src/lib/lttng-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 <limits.h>
  11 #include <stddef.h>
  12 #include <sys/types.h>
  13 #include <unistd.h>
  14 #include <lttng/ust-events.h>
  15 #include <lttng/ust-tracer.h>
  16 #include <lttng/ust-ringbuffer-context.h>
  17
  18 #include "context-internal.h"
  19
  20 /*
  21  * We cache the result to ensure we don't trigger a system call for
  22  * each event.
  23  */
  24 static pid_t cached_vpid;
  25
  26 static inline
  27 pid_t wrapper_getvpid(void)
  28 {
  29         pid_t vpid;
  30
  31         vpid = CMM_LOAD_SHARED(cached_vpid);
  32         if (caa_unlikely(!vpid)) {
  33                 vpid = getpid();
  34                 CMM_STORE_SHARED(cached_vpid, vpid);
  35         }
  36         return vpid;
  37 }
  38
  39 /*
  40  * Upon fork or clone, the PID assigned to our thread is not the same as
  41  * we kept in cache.
  42  */
  43 void lttng_context_vpid_reset(void)
  44 {
  45         CMM_STORE_SHARED(cached_vpid, 0);
  46 }
  47
  48 static
  49 size_t vpid_get_size(void *priv __attribute__((unused)),
  50                 size_t offset)
  51 {
  52         size_t size = 0;
  53
  54         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(pid_t));
  55         size += sizeof(pid_t);
  56         return size;
  57 }
  58
  59 static
  60 void vpid_record(void *priv __attribute__((unused)),
  61                  struct lttng_ust_ring_buffer_ctx *ctx,
  62                  struct lttng_ust_channel_buffer *chan)
  63 {
  64         pid_t vpid = wrapper_getvpid();
  65
  66         chan->ops->event_write(ctx, &vpid, sizeof(vpid), lttng_ust_rb_alignof(vpid));
  67 }
  68
  69 static
  70 void vpid_get_value(void *priv __attribute__((unused)),
  71                 struct lttng_ust_ctx_value *value)
  72 {
  73         value->u.s64 = wrapper_getvpid();
  74 }
  75
  76 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
  77         lttng_ust_static_event_field("vpid",
  78                 lttng_ust_static_type_integer(sizeof(pid_t) * CHAR_BIT,
  79                                 lttng_ust_rb_alignof(pid_t) * CHAR_BIT,
  80                                 lttng_ust_is_signed_type(pid_t),
  81                                 LTTNG_UST_BYTE_ORDER, 10),
  82                 false, false),
  83         vpid_get_size,
  84         vpid_record,
  85         vpid_get_value,
  86         NULL, NULL);
  87
  88 int lttng_add_vpid_to_ctx(struct lttng_ust_ctx **ctx)
  89 {
  90         int ret;
  91
  92         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
  93                 ret = -EEXIST;
  94                 goto error_find_context;
  95         }
  96         ret = lttng_ust_context_append(ctx, ctx_field);
  97         if (ret)
  98                 return ret;
  99         return 0;
 100
 101 error_find_context:
 102         return ret;
 103 }