src/lib/lttng-ust/lttng-context-uts-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 uts 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 #include "common/compat/tid.h"
  20 #include <urcu/tls-compat.h>
  21
  22 #include "context-internal.h"
  23 #include "lttng-tracer-core.h"
  24 #include "common/ns.h"
  25
  26
  27 /*
  28  * We cache the result to ensure we don't stat(2) the proc filesystem on
  29  * each event.
  30  */
  31 static DEFINE_URCU_TLS_INIT(ino_t, cached_uts_ns, NS_INO_UNINITIALIZED);
  32
  33 static
  34 ino_t get_uts_ns(void)
  35 {
  36         struct stat sb;
  37         ino_t uts_ns;
  38
  39         uts_ns = CMM_LOAD_SHARED(URCU_TLS(cached_uts_ns));
  40
  41         /*
  42          * If the cache is populated, do nothing and return the
  43          * cached inode number.
  44          */
  45         if (caa_likely(uts_ns != NS_INO_UNINITIALIZED))
  46                 return uts_ns;
  47
  48         /*
  49          * At this point we have to populate the cache, set the initial
  50          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  51          * number from the proc filesystem, this is the value we will
  52          * cache.
  53          */
  54         uts_ns = NS_INO_UNAVAILABLE;
  55
  56         /*
  57          * /proc/thread-self was introduced in kernel v3.17
  58          */
  59         if (stat("/proc/thread-self/ns/uts", &sb) == 0) {
  60                 uts_ns = sb.st_ino;
  61         } else {
  62                 char proc_ns_path[LTTNG_PROC_NS_PATH_MAX];
  63
  64                 if (snprintf(proc_ns_path, LTTNG_PROC_NS_PATH_MAX,
  65                                 "/proc/self/task/%d/ns/uts",
  66                                 lttng_gettid()) >= 0) {
  67
  68                         if (stat(proc_ns_path, &sb) == 0) {
  69                                 uts_ns = sb.st_ino;
  70                         }
  71                 }
  72         }
  73
  74         /*
  75          * And finally, store the inode number in the cache.
  76          */
  77         CMM_STORE_SHARED(URCU_TLS(cached_uts_ns), uts_ns);
  78
  79         return uts_ns;
  80 }
  81
  82 /*
  83  * The uts namespace can change for 3 reasons
  84  *  * clone(2) called with CLONE_NEWUTS
  85  *  * setns(2) called with the fd of a different uts ns
  86  *  * unshare(2) called with CLONE_NEWUTS
  87  */
  88 void lttng_context_uts_ns_reset(void)
  89 {
  90         CMM_STORE_SHARED(URCU_TLS(cached_uts_ns), NS_INO_UNINITIALIZED);
  91 }
  92
  93 static
  94 size_t uts_ns_get_size(void *priv __attribute__((unused)),
  95                 size_t offset)
  96 {
  97         size_t size = 0;
  98
  99         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
 100         size += sizeof(ino_t);
 101         return size;
 102 }
 103
 104 static
 105 void uts_ns_record(void *priv __attribute__((unused)),
 106                  struct lttng_ust_ring_buffer_ctx *ctx,
 107                  struct lttng_ust_channel_buffer *chan)
 108 {
 109         ino_t uts_ns;
 110
 111         uts_ns = get_uts_ns();
 112         chan->ops->event_write(ctx, &uts_ns, sizeof(uts_ns), lttng_ust_rb_alignof(uts_ns));
 113 }
 114
 115 static
 116 void uts_ns_get_value(void *priv __attribute__((unused)),
 117                 struct lttng_ust_ctx_value *value)
 118 {
 119         value->u.s64 = get_uts_ns();
 120 }
 121
 122 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
 123         lttng_ust_static_event_field("uts_ns",
 124                 lttng_ust_static_type_integer(sizeof(ino_t) * CHAR_BIT,
 125                                 lttng_ust_rb_alignof(ino_t) * CHAR_BIT,
 126                                 lttng_ust_is_signed_type(ino_t),
 127                                 LTTNG_UST_BYTE_ORDER, 10),
 128                 false, false),
 129         uts_ns_get_size,
 130         uts_ns_record,
 131         uts_ns_get_value,
 132         NULL, NULL);
 133
 134 int lttng_add_uts_ns_to_ctx(struct lttng_ust_ctx **ctx)
 135 {
 136         int ret;
 137
 138         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
 139                 ret = -EEXIST;
 140                 goto error_find_context;
 141         }
 142         ret = lttng_ust_context_append(ctx, ctx_field);
 143         if (ret)
 144                 return ret;
 145         return 0;
 146
 147 error_find_context:
 148         return ret;
 149 }
 150
 151 /*
 152  *  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 153  *   */
 154 void lttng_fixup_uts_ns_tls(void)
 155 {
 156         asm volatile ("" : : "m" (URCU_TLS(cached_uts_ns)));
 157 }