liblttng-ust/lttng-context-vpid.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 vpid 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
  18 #include "context-internal.h"
  19
  20 /*
  21  * We cache the result to ensure we don't trigger a system call for
  22  * each event.
  23  */
  24 static pid_t cached_vpid;
  25
  26 static inline
  27 pid_t wrapper_getvpid(void)
  28 {
  29         pid_t vpid;
  30
  31         vpid = CMM_LOAD_SHARED(cached_vpid);
  32         if (caa_unlikely(!vpid)) {
  33                 vpid = getpid();
  34                 CMM_STORE_SHARED(cached_vpid, vpid);
  35         }
  36         return vpid;
  37 }
  38
  39 /*
  40  * Upon fork or clone, the PID assigned to our thread is not the same as
  41  * we kept in cache.
  42  */
  43 void lttng_context_vpid_reset(void)
  44 {
  45         CMM_STORE_SHARED(cached_vpid, 0);
  46 }
  47
  48 static
  49 size_t vpid_get_size(struct lttng_ust_ctx_field *field, size_t offset)
  50 {
  51         size_t size = 0;
  52
  53         size += lttng_ust_lib_ring_buffer_align(offset, lttng_ust_rb_alignof(pid_t));
  54         size += sizeof(pid_t);
  55         return size;
  56 }
  57
  58 static
  59 void vpid_record(struct lttng_ust_ctx_field *field,
  60                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  61                  struct lttng_ust_channel_buffer *chan)
  62 {
  63         pid_t vpid = wrapper_getvpid();
  64
  65         chan->ops->event_write(ctx, &vpid, sizeof(vpid), lttng_ust_rb_alignof(vpid));
  66 }
  67
  68 static
  69 void vpid_get_value(struct lttng_ust_ctx_field *field,
  70                 struct lttng_ust_ctx_value *value)
  71 {
  72         value->u.s64 = wrapper_getvpid();
  73 }
  74
  75 int lttng_add_vpid_to_ctx(struct lttng_ust_ctx **ctx)
  76 {
  77         struct lttng_ust_ctx_field *field;
  78         struct lttng_ust_type_common *type;
  79         int ret;
  80
  81         type = lttng_ust_create_type_integer(sizeof(pid_t) * CHAR_BIT,
  82                         lttng_ust_rb_alignof(pid_t) * CHAR_BIT,
  83                         lttng_ust_is_signed_type(pid_t),
  84                         BYTE_ORDER, 10);
  85         if (!type)
  86                 return -ENOMEM;
  87         field = lttng_append_context(ctx);
  88         if (!field) {
  89                 ret = -ENOMEM;
  90                 goto error_context;
  91         }
  92         if (lttng_find_context(*ctx, "vpid")) {
  93                 ret = -EEXIST;
  94                 goto error_find_context;
  95         }
  96         field->event_field->name = strdup("vpid");
  97         if (!field->event_field->name) {
  98                 ret = -ENOMEM;
  99                 goto error_name;
 100         }
 101         field->event_field->type = type;
 102         field->get_size = vpid_get_size;
 103         field->record = vpid_record;
 104         field->get_value = vpid_get_value;
 105         lttng_context_update(*ctx);
 106         return 0;
 107
 108 error_name:
 109 error_find_context:
 110         lttng_remove_context_field(ctx, field);
 111 error_context:
 112         lttng_ust_destroy_type(type);
 113         return ret;
 114 }