lttng-context-procname.c

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * lttng-context-procname.c
   4  *
   5  * LTTng procname context.
   6  *
   7  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/slab.h>
  12 #include <linux/sched.h>
  13 #include <lttng/lttng-events.h>
  14 #include <ringbuffer/frontend_types.h>
  15 #include <lttng/lttng-tracer.h>
  16 #include <lttng/lttng-endian.h>
  17
  18 static
  19 size_t procname_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 procname. We simply copy its whole array size.
  29  * Races with /proc/<task>/procname 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 procname_record(struct lttng_ctx_field *field,
  35                  struct lib_ring_buffer_ctx *ctx,
  36                  struct lttng_channel *chan)
  37 {
  38         chan->ops->event_write(ctx, current->comm, sizeof(current->comm));
  39 }
  40
  41 static
  42 void procname_get_value(struct lttng_ctx_field *field,
  43                 struct lttng_probe_ctx *lttng_probe_ctx,
  44                 union lttng_ctx_value *value)
  45 {
  46         value->str = current->comm;
  47 }
  48
  49 static const struct lttng_type procname_array_elem_type =
  50         __type_integer(char, 0, 0, -1, __BYTE_ORDER, 10, UTF8);
  51
  52 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
  53 {
  54         struct lttng_ctx_field *field;
  55
  56         field = lttng_append_context(ctx);
  57         if (!field)
  58                 return -ENOMEM;
  59         if (lttng_find_context(*ctx, "procname")) {
  60                 lttng_remove_context_field(ctx, field);
  61                 return -EEXIST;
  62         }
  63         field->event_field.name = "procname";
  64         field->event_field.type.atype = atype_array_nestable;
  65         field->event_field.type.u.array_nestable.elem_type = &procname_array_elem_type;
  66         field->event_field.type.u.array_nestable.length = sizeof(current->comm);
  67         field->event_field.type.u.array_nestable.alignment = 0;
  68
  69         field->get_size = procname_get_size;
  70         field->record = procname_record;
  71         field->get_value = procname_get_value;
  72         lttng_context_update(*ctx);
  73         return 0;
  74 }
  75 EXPORT_SYMBOL_GPL(lttng_add_procname_to_ctx);