src/lib/lttng-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/ust-ringbuffer-context.h>
  17 #include "common/compat/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(void *priv __attribute__((unused)),
  41                 size_t offset)
  42 {
  43         size_t size = 0;
  44
  45         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(pid_t));
  46         size += sizeof(pid_t);
  47         return size;
  48 }
  49
  50 static inline
  51 pid_t wrapper_getvtid(void)
  52 {
  53         pid_t vtid;
  54
  55         vtid = CMM_LOAD_SHARED(URCU_TLS(cached_vtid));
  56         if (caa_unlikely(!vtid)) {
  57                 vtid = lttng_gettid();
  58                 CMM_STORE_SHARED(URCU_TLS(cached_vtid), vtid);
  59         }
  60         return vtid;
  61 }
  62
  63 static
  64 void vtid_record(void *priv __attribute__((unused)),
  65                  struct lttng_ust_ring_buffer_ctx *ctx,
  66                  struct lttng_ust_channel_buffer *chan)
  67 {
  68         pid_t vtid = wrapper_getvtid();
  69
  70         chan->ops->event_write(ctx, &vtid, sizeof(vtid), lttng_ust_rb_alignof(vtid));
  71 }
  72
  73 static
  74 void vtid_get_value(void *priv __attribute__((unused)),
  75                 struct lttng_ust_ctx_value *value)
  76 {
  77         value->u.s64 = wrapper_getvtid();
  78 }
  79
  80 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
  81         lttng_ust_static_event_field("vtid",
  82                 lttng_ust_static_type_integer(sizeof(pid_t) * CHAR_BIT,
  83                                 lttng_ust_rb_alignof(pid_t) * CHAR_BIT,
  84                                 lttng_ust_is_signed_type(pid_t),
  85                                 LTTNG_UST_BYTE_ORDER, 10),
  86                 false, false),
  87         vtid_get_size,
  88         vtid_record,
  89         vtid_get_value,
  90         NULL, NULL);
  91
  92 int lttng_add_vtid_to_ctx(struct lttng_ust_ctx **ctx)
  93 {
  94         int ret;
  95
  96         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
  97                 ret = -EEXIST;
  98                 goto error_find_context;
  99         }
 100         ret = lttng_ust_context_append(ctx, ctx_field);
 101         if (ret)
 102                 return ret;
 103         return 0;
 104
 105 error_find_context:
 106         return ret;
 107 }
 108
 109 /*
 110  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 111  */
 112 void lttng_fixup_vtid_tls(void)
 113 {
 114         asm volatile ("" : : "m" (URCU_TLS(cached_vtid)));
 115 }