liblttng-ust/ltt-events.c

   1 /*
   2  * ltt-events.c
   3  *
   4  * Copyright 2010 (c) - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * Holds LTTng per-session event registry.
   7  *
   8  * Dual LGPL v2.1/GPL v2 license.
   9  */
  10
  11 #define _GNU_SOURCE
  12 #include <stdio.h>
  13 #include <endian.h>
  14 #include <urcu/list.h>
  15 #include <urcu/hlist.h>
  16 #include <pthread.h>
  17 #include <uuid/uuid.h>
  18 #include <errno.h>
  19 #include <sys/shm.h>
  20 #include <sys/ipc.h>
  21 #include <stdint.h>
  22 #include <stddef.h>
  23
  24 #include <urcu-bp.h>
  25 #include <urcu/compiler.h>
  26 #include <urcu/uatomic.h>
  27 #include <urcu/arch.h>
  28
  29 #include <lttng/tracepoint.h>
  30 #include <lttng/ust-events.h>
  31
  32 #include <usterr-signal-safe.h>
  33 #include <helper.h>
  34
  35 #include "ltt-tracer.h"
  36 #include "ltt-tracer-core.h"
  37 #include "wait.h"
  38 #include "../libringbuffer/shm.h"
  39 #include "jhash.h"
  40
  41 /*
  42  * The sessions mutex is the centralized mutex across UST tracing
  43  * control and probe registration. All operations within this file are
  44  * called by the communication thread, under ust_lock protection.
  45  */
  46 static pthread_mutex_t sessions_mutex = PTHREAD_MUTEX_INITIALIZER;
  47
  48 void ust_lock(void)
  49 {
  50         pthread_mutex_lock(&sessions_mutex);
  51 }
  52
  53 void ust_unlock(void)
  54 {
  55         pthread_mutex_unlock(&sessions_mutex);
  56 }
  57
  58 static CDS_LIST_HEAD(sessions);
  59
  60 /*
  61  * Pending probes hash table, containing the registered ltt events for
  62  * which tracepoint probes are still missing. Protected by the sessions
  63  * mutex.
  64  */
  65 #define PENDING_PROBE_HASH_BITS         6
  66 #define PENDING_PROBE_HASH_SIZE         (1 << PENDING_PROBE_HASH_BITS)
  67 static struct cds_hlist_head pending_probe_table[PENDING_PROBE_HASH_SIZE];
  68
  69 struct ust_pending_probe {
  70         struct ltt_event *event;
  71         struct cds_hlist_node node;
  72         char name[];
  73 };
  74
  75 static void _ltt_event_destroy(struct ltt_event *event);
  76 static void _ltt_channel_destroy(struct ltt_channel *chan);
  77 static int _ltt_event_unregister(struct ltt_event *event);
  78 static
  79 int _ltt_event_metadata_statedump(struct ltt_session *session,
  80                                   struct ltt_channel *chan,
  81                                   struct ltt_event *event);
  82 static
  83 int _ltt_session_metadata_statedump(struct ltt_session *session);
  84
  85 /*
  86  * called at event creation if probe is missing.
  87  * called with session mutex held.
  88  */
  89 static
  90 int add_pending_probe(struct ltt_event *event, const char *name)
  91 {
  92         struct cds_hlist_head *head;
  93         struct ust_pending_probe *e;
  94         size_t name_len = strlen(name) + 1;
  95         uint32_t hash = jhash(name, name_len - 1, 0);
  96
  97         head = &pending_probe_table[hash & (PENDING_PROBE_HASH_SIZE - 1)];
  98         e = zmalloc(sizeof(struct ust_pending_probe) + name_len);
  99         if (!e)
 100                 return -ENOMEM;
 101         memcpy(&e->name[0], name, name_len);
 102         cds_hlist_add_head(&e->node, head);
 103         e->event = event;
 104         event->pending_probe = e;
 105         return 0;
 106 }
 107
 108 /*
 109  * remove a pending probe. called when at event teardown and when an
 110  * event is fixed (probe is loaded).
 111  * called with session mutex held.
 112  */
 113 static
 114 void remove_pending_probe(struct ust_pending_probe *e)
 115 {
 116         if (!e)
 117                 return;
 118         cds_hlist_del(&e->node);
 119         free(e);
 120 }
 121
 122 /*
 123  * Called at library load: connect the probe on the events pending on
 124  * probe load.
