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 <lttng/events-internal.h>
  15 #include <ringbuffer/frontend_types.h>
  16 #include <wrapper/vmalloc.h>
  17 #include <lttng/tracer.h>
  18 #include <lttng/endian.h>
  19
  20 static
  21 size_t procname_get_size(size_t offset)
  22 {
  23         size_t size = 0;
  24
  25         size += sizeof(current->comm);
  26         return size;
  27 }
  28
  29 /*
  30  * Racy read of procname. We simply copy its whole array size.
  31  * Races with /proc/<task>/procname write only.
  32  * Otherwise having to take a mutex for each event is cumbersome and
  33  * could lead to crash in IRQ context and deadlock of the lockdep tracer.
  34  */
  35 static
  36 void procname_record(struct lttng_kernel_ctx_field *field,
  37                  struct lib_ring_buffer_ctx *ctx,
  38                  struct lttng_channel *chan)
  39 {
  40         chan->ops->event_write(ctx, current->comm, sizeof(current->comm));
  41 }
  42
  43 static
  44 void procname_get_value(struct lttng_kernel_ctx_field *field,
  45                 struct lttng_probe_ctx *lttng_probe_ctx,
  46                 union lttng_ctx_value *value)
  47 {
  48         value->str = current->comm;
  49 }
  50
  51 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
  52         lttng_kernel_static_event_field("procname",
  53                 lttng_kernel_static_type_array_text(sizeof(current->comm)),
  54                 false, false, false),
  55         procname_get_size,
  56         NULL,
  57         procname_record,
  58         procname_get_value,
  59         NULL, NULL);
  60
  61 int lttng_add_procname_to_ctx(struct lttng_kernel_ctx **ctx)
  62 {
  63         int ret;
  64
  65         if (lttng_kernel_find_context(*ctx, ctx_field->event_field->name))
  66                 return -EEXIST;
  67         ret = lttng_kernel_context_append(ctx, ctx_field);
  68         wrapper_vmalloc_sync_mappings();
  69         return ret;
  70 }
  71 EXPORT_SYMBOL_GPL(lttng_add_procname_to_ctx);