liblttng-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 <lttng/ust-events.h>
  20 #include <lttng/ust-tracer.h>
  21 #include <lttng/ringbuffer-config.h>
  22 #include "../libringbuffer/getcpu.h"
  23
  24 static
  25 size_t cpu_id_get_size(struct lttng_ctx_field *field, size_t offset)
  26 {
  27         size_t size = 0;
  28
  29         size += lib_ring_buffer_align(offset, lttng_alignof(int));
  30         size += sizeof(int);
  31         return size;
  32 }
  33
  34 static
  35 void cpu_id_record(struct lttng_ctx_field *field,
  36                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  37                  struct lttng_channel *chan)
  38 {
  39         int cpu;
  40
  41         cpu = lttng_ust_get_cpu();
  42         lib_ring_buffer_align_ctx(ctx, lttng_alignof(cpu));
  43         chan->ops->event_write(ctx, &cpu, sizeof(cpu));
  44 }
  45
  46 static
  47 void cpu_id_get_value(struct lttng_ctx_field *field,
  48                 struct lttng_ctx_value *value)
  49 {
  50         value->u.s64 = lttng_ust_get_cpu();
  51 }
  52
  53 int lttng_add_cpu_id_to_ctx(struct lttng_ctx **ctx)
  54 {
  55         struct lttng_ctx_field *field;
  56
  57         field = lttng_append_context(ctx);
  58         if (!field)
  59                 return -ENOMEM;
  60         if (lttng_find_context(*ctx, "cpu_id")) {
  61                 lttng_remove_context_field(ctx, field);
  62                 return -EEXIST;
  63         }
  64         field->event_field.name = "cpu_id";
  65         field->event_field.type.atype = atype_integer;
  66         field->event_field.type.u.integer.size = sizeof(int) * CHAR_BIT;
  67         field->event_field.type.u.integer.alignment = lttng_alignof(int) * CHAR_BIT;
  68         field->event_field.type.u.integer.signedness = lttng_is_signed_type(int);
  69         field->event_field.type.u.integer.reverse_byte_order = 0;
  70         field->event_field.type.u.integer.base = 10;
  71         field->event_field.type.u.integer.encoding = lttng_encode_none;
  72         field->get_size = cpu_id_get_size;
  73         field->record = cpu_id_record;
  74         field->get_value = cpu_id_get_value;
  75         lttng_context_update(*ctx);
  76         return 0;
  77 }