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 <stddef.h>
  25 #include <lttng/ust-events.h>
  26 #include <lttng/ust-tracer.h>
  27 #include <lttng/ringbuffer-config.h>
  28 #include <urcu/tls-compat.h>
  29 #include <assert.h>
  30 #include "compat.h"
  31
  32 /* Maximum number of nesting levels for the procname cache. */
  33 #define PROCNAME_NESTING_MAX    2
  34
  35 /*
  36  * We cache the result to ensure we don't trigger a system call for
  37  * each event.
  38  * Upon exec, procname changes, but exec takes care of throwing away
  39  * this cached version.
  40  * The procname can also change by calling prctl(). The procname should
  41  * be set for a thread before the first event is logged within this
  42  * thread.
  43  */
  44 typedef char procname_array[PROCNAME_NESTING_MAX][17];
  45
  46 static DEFINE_URCU_TLS(procname_array, cached_procname);
  47
  48 static DEFINE_URCU_TLS(int, procname_nesting);
  49
  50 static inline
  51 char *wrapper_getprocname(void)
  52 {
  53         int nesting = CMM_LOAD_SHARED(URCU_TLS(procname_nesting));
  54
  55         if (caa_unlikely(nesting >= PROCNAME_NESTING_MAX))
  56                 return "<unknown>";
  57         if (caa_unlikely(!URCU_TLS(cached_procname)[nesting][0])) {
  58                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting + 1);
  59                 /* Increment nesting before updating cache. */
  60                 cmm_barrier();
  61                 lttng_pthread_getname_np(URCU_TLS(cached_procname)[nesting], LTTNG_UST_ABI_PROCNAME_LEN);
  62                 URCU_TLS(cached_procname)[nesting][LTTNG_UST_ABI_PROCNAME_LEN - 1] = '\0';
  63                 /* Decrement nesting after updating cache. */
  64                 cmm_barrier();
  65                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting);
  66         }
  67         return URCU_TLS(cached_procname)[nesting];
  68 }
  69
  70 /* Reset should not be called from a signal handler. */
  71 void lttng_context_procname_reset(void)
  72 {
  73         CMM_STORE_SHARED(URCU_TLS(cached_procname)[1][0], '\0');
  74         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 1);
  75         CMM_STORE_SHARED(URCU_TLS(cached_procname)[0][0], '\0');
  76         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 0);
  77 }
  78
  79 static
  80 size_t procname_get_size(struct lttng_ctx_field *field, size_t offset)
  81 {
  82         return LTTNG_UST_ABI_PROCNAME_LEN;
  83 }
  84
  85 static
  86 void procname_record(struct lttng_ctx_field *field,
  87                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  88                  struct lttng_channel *chan)
  89 {
  90         char *procname;
  91
  92         procname = wrapper_getprocname();
  93         chan->ops->event_write(ctx, procname, LTTNG_UST_ABI_PROCNAME_LEN);
  94 }
  95
  96 static
  97 void procname_get_value(struct lttng_ctx_field *field,
  98                 struct lttng_ctx_value *value)
  99 {
 100         value->u.str = wrapper_getprocname();
 101 }
 102
 103 static const struct lttng_type procname_array_elem_type =
 104         __type_integer(char, BYTE_ORDER, 10, UTF8);
 105
 106 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
 107 {
 108         struct lttng_ctx_field *field;
 109
 110         field = lttng_append_context(ctx);
 111         if (!field)
 112                 return -ENOMEM;
 113         if (lttng_find_context(*ctx, "procname")) {
 114                 lttng_remove_context_field(ctx, field);
 115                 return -EEXIST;
 116         }
 117         field->event_field.name = "procname";
 118         field->event_field.type.atype = atype_array_nestable;
 119         field->event_field.type.u.array_nestable.elem_type =
 120                 &procname_array_elem_type;
 121         field->event_field.type.u.array_nestable.length = LTTNG_UST_ABI_PROCNAME_LEN;
 122         field->get_size = procname_get_size;
 123         field->record = procname_record;
 124         field->get_value = procname_get_value;
 125         lttng_context_update(*ctx);
 126         return 0;
 127 }
 128
 129 /*
 130  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 131  */
 132 void lttng_fixup_procname_tls(void)
 133 {
 134         asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
 135 }