liblttng-ust/lttng-context-procname.c

   1 /*
   2  * lttng-context-procname.c
   3  *
   4  * LTTng UST procname 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 <lttng/ust-events.h>
  25 #include <lttng/ust-tracer.h>
  26 #include <lttng/ringbuffer-config.h>
  27 #include <urcu/tls-compat.h>
  28 #include <assert.h>
  29 #include "compat.h"
  30
  31 /*
  32  * We cache the result to ensure we don't trigger a system call for
  33  * each event.
  34  * Upon exec, procname changes, but exec takes care of throwing away
  35  * this cached version.
  36  * The procname can also change by calling prctl(). The procname should
  37  * be set for a thread before the first event is logged within this
  38  * thread.
  39  */
  40 typedef char procname_array[17];
  41 static DEFINE_URCU_TLS(procname_array, cached_procname);
  42
  43 static inline
  44 char *wrapper_getprocname(void)
  45 {
  46         if (caa_unlikely(!URCU_TLS(cached_procname)[0])) {
  47                 lttng_ust_getprocname(URCU_TLS(cached_procname));
  48                 URCU_TLS(cached_procname)[LTTNG_UST_PROCNAME_LEN - 1] = '\0';
  49         }
  50         return URCU_TLS(cached_procname);
  51 }
  52
  53 void lttng_context_procname_reset(void)
  54 {
  55         URCU_TLS(cached_procname)[0] = '\0';
  56 }
  57
  58 static
  59 size_t procname_get_size(struct lttng_ctx_field *field, size_t offset)
  60 {
  61         size_t size = 0;
  62
  63         size += LTTNG_UST_PROCNAME_LEN;
  64         return size;
  65 }
  66
  67 static
  68 void procname_record(struct lttng_ctx_field *field,
  69                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  70                  struct lttng_channel *chan)
  71 {
  72         char *procname;
  73
  74         procname = wrapper_getprocname();
  75         chan->ops->event_write(ctx, procname, LTTNG_UST_PROCNAME_LEN);
  76 }
  77
  78 static
  79 void procname_get_value(struct lttng_ctx_field *field,
  80                 struct lttng_ctx_value *value)
  81 {
  82         char *procname;
  83
  84         procname = wrapper_getprocname();
  85         value->u.str = procname;
  86 }
  87
  88 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
  89 {
  90         struct lttng_ctx_field *field;
  91
  92         field = lttng_append_context(ctx);
  93         if (!field)
  94                 return -ENOMEM;
  95         if (lttng_find_context(*ctx, "procname")) {
  96                 lttng_remove_context_field(ctx, field);
  97                 return -EEXIST;
  98         }
  99         field->event_field.name = "procname";
 100         field->event_field.type.atype = atype_array;
 101         field->event_field.type.u.array.elem_type.atype = atype_integer;
 102         field->event_field.type.u.array.elem_type.u.basic.integer.size = sizeof(char) * CHAR_BIT;
 103         field->event_field.type.u.array.elem_type.u.basic.integer.alignment = lttng_alignof(char) * CHAR_BIT;
 104         field->event_field.type.u.array.elem_type.u.basic.integer.signedness = lttng_is_signed_type(char);
 105         field->event_field.type.u.array.elem_type.u.basic.integer.reverse_byte_order = 0;
 106         field->event_field.type.u.array.elem_type.u.basic.integer.base = 10;
 107         field->event_field.type.u.array.elem_type.u.basic.integer.encoding = lttng_encode_UTF8;
 108         field->event_field.type.u.array.length = LTTNG_UST_PROCNAME_LEN;
 109         field->get_size = procname_get_size;
 110         field->record = procname_record;
 111         field->get_value = procname_get_value;
 112         lttng_context_update(*ctx);
 113         return 0;
 114 }
 115
 116 /*
 117  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 118  */
 119 void lttng_fixup_procname_tls(void)
 120 {
 121         asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
 122 }