liblttng-ust/lttng-context-vtid.c

   1 /*
   2  * lttng-context-vtid.c
   3  *
   4  * LTTng UST vtid 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 #include <lttng/ust-tid.h>
  30 #include <urcu/tls-compat.h>
  31 #include "lttng-tracer-core.h"
  32
  33 /*
  34  * We cache the result to ensure we don't trigger a system call for
  35  * each event.
  36  */
  37 static DEFINE_URCU_TLS(pid_t, cached_vtid);
  38
  39 /*
  40  * Upon fork or clone, the TID assigned to our thread is not the same as
  41  * we kept in cache. Luckily, we are the only thread surviving in the
  42  * child process, so we can simply clear our cached version.
  43  */
  44 void lttng_context_vtid_reset(void)
  45 {
  46         URCU_TLS(cached_vtid) = 0;
  47 }
  48
  49 static
  50 size_t vtid_get_size(struct lttng_ctx_field *field, size_t offset)
  51 {
  52         size_t size = 0;
  53
  54         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  55         size += sizeof(pid_t);
  56         return size;
  57 }
  58
  59 static
  60 void vtid_record(struct lttng_ctx_field *field,
  61                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  62                  struct lttng_channel *chan)
  63 {
  64         if (caa_unlikely(!URCU_TLS(cached_vtid)))
  65                 URCU_TLS(cached_vtid) = gettid();
  66         lib_ring_buffer_align_ctx(ctx, lttng_alignof(URCU_TLS(cached_vtid)));
  67         chan->ops->event_write(ctx, &URCU_TLS(cached_vtid),
  68                 sizeof(URCU_TLS(cached_vtid)));
  69 }
  70
  71 static
  72 void vtid_get_value(struct lttng_ctx_field *field,
  73                 struct lttng_ctx_value *value)
  74 {
  75         if (caa_unlikely(!URCU_TLS(cached_vtid)))
  76                 URCU_TLS(cached_vtid) = gettid();
  77         value->u.s64 = URCU_TLS(cached_vtid);
  78 }
  79
  80 int lttng_add_vtid_to_ctx(struct lttng_ctx **ctx)
  81 {
  82         struct lttng_ctx_field *field;
  83
  84         field = lttng_append_context(ctx);
  85         if (!field)
  86                 return -ENOMEM;
  87         if (lttng_find_context(*ctx, "vtid")) {
  88                 lttng_remove_context_field(ctx, field);
  89                 return -EEXIST;
  90         }
  91         field->event_field.name = "vtid";
  92         field->event_field.type.atype = atype_integer;
  93         field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
  94         field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
  95         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
  96         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
  97         field->event_field.type.u.basic.integer.base = 10;
  98         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
  99         field->get_size = vtid_get_size;
 100         field->record = vtid_record;
 101         field->get_value = vtid_get_value;
 102         lttng_context_update(*ctx);
 103         return 0;
 104 }
 105
 106 /*
 107  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 108  */
 109 void lttng_fixup_vtid_tls(void)
 110 {
 111         asm volatile ("" : : "m" (URCU_TLS(cached_vtid)));
 112 }