src/lib/lttng-ust/lttng-context-mnt-ns.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
   6  *
   7  * LTTng UST mnt namespace context.
   8  */
   9
  10 #define _LGPL_SOURCE
  11 #include <limits.h>
  12 #include <stddef.h>
  13 #include <sys/types.h>
  14 #include <sys/stat.h>
  15 #include <unistd.h>
  16 #include <lttng/ust-events.h>
  17 #include <lttng/ust-tracer.h>
  18 #include <lttng/ust-ringbuffer-context.h>
  19
  20 #include "context-internal.h"
  21 #include "common/ns.h"
  22
  23 /*
  24  * We cache the result to ensure we don't stat(2) the proc filesystem on
  25  * each event. The mount namespace is global to the process.
  26  */
  27 static ino_t cached_mnt_ns = NS_INO_UNINITIALIZED;
  28
  29 static
  30 ino_t get_mnt_ns(void)
  31 {
  32         struct stat sb;
  33         ino_t mnt_ns;
  34
  35         mnt_ns = CMM_LOAD_SHARED(cached_mnt_ns);
  36
  37         /*
  38          * If the cache is populated, do nothing and return the
  39          * cached inode number.
  40          */
  41         if (caa_likely(mnt_ns != NS_INO_UNINITIALIZED))
  42                 return mnt_ns;
  43
  44         /*
  45          * At this point we have to populate the cache, set the initial
  46          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  47          * number from the proc filesystem, this is the value we will
  48          * cache.
  49          */
  50         mnt_ns = NS_INO_UNAVAILABLE;
  51
  52         if (stat("/proc/self/ns/mnt", &sb) == 0) {
  53                 mnt_ns = sb.st_ino;
  54         }
  55
  56         /*
  57          * And finally, store the inode number in the cache.
  58          */
  59         CMM_STORE_SHARED(cached_mnt_ns, mnt_ns);
  60
  61         return mnt_ns;
  62 }
  63
  64 /*
  65  * The mnt namespace can change for 3 reasons
  66  *  * clone(2) called with CLONE_NEWNS
  67  *  * setns(2) called with the fd of a different mnt ns
  68  *  * unshare(2) called with CLONE_NEWNS
  69  */
  70 void lttng_context_mnt_ns_reset(void)
  71 {
  72         CMM_STORE_SHARED(cached_mnt_ns, NS_INO_UNINITIALIZED);
  73 }
  74
  75 static
  76 size_t mnt_ns_get_size(void *priv __attribute__((unused)),
  77                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
  78                 size_t offset)
  79 {
  80         size_t size = 0;
  81
  82         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
  83         size += sizeof(ino_t);
  84         return size;
  85 }
  86
  87 static
  88 void mnt_ns_record(void *priv __attribute__((unused)),
  89                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
  90                 struct lttng_ust_ring_buffer_ctx *ctx,
  91                 struct lttng_ust_channel_buffer *chan)
  92 {
  93         ino_t mnt_ns;
  94
  95         mnt_ns = get_mnt_ns();
  96         chan->ops->event_write(ctx, &mnt_ns, sizeof(mnt_ns), lttng_ust_rb_alignof(mnt_ns));
  97 }
  98
  99 static
 100 void mnt_ns_get_value(void *priv __attribute__((unused)),
 101                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
 102                 struct lttng_ust_ctx_value *value)
 103 {
 104         value->u.u64 = get_mnt_ns();
 105 }
 106
 107 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
 108         lttng_ust_static_event_field("mnt_ns",
 109                 lttng_ust_static_type_integer(sizeof(ino_t) * CHAR_BIT,
 110                                 lttng_ust_rb_alignof(ino_t) * CHAR_BIT,
 111                                 lttng_ust_is_signed_type(ino_t),
 112                                 LTTNG_UST_BYTE_ORDER, 10),
 113                 false, false),
 114         mnt_ns_get_size,
 115         mnt_ns_record,
 116         mnt_ns_get_value,
 117         NULL, NULL);
 118
 119 int lttng_add_mnt_ns_to_ctx(struct lttng_ust_ctx **ctx)
 120 {
 121         int ret;
 122
 123         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
 124                 ret = -EEXIST;
 125                 goto error_find_context;
 126         }
 127         ret = lttng_ust_context_append(ctx, ctx_field);
 128         if (ret)
 129                 return ret;
 130         return 0;
 131
 132 error_find_context:
 133         return ret;
 134 }