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