 125  * called with session mutex held.
 126  */
 127 int pending_probe_fix_events(const struct lttng_event_desc *desc)
 128 {
 129         struct cds_hlist_head *head;
 130         struct cds_hlist_node *node, *p;
 131         struct ust_pending_probe *e;
 132         const char *name = desc->name;
 133         size_t name_len = strlen(name) + 1;
 134         uint32_t hash = jhash(name, name_len - 1, 0);
 135         int ret = 0;
 136
 137         head = &pending_probe_table[hash & (PENDING_PROBE_HASH_SIZE - 1)];
 138         cds_hlist_for_each_entry_safe(e, node, p, head, node) {
 139                 struct ltt_event *event;
 140                 struct ltt_channel *chan;
 141
 142                 if (strcmp(name, e->name))
 143                         continue;
 144                 event = e->event;
 145                 chan = event->chan;
 146                 assert(!event->desc);
 147                 event->desc = desc;
 148                 event->pending_probe = NULL;
 149                 remove_pending_probe(e);
 150                 ret |= __tracepoint_probe_register(name,
 151                                 event->desc->probe_callback,
 152                                 event);
 153                 if (ret)
 154                         continue;
 155                 event->id = chan->free_event_id++;
 156                 ret |= _ltt_event_metadata_statedump(chan->session, chan,
 157                                 event);
 158         }
 159         return ret;
 160 }
 161
 162 void synchronize_trace(void)
 163 {
 164         synchronize_rcu();
 165 }
 166
 167 struct ltt_session *ltt_session_create(void)
 168 {
 169         struct ltt_session *session;
 170
 171         session = zmalloc(sizeof(struct ltt_session));
 172         if (!session)
 173                 return NULL;
 174         CDS_INIT_LIST_HEAD(&session->chan);
 175         CDS_INIT_LIST_HEAD(&session->events);
 176         uuid_generate(session->uuid);
 177         cds_list_add(&session->list, &sessions);
 178         return session;
 179 }
 180
 181 void ltt_session_destroy(struct ltt_session *session)
 182 {
 183         struct ltt_channel *chan, *tmpchan;
 184         struct ltt_event *event, *tmpevent;
 185         int ret;
 186
 187         CMM_ACCESS_ONCE(session->active) = 0;
 188         cds_list_for_each_entry(event, &session->events, list) {
 189                 ret = _ltt_event_unregister(event);
 190                 WARN_ON(ret);
 191         }
 192         synchronize_trace();    /* Wait for in-flight events to complete */
 193         cds_list_for_each_entry_safe(event, tmpevent, &session->events, list)
 194                 _ltt_event_destroy(event);
 195         cds_list_for_each_entry_safe(chan, tmpchan, &session->chan, list)
 196                 _ltt_channel_destroy(chan);
 197         cds_list_del(&session->list);
 198         free(session);
 199 }
 200
 201 int ltt_session_enable(struct ltt_session *session)
 202 {
 203         int ret = 0;
 204         struct ltt_channel *chan;
 205
 206         if (session->active) {
 207                 ret = -EBUSY;
 208                 goto end;
 209         }
 210
 211         /*
 212          * Snapshot the number of events per channel to know the type of header
 213          * we need to use.
