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_getvpid(void)
  38 {
  39         pid_t vpid;
  40
  41         vpid = CMM_LOAD_SHARED(cached_vpid);
  42         if (caa_unlikely(!vpid)) {
  43                 vpid = getpid();
  44                 CMM_STORE_SHARED(cached_vpid, vpid);
  45         }
  46         return vpid;
  47 }
  48
  49 /*
  50  * Upon fork or clone, the PID assigned to our thread is not the same as
  51  * we kept in cache.
  52  */
  53 void lttng_context_vpid_reset(void)
  54 {
  55         CMM_STORE_SHARED(cached_vpid, 0);
  56 }
  57
  58 static
  59 size_t vpid_get_size(struct lttng_ctx_field *field, size_t offset)
  60 {
  61         size_t size = 0;
  62
  63         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  64         size += sizeof(pid_t);
  65         return size;
  66 }
  67
  68 static
  69 void vpid_record(struct lttng_ctx_field *field,
  70                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  71                  struct lttng_channel *chan)
  72 {
  73         pid_t vpid = wrapper_getvpid();
  74
  75         lib_ring_buffer_align_ctx(ctx, lttng_alignof(vpid));
  76         chan->ops->event_write(ctx, &vpid, sizeof(vpid));
  77 }
  78
  79 static
  80 void vpid_get_value(struct lttng_ctx_field *field,
  81                 struct lttng_ctx_value *value)
  82 {
  83         value->u.s64 = wrapper_getvpid();
  84 }
  85
  86 int lttng_add_vpid_to_ctx(struct lttng_ctx **ctx)
  87 {
  88         struct lttng_ctx_field *field;
  89
  90         field = lttng_append_context(ctx);
  91         if (!field)
  92                 return -ENOMEM;
  93         if (lttng_find_context(*ctx, "vpid")) {
  94                 lttng_remove_context_field(ctx, field);
  95                 return -EEXIST;
  96         }
  97         field->event_field.name = "vpid";
  98         field->event_field.type.atype = atype_integer;
  99         field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
 100         field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
 101         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
 102         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
 103         field->event_field.type.u.basic.integer.base = 10;
 104         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
 105         field->get_size = vpid_get_size;
 106         field->record = vpid_record;
 107         field->get_value = vpid_get_value;
 108         lttng_context_update(*ctx);
 109         return 0;
 110 }