lttng-context-comm.c

   1 /*
   2  * (C) Copyright        2009-2011 -
   3  *              Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   4  *
   5  * LTTng comm name context.
   6  *
   7  * Dual LGPL v2.1/GPL v2 license.
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/slab.h>
  12 #include <linux/sched.h>
  13 #include "ltt-events.h"
  14 #include "wrapper/ringbuffer/frontend_types.h"
  15 #include "wrapper/vmalloc.h"
  16 #include "ltt-tracer.h"
  17
  18 static
  19 size_t comm_get_size(size_t offset)
  20 {
  21         size_t size = 0;
  22
  23         size += sizeof(current->comm);
  24         return size;
  25 }
  26
  27 /*
  28  * Racy read of comm. We simply copy its whole array size.
  29  * Races with /proc/<task>/comm write only.
  30  * Otherwise having to take a mutex for each event is cumbersome and
  31  * could lead to crash in IRQ context and deadlock of the lockdep tracer.
  32  */
  33 static
  34 void comm_record(struct lttng_ctx_field *field,
  35                  struct lib_ring_buffer_ctx *ctx,
  36                  struct ltt_channel *chan)
  37 {
  38         chan->ops->event_write(ctx, current->comm, sizeof(current->comm));
  39 }
  40
  41 int lttng_add_comm_to_ctx(struct lttng_ctx **ctx)
  42 {
  43         struct lttng_ctx_field *field;
  44
  45         field = lttng_append_context(ctx);
  46         if (!field)
  47                 return -ENOMEM;
  48         if (lttng_find_context(*ctx, "comm")) {
  49                 lttng_remove_context_field(ctx, field);
  50                 return -EEXIST;
  51         }
  52         field->event_field.name = "comm";
  53         field->event_field.type.atype = atype_array;
  54         field->event_field.type.u.array.elem_type.atype = atype_integer;
  55         field->event_field.type.u.array.elem_type.u.basic.integer.size = sizeof(char) * CHAR_BIT;
  56         field->event_field.type.u.array.elem_type.u.basic.integer.alignment = ltt_alignof(char) * CHAR_BIT;
  57         field->event_field.type.u.array.elem_type.u.basic.integer.signedness = is_signed_type(char);
  58         field->event_field.type.u.array.elem_type.u.basic.integer.reverse_byte_order = 0;
  59         field->event_field.type.u.array.elem_type.u.basic.integer.base = 10;
  60         field->event_field.type.u.array.elem_type.u.basic.integer.encoding = lttng_encode_UTF8;
  61         field->event_field.type.u.array.length = sizeof(current->comm);
  62
  63         field->get_size = comm_get_size;
  64         field->record = comm_record;
  65         wrapper_vmalloc_sync_all();
  66         return 0;
  67 }
  68 EXPORT_SYMBOL_GPL(lttng_add_comm_to_ctx);
  69
  70 MODULE_LICENSE("GPL and additional rights");
  71 MODULE_AUTHOR("Mathieu Desnoyers");
  72 MODULE_DESCRIPTION("Linux Trace Toolkit Perf Support");