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