 214          */
 215         cds_list_for_each_entry(chan, &session->chan, list) {
 216                 if (chan->header_type)
 217                         continue;               /* don't change it if session stop/restart */
 218                 if (chan->free_event_id < 31)
 219                         chan->header_type = 1;  /* compact */
 220                 else
 221                         chan->header_type = 2;  /* large */
 222         }
 223
 224         CMM_ACCESS_ONCE(session->active) = 1;
 225         CMM_ACCESS_ONCE(session->been_active) = 1;
 226         ret = _ltt_session_metadata_statedump(session);
 227         if (ret)
 228                 CMM_ACCESS_ONCE(session->active) = 0;
 229 end:
 230         return ret;
 231 }
 232
 233 int ltt_session_disable(struct ltt_session *session)
 234 {
 235         int ret = 0;
 236
 237         if (!session->active) {
 238                 ret = -EBUSY;
 239                 goto end;
 240         }
 241         CMM_ACCESS_ONCE(session->active) = 0;
 242 end:
 243         return ret;
 244 }
 245
 246 int ltt_channel_enable(struct ltt_channel *channel)
 247 {
 248         int old;
 249
 250         if (channel == channel->session->metadata)
 251                 return -EPERM;
 252         old = uatomic_xchg(&channel->enabled, 1);
 253         if (old)
 254                 return -EEXIST;
 255         return 0;
 256 }
 257
 258 int ltt_channel_disable(struct ltt_channel *channel)
 259 {
 260         int old;
 261
 262         if (channel == channel->session->metadata)
 263                 return -EPERM;
 264         old = uatomic_xchg(&channel->enabled, 0);
 265         if (!old)
 266                 return -EEXIST;
 267         return 0;
 268 }
 269
 270 int ltt_event_enable(struct ltt_event *event)
 271 {
 272         int old;
 273
 274         if (event->chan == event->chan->session->metadata)
 275                 return -EPERM;
 276         old = uatomic_xchg(&event->enabled, 1);
 277         if (old)
 278                 return -EEXIST;
 279         return 0;
 280 }
 281
 282 int ltt_event_disable(struct ltt_event *event)
 283 {
 284         int old;
 285
 286         if (event->chan == event->chan->session->metadata)
 287                 return -EPERM;
 288         old = uatomic_xchg(&event->enabled, 0);
 289         if (!old)
 290                 return -EEXIST;
 291         return 0;
 292 }
 293
 294 struct ltt_channel *ltt_channel_create(struct ltt_session *session,
 295                                        const char *transport_name,
 296                                        void *buf_addr,
 297                                        size_t subbuf_size, size_t num_subbuf,
 298                                        unsigned int switch_timer_interval,
 299                                        unsigned int read_timer_interval,
 300                                        int *shm_fd, int *wait_fd,
 301                                        uint64_t *memory_map_size,
 302                                        struct ltt_channel *chan_priv_init)
 303 {
 304         struct ltt_channel *chan = NULL;
 305         struct ltt_transport *transport;
 306
 307         if (session->been_active)
 308                 goto active;    /* Refuse to add channel to active session */
 309         transport = ltt_transport_find(transport_name);
 310         if (!transport) {
 311                 DBG("LTTng transport %s not found\n",
 312                        transport_name);
 313                 goto notransport;
 314         }
 315         chan_priv_init->id = session->free_chan_id++;
 316         chan_priv_init->session = session;
 317         /*
 318          * Note: the channel creation op already writes into the packet
 319          * headers. Therefore the "chan" information used as input
 320          * should be already accessible.
 321          */
 322         chan = transport->ops.channel_create("[lttng]", buf_addr,
 323                         subbuf_size, num_subbuf, switch_timer_interval,
 324                         read_timer_interval, shm_fd, wait_fd,
 325                         memory_map_size, chan_priv_init);
 326         if (!chan)
 327                 goto create_error;
 328         chan->enabled = 1;
 329         chan->ops = &transport->ops;
 330         cds_list_add(&chan->list, &session->chan);
 331         return chan;
 332
 333 create_error:
 334 notransport:
 335 active:
 336         return NULL;
 337 }
 338
 339 /*
 340  * Only used internally at session destruction.
 341  */
 342 static
 343 void _ltt_channel_destroy(struct ltt_channel *chan)
 344 {
 345         cds_list_del(&chan->list);
 346         lttng_destroy_context(chan->ctx);
 347         chan->ops->channel_destroy(chan);
 348 }
 349
 350 /*
 351  * Supports event creation while tracing session is active.
 352  */
 353 struct ltt_event *ltt_event_create(struct ltt_channel *chan,
 354                                    struct lttng_ust_event *event_param,
 355                                    void *filter)
 356 {
 357         struct ltt_event *event;
 358         int ret;
 359
 360         if (chan->used_event_id == -1UL)
 361                 goto full;
 362         /*
 363          * This is O(n^2) (for each event, the loop is called at event
 364          * creation). Might require a hash if we have lots of events.
 365          */
 366         cds_list_for_each_entry(event, &chan->session->events, list)
 367                 if (event->desc && !strcmp(event->desc->name, event_param->name))
 368                         goto exist;
 369         event = zmalloc(sizeof(struct ltt_event));
 370         if (!event)
 371                 goto cache_error;
 372         event->chan = chan;
 373         event->filter = filter;
 374         /*
 375          * used_event_id counts the maximum number of event IDs that can
 376          * register if all probes register.
