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
  30 #ifdef __linux__
  31 #include <syscall.h>
  32 #endif
  33
  34 #if defined(_syscall0)
  35 _syscall0(pid_t, gettid)
  36 #elif defined(__NR_gettid)
  37 static inline pid_t gettid(void)
  38 {
  39         return syscall(__NR_gettid);
  40 }
  41 #else
  42 #warning "use pid as tid"
  43 static inline pid_t gettid(void)
  44 {
  45         return getpid();
  46 }
  47 #endif
  48
  49 /*
  50  * We cache the result to ensure we don't trigger a system call for
  51  * each event.
  52  */
  53 static __thread pid_t cached_vtid;
  54
  55 /*
  56  * Upon fork or clone, the TID assigned to our thread is not the same as
  57  * we kept in cache. Luckily, we are the only thread surviving in the
  58  * child process, so we can simply clear our cached version.
  59  */
  60 void lttng_context_vtid_reset(void)
  61 {
  62         cached_vtid = 0;
  63 }
  64
  65 static
  66 size_t vtid_get_size(size_t offset)
  67 {
  68         size_t size = 0;
  69
  70         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  71         size += sizeof(pid_t);
  72         return size;
  73 }
  74
  75 static
  76 void vtid_record(struct lttng_ctx_field *field,
  77                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  78                  struct ltt_channel *chan)
  79 {
  80         if (caa_unlikely(!cached_vtid))
  81                 cached_vtid = gettid();
  82         lib_ring_buffer_align_ctx(ctx, lttng_alignof(cached_vtid));
  83         chan->ops->event_write(ctx, &cached_vtid, sizeof(cached_vtid));
  84 }
  85
  86 int lttng_add_vtid_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, "vtid")) {
  94                 lttng_remove_context_field(ctx, field);
  95                 return -EEXIST;
  96         }
  97         field->event_field.name = "vtid";
  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 = vtid_get_size;
 106         field->record = vtid_record;
 107         return 0;
 108 }
 109
 110 /*
 111  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 112  */
 113 void lttng_fixup_vtid_tls(void)
 114 {
 115         asm volatile ("" : : "m" (cached_vtid));
 116 }