src/lttng-context-ppid.c

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * lttng-context-ppid.c
   4  *
   5  * LTTng PPID 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 <linux/syscalls.h>
  14 #include <lttng/events.h>
  15 #include <lttng/events-internal.h>
  16 #include <ringbuffer/frontend_types.h>
  17 #include <wrapper/vmalloc.h>
  18 #include <lttng/tracer.h>
  19
  20 static
  21 size_t ppid_get_size(void *priv, struct lttng_kernel_probe_ctx *probe_ctx, size_t offset)
  22 {
  23         size_t size = 0;
  24
  25         size += lib_ring_buffer_align(offset, lttng_alignof(pid_t));
  26         size += sizeof(pid_t);
  27         return size;
  28 }
  29
  30 static
  31 void ppid_record(void *priv, struct lttng_kernel_probe_ctx *probe_ctx,
  32                  struct lttng_kernel_ring_buffer_ctx *ctx,
  33                  struct lttng_kernel_channel_buffer *chan)
  34 {
  35         pid_t ppid;
  36
  37         /*
  38          * TODO: when we eventually add RCU subsystem instrumentation,
  39          * taking the rcu read lock here will trigger RCU tracing
  40          * recursively. We should modify the kernel synchronization so
  41          * it synchronizes both for RCU and RCU sched, and rely on
  42          * rcu_read_lock_sched_notrace.
  43          */
  44         rcu_read_lock();
  45         ppid = task_tgid_nr(current->real_parent);
  46         rcu_read_unlock();
  47         lib_ring_buffer_align_ctx(ctx, lttng_alignof(ppid));
  48         chan->ops->event_write(ctx, &ppid, sizeof(ppid));
  49 }
  50
  51 static
  52 void ppid_get_value(void *priv,
  53                 struct lttng_kernel_probe_ctx *lttng_probe_ctx,
  54                 struct lttng_ctx_value *value)
  55 {
  56         pid_t ppid;
  57
  58         /*
  59          * TODO: when we eventually add RCU subsystem instrumentation,
  60          * taking the rcu read lock here will trigger RCU tracing
  61          * recursively. We should modify the kernel synchronization so
  62          * it synchronizes both for RCU and RCU sched, and rely on
  63          * rcu_read_lock_sched_notrace.
  64          */
  65         rcu_read_lock();
  66         ppid = task_tgid_nr(current->real_parent);
  67         rcu_read_unlock();
  68         value->u.s64 = ppid;
  69 }
  70
  71 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
  72         lttng_kernel_static_event_field("ppid",
  73                 lttng_kernel_static_type_integer_from_type(pid_t, __BYTE_ORDER, 10),
  74                 false, false, false),
  75         ppid_get_size,
  76         ppid_record,
  77         ppid_get_value,
  78         NULL, NULL);
  79
  80 int lttng_add_ppid_to_ctx(struct lttng_kernel_ctx **ctx)
  81 {
  82         int ret;
  83
  84         if (lttng_kernel_find_context(*ctx, ctx_field->event_field->name))
  85                 return -EEXIST;
  86         ret = lttng_kernel_context_append(ctx, ctx_field);
  87         wrapper_vmalloc_sync_mappings();
  88         return ret;
  89 }
  90 EXPORT_SYMBOL_GPL(lttng_add_ppid_to_ctx);