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         lttng_ust_lib_ring_buffer_align_ctx(ctx, lttng_ust_rb_alignof(vpid));
  66         chan->ops->event_write(ctx, &vpid, sizeof(vpid));
  67 }
  68
  69 static
  70 void vpid_get_value(struct lttng_ust_ctx_field *field,
  71                 struct lttng_ust_ctx_value *value)
  72 {
  73         value->u.s64 = wrapper_getvpid();
  74 }
  75
  76 int lttng_add_vpid_to_ctx(struct lttng_ust_ctx **ctx)
  77 {
  78         struct lttng_ust_ctx_field *field;
  79         struct lttng_ust_type_common *type;
  80         int ret;
  81
  82         type = lttng_ust_create_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                         BYTE_ORDER, 10);
  86         if (!type)
  87                 return -ENOMEM;
  88         field = lttng_append_context(ctx);
  89         if (!field) {
  90                 ret = -ENOMEM;
  91                 goto error_context;
  92         }
  93         if (lttng_find_context(*ctx, "vpid")) {
  94                 ret = -EEXIST;
  95                 goto error_find_context;
  96         }
  97         field->event_field->name = strdup("vpid");
  98         if (!field->event_field->name) {
  99                 ret = -ENOMEM;
 100                 goto error_name;
 101         }
 102         field->event_field->type = type;
 103         field->get_size = vpid_get_size;
 104         field->record = vpid_record;
 105         field->get_value = vpid_get_value;
 106         lttng_context_update(*ctx);
 107         return 0;
 108
 109 error_name:
 110 error_find_context:
 111         lttng_remove_context_field(ctx, field);
 112 error_context:
 113         lttng_ust_destroy_type(type);
 114         return ret;
 115 }