 377          */
 378         chan->used_event_id++;
 379         event->enabled = 1;
 380         event->instrumentation = event_param->instrumentation;
 381         /* Populate ltt_event structure before tracepoint registration. */
 382         cmm_smp_wmb();
 383         switch (event_param->instrumentation) {
 384         case LTTNG_UST_TRACEPOINT:
 385                 event->desc = ltt_event_get(event_param->name);
 386                 if (event->desc) {
 387                         ret = __tracepoint_probe_register(event_param->name,
 388                                         event->desc->probe_callback,
 389                                         event);
 390                         if (ret)
 391                                 goto register_error;
 392                         event->id = chan->free_event_id++;
 393                 } else {
 394                         /*
 395                          * If the probe is not present, event->desc stays NULL,
 396                          * waiting for the probe to register, and the event->id
 397                          * stays unallocated.
 398                          */
 399                         ret = add_pending_probe(event, event_param->name);
 400                         if (ret)
 401                                 goto add_pending_error;
 402                 }
 403                 break;
 404         default:
 405                 WARN_ON_ONCE(1);
 406         }
 407         if (event->desc) {
 408                 ret = _ltt_event_metadata_statedump(chan->session, chan, event);
 409                 if (ret)
 410                         goto statedump_error;
 411         }
 412         cds_list_add(&event->list, &chan->session->events);
 413         return event;
 414
 415 statedump_error:
 416         if (event->desc) {
 417                 WARN_ON_ONCE(__tracepoint_probe_unregister(event_param->name,
 418                                         event->desc->probe_callback,
 419                                         event));
 420                 ltt_event_put(event->desc);
 421         }
 422 add_pending_error:
 423 register_error:
 424         free(event);
 425 cache_error:
 426 exist:
 427 full:
 428         return NULL;
 429 }
 430
 431 /*
 432  * Only used internally at session destruction.
 433  */
 434 int _ltt_event_unregister(struct ltt_event *event)
 435 {
 436         int ret = -EINVAL;
 437
 438         switch (event->instrumentation) {
 439         case LTTNG_UST_TRACEPOINT:
 440                 if (event->desc) {
 441                         ret = __tracepoint_probe_unregister(event->desc->name,
 442                                                           event->desc->probe_callback,
 443                                                           event);
 444                         if (ret)
 445                                 return ret;
 446                 } else {
 447                         remove_pending_probe(event->pending_probe);
 448                         ret = 0;
 449                 }
 450                 break;
 451         default:
 452                 WARN_ON_ONCE(1);
 453         }
 454         return ret;
 455 }
 456
 457 /*
 458  * Only used internally at session destruction.
 459  */
 460 static
 461 void _ltt_event_destroy(struct ltt_event *event)
 462 {
 463         switch (event->instrumentation) {
 464         case LTTNG_UST_TRACEPOINT:
 465                 if (event->desc) {
 466                         ltt_event_put(event->desc);
 467                 }
 468                 break;
 469         default:
 470                 WARN_ON_ONCE(1);
 471         }
 472         cds_list_del(&event->list);
 473         lttng_destroy_context(event->ctx);
 474         free(event);
 475 }
 476
 477 /*
 478  * We have exclusive access to our metadata buffer (protected by the
 479  * ust_lock), so we can do racy operations such as looking for
 480  * remaining space left in packet and write, since mutual exclusion
 481  * protects us from concurrent writes.
 482  */
 483 int lttng_metadata_printf(struct ltt_session *session,
 484                           const char *fmt, ...)
 485 {
 486         struct lttng_ust_lib_ring_buffer_ctx ctx;
 487         struct ltt_channel *chan = session->metadata;
 488         char *str = NULL;
 489         int ret = 0, waitret;
 490         size_t len, reserve_len, pos;
 491         va_list ap;
 492
 493         WARN_ON_ONCE(!CMM_ACCESS_ONCE(session->active));
 494
 495         va_start(ap, fmt);
 496         ret = vasprintf(&str, fmt, ap);
 497         va_end(ap);
 498         if (ret < 0)
 499                 return -ENOMEM;
 500
 501         len = strlen(str);
 502         pos = 0;
 503
 504         for (pos = 0; pos < len; pos += reserve_len) {
 505                 reserve_len = min_t(size_t,
 506                                 chan->ops->packet_avail_size(chan->chan, chan->handle),
 507                                 len - pos);
 508                 lib_ring_buffer_ctx_init(&ctx, chan->chan, NULL, reserve_len,
 509                                          sizeof(char), -1, chan->handle);
 510                 /*
 511                  * We don't care about metadata buffer's records lost
 512                  * count, because we always retry here. Report error if
 513                  * we need to bail out after timeout or being
 514                  * interrupted.
