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 <stddef.h>
  11 #include <sys/types.h>
  12 #include <unistd.h>
  13 #include <lttng/ust-events.h>
  14 #include <lttng/ust-tracer.h>
  15 #include <lttng/ringbuffer-context.h>
  16
  17 #include "context-internal.h"
  18
  19 /*
  20  * We cache the result to ensure we don't trigger a system call for
  21  * each event.
  22  */
  23 static pid_t cached_vpid;
  24
  25 static inline
  26 pid_t wrapper_getvpid(void)
  27 {
  28         pid_t vpid;
  29
  30         vpid = CMM_LOAD_SHARED(cached_vpid);
  31         if (caa_unlikely(!vpid)) {
  32                 vpid = getpid();
  33                 CMM_STORE_SHARED(cached_vpid, vpid);
  34         }
  35         return vpid;
  36 }
  37
  38 /*
  39  * Upon fork or clone, the PID assigned to our thread is not the same as
  40  * we kept in cache.
  41  */
  42 void lttng_context_vpid_reset(void)
  43 {
  44         CMM_STORE_SHARED(cached_vpid, 0);
  45 }
  46
  47 static
  48 size_t vpid_get_size(struct lttng_ust_ctx_field *field, size_t offset)
  49 {
  50         size_t size = 0;
  51
  52         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  53         size += sizeof(pid_t);
  54         return size;
  55 }
  56
  57 static
  58 void vpid_record(struct lttng_ust_ctx_field *field,
  59                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  60                  struct lttng_channel *chan)
  61 {
  62         pid_t vpid = wrapper_getvpid();
  63
  64         lib_ring_buffer_align_ctx(ctx, lttng_alignof(vpid));
  65         chan->ops->event_write(ctx, &vpid, sizeof(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_alignof(pid_t) * CHAR_BIT,
  83                         lttng_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 }