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                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
  51                 size_t offset)
  52 {
  53         size_t size = 0;
  54
  55         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(pid_t));
  56         size += sizeof(pid_t);
  57         return size;
  58 }
  59
  60 static
  61 void vpid_record(void *priv __attribute__((unused)),
  62                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
  63                 struct lttng_ust_ring_buffer_ctx *ctx,
  64                 struct lttng_ust_channel_buffer *chan)
  65 {
  66         pid_t vpid = wrapper_getvpid();
  67
  68         chan->ops->event_write(ctx, &vpid, sizeof(vpid), lttng_ust_rb_alignof(vpid));
  69 }
  70
  71 static
  72 void vpid_get_value(void *priv __attribute__((unused)),
  73                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
  74                 struct lttng_ust_ctx_value *value)
  75 {
  76         value->u.s64 = wrapper_getvpid();
  77 }
  78
  79 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
  80         lttng_ust_static_event_field("vpid",
  81                 lttng_ust_static_type_integer(sizeof(pid_t) * CHAR_BIT,
  82                                 lttng_ust_rb_alignof(pid_t) * CHAR_BIT,
  83                                 lttng_ust_is_signed_type(pid_t),
  84                                 LTTNG_UST_BYTE_ORDER, 10),
  85                 false, false),
  86         vpid_get_size,
  87         vpid_record,
  88         vpid_get_value,
  89         NULL, NULL);
  90
  91 int lttng_add_vpid_to_ctx(struct lttng_ust_ctx **ctx)
  92 {
  93         int ret;
  94
  95         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
  96                 ret = -EEXIST;
  97                 goto error_find_context;
  98         }
  99         ret = lttng_ust_context_append(ctx, ctx_field);
 100         if (ret)
 101                 return ret;
 102         return 0;
 103
 104 error_find_context:
 105         return ret;
 106 }