 515                  */
 516                 waitret = wait_cond_interruptible_timeout(
 517                         ({
 518                                 ret = chan->ops->event_reserve(&ctx, 0);
 519                                 ret != -ENOBUFS || !ret;
 520                         }),
 521                         LTTNG_METADATA_TIMEOUT_MSEC);
 522                 if (waitret == -ETIMEDOUT || waitret == -EINTR || ret) {
 523                         DBG("LTTng: Failure to write metadata to buffers (%s)\n",
 524                                 waitret == -EINTR ? "interrupted" :
 525                                         (ret == -ENOBUFS ? "timeout" : "I/O error"));
 526                         if (waitret == -EINTR)
 527                                 ret = waitret;
 528                         goto end;
 529                 }
 530                 chan->ops->event_write(&ctx, &str[pos], reserve_len);
 531                 chan->ops->event_commit(&ctx);
 532         }
 533 end:
 534         free(str);
 535         return ret;
 536 }
 537
 538 static
 539 int _ltt_field_statedump(struct ltt_session *session,
 540                          const struct lttng_event_field *field)
 541 {
 542         int ret = 0;
 543
 544         switch (field->type.atype) {
 545         case atype_integer:
 546                 ret = lttng_metadata_printf(session,
 547                         "               integer { size = %u; align = %u; signed = %u; encoding = %s; base = %u;%s } _%s;\n",
 548                         field->type.u.basic.integer.size,
 549                         field->type.u.basic.integer.alignment,
 550                         field->type.u.basic.integer.signedness,
 551                         (field->type.u.basic.integer.encoding == lttng_encode_none)
 552                                 ? "none"
 553                                 : (field->type.u.basic.integer.encoding == lttng_encode_UTF8)
 554                                         ? "UTF8"
 555                                         : "ASCII",
 556                         field->type.u.basic.integer.base,
 557 #if (BYTE_ORDER == BIG_ENDIAN)
 558                         field->type.u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
 559 #else
 560                         field->type.u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
 561 #endif
 562                         field->name);
 563                 break;
 564         case atype_float:
 565                 ret = lttng_metadata_printf(session,
 566                         "               floating_point { exp_dig = %u; mant_dig = %u; align = %u;%s } _%s;\n",
 567                         field->type.u.basic._float.exp_dig,
 568                         field->type.u.basic._float.mant_dig,
 569                         field->type.u.basic._float.alignment,
 570 #if (BYTE_ORDER == BIG_ENDIAN)
 571                         field->type.u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
 572 #else
 573                         field->type.u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
 574 #endif
 575                         field->name);
 576                 break;
 577         case atype_enum:
 578                 ret = lttng_metadata_printf(session,
 579                         "               %s %s;\n",
 580                         field->type.u.basic.enumeration.name,
 581                         field->name);
 582                 break;
 583         case atype_array:
 584         {
 585                 const struct lttng_basic_type *elem_type;
 586
 587                 elem_type = &field->type.u.array.elem_type;
 588                 ret = lttng_metadata_printf(session,
 589                         "               integer { size = %u; align = %u; signed = %u; encoding = %s; base = %u;%s } _%s[%u];\n",
 590                         elem_type->u.basic.integer.size,
 591                         elem_type->u.basic.integer.alignment,
 592                         elem_type->u.basic.integer.signedness,
 593                         (elem_type->u.basic.integer.encoding == lttng_encode_none)
 594                                 ? "none"
 595                                 : (elem_type->u.basic.integer.encoding == lttng_encode_UTF8)
 596                                         ? "UTF8"
 597                                         : "ASCII",
 598                         elem_type->u.basic.integer.base,
 599 #if (BYTE_ORDER == BIG_ENDIAN)
 600                         elem_type->u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
 601 #else
 602                         elem_type->u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
 603 #endif
 604                         field->name, field->type.u.array.length);
 605                 break;
 606         }
 607         case atype_sequence:
 608         {
 609                 const struct lttng_basic_type *elem_type;
