liblttng-ust/lttng-context-vpid.c

   1 /*
   2  * lttng-context-vpid.c
   3  *
   4  * LTTng UST vpid 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 <sys/types.h>
  24 #include <unistd.h>
  25 #include <lttng/ust-events.h>
  26 #include <lttng/ust-tracer.h>
  27 #include <lttng/ringbuffer-config.h>
  28
  29 #ifdef __linux__
  30 static inline
  31 pid_t wrapper_getpid(void)
  32 {
  33         return getpid();
  34 }
  35
  36 void lttng_context_vpid_reset(void)
  37 {
  38 }
  39 #else
  40 /*
  41  * We cache the result to ensure we don't trigger a system call for
  42  * each event.
  43  */
  44 static pid_t cached_vpid;
  45
  46 static inline
  47 pid_t wrapper_getpid(void)
  48 {
  49         if (caa_unlikely(!cached_vpid))
  50                 cached_vpid = getpid();
  51         return cached_vpid;
  52 }
  53
  54 /*
  55  * Upon fork or clone, the PID assigned to our thread is not the same as
  56  * we kept in cache.
  57  */
  58 void lttng_context_vpid_reset(void)
  59 {
  60         cached_vpid = 0;
  61 }
  62 #endif
  63
  64 static
  65 size_t vpid_get_size(size_t offset)
  66 {
  67         size_t size = 0;
  68
  69         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  70         size += sizeof(pid_t);
  71         return size;
  72 }
  73
  74 static
  75 void vpid_record(struct lttng_ctx_field *field,
  76                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  77                  struct lttng_channel *chan)
  78 {
  79         pid_t pid;
  80
  81         pid = wrapper_getpid();
  82         lib_ring_buffer_align_ctx(ctx, lttng_alignof(pid));
  83         chan->ops->event_write(ctx, &pid, sizeof(pid));
  84 }
  85
  86 static
  87 void vpid_get_value(struct lttng_ctx_field *field,
  88                 union lttng_ctx_value *value)
  89 {
  90         pid_t pid;
  91
  92         pid = wrapper_getpid();
  93         value->s64 = pid;
  94 }
  95
  96 int lttng_add_vpid_to_ctx(struct lttng_ctx **ctx)
  97 {
  98         struct lttng_ctx_field *field;
  99
 100         field = lttng_append_context(ctx);
 101         if (!field)
 102                 return -ENOMEM;
 103         if (lttng_find_context(*ctx, "vpid")) {
 104                 lttng_remove_context_field(ctx, field);
 105                 return -EEXIST;
 106         }
 107         field->event_field.name = "vpid";
 108         field->event_field.type.atype = atype_integer;
 109         field->event_field.type.u.basic.integer.size = sizeof(pid_t) * CHAR_BIT;
 110         field->event_field.type.u.basic.integer.alignment = lttng_alignof(pid_t) * CHAR_BIT;
 111         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(pid_t);
 112         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
 113         field->event_field.type.u.basic.integer.base = 10;
 114         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
 115         field->get_size = vpid_get_size;
 116         field->record = vpid_record;
 117         field->get_value = vpid_get_value;
 118         return 0;
 119 }