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 "context-internal.h"
  20 #include "ns.h"
  21
  22 /*
  23  * We cache the result to ensure we don't stat(2) the proc filesystem on
  24  * each event. The user namespace is global to the process.
  25  */
  26 static ino_t cached_user_ns = NS_INO_UNINITIALIZED;
  27
  28 static
  29 ino_t get_user_ns(void)
  30 {
  31         struct stat sb;
  32         ino_t user_ns;
  33
  34         user_ns = CMM_LOAD_SHARED(cached_user_ns);
  35
  36         /*
  37          * If the cache is populated, do nothing and return the
  38          * cached inode number.
  39          */
  40         if (caa_likely(user_ns != NS_INO_UNINITIALIZED))
  41                 return user_ns;
  42
  43         /*
  44          * At this point we have to populate the cache, set the initial
  45          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  46          * number from the proc filesystem, this is the value we will
  47          * cache.
  48          */
  49         user_ns = NS_INO_UNAVAILABLE;
  50
  51         if (stat("/proc/self/ns/user", &sb) == 0) {
  52                 user_ns = sb.st_ino;
  53         }
  54
  55         /*
  56          * And finally, store the inode number in the cache.
  57          */
  58         CMM_STORE_SHARED(cached_user_ns, user_ns);
  59
  60         return user_ns;
  61 }
  62
  63 /*
  64  * The user namespace can change for 3 reasons
  65  *  * clone(2) called with CLONE_NEWUSER
  66  *  * setns(2) called with the fd of a different user ns
  67  *  * unshare(2) called with CLONE_NEWUSER
  68  */
  69 void lttng_context_user_ns_reset(void)
  70 {
  71         CMM_STORE_SHARED(cached_user_ns, NS_INO_UNINITIALIZED);
  72 }
  73
  74 static
  75 size_t user_ns_get_size(struct lttng_ctx_field *field, size_t offset)
  76 {
  77         size_t size = 0;
  78
  79         size += lib_ring_buffer_align(offset, lttng_alignof(ino_t));
  80         size += sizeof(ino_t);
  81         return size;
  82 }
  83
  84 static
  85 void user_ns_record(struct lttng_ctx_field *field,
  86                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  87                  struct lttng_channel *chan)
  88 {
  89         ino_t user_ns;
  90
  91         user_ns = get_user_ns();
  92         lib_ring_buffer_align_ctx(ctx, lttng_alignof(user_ns));
  93         chan->ops->event_write(ctx, &user_ns, sizeof(user_ns));
  94 }
  95
  96 static
  97 void user_ns_get_value(struct lttng_ctx_field *field,
  98                 struct lttng_ctx_value *value)
  99 {
 100         value->u.s64 = get_user_ns();
 101 }
 102
 103 int lttng_add_user_ns_to_ctx(struct lttng_ctx **ctx)
 104 {
 105         struct lttng_ctx_field *field;
 106
 107         field = lttng_append_context(ctx);
 108         if (!field)
 109                 return -ENOMEM;
 110         if (lttng_find_context(*ctx, "user_ns")) {
 111                 lttng_remove_context_field(ctx, field);
 112                 return -EEXIST;
 113         }
 114         field->event_field.name = "user_ns";
 115         field->event_field.type.atype = atype_integer;
 116         field->event_field.type.u.integer.size = sizeof(ino_t) * CHAR_BIT;
 117         field->event_field.type.u.integer.alignment = lttng_alignof(ino_t) * CHAR_BIT;
 118         field->event_field.type.u.integer.signedness = lttng_is_signed_type(ino_t);
 119         field->event_field.type.u.integer.reverse_byte_order = 0;
 120         field->event_field.type.u.integer.base = 10;
 121         field->event_field.type.u.integer.encoding = lttng_encode_none;
 122         field->get_size = user_ns_get_size;
 123         field->record = user_ns_record;
 124         field->get_value = user_ns_get_value;
 125         lttng_context_update(*ctx);
 126         return 0;
 127 }