liblttng-ust/lttng-context-vtid.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * LTTng UST vtid context.
   7  */
   8
   9 #define _LGPL_SOURCE
  10 #include <limits.h>
  11 #include <stddef.h>
  12 #include <sys/types.h>
  13 #include <unistd.h>
  14 #include <lttng/ust-events.h>
  15 #include <lttng/ust-tracer.h>
  16 #include <lttng/ringbuffer-context.h>
  17 #include <ust-tid.h>
  18 #include <urcu/tls-compat.h>
  19
  20 #include "context-internal.h"
  21 #include "lttng-tracer-core.h"
  22
  23 /*
  24  * We cache the result to ensure we don't trigger a system call for
  25  * each event.
  26  */
  27 static DEFINE_URCU_TLS(pid_t, cached_vtid);
  28
  29 /*
  30  * Upon fork or clone, the TID assigned to our thread is not the same as
  31  * we kept in cache. Luckily, we are the only thread surviving in the
  32  * child process, so we can simply clear our cached version.
  33  */
  34 void lttng_context_vtid_reset(void)
  35 {
  36         CMM_STORE_SHARED(URCU_TLS(cached_vtid), 0);
  37 }
  38
  39 static
  40 size_t vtid_get_size(struct lttng_ust_ctx_field *field, size_t offset)
  41 {
  42         size_t size = 0;
  43
  44         size += lttng_ust_lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  45         size += sizeof(pid_t);
  46         return size;
  47 }
  48
  49 static inline
  50 pid_t wrapper_getvtid(void)
  51 {
  52         pid_t vtid;
  53
  54         vtid = CMM_LOAD_SHARED(URCU_TLS(cached_vtid));
  55         if (caa_unlikely(!vtid)) {
  56                 vtid = lttng_gettid();
  57                 CMM_STORE_SHARED(URCU_TLS(cached_vtid), vtid);
  58         }
  59         return vtid;
  60 }
  61
  62 static
  63 void vtid_record(struct lttng_ust_ctx_field *field,
  64                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  65                  struct lttng_ust_channel_buffer *chan)
  66 {
  67         pid_t vtid = wrapper_getvtid();
  68
  69         lttng_ust_lib_ring_buffer_align_ctx(ctx, lttng_alignof(vtid));
  70         chan->ops->event_write(ctx, &vtid, sizeof(vtid));
  71 }
  72
  73 static
  74 void vtid_get_value(struct lttng_ust_ctx_field *field,
  75                 struct lttng_ust_ctx_value *value)
  76 {
  77         value->u.s64 = wrapper_getvtid();
  78 }
  79
  80 int lttng_add_vtid_to_ctx(struct lttng_ust_ctx **ctx)
  81 {
  82         struct lttng_ust_ctx_field *field;
  83         struct lttng_ust_type_common *type;
  84         int ret;
  85
  86         type = lttng_ust_create_type_integer(sizeof(pid_t) * CHAR_BIT,
  87                         lttng_alignof(pid_t) * CHAR_BIT,
  88                         lttng_ust_is_signed_type(pid_t),
  89                         BYTE_ORDER, 10);
  90         if (!type)
  91                 return -ENOMEM;
  92         field = lttng_append_context(ctx);
  93         if (!field) {
  94                 ret = -ENOMEM;
  95                 goto error_context;
  96         }
  97         if (lttng_find_context(*ctx, "vtid")) {
  98                 ret = -EEXIST;
  99                 goto error_find_context;
 100         }
 101         field->event_field->name = strdup("vtid");
 102         if (!field->event_field->name) {
 103                 ret = -ENOMEM;
 104                 goto error_name;
 105         }
 106         field->event_field->type = type;
 107         field->get_size = vtid_get_size;
 108         field->record = vtid_record;
 109         field->get_value = vtid_get_value;
 110         lttng_context_update(*ctx);
 111         return 0;
 112
 113 error_name:
 114 error_find_context:
 115         lttng_remove_context_field(ctx, field);
 116 error_context:
 117         lttng_ust_destroy_type(type);
 118         return ret;
 119 }
 120
 121 /*
 122  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 123  */
 124 void lttng_fixup_vtid_tls(void)
 125 {
 126         asm volatile ("" : : "m" (URCU_TLS(cached_vtid)));
 127 }