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