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

   1 /*
   2  * lttng-context-user-ns.c
   3  *
   4  * LTTng UST user 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 <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28 #include <lttng/ust-events.h>
  29 #include <lttng/ust-tracer.h>
  30 #include <lttng/ringbuffer-config.h>
  31
  32 #include "ns.h"
  33
  34 /*
  35  * We cache the result to ensure we don't stat(2) the proc filesystem on
  36  * each event. The user namespace is global to the process.
  37  */
  38 static ino_t cached_user_ns = NS_INO_UNINITIALIZED;
  39
  40 static
  41 ino_t get_user_ns(void)
  42 {
  43         struct stat sb;
  44         ino_t user_ns;
  45
  46         user_ns = CMM_LOAD_SHARED(cached_user_ns);
  47
  48         /*
  49          * If the cache is populated, do nothing and return the
  50          * cached inode number.
  51          */
  52         if (caa_likely(user_ns != NS_INO_UNINITIALIZED))
  53                 return user_ns;
  54
  55         /*
  56          * At this point we have to populate the cache, set the initial
  57          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  58          * number from the proc filesystem, this is the value we will
  59          * cache.
  60          */
  61         user_ns = NS_INO_UNAVAILABLE;
  62
  63         if (stat("/proc/self/ns/user", &sb) == 0) {
  64                 user_ns = sb.st_ino;
  65         }
  66
  67         /*
  68          * And finally, store the inode number in the cache.
  69          */
  70         CMM_STORE_SHARED(cached_user_ns, user_ns);
  71
  72         return user_ns;
  73 }
  74
  75 /*
  76  * The user namespace can change for 3 reasons
  77  *  * clone(2) called with CLONE_NEWUSER
  78  *  * setns(2) called with the fd of a different user ns
  79  *  * unshare(2) called with CLONE_NEWUSER
  80  */
  81 void lttng_context_user_ns_reset(void)
  82 {
  83         CMM_STORE_SHARED(cached_user_ns, NS_INO_UNINITIALIZED);
  84 }
  85
  86 static
  87 size_t user_ns_get_size(struct lttng_ctx_field *field, size_t offset)
  88 {
  89         size_t size = 0;
  90
  91         size += lib_ring_buffer_align(offset, lttng_alignof(ino_t));
  92         size += sizeof(ino_t);
  93         return size;
  94 }
  95
  96 static
  97 void user_ns_record(struct lttng_ctx_field *field,
  98                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  99                  struct lttng_channel *chan)
 100 {
 101         ino_t user_ns;
 102
 103         user_ns = get_user_ns();
 104         lib_ring_buffer_align_ctx(ctx, lttng_alignof(user_ns));
 105         chan->ops->event_write(ctx, &user_ns, sizeof(user_ns));
 106 }
 107
 108 static
 109 void user_ns_get_value(struct lttng_ctx_field *field,
 110                 struct lttng_ctx_value *value)
 111 {
 112         value->u.s64 = get_user_ns();
 113 }
 114
 115 int lttng_add_user_ns_to_ctx(struct lttng_ctx **ctx)
 116 {
 117         struct lttng_ctx_field *field;
 118
 119         field = lttng_append_context(ctx);
 120         if (!field)
 121                 return -ENOMEM;
 122         if (lttng_find_context(*ctx, "user_ns")) {
 123                 lttng_remove_context_field(ctx, field);
 124                 return -EEXIST;
 125         }
 126         field->event_field.name = "user_ns";
 127         field->event_field.type.atype = atype_integer;
 128         field->event_field.type.u.basic.integer.size = sizeof(ino_t) * CHAR_BIT;
 129         field->event_field.type.u.basic.integer.alignment = lttng_alignof(ino_t) * CHAR_BIT;
 130         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(ino_t);
 131         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
 132         field->event_field.type.u.basic.integer.base = 10;
 133         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
 134         field->get_size = user_ns_get_size;
 135         field->record = user_ns_record;
 136         field->get_value = user_ns_get_value;
 137         lttng_context_update(*ctx);
 138         return 0;
 139 }