liblttng-ust/lttng-context-user-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 user namespace context.
   8  */
   9
  10 #define _LGPL_SOURCE
  11 #include <stddef.h>
  12 #include <sys/types.h>
  13 #include <sys/stat.h>
  14 #include <unistd.h>
  15 #include <lttng/ust-events.h>
  16 #include <lttng/ust-tracer.h>
  17 #include <lttng/ringbuffer-config.h>
  18
  19 #include "ns.h"
  20
  21 /*
  22  * We cache the result to ensure we don't stat(2) the proc filesystem on
  23  * each event. The user namespace is global to the process.
  24  */
  25 static ino_t cached_user_ns = NS_INO_UNINITIALIZED;
  26
  27 static
  28 ino_t get_user_ns(void)
  29 {
  30         struct stat sb;
  31         ino_t user_ns;
  32
  33         user_ns = CMM_LOAD_SHARED(cached_user_ns);
  34
  35         /*
  36          * If the cache is populated, do nothing and return the
  37          * cached inode number.
  38          */
  39         if (caa_likely(user_ns != NS_INO_UNINITIALIZED))
  40                 return user_ns;
  41
  42         /*
  43          * At this point we have to populate the cache, set the initial
  44          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  45          * number from the proc filesystem, this is the value we will
  46          * cache.
  47          */
  48         user_ns = NS_INO_UNAVAILABLE;
  49
  50         if (stat("/proc/self/ns/user", &sb) == 0) {
  51                 user_ns = sb.st_ino;
  52         }
  53
  54         /*
  55          * And finally, store the inode number in the cache.
  56          */
  57         CMM_STORE_SHARED(cached_user_ns, user_ns);
  58
  59         return user_ns;
  60 }
  61
  62 /*
  63  * The user namespace can change for 3 reasons
  64  *  * clone(2) called with CLONE_NEWUSER
  65  *  * setns(2) called with the fd of a different user ns
  66  *  * unshare(2) called with CLONE_NEWUSER
  67  */
  68 void lttng_context_user_ns_reset(void)
  69 {
  70         CMM_STORE_SHARED(cached_user_ns, NS_INO_UNINITIALIZED);
  71 }
  72
  73 static
  74 size_t user_ns_get_size(struct lttng_ctx_field *field, size_t offset)
  75 {
  76         size_t size = 0;
  77
  78         size += lib_ring_buffer_align(offset, lttng_alignof(ino_t));
  79         size += sizeof(ino_t);
  80         return size;
  81 }
  82
  83 static
  84 void user_ns_record(struct lttng_ctx_field *field,
  85                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  86                  struct lttng_channel *chan)
  87 {
  88         ino_t user_ns;
  89
  90         user_ns = get_user_ns();
  91         lib_ring_buffer_align_ctx(ctx, lttng_alignof(user_ns));
  92         chan->ops->event_write(ctx, &user_ns, sizeof(user_ns));
  93 }
  94
  95 static
  96 void user_ns_get_value(struct lttng_ctx_field *field,
  97                 struct lttng_ctx_value *value)
  98 {
  99         value->u.s64 = get_user_ns();
 100 }
 101
 102 int lttng_add_user_ns_to_ctx(struct lttng_ctx **ctx)
 103 {
 104         struct lttng_ctx_field *field;
 105
 106         field = lttng_append_context(ctx);
 107         if (!field)
 108                 return -ENOMEM;
 109         if (lttng_find_context(*ctx, "user_ns")) {
 110                 lttng_remove_context_field(ctx, field);
 111                 return -EEXIST;
 112         }
 113         field->event_field.name = "user_ns";
 114         field->event_field.type.atype = atype_integer;
 115         field->event_field.type.u.integer.size = sizeof(ino_t) * CHAR_BIT;
 116         field->event_field.type.u.integer.alignment = lttng_alignof(ino_t) * CHAR_BIT;
 117         field->event_field.type.u.integer.signedness = lttng_is_signed_type(ino_t);
 118         field->event_field.type.u.integer.reverse_byte_order = 0;
 119         field->event_field.type.u.integer.base = 10;
 120         field->event_field.type.u.integer.encoding = lttng_encode_none;
 121         field->get_size = user_ns_get_size;
 122         field->record = user_ns_record;
 123         field->get_value = user_ns_get_value;
 124         lttng_context_update(*ctx);
 125         return 0;
 126 }