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 /* Maximum number of nesting levels for the procname cache. */
  32 #define PROCNAME_NESTING_MAX    2
  33
  34 /*
  35  * We cache the result to ensure we don't trigger a system call for
  36  * each event.
  37  * Upon exec, procname changes, but exec takes care of throwing away
  38  * this cached version.
  39  * The procname can also change by calling prctl(). The procname should
  40  * be set for a thread before the first event is logged within this
  41  * thread.
  42  */
  43 typedef char procname_array[PROCNAME_NESTING_MAX][17];
  44
  45 static DEFINE_URCU_TLS(procname_array, cached_procname);
  46
  47 static DEFINE_URCU_TLS(int, procname_nesting);
  48
  49 static inline
  50 char *wrapper_getprocname(void)
  51 {
  52         int nesting = CMM_LOAD_SHARED(URCU_TLS(procname_nesting));
  53
  54         if (caa_unlikely(nesting >= PROCNAME_NESTING_MAX))
  55                 return "<unknown>";
  56         if (caa_unlikely(!URCU_TLS(cached_procname)[nesting][0])) {
  57                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting + 1);
  58                 /* Increment nesting before updating cache. */
  59                 cmm_barrier();
  60                 lttng_ust_getprocname(URCU_TLS(cached_procname)[nesting]);
  61                 URCU_TLS(cached_procname)[nesting][LTTNG_UST_PROCNAME_LEN - 1] = '\0';
  62                 /* Decrement nesting after updating cache. */
  63                 cmm_barrier();
  64                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting);
  65         }
  66         return URCU_TLS(cached_procname)[nesting];
  67 }
  68
  69 /* Reset should not be called from a signal handler. */
  70 void lttng_context_procname_reset(void)
  71 {
  72         CMM_STORE_SHARED(URCU_TLS(cached_procname)[1][0], '\0');
  73         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 1);
  74         CMM_STORE_SHARED(URCU_TLS(cached_procname)[0][0], '\0');
  75         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 0);
  76 }
  77
  78 static
  79 size_t procname_get_size(struct lttng_ctx_field *field, size_t offset)
  80 {
  81         return LTTNG_UST_PROCNAME_LEN;
  82 }
  83
  84 static
  85 void procname_record(struct lttng_ctx_field *field,
  86                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  87                  struct lttng_channel *chan)
  88 {
  89         char *procname;
  90
  91         procname = wrapper_getprocname();
  92         chan->ops->event_write(ctx, procname, LTTNG_UST_PROCNAME_LEN);
  93 }
  94
  95 static
  96 void procname_get_value(struct lttng_ctx_field *field,
  97                 struct lttng_ctx_value *value)
  98 {
  99         value->u.str = wrapper_getprocname();
 100 }
 101
 102 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
 103 {
 104         struct lttng_ctx_field *field;
 105
 106         field = lttng_append_context(ctx);
 107         if (!field)
 108                 return -ENOMEM;
 109         if (lttng_find_context(*ctx, "procname")) {
 110                 lttng_remove_context_field(ctx, field);
 111                 return -EEXIST;
 112         }
 113         field->event_field.name = "procname";
 114         field->event_field.type.atype = atype_array;
 115         field->event_field.type.u.array.elem_type.atype = atype_integer;
 116         field->event_field.type.u.array.elem_type.u.basic.integer.size = sizeof(char) * CHAR_BIT;
 117         field->event_field.type.u.array.elem_type.u.basic.integer.alignment = lttng_alignof(char) * CHAR_BIT;
 118         field->event_field.type.u.array.elem_type.u.basic.integer.signedness = lttng_is_signed_type(char);
 119         field->event_field.type.u.array.elem_type.u.basic.integer.reverse_byte_order = 0;
 120         field->event_field.type.u.array.elem_type.u.basic.integer.base = 10;
 121         field->event_field.type.u.array.elem_type.u.basic.integer.encoding = lttng_encode_UTF8;
 122         field->event_field.type.u.array.length = LTTNG_UST_PROCNAME_LEN;
 123         field->get_size = procname_get_size;
 124         field->record = procname_record;
 125         field->get_value = procname_get_value;
 126         lttng_context_update(*ctx);
 127         return 0;
 128 }
 129
 130 /*
 131  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 132  */
 133 void lttng_fixup_procname_tls(void)
 134 {
 135         asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
 136 }