS, ctx->tsc);
 260                         lib_ring_buffer_write(config, ctx, &id_time, sizeof(id_time));
 261                 } else {
 262                         uint8_t id = 0;
 263                         uint64_t timestamp = ctx->tsc;
 264
 265                         bt_bitfield_write(&id, uint8_t,
 266                                         0,
 267                                         LTTNG_COMPACT_EVENT_BITS,
 268                                         31);
 269                         lib_ring_buffer_write(config, ctx, &id, sizeof(id));
 270                         /* Align extended struct on largest member */
 271                         lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint64_t));
 272                         lib_ring_buffer_write(config, ctx, &event_id, sizeof(event_id));
 273                         lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint64_t));
 274                         lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
 275                 }
 276                 break;
 277         case 2: /* large */
 278         {
 279                 if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
 280                         uint32_t timestamp = (uint32_t) ctx->tsc;
 281                         uint16_t id = event_id;
 282
 283                         lib_ring_buffer_write(config, ctx, &id, sizeof(id));
 284                         lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint32_t));
 285                         lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
 286                 } else {
 287                         uint16_t id = 65535;
 288                         uint64_t timestamp = ctx->tsc;
 289
 290                         lib_ring_buffer_write(config, ctx, &id, sizeof(id));
 291                         /* Align extended struct on largest member */
 292                         lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint64_t));
 293                         lib_ring_buffer_write(config, ctx, &event_id, sizeof(event_id));
 294                         lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint64_t));
 295                         lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
 296                 }
 297                 break;
 298         }
 299         default:
 300                 WARN_ON_ONCE(1);
 301         }
 302         ctx_record(ctx, lttng_chan, lttng_chan->ctx);
 303         ctx_record(ctx, lttng_chan, event->ctx);
 304         lib_ring_buffer_align_ctx(ctx, ctx->largest_align);
 305 }
 306
 307 static const struct lib_ring_buffer_config client_config;
 308
 309 static u64 client_ring_buffer_clock_read(struct channel *chan)
 310 {
 311         return lib_ring_buffer_clock_read(chan);
 312 }
 313
 314 static
 315 size_t client_record_header_size(const struct lib_ring_buffer_config *config,
 316                                  struct channel *chan, size_t offset,
 317                                  size_t *pre_header_padding,
 318                                  struct lib_ring_buffer_ctx *ctx)
 319 {
 320         return record_header_size(config, chan, offset,
 321                                   pre_header_padding, ctx);
 322 }
 323
 324 /**
 325  * client_packet_header_size - called on buffer-switch to a new sub-buffer
 326  *
 327  * Return header size without padding after the structure. Don't use packed
 328  * structure because gcc generates inefficient code on some architectures
 329  * (powerpc, mips..)
 330  */
 331 static size_t client_packet_header_size(void)
 332 {
 333         return offsetof(struct packet_header, ctx.header_end);
 334 }
 335
 336 static void client_buffer_begin(struct lib_ring_buffer *buf, u64 tsc,
 337                                 unsigned int subbuf_idx)
 338 {
 339         struct channel *chan = buf->backend.chan;
 340         struct packet_header *header =
 341                 (struct packet_header *)
 342                         lib_ring_buffer_offset_address(&buf->backend,
 343                                 subbuf_idx * chan->backend.subbuf_size);
 344         struct lttng_channel *lttng_chan = channel_get_private(chan);
 345         struct lttng_session *session = lttng_chan->session;
 346
 347         header->magic = CTF_MAGIC_NUMBER;
 348         memcpy(header->uuid, session->uuid.b, sizeof(session->uuid));
 349         header->stream_id = lttng_chan->id;
 350         header->ctx.timestamp_begin = tsc;
 351         header->ctx.timestamp_end = 0;
 352         header->ctx.content_size = ~0ULL; /* for debugging */
 353         header->ctx.packet_size = ~0ULL;
 354         header->ctx.events_discarded = 0;
 355         header->ctx.cpu_id = buf->backend.cpu;
 356 }
 357
 358 /*
 359  * offset is assumed to never be 0 here : never deliver a completely empty
 360  * subbuffer. data_size is between 1 and subbuf_size.
