liblttng-ust/lttng-context-mnt-ns.c

   1 /*
   2  * lttng-context-mnt-ns.c
   3  *
   4  * LTTng UST mnt namespace context.
   5  *
   6  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *               2019 Michael Jeanson <mjeanson@efficios.com>
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; only
  12  * version 2.1 of the License.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  */
  23
  24 #define _LGPL_SOURCE
  25 #include <stddef.h>
  26 #include <sys/types.h>
  27 #include <sys/stat.h>
  28 #include <unistd.h>
  29 #include <lttng/ust-events.h>
  30 #include <lttng/ust-tracer.h>
  31 #include <lttng/ringbuffer-config.h>
  32
  33 #include "ns.h"
  34
  35 /*
  36  * We cache the result to ensure we don't stat(2) the proc filesystem on
  37  * each event. The mount namespace is global to the process.
  38  */
  39 static ino_t cached_mnt_ns = NS_INO_UNINITIALIZED;
  40
  41 static
  42 ino_t get_mnt_ns(void)
  43 {
  44         struct stat sb;
  45         ino_t mnt_ns;
  46
  47         mnt_ns = CMM_LOAD_SHARED(cached_mnt_ns);
  48
  49         /*
  50          * If the cache is populated, do nothing and return the
  51          * cached inode number.
  52          */
  53         if (caa_likely(mnt_ns != NS_INO_UNINITIALIZED))
  54                 return mnt_ns;
  55
  56         /*
  57          * At this point we have to populate the cache, set the initial
  58          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  59          * number from the proc filesystem, this is the value we will
  60          * cache.
  61          */
  62         mnt_ns = NS_INO_UNAVAILABLE;
  63
  64         if (stat("/proc/self/ns/mnt", &sb) == 0) {
  65                 mnt_ns = sb.st_ino;
  66         }
  67
  68         /*
  69          * And finally, store the inode number in the cache.
  70          */
  71         CMM_STORE_SHARED(cached_mnt_ns, mnt_ns);
  72
  73         return mnt_ns;
  74 }
  75
  76 /*
  77  * The mnt namespace can change for 3 reasons
  78  *  * clone(2) called with CLONE_NEWNS
  79  *  * setns(2) called with the fd of a different mnt ns
  80  *  * unshare(2) called with CLONE_NEWNS
  81  */
  82 void lttng_context_mnt_ns_reset(void)
  83 {
  84         CMM_STORE_SHARED(cached_mnt_ns, NS_INO_UNINITIALIZED);
  85 }
  86
  87 static
  88 size_t mnt_ns_get_size(struct lttng_ctx_field *field, size_t offset)
  89 {
  90         size_t size = 0;
  91
  92         size += lib_ring_buffer_align(offset, lttng_alignof(ino_t));
  93         size += sizeof(ino_t);
  94         return size;
  95 }
  96
  97 static
  98 void mnt_ns_record(struct lttng_ctx_field *field,
  99                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
 100                  struct lttng_channel *chan)
 101 {
 102         ino_t mnt_ns;
 103
 104         mnt_ns = get_mnt_ns();
 105         lib_ring_buffer_align_ctx(ctx, lttng_alignof(mnt_ns));
 106         chan->ops->event_write(ctx, &mnt_ns, sizeof(mnt_ns));
 107 }
 108
 109 static
 110 void mnt_ns_get_value(struct lttng_ctx_field *field,
 111                 struct lttng_ctx_value *value)
 112 {
 113         value->u.s64 = get_mnt_ns();
 114 }
 115
 116 int lttng_add_mnt_ns_to_ctx(struct lttng_ctx **ctx)
 117 {
 118         struct lttng_ctx_field *field;
 119
 120         field = lttng_append_context(ctx);
 121         if (!field)
 122                 return -ENOMEM;
 123         if (lttng_find_context(*ctx, "mnt_ns")) {
 124                 lttng_remove_context_field(ctx, field);
 125                 return -EEXIST;
 126         }
 127         field->event_field.name = "mnt_ns";
 128         field->event_field.type.atype = atype_integer;
 129         field->event_field.type.u.integer.size = sizeof(ino_t) * CHAR_BIT;
 130         field->event_field.type.u.integer.alignment = lttng_alignof(ino_t) * CHAR_BIT;
 131         field->event_field.type.u.integer.signedness = lttng_is_signed_type(ino_t);
 132         field->event_field.type.u.integer.reverse_byte_order = 0;
 133         field->event_field.type.u.integer.base = 10;
 134         field->event_field.type.u.integer.encoding = lttng_encode_none;
 135         field->get_size = mnt_ns_get_size;
 136         field->record = mnt_ns_record;
 137         field->get_value = mnt_ns_get_value;
 138         lttng_context_update(*ctx);
 139         return 0;
 140 }