src/lib/lttng-ust/lttng-context-cpu-id.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2009-2015 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * LTTng UST CPU id context.
   7  *
   8  * Note: threads can be migrated at any point while executing the
   9  * tracepoint probe. This means the CPU id field (and filter) is only
  10  * statistical. For instance, even though a user might select a
  11  * cpu_id==1 filter, there may be few events recorded into the channel
  12  * appearing from other CPUs, due to migration.
  13  */
  14
  15 #define _LGPL_SOURCE
  16 #include <stddef.h>
  17 #include <sys/types.h>
  18 #include <unistd.h>
  19 #include <limits.h>
  20 #include <lttng/ust-events.h>
  21 #include <lttng/ust-tracer.h>
  22 #include "lib/lttng-ust/getcpu.h"
  23 #include <lttng/ust-ringbuffer-context.h>
  24
  25 #include "context-internal.h"
  26
  27 static
  28 size_t cpu_id_get_size(void *priv __attribute__((unused)),
  29                 size_t offset)
  30 {
  31         size_t size = 0;
  32
  33         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(int));
  34         size += sizeof(int);
  35         return size;
  36 }
  37
  38 static
  39 void cpu_id_record(void *priv __attribute__((unused)),
  40                  struct lttng_ust_ring_buffer_ctx *ctx,
  41                  struct lttng_ust_channel_buffer *chan)
  42 {
  43         int cpu;
  44
  45         cpu = lttng_ust_get_cpu();
  46         chan->ops->event_write(ctx, &cpu, sizeof(cpu), lttng_ust_rb_alignof(cpu));
  47 }
  48
  49 static
  50 void cpu_id_get_value(void *priv __attribute__((unused)),
  51                 struct lttng_ust_ctx_value *value)
  52 {
  53         value->u.s64 = lttng_ust_get_cpu();
  54 }
  55
  56 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
  57         lttng_ust_static_event_field("cpu_id",
  58                 lttng_ust_static_type_integer(sizeof(int) * CHAR_BIT,
  59                                 lttng_ust_rb_alignof(int) * CHAR_BIT,
  60                                 lttng_ust_is_signed_type(int),
  61                                 LTTNG_UST_BYTE_ORDER, 10),
  62                 false, false),
  63         cpu_id_get_size,
  64         cpu_id_record,
  65         cpu_id_get_value,
  66         NULL, NULL);
  67
  68 int lttng_add_cpu_id_to_ctx(struct lttng_ust_ctx **ctx)
  69 {
  70         int ret;
  71
  72         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
  73                 ret = -EEXIST;
  74                 goto error_find_context;
  75         }
  76         ret = lttng_ust_context_append(ctx, ctx_field);
  77         if (ret)
  78                 return ret;
  79         return 0;
  80
  81 error_find_context:
  82         return ret;
  83 }