 610                 const struct lttng_basic_type *length_type;
 611
 612                 elem_type = &field->type.u.sequence.elem_type;
 613                 length_type = &field->type.u.sequence.length_type;
 614                 ret = lttng_metadata_printf(session,
 615                         "               integer { size = %u; align = %u; signed = %u; encoding = %s; base = %u;%s } __%s_length;\n",
 616                         length_type->u.basic.integer.size,
 617                         (unsigned int) length_type->u.basic.integer.alignment,
 618                         length_type->u.basic.integer.signedness,
 619                         (length_type->u.basic.integer.encoding == lttng_encode_none)
 620                                 ? "none"
 621                                 : ((length_type->u.basic.integer.encoding == lttng_encode_UTF8)
 622                                         ? "UTF8"
 623                                         : "ASCII"),
 624                         length_type->u.basic.integer.base,
 625 #if (BYTE_ORDER == BIG_ENDIAN)
 626                         length_type->u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
 627 #else
 628                         length_type->u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
 629 #endif
 630                         field->name);
 631                 if (ret)
 632                         return ret;
 633
 634                 ret = lttng_metadata_printf(session,
 635                         "               integer { size = %u; align = %u; signed = %u; encoding = %s; base = %u;%s } _%s[ __%s_length ];\n",
 636                         elem_type->u.basic.integer.size,
 637                         (unsigned int) elem_type->u.basic.integer.alignment,
 638                         elem_type->u.basic.integer.signedness,
 639                         (elem_type->u.basic.integer.encoding == lttng_encode_none)
 640                                 ? "none"
 641                                 : ((elem_type->u.basic.integer.encoding == lttng_encode_UTF8)
 642                                         ? "UTF8"
 643                                         : "ASCII"),
 644                         elem_type->u.basic.integer.base,
 645 #if (BYTE_ORDER == BIG_ENDIAN)
 646                         elem_type->u.basic.integer.reverse_byte_order ? " byte_order = le;" : "",
 647 #else
 648                         elem_type->u.basic.integer.reverse_byte_order ? " byte_order = be;" : "",
 649 #endif
 650                         field->name,
 651                         field->name);
 652                 break;
 653         }
 654
 655         case atype_string:
 656                 /* Default encoding is UTF8 */
 657                 ret = lttng_metadata_printf(session,
 658                         "               string%s _%s;\n",
 659                         field->type.u.basic.string.encoding == lttng_encode_ASCII ?
 660                                 " { encoding = ASCII; }" : "",
 661                         field->name);
 662                 break;
 663         default:
 664                 WARN_ON_ONCE(1);
 665                 return -EINVAL;
 666         }
 667         return ret;
 668 }
 669
 670 static
 671 int _ltt_context_metadata_statedump(struct ltt_session *session,
 672                                     struct lttng_ctx *ctx)
 673 {
 674         int ret = 0;
 675         int i;
 676
 677         if (!ctx)
 678                 return 0;
 679         for (i = 0; i < ctx->nr_fields; i++) {
 680                 const struct lttng_ctx_field *field = &ctx->fields[i];
 681
 682                 ret = _ltt_field_statedump(session, &field->event_field);
 683                 if (ret)
 684                         return ret;
 685         }
 686         return ret;
 687 }
 688
 689 static
 690 int _ltt_fields_metadata_statedump(struct ltt_session *session,
 691                                    struct ltt_event *event)
 692 {
 693         const struct lttng_event_desc *desc = event->desc;
 694         int ret = 0;
 695         int i;
 696
 697         for (i = 0; i < desc->nr_fields; i++) {
 698                 const struct lttng_event_field *field = &desc->fields[i];
 699
 700                 ret = _ltt_field_statedump(session, field);
 701                 if (ret)
 702                         return ret;
 703         }
 704         return ret;
 705 }
 706
 707 static
 708 int _ltt_event_metadata_statedump(struct ltt_session *session,
 709                                   struct ltt_channel *chan,
 710                                   struct ltt_event *event)
 711 {
 712         int ret = 0;
 713
 714         if (event->metadata_dumped || !CMM_ACCESS_ONCE(session->active))
 715                 return 0;
 716         if (chan == session->metadata)
 717                 return 0;
 718         /*
 719          * Don't print events for which probe load is pending.
