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-config.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_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_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_ctx_field *field,
  70                 struct lttng_ctx_value *value)
  71 {
  72         value->u.s64 = wrapper_getvpid();
  73 }
  74
  75 int lttng_add_vpid_to_ctx(struct lttng_ctx **ctx)
  76 {
  77         struct lttng_ctx_field *field;
  78
  79         field = lttng_append_context(ctx);
  80         if (!field)
  81                 return -ENOMEM;
  82         if (lttng_find_context(*ctx, "vpid")) {
  83                 lttng_remove_context_field(ctx, field);
  84                 return -EEXIST;
  85         }
  86         field->event_field.name = "vpid";
  87         field->event_field.type.atype = atype_integer;
  88         field->event_field.type.u.integer.size = sizeof(pid_t) * CHAR_BIT;
  89         field->event_field.type.u.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
  90         field->event_field.type.u.integer.signedness = lttng_is_signed_type(pid_t);
  91         field->event_field.type.u.integer.reverse_byte_order = 0;
  92         field->event_field.type.u.integer.base = 10;
  93         field->event_field.type.u.integer.encoding = lttng_encode_none;
  94         field->get_size = vpid_get_size;
  95         field->record = vpid_record;
  96         field->get_value = vpid_get_value;
  97         lttng_context_update(*ctx);
  98         return 0;
  99 }