src/lttng-context-hostname.c

   1 /* SPDX-License-Identifier: (GPL-2.0-only or LGPL-2.1-only)
   2  *
   3  * lttng-context-hostname.c
   4  *
   5  * LTTng hostname 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/utsname.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 #define LTTNG_HOSTNAME_CTX_LEN  (__NEW_UTS_LEN + 1)
  21
  22 static
  23 size_t hostname_get_size(void *priv, struct lttng_kernel_probe_ctx *probe_ctx, size_t offset)
  24 {
  25         size_t size = 0;
  26
  27         size += LTTNG_HOSTNAME_CTX_LEN;
  28         return size;
  29 }
  30
  31 static
  32 void hostname_record(void *priv, struct lttng_kernel_probe_ctx *probe_ctx,
  33                  struct lttng_kernel_ring_buffer_ctx *ctx,
  34                  struct lttng_kernel_channel_buffer *chan)
  35 {
  36         struct nsproxy *nsproxy;
  37         struct uts_namespace *ns;
  38         char *hostname;
  39
  40         /*
  41          * No need to take the RCU read-side lock to read current
  42          * nsproxy. (documented in nsproxy.h)
  43          */
  44         nsproxy = current->nsproxy;
  45         if (nsproxy) {
  46                 ns = nsproxy->uts_ns;
  47                 hostname = ns->name.nodename;
  48                 chan->ops->event_write(ctx, hostname,
  49                                 LTTNG_HOSTNAME_CTX_LEN, 1);
  50         } else {
  51                 chan->ops->event_memset(ctx, 0,
  52                                 LTTNG_HOSTNAME_CTX_LEN);
  53         }
  54 }
  55
  56 static
  57 void hostname_get_value(void *priv,
  58                 struct lttng_kernel_probe_ctx *lttng_probe_ctx,
  59                 struct lttng_ctx_value *value)
  60 {
  61         struct nsproxy *nsproxy;
  62         struct uts_namespace *ns;
  63         char *hostname;
  64
  65         /*
  66          * No need to take the RCU read-side lock to read current
  67          * nsproxy. (documented in nsproxy.h)
  68          */
  69         nsproxy = current->nsproxy;
  70         if (nsproxy) {
  71                 ns = nsproxy->uts_ns;
  72                 hostname = ns->name.nodename;
  73         } else {
  74                 hostname = "";
  75         }
  76         value->u.str = hostname;
  77 }
  78
  79 static const struct lttng_kernel_ctx_field *ctx_field = lttng_kernel_static_ctx_field(
  80         lttng_kernel_static_event_field("hostname",
  81                 lttng_kernel_static_type_array_text(LTTNG_HOSTNAME_CTX_LEN),
  82                 false, false),
  83         hostname_get_size,
  84         hostname_record,
  85         hostname_get_value,
  86         NULL, NULL);
  87
  88 int lttng_add_hostname_to_ctx(struct lttng_kernel_ctx **ctx)
  89 {
  90         int ret;
  91
  92         if (lttng_kernel_find_context(*ctx, ctx_field->event_field->name))
  93                 return -EEXIST;
  94         ret = lttng_kernel_context_append(ctx, ctx_field);
  95         wrapper_vmalloc_sync_mappings();
  96         return ret;
  97 }
  98 EXPORT_SYMBOL_GPL(lttng_add_hostname_to_ctx);