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 = 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                 lttng_ust_getprocname(URCU_TLS(cached_procname)[nesting]);
  59                 URCU_TLS(cached_procname)[nesting][LTTNG_UST_PROCNAME_LEN - 1] = '\0';
  60                 CMM_STORE_SHARED(URCU_TLS(procname_nesting), nesting);
  61         }
  62         return URCU_TLS(cached_procname)[nesting];
  63 }
  64
  65 void lttng_context_procname_reset(void)
  66 {
  67         URCU_TLS(cached_procname)[1][0] = '\0';
  68         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 1);
  69         URCU_TLS(cached_procname)[0][0] = '\0';
  70         CMM_STORE_SHARED(URCU_TLS(procname_nesting), 0);
  71 }
  72
  73 static
  74 size_t procname_get_size(struct lttng_ctx_field *field, size_t offset)
  75 {
  76         size_t size = 0;
  77
  78         size += LTTNG_UST_PROCNAME_LEN;
  79         return size;
  80 }
  81
  82 static
  83 void procname_record(struct lttng_ctx_field *field,
  84                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  85                  struct lttng_channel *chan)
  86 {
  87         char *procname;
  88
  89         procname = wrapper_getprocname();
  90         chan->ops->event_write(ctx, procname, LTTNG_UST_PROCNAME_LEN);
  91 }
  92
  93 static
  94 void procname_get_value(struct lttng_ctx_field *field,
  95                 struct lttng_ctx_value *value)
  96 {
  97         char *procname;
  98
  99         procname = wrapper_getprocname();
 100         value->u.str = procname;
 101 }
 102
 103 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
 104 {
 105         struct lttng_ctx_field *field;
 106
 107         field = lttng_append_context(ctx);
 108         if (!field)
 109                 return -ENOMEM;
 110         if (lttng_find_context(*ctx, "procname")) {
 111                 lttng_remove_context_field(ctx, field);
 112                 return -EEXIST;
 113         }
 114         field->event_field.name = "procname";
 115         field->event_field.type.atype = atype_array;
 116         field->event_field.type.u.array.elem_type.atype = atype_integer;
 117         field->event_field.type.u.array.elem_type.u.basic.integer.size = sizeof(char) * CHAR_BIT;
 118         field->event_field.type.u.array.elem_type.u.basic.integer.alignment = lttng_alignof(char) * CHAR_BIT;
 119         field->event_field.type.u.array.elem_type.u.basic.integer.signedness = lttng_is_signed_type(char);
 120         field->event_field.type.u.array.elem_type.u.basic.integer.reverse_byte_order = 0;
 121         field->event_field.type.u.array.elem_type.u.basic.integer.base = 10;
 122         field->event_field.type.u.array.elem_type.u.basic.integer.encoding = lttng_encode_UTF8;
 123         field->event_field.type.u.array.length = LTTNG_UST_PROCNAME_LEN;
 124         field->get_size = procname_get_size;
 125         field->record = procname_record;
 126         field->get_value = procname_get_value;
 127         lttng_context_update(*ctx);
 128         return 0;
 129 }
 130
 131 /*
 132  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 133  */
 134 void lttng_fixup_procname_tls(void)
 135 {
 136         asm volatile ("" : : "m" (URCU_TLS(cached_procname)[0]));
 137 }