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                 size_t offset)
  78 {
  79         size_t size = 0;
  80
  81         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
  82         size += sizeof(ino_t);
  83         return size;
  84 }
  85
  86 static
  87 void mnt_ns_record(void *priv __attribute__((unused)),
  88                  struct lttng_ust_ring_buffer_ctx *ctx,
  89                  struct lttng_ust_channel_buffer *chan)
  90 {
  91         ino_t mnt_ns;
  92
  93         mnt_ns = get_mnt_ns();
  94         chan->ops->event_write(ctx, &mnt_ns, sizeof(mnt_ns), lttng_ust_rb_alignof(mnt_ns));
  95 }
  96
  97 static
  98 void mnt_ns_get_value(void *priv __attribute__((unused)),
  99                 struct lttng_ust_ctx_value *value)
 100 {
 101         value->u.s64 = get_mnt_ns();
 102 }
 103
 104 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
 105         lttng_ust_static_event_field("mnt_ns",
 106                 lttng_ust_static_type_integer(sizeof(ino_t) * CHAR_BIT,
 107                                 lttng_ust_rb_alignof(ino_t) * CHAR_BIT,
 108                                 lttng_ust_is_signed_type(ino_t),
 109                                 LTTNG_UST_BYTE_ORDER, 10),
 110                 false, false),
 111         mnt_ns_get_size,
 112         mnt_ns_record,
 113         mnt_ns_get_value,
 114         NULL, NULL);
 115
 116 int lttng_add_mnt_ns_to_ctx(struct lttng_ust_ctx **ctx)
 117 {
 118         int ret;
 119
 120         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
 121                 ret = -EEXIST;
 122                 goto error_find_context;
 123         }
 124         ret = lttng_ust_context_append(ctx, ctx_field);
 125         if (ret)
 126                 return ret;
 127         return 0;
 128
 129 error_find_context:
 130         return ret;
 131 }