 361  */
 362 static void client_buffer_end(struct lib_ring_buffer *buf, u64 tsc,
 363                               unsigned int subbuf_idx, unsigned long data_size)
 364 {
 365         struct channel *chan = buf->backend.chan;
 366         struct packet_header *header =
 367                 (struct packet_header *)
 368                         lib_ring_buffer_offset_address(&buf->backend,
 369                                 subbuf_idx * chan->backend.subbuf_size);
 370         unsigned long records_lost = 0;
 371
 372         header->ctx.timestamp_end = tsc;
 373         header->ctx.content_size = data_size * CHAR_BIT;        /* in bits */
 374         header->ctx.packet_size = PAGE_ALIGN(data_size) * CHAR_BIT; /* in bits */
 375         records_lost += lib_ring_buffer_get_records_lost_full(&client_config, buf);
 376         records_lost += lib_ring_buffer_get_records_lost_wrap(&client_config, buf);
 377         records_lost += lib_ring_buffer_get_records_lost_big(&client_config, buf);
 378         header->ctx.events_discarded = records_lost;
 379 }
 380
 381 static int client_buffer_create(struct lib_ring_buffer *buf, void *priv,
 382                                 int cpu, const char *name)
 383 {
 384         return 0;
 385 }
 386
 387 static void client_buffer_finalize(struct lib_ring_buffer *buf, void *priv, int cpu)
 388 {
 389 }
 390
 391 static const struct lib_ring_buffer_config client_config = {
 392         .cb.ring_buffer_clock_read = client_ring_buffer_clock_read,
 393         .cb.record_header_size = client_record_header_size,
 394         .cb.subbuffer_header_size = client_packet_header_size,
 395         .cb.buffer_begin = client_buffer_begin,
 396         .cb.buffer_end = client_buffer_end,
 397         .cb.buffer_create = client_buffer_create,
 398         .cb.buffer_finalize = client_buffer_finalize,
 399
 400         .tsc_bits = LTTNG_COMPACT_TSC_BITS,
 401         .alloc = RING_BUFFER_ALLOC_PER_CPU,
 402         .sync = RING_BUFFER_SYNC_PER_CPU,
 403         .mode = RING_BUFFER_MODE_TEMPLATE,
 404         .backend = RING_BUFFER_PAGE,
 405         .output = RING_BUFFER_OUTPUT_TEMPLATE,
 406         .oops = RING_BUFFER_OOPS_CONSISTENCY,
 407         .ipi = RING_BUFFER_IPI_BARRIER,
 408         .wakeup = RING_BUFFER_WAKEUP_BY_TIMER,
 409 };
 410
 411 static
 412 struct channel *_channel_create(const char *name,
 413                                 struct lttng_channel *lttng_chan, void *buf_addr,
 414                                 size_t subbuf_size, size_t num_subbuf,
 415                                 unsigned int switch_timer_interval,
 416                                 unsigned int read_timer_interval)
 417 {
 418         return channel_create(&client_config, name, lttng_chan, buf_addr,
 419                               subbuf_size, num_subbuf, switch_timer_interval,
 420                               read_timer_interval);
 421 }
 422
 423 static
 424 void lttng_channel_destroy(struct channel *chan)
 425 {
 426         channel_destroy(chan);
 427 }
 428
 429 static
 430 struct lib_ring_buffer *lttng_buffer_read_open(struct channel *chan)
 431 {
 432         struct lib_ring_buffer *buf;
 433         int cpu;
 434
 435         for_each_channel_cpu(cpu, chan) {
 436                 buf = channel_get_ring_buffer(&client_config, chan, cpu);
 437                 if (!lib_ring_buffer_open_read(buf))
 438                         return buf;
 439         }
 440         return NULL;
 441 }
 442
 443 static
 444 int lttng_buffer_has_read_closed_stream(struct channel *chan)
 445 {
 446         struct lib_ring_buffer *buf;
 447         int cpu;
 448
 449         for_each_channel_cpu(cpu, chan) {
 450                 buf = channel_get_ring_buffer(&client_config, chan, cpu);
 451                 if (!atomic_long_read(&buf->active_readers))
 452                         return 1;
 453         }
 454         return 0;
 455 }
 456
 457 static
 458 void lttng_buffer_read_close(struct lib_ring_buffer *buf)
 459 {
 460         lib_ring_buffer_release_read(buf);
 461 }
 462
 463 static
 464 int lttng_event_reserve(struct lib_ring_buffer_ctx *ctx,
 465                       uint32_t event_id)
 466 {
 467         struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
 468         int ret, cpu;
 469
 470         cpu = lib_ring_buffer_get_cpu(&client_config);
 471         if (cpu < 0)
 472                 return -EPERM;
 473         ctx->cpu = cpu;
 474
