liblttng-ust/lttng-context-vpid.c

   1 /*
   2  * lttng-context-vpid.c
   3  *
   4  * LTTng UST vpid context.
   5  *
   6  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; only
  11  * version 2.1 of the License.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #define _LGPL_SOURCE
  24 #include <sys/types.h>
  25 #include <unistd.h>
  26 #include <lttng/ust-events.h>
  27 #include <lttng/ust-tracer.h>
  28 #include <lttng/ringbuffer-config.h>
  29
  30 /*
  31  * We cache the result to ensure we don't trigger a system call for
  32  * each event.
  33  */
  34 static pid_t cached_vpid;
  35
  36 static inline
  37 pid_t wrapper_getpid(void)
  38 {
  39         if (caa_unlikely(!cached_vpid))
  40                 cached_vpid = getpid();
  41         return cached_vpid;
  42 }
  43
  44 /*
  45  * Upon fork or clone, the PID assigned to our thread is not the same as
  46  * we kept in cache.
  47  */
  48 void lttng_context_vpid_reset(void)
  49 {
  50         cached_vpid = 0;
  51 }
  52
  53 static
  54 size_t vpid_get_size(struct lttng_ctx_field *field, size_t offset)
  55 {
  56         size_t size = 0;
  57
  58         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  59         size += sizeof(pid_t);
  60         return size;
  61 }
  62
  63 static
  64 void vpid_record(struct lttng_ctx_field *field,
  65                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  66                  struct lttng_channel *chan)
  67 {
  68         pid_t pid;
  69
  70         pid = wrapper_getpid();
  71         lib_ring_buffer_align_ctx(ctx, lttng_alignof(pid));
  72         chan->ops->event_write(ctx, &pid, sizeof(pid));
  73 }
  74
  75 static
  76 void vpid_get_value(struct lttng_ctx_field *field,
  77                 struct lttng_ctx_value *value)
  78 {
  79         pid_t pid;
  80
  81         pid = wrapper_getpid();
  82         value->u.s64 = pid;
  83 }
  84
  85 int lttng_add_vpid_to_ctx(struct lttng_ctx **ctx)
  86 {
  87         struct lttng_ctx_field *field;
  88
  89         field = lttng_append_context(ctx);
  90         if (!field)
  91                 return -ENOMEM;
  92         if (lttng_find_context(*ctx, "vpid")) {
  93                 lttng_remove_context_field(ctx, field);
  94                 return -EEXIST;
  95         }
  96         field->event_field.name = "vpid";
  97         field->event_field.type.atype = atype_integer;
  98         field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
  99         field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
 100         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
 101         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
 102         field->event_field.type.u.basic.integer.base = 10;
 103         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
 104         field->get_size = vpid_get_size;
 105         field->record = vpid_record;
 106         field->get_value = vpid_get_value;
 107         lttng_context_update(*ctx);
 108         return 0;
 109 }