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 /*
  18  * We cache the result to ensure we don't trigger a system call for
  19  * each event.
  20  */
  21 static pid_t cached_vpid;
  22
  23 static inline
  24 pid_t wrapper_getvpid(void)
  25 {
  26         pid_t vpid;
  27
  28         vpid = CMM_LOAD_SHARED(cached_vpid);
  29         if (caa_unlikely(!vpid)) {
  30                 vpid = getpid();
  31                 CMM_STORE_SHARED(cached_vpid, vpid);
  32         }
  33         return vpid;
  34 }
  35
  36 /*
  37  * Upon fork or clone, the PID assigned to our thread is not the same as
  38  * we kept in cache.
  39  */
  40 void lttng_context_vpid_reset(void)
  41 {
  42         CMM_STORE_SHARED(cached_vpid, 0);
  43 }
  44
  45 static
  46 size_t vpid_get_size(struct lttng_ctx_field *field, size_t offset)
  47 {
  48         size_t size = 0;
  49
  50         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  51         size += sizeof(pid_t);
  52         return size;
  53 }
  54
  55 static
  56 void vpid_record(struct lttng_ctx_field *field,
  57                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  58                  struct lttng_channel *chan)
  59 {
  60         pid_t vpid = wrapper_getvpid();
  61
  62         lib_ring_buffer_align_ctx(ctx, lttng_alignof(vpid));
  63         chan->ops->event_write(ctx, &vpid, sizeof(vpid));
  64 }
  65
  66 static
  67 void vpid_get_value(struct lttng_ctx_field *field,
  68                 struct lttng_ctx_value *value)
  69 {
  70         value->u.s64 = wrapper_getvpid();
  71 }
  72
  73 int lttng_add_vpid_to_ctx(struct lttng_ctx **ctx)
  74 {
  75         struct lttng_ctx_field *field;
  76
  77         field = lttng_append_context(ctx);
  78         if (!field)
  79                 return -ENOMEM;
  80         if (lttng_find_context(*ctx, "vpid")) {
  81                 lttng_remove_context_field(ctx, field);
  82                 return -EEXIST;
  83         }
  84         field->event_field.name = "vpid";
  85         field->event_field.type.atype = atype_integer;
  86         field->event_field.type.u.integer.size = sizeof(pid_t) * CHAR_BIT;
  87         field->event_field.type.u.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
  88         field->event_field.type.u.integer.signedness = lttng_is_signed_type(pid_t);
  89         field->event_field.type.u.integer.reverse_byte_order = 0;
  90         field->event_field.type.u.integer.base = 10;
  91         field->event_field.type.u.integer.encoding = lttng_encode_none;
  92         field->get_size = vpid_get_size;
  93         field->record = vpid_record;
  94         field->get_value = vpid_get_value;
  95         lttng_context_update(*ctx);
  96         return 0;
  97 }