 475         switch (lttng_chan->header_type) {
 476         case 1: /* compact */
 477                 if (event_id > 30)
 478                         ctx->rflags |= LTTNG_RFLAG_EXTENDED;
 479                 break;
 480         case 2: /* large */
 481                 if (event_id > 65534)
 482                         ctx->rflags |= LTTNG_RFLAG_EXTENDED;
 483                 break;
 484         default:
 485                 WARN_ON_ONCE(1);
 486         }
 487
 488         ret = lib_ring_buffer_reserve(&client_config, ctx);
 489         if (ret)
 490                 goto put;
 491         lttng_write_event_header(&client_config, ctx, event_id);
 492         return 0;
 493 put:
 494         lib_ring_buffer_put_cpu(&client_config);
 495         return ret;
 496 }
 497
 498 static
 499 void lttng_event_commit(struct lib_ring_buffer_ctx *ctx)
 500 {
 501         lib_ring_buffer_commit(&client_config, ctx);
 502         lib_ring_buffer_put_cpu(&client_config);
 503 }
 504
 505 static
 506 void lttng_event_write(struct lib_ring_buffer_ctx *ctx, const void *src,
 507                      size_t len)
 508 {
 509         lib_ring_buffer_write(&client_config, ctx, src, len);
 510 }
 511
 512 static
 513 void lttng_event_write_from_user(struct lib_ring_buffer_ctx *ctx,
 514                                const void __user *src, size_t len)
 515 {
 516         lib_ring_buffer_copy_from_user_inatomic(&client_config, ctx, src, len);
 517 }
 518
 519 static
 520 void lttng_event_memset(struct lib_ring_buffer_ctx *ctx,
 521                 int c, size_t len)
 522 {
 523         lib_ring_buffer_memset(&client_config, ctx, c, len);
 524 }
 525
 526 static
 527 wait_queue_head_t *lttng_get_writer_buf_wait_queue(struct channel *chan, int cpu)
 528 {
 529         struct lib_ring_buffer *buf = channel_get_ring_buffer(&client_config,
 530                                         chan, cpu);
 531         return &buf->write_wait;
 532 }
 533
 534 static
 535 wait_queue_head_t *lttng_get_hp_wait_queue(struct channel *chan)
 536 {
 537         return &chan->hp_wait;
 538 }
 539
 540 static
 541 int lttng_is_finalized(struct channel *chan)
 542 {
 543         return lib_ring_buffer_channel_is_finalized(chan);
 544 }
 545
 546 static
 547 int lttng_is_disabled(struct channel *chan)
 548 {
 549         return lib_ring_buffer_channel_is_disabled(chan);
 550 }
 551
 552 static struct lttng_transport lttng_relay_transport = {
 553         .name = "relay-" RING_BUFFER_MODE_TEMPLATE_STRING,
 554         .owner = THIS_MODULE,
 555         .ops = {
 556                 .channel_create = _channel_create,
 557                 .channel_destroy = lttng_channel_destroy,
 558                 .buffer_read_open = lttng_buffer_read_open,
 559                 .buffer_has_read_closed_stream =
 560                         lttng_buffer_has_read_closed_stream,
 561                 .buffer_read_close = lttng_buffer_read_close,
 562                 .event_reserve = lttng_event_reserve,
 563                 .event_commit = lttng_event_commit,
 564                 .event_write = lttng_event_write,
 565                 .event_write_from_user = lttng_event_write_from_user,
 566                 .event_memset = lttng_event_memset,
 567                 .packet_avail_size = NULL,      /* Would be racy anyway */
 568                 .get_writer_buf_wait_queue = lttng_get_writer_buf_wait_queue,
 569                 .get_hp_wait_queue = lttng_get_hp_wait_queue,
 570                 .is_finalized = lttng_is_finalized,
 571                 .is_disabled = lttng_is_disabled,
 572         },
 573 };
 574
 575 static int __init lttng_ring_buffer_client_init(void)
 576 {
 577         /*
 578          * This vmalloc sync all also takes care of the lib ring buffer
 579          * vmalloc'd module pages when it is built as a module into LTTng.
 580          */
 581         wrapper_vmalloc_sync_all();
 582         lttng_transport_register(&lttng_relay_transport);
 583         return 0;
 584 }
 585
 586 module_init(lttng_ring_buffer_client_init);
 587
 588 static void __exit lttng_ring_buffer_client_exit(void)
 589 {
 590         lttng_transport_unregister(&lttng_relay_transport);
 591 }
 592
 593 module_exit(lttng_ring_buffer_client_exit);
 594
 595 MODULE_LICENSE("GPL and additional rights");
 596 MODULE_AUTHOR("Mathieu Desnoyers");
 597 MODULE_DESCRIPTION("LTTng ring buffer " RING_BUFFER_MODE_TEMPLATE_STRING
 598                    " client");