 720          */
 721         if (!event->desc)
 722                 return 0;
 723
 724         ret = lttng_metadata_printf(session,
 725                 "event {\n"
 726                 "       name = \"%s\";\n"
 727                 "       id = %u;\n"
 728                 "       stream_id = %u;\n",
 729                 event->desc->name,
 730                 event->id,
 731                 event->chan->id);
 732         if (ret)
 733                 goto end;
 734
 735         if (event->ctx) {
 736                 ret = lttng_metadata_printf(session,
 737                         "       context := struct {\n");
 738                 if (ret)
 739                         goto end;
 740         }
 741         ret = _ltt_context_metadata_statedump(session, event->ctx);
 742         if (ret)
 743                 goto end;
 744         if (event->ctx) {
 745                 ret = lttng_metadata_printf(session,
 746                         "       };\n");
 747                 if (ret)
 748                         goto end;
 749         }
 750
 751         ret = lttng_metadata_printf(session,
 752                 "       fields := struct {\n"
 753                 );
 754         if (ret)
 755                 goto end;
 756
 757         ret = _ltt_fields_metadata_statedump(session, event);
 758         if (ret)
 759                 goto end;
 760
 761         /*
 762          * LTTng space reservation can only reserve multiples of the
 763          * byte size.
 764          */
 765         ret = lttng_metadata_printf(session,
 766                 "       };\n"
 767                 "};\n\n");
 768         if (ret)
 769                 goto end;
 770
 771         event->metadata_dumped = 1;
 772 end:
 773         return ret;
 774
 775 }
 776
 777 static
 778 int _ltt_channel_metadata_statedump(struct ltt_session *session,
 779                                     struct ltt_channel *chan)
 780 {
 781         int ret = 0;
 782
 783         if (chan->metadata_dumped || !CMM_ACCESS_ONCE(session->active))
 784                 return 0;
 785         if (chan == session->metadata)
 786                 return 0;
 787
 788         WARN_ON_ONCE(!chan->header_type);
 789         ret = lttng_metadata_printf(session,
 790                 "stream {\n"
 791                 "       id = %u;\n"
 792                 "       event.header := %s;\n"
 793                 "       packet.context := struct packet_context;\n",
 794                 chan->id,
 795                 chan->header_type == 1 ? "struct event_header_compact" :
 796                         "struct event_header_large");
 797         if (ret)
 798                 goto end;
 799
 800         if (chan->ctx) {
 801                 ret = lttng_metadata_printf(session,
 802                         "       event.context := struct {\n");
 803                 if (ret)
 804                         goto end;
 805         }
 806         ret = _ltt_context_metadata_statedump(session, chan->ctx);
 807         if (ret)
 808                 goto end;
 809         if (chan->ctx) {
 810                 ret = lttng_metadata_printf(session,
 811                         "       };\n");
 812                 if (ret)
 813                         goto end;
 814         }
 815
 816         ret = lttng_metadata_printf(session,
 817                 "};\n\n");
 818
 819         chan->metadata_dumped = 1;
 820 end:
 821         return ret;
 822 }
 823
 824 static
 825 int _ltt_stream_packet_context_declare(struct ltt_session *session)
 826 {
 827         return lttng_metadata_printf(session,
 828                 "struct packet_context {\n"
 829                 "       uint64_t timestamp_begin;\n"
 830                 "       uint64_t timestamp_end;\n"
 831                 "       uint32_t events_discarded;\n"
 832                 "       uint32_t content_size;\n"
 833                 "       uint32_t packet_size;\n"
 834                 "       uint32_t cpu_id;\n"
 835                 "};\n\n"
 836                 );
 837 }
 838
 839 /*
 840  * Compact header:
 841  * id: range: 0 - 30.
 842  * id 31 is reserved to indicate an extended header.
 843  *
 844  * Large header:
 845  * id: range: 0 - 65534.
 846  * id 65535 is reserved to indicate an extended header.
 847  */
 848 static
 849 int _ltt_event_header_declare(struct ltt_session *session)
 850 {
 851         return lttng_metadata_printf(session,
 852         "struct event_header_compact {\n"
 853         "       enum : uint5_t { compact = 0 ... 30, extended = 31 } id;\n"
 854         "       variant <id> {\n"
 855         "               struct {\n"
 856         "                       uint27_t timestamp;\n"
 857         "               } compact;\n"
 858         "               struct {\n"
 859         "                       uint32_t id;\n"
 860         "                       uint64_t timestamp;\n"
 861         "               } extended;\n"
 862         "       } v;\n"
 863         "} align(%u);\n"
 864         "\n"
 865         "struct event_header_large {\n"
 866         "       enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;\n"
 867         "       variant <id> {\n"
 868         "               struct {\n"
 869         "                       uint32_t timestamp;\n"
 870         "               } compact;\n"
 871         "               struct {\n"
 872         "                       uint32_t id;\n"
 873         "                       uint64_t timestamp;\n"
 874         "               } extended;\n"
 875         "       } v;\n"
 876         "} align(%u);\n\n",
 877         lttng_alignof(uint32_t) * CHAR_BIT,
 878         lttng_alignof(uint16_t) * CHAR_BIT
 879         );
 880 }
 881
 882 /*
 883  * Output metadata into this session's metadata buffers.
