src/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/events.h>
  14 #include <ringbuffer/frontend_types.h>
  15 #include <wrapper/vmalloc.h>
  16 #include <lttng/tracer.h>
  17 #include <lttng/endian.h>
  18
  19 static
  20 size_t procname_get_size(size_t offset)
  21 {
  22         size_t size = 0;
  23
  24         size += sizeof(current->comm);
  25         return size;
  26 }
  27
  28 /*
  29  * Racy read of procname. We simply copy its whole array size.
  30  * Races with /proc/<task>/procname write only.
  31  * Otherwise having to take a mutex for each event is cumbersome and
  32  * could lead to crash in IRQ context and deadlock of the lockdep tracer.
  33  */
  34 static
  35 void procname_record(struct lttng_ctx_field *field,
  36                  struct lib_ring_buffer_ctx *ctx,
  37                  struct lttng_channel *chan)
  38 {
  39         chan->ops->event_write(ctx, current->comm, sizeof(current->comm));
  40 }
  41
  42 static
  43 void procname_get_value(struct lttng_ctx_field *field,
  44                 struct lttng_probe_ctx *lttng_probe_ctx,
  45                 union lttng_ctx_value *value)
  46 {
  47         value->str = current->comm;
  48 }
  49
  50 static const struct lttng_type procname_array_elem_type =
  51         __type_integer(char, 0, 0, -1, __BYTE_ORDER, 10, UTF8);
  52
  53 int lttng_add_procname_to_ctx(struct lttng_ctx **ctx)
  54 {
  55         struct lttng_ctx_field *field;
  56
  57         field = lttng_append_context(ctx);
  58         if (!field)
  59                 return -ENOMEM;
  60         if (lttng_find_context(*ctx, "procname")) {
  61                 lttng_remove_context_field(ctx, field);
  62                 return -EEXIST;
  63         }
  64         field->event_field.name = "procname";
  65         field->event_field.type.atype = atype_array_nestable;
  66         field->event_field.type.u.array_nestable.elem_type = &procname_array_elem_type;
  67         field->event_field.type.u.array_nestable.length = sizeof(current->comm);
  68         field->event_field.type.u.array_nestable.alignment = 0;
  69
  70         field->get_size = procname_get_size;
  71         field->record = procname_record;
  72         field->get_value = procname_get_value;
  73         lttng_context_update(*ctx);
  74         wrapper_vmalloc_sync_mappings();
  75         return 0;
  76 }
  77 EXPORT_SYMBOL_GPL(lttng_add_procname_to_ctx);