lttng-context-procname.c

   1 /*
   2  * lttng-context-procname.c
   3  *
   4  * LTTng 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 #include <linux/module.h>
  24 #include <linux/slab.h>
  25 #include <linux/sched.h>
  26 #include <lttng-events.h>
  27 #include <wrapper/ringbuffer/frontend_types.h>
  28 #include <wrapper/vmalloc.h>
  29 #include <lttng-tracer.h>
  30
  31 static
  32 size_t procname_get_size(size_t offset)
  33 {
  34         size_t size = 0;
  35
  36         size += sizeof(current->comm);
  37         return size;
  38 }
  39
  40 /*
  41  * Racy read of procname. We simply copy its whole array size.
  42  * Races with /proc/<task>/procname write only.
  43  * Otherwise having to take a mutex for each event is cumbersome and
  44  * could lead to crash in IRQ context and deadlock of the lockdep tracer.
  45  */
  46 static
  47 void procname_record(struct lttng_ctx_field *field,
  48                  struct lib_ring_buffer_ctx *ctx,
  49                  struct lttng_channel *chan)
  50 {
  51         chan->ops->event_write(ctx, current->comm, sizeof(current->comm));
  52 }
  53
  54 static
  55 void procname_get_value(struct lttng_ctx_field *field,
  56                 struct lttng_probe_ctx *lttng_probe_ctx,
  57                 union lttng_ctx_value *value)
  58 {
  59         value->str = current->comm;
  60 }
  61
  62 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
  63 {
  64         struct lttng_ctx_field *field;
  65
  66         field = lttng_append_context(ctx);
  67         if (!field)
  68                 return -ENOMEM;
  69         if (lttng_find_context(*ctx, "procname")) {
  70                 lttng_remove_context_field(ctx, field);
  71                 return -EEXIST;
  72         }
  73         field->event_field.name = "procname";
  74         field->event_field.type.atype = atype_array;
  75         field->event_field.type.u.array.elem_type.atype = atype_integer;
  76         field->event_field.type.u.array.elem_type.u.basic.integer.size = sizeof(char) * CHAR_BIT;
  77         field->event_field.type.u.array.elem_type.u.basic.integer.alignment = lttng_alignof(char) * CHAR_BIT;
  78         field->event_field.type.u.array.elem_type.u.basic.integer.signedness = lttng_is_signed_type(char);
  79         field->event_field.type.u.array.elem_type.u.basic.integer.reverse_byte_order = 0;
  80         field->event_field.type.u.array.elem_type.u.basic.integer.base = 10;
  81         field->event_field.type.u.array.elem_type.u.basic.integer.encoding = lttng_encode_UTF8;
  82         field->event_field.type.u.array.length = sizeof(current->comm);
  83
  84         field->get_size = procname_get_size;
  85         field->record = procname_record;
  86         field->get_value = procname_get_value;
  87         lttng_context_update(*ctx);
  88         wrapper_vmalloc_sync_all();
  89         return 0;
  90 }
  91 EXPORT_SYMBOL_GPL(lttng_add_procname_to_ctx);