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