src/lttng-context-vppid.c

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * lttng-context-vppid.c
   4  *
   5  * LTTng vPPID 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 vppid_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 vppid_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         struct task_struct *parent;
  36         pid_t vppid;
  37
  38         /*
  39          * current nsproxy can be NULL when scheduled out of exit. pid_vnr uses
  40          * the current thread nsproxy to perform the lookup.
  41          */
  42
  43         /*
  44          * TODO: when we eventually add RCU subsystem instrumentation,
  45          * taking the rcu read lock here will trigger RCU tracing
  46          * recursively. We should modify the kernel synchronization so
  47          * it synchronizes both for RCU and RCU sched, and rely on
  48          * rcu_read_lock_sched_notrace.
  49          */
  50
  51         rcu_read_lock();
  52         parent = rcu_dereference(current->real_parent);
  53         if (!current->nsproxy)
  54                 vppid = 0;
  55         else
  56                 vppid = task_tgid_vnr(parent);
  57         rcu_read_unlock();
  58         chan->ops->event_write(ctx, &vppid, sizeof(vppid), lttng_alignof(vppid));
  59 }
  60
  61 static
  62 void vppid_get_value(void *priv,
  63                 struct lttng_kernel_probe_ctx *lttng_probe_ctx,
  64                 struct lttng_ctx_value *value)
  65 {
  66         struct task_struct *parent;
  67         pid_t vppid;
  68
  69         /*
  70          * current nsproxy can be NULL when scheduled out of exit. pid_vnr uses
  71          * the current thread nsproxy to perform the lookup.
  72          */
  73
  74         /*
  75          * TODO: when we eventually add RCU subsystem instrumentation,
  76          * taking the rcu read lock here will trigger RCU tracing
  77          * recursively. We should modify the kernel synchronization so
  78          * it synchronizes both for RCU and RCU sched, and rely on
  79          * rcu_read_lock_sched_notrace.
  80          */
  81
  82         rcu_read_lock();
  83         parent = rcu_dereference(current->real_parent);
  84         if (!current->nsproxy)
  85                 vppid = 0;
  86         else
  87                 vppid = task_tgid_vnr(parent);
  88         rcu_read_unlock();
  89         value->u.s64 = vppid;
  90 }
  91
  92 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
  93         lttng_kernel_static_event_field("vppid",
  94                 lttng_kernel_static_type_integer_from_type(pid_t, __BYTE_ORDER, 10),
  95                 false, false, false),
  96         vppid_get_size,
  97         vppid_record,
  98         vppid_get_value,
  99         NULL, NULL);
 100
 101 int lttng_add_vppid_to_ctx(struct lttng_kernel_ctx **ctx)
 102 {
 103         int ret;
 104
 105         if (lttng_kernel_find_context(*ctx, ctx_field->event_field->name))
 106                 return -EEXIST;
 107         ret = lttng_kernel_context_append(ctx, ctx_field);
 108         wrapper_vmalloc_sync_mappings();
 109         return ret;
 110 }
 111 EXPORT_SYMBOL_GPL(lttng_add_vppid_to_ctx);