liblttng-ust/lttng-context-procname.c

   1 /*
   2  * (C) Copyright        2009-2011 -
   3  *              Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  *
   5  * LTTng UST procname context.
   6  *
   7  * Dual LGPL v2.1/GPL v2 license.
   8  */
   9
  10 #include <lttng/ust-events.h>
  11 #include <lttng/ust-tracer.h>
  12 #include <lttng/ringbuffer-config.h>
  13 #include <assert.h>
  14 #include "compat.h"
  15
  16 /*
  17  * We cache the result to ensure we don't trigger a system call for
  18  * each event.
  19  * Upon exec, procname changes, but exec takes care of throwing away
  20  * this cached version.
  21  */
  22 static char cached_procname[17];
  23
  24 static inline
  25 char *wrapper_getprocname(void)
  26 {
  27         if (caa_unlikely(!cached_procname[0])) {
  28                 lttng_ust_getprocname(cached_procname);
  29                 cached_procname[LTTNG_UST_PROCNAME_LEN - 1] = '\0';
  30         }
  31         return cached_procname;
  32 }
  33
  34 void lttng_context_procname_reset(void)
  35 {
  36         cached_procname[0] = '\0';
  37 }
  38
  39 static
  40 size_t procname_get_size(size_t offset)
  41 {
  42         size_t size = 0;
  43
  44         size += LTTNG_UST_PROCNAME_LEN;
  45         return size;
  46 }
  47
  48 static
  49 void procname_record(struct lttng_ctx_field *field,
  50                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  51                  struct ltt_channel *chan)
  52 {
  53         char *procname;
  54
  55         procname = wrapper_getprocname();
  56         chan->ops->event_write(ctx, procname, LTTNG_UST_PROCNAME_LEN);
  57 }
  58
  59 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
  60 {
  61         struct lttng_ctx_field *field;
  62
  63         field = lttng_append_context(ctx);
  64         if (!field)
  65                 return -ENOMEM;
  66         if (lttng_find_context(*ctx, "procname")) {
  67                 lttng_remove_context_field(ctx, field);
  68                 return -EEXIST;
  69         }
  70         field->event_field.name = "procname";
  71         field->event_field.type.atype = atype_array;
  72         field->event_field.type.u.array.elem_type.atype = atype_integer;
  73         field->event_field.type.u.array.elem_type.u.basic.integer.size = sizeof(char) * CHAR_BIT;
  74         field->event_field.type.u.array.elem_type.u.basic.integer.alignment = lttng_alignof(char) * CHAR_BIT;
  75         field->event_field.type.u.array.elem_type.u.basic.integer.signedness = lttng_is_signed_type(char);
  76         field->event_field.type.u.array.elem_type.u.basic.integer.reverse_byte_order = 0;
  77         field->event_field.type.u.array.elem_type.u.basic.integer.base = 10;
  78         field->event_field.type.u.array.elem_type.u.basic.integer.encoding = lttng_encode_UTF8;
  79         field->event_field.type.u.array.length = LTTNG_UST_PROCNAME_LEN;
  80         field->get_size = procname_get_size;
  81         field->record = procname_record;
  82         return 0;
  83 }