 884  */
 885 static
 886 int _ltt_session_metadata_statedump(struct ltt_session *session)
 887 {
 888         unsigned char *uuid_c = session->uuid;
 889         char uuid_s[37];
 890         struct ltt_channel *chan;
 891         struct ltt_event *event;
 892         int ret = 0;
 893
 894         if (!CMM_ACCESS_ONCE(session->active))
 895                 return 0;
 896         if (session->metadata_dumped)
 897                 goto skip_session;
 898         if (!session->metadata) {
 899                 DBG("LTTng: attempt to start tracing, but metadata channel is not found. Operation abort.\n");
 900                 return -EPERM;
 901         }
 902
 903         snprintf(uuid_s, sizeof(uuid_s),
 904                 "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
 905                 uuid_c[0], uuid_c[1], uuid_c[2], uuid_c[3],
 906                 uuid_c[4], uuid_c[5], uuid_c[6], uuid_c[7],
 907                 uuid_c[8], uuid_c[9], uuid_c[10], uuid_c[11],
 908                 uuid_c[12], uuid_c[13], uuid_c[14], uuid_c[15]);
 909
 910         ret = lttng_metadata_printf(session,
 911                 "typealias integer { size = 8; align = %u; signed = false; } := uint8_t;\n"
 912                 "typealias integer { size = 16; align = %u; signed = false; } := uint16_t;\n"
 913                 "typealias integer { size = 32; align = %u; signed = false; } := uint32_t;\n"
 914                 "typealias integer { size = 64; align = %u; signed = false; } := uint64_t;\n"
 915                 "typealias integer { size = 5; align = 1; signed = false; } := uint5_t;\n"
 916                 "typealias integer { size = 27; align = 1; signed = false; } := uint27_t;\n"
 917                 "\n"
 918                 "trace {\n"
 919                 "       major = %u;\n"
 920                 "       minor = %u;\n"
 921                 "       uuid = \"%s\";\n"
 922                 "       byte_order = %s;\n"
 923                 "       packet.header := struct {\n"
 924                 "               uint32_t magic;\n"
 925                 "               uint8_t  uuid[16];\n"
 926                 "               uint32_t stream_id;\n"
 927                 "       };\n"
 928                 "};\n\n",
 929                 lttng_alignof(uint8_t) * CHAR_BIT,
 930                 lttng_alignof(uint16_t) * CHAR_BIT,
 931                 lttng_alignof(uint32_t) * CHAR_BIT,
 932                 lttng_alignof(uint64_t) * CHAR_BIT,
 933                 CTF_VERSION_MAJOR,
 934                 CTF_VERSION_MINOR,
 935                 uuid_s,
 936 #if (BYTE_ORDER == BIG_ENDIAN)
 937                 "be"
 938 #else
 939                 "le"
 940 #endif
 941                 );
 942         if (ret)
 943                 goto end;
 944
 945         ret = _ltt_stream_packet_context_declare(session);
 946         if (ret)
 947                 goto end;
 948
 949         ret = _ltt_event_header_declare(session);
 950         if (ret)
 951                 goto end;
 952
 953 skip_session:
 954         cds_list_for_each_entry(chan, &session->chan, list) {
 955                 ret = _ltt_channel_metadata_statedump(session, chan);
 956                 if (ret)
 957                         goto end;
 958         }
 959
 960         cds_list_for_each_entry(event, &session->events, list) {
 961                 ret = _ltt_event_metadata_statedump(session, event->chan, event);
 962                 if (ret)
 963                         goto end;
 964         }
 965         session->metadata_dumped = 1;
 966 end:
 967         return ret;
 968 }
 969
 970 void lttng_ust_events_exit(void)
 971 {
 972         struct ltt_session *session, *tmpsession;
 973
 974         cds_list_for_each_entry_safe(session, tmpsession, &sessions, list)
 975                 ltt_session_destroy(session);
 976 }