liblttng-ust/lttng-context-time-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) 2020 Michael Jeanson <mjeanson@efficios.com>
   6  *
   7  * LTTng UST time 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/ringbuffer-context.h>
  19 #include <ust-tid.h>
  20 #include <urcu/tls-compat.h>
  21 #include "lttng-tracer-core.h"
  22 #include "ns.h"
  23 #include "context-internal.h"
  24
  25
  26 /*
  27  * We cache the result to ensure we don't stat(2) the proc filesystem on
  28  * each event.
  29  */
  30 static DEFINE_URCU_TLS_INIT(ino_t, cached_time_ns, NS_INO_UNINITIALIZED);
  31
  32 static
  33 ino_t get_time_ns(void)
  34 {
  35         struct stat sb;
  36         ino_t time_ns;
  37
  38         time_ns = CMM_LOAD_SHARED(URCU_TLS(cached_time_ns));
  39
  40         /*
  41          * If the cache is populated, do nothing and return the
  42          * cached inode number.
  43          */
  44         if (caa_likely(time_ns != NS_INO_UNINITIALIZED))
  45                 return time_ns;
  46
  47         /*
  48          * At this point we have to populate the cache, set the initial
  49          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  50          * number from the proc filesystem, this is the value we will
  51          * cache.
  52          */
  53         time_ns = NS_INO_UNAVAILABLE;
  54
  55         /*
  56          * /proc/thread-self was introduced in kernel v3.17
  57          */
  58         if (stat("/proc/thread-self/ns/time", &sb) == 0) {
  59                 time_ns = sb.st_ino;
  60         } else {
  61                 char proc_ns_path[LTTNG_PROC_NS_PATH_MAX];
  62
  63                 if (snprintf(proc_ns_path, LTTNG_PROC_NS_PATH_MAX,
  64                                 "/proc/self/task/%d/ns/time",
  65                                 lttng_gettid()) >= 0) {
  66
  67                         if (stat(proc_ns_path, &sb) == 0) {
  68                                 time_ns = sb.st_ino;
  69                         }
  70                 }
  71         }
  72
  73         /*
  74          * And finally, store the inode number in the cache.
  75          */
  76         CMM_STORE_SHARED(URCU_TLS(cached_time_ns), time_ns);
  77
  78         return time_ns;
  79 }
  80
  81 /*
  82  * The time namespace can change for 2 reasons
  83  *  * setns(2) called with the fd of a different time ns
  84  *  * clone(2) / fork(2) after a call to unshare(2) with the CLONE_NEWTIME flag
  85  */
  86 void lttng_context_time_ns_reset(void)
  87 {
  88         CMM_STORE_SHARED(URCU_TLS(cached_time_ns), NS_INO_UNINITIALIZED);
  89 }
  90
  91 static
  92 size_t time_ns_get_size(struct lttng_ust_ctx_field *field, size_t offset)
  93 {
  94         size_t size = 0;
  95
  96         size += lttng_ust_lib_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
  97         size += sizeof(ino_t);
  98         return size;
  99 }
 100
 101 static
 102 void time_ns_record(struct lttng_ust_ctx_field *field,
 103                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
 104                  struct lttng_ust_channel_buffer *chan)
 105 {
 106         ino_t time_ns;
 107
 108         time_ns = get_time_ns();
 109         chan->ops->event_write(ctx, &time_ns, sizeof(time_ns), lttng_ust_rb_alignof(time_ns));
 110 }
 111
 112 static
 113 void time_ns_get_value(struct lttng_ust_ctx_field *field,
 114                 struct lttng_ust_ctx_value *value)
 115 {
 116         value->u.s64 = get_time_ns();
 117 }
 118
 119 int lttng_add_time_ns_to_ctx(struct lttng_ust_ctx **ctx)
 120 {
 121         struct lttng_ust_ctx_field *field;
 122         struct lttng_ust_type_common *type;
 123         int ret;
 124
 125         type = lttng_ust_create_type_integer(sizeof(ino_t) * CHAR_BIT,
 126                         lttng_ust_rb_alignof(ino_t) * CHAR_BIT,
 127                         lttng_ust_is_signed_type(ino_t),
 128                         BYTE_ORDER, 10);
 129         if (!type)
 130                 return -ENOMEM;
 131         field = lttng_append_context(ctx);
 132         if (!field) {
 133                 ret = -ENOMEM;
 134                 goto error_context;
 135         }
 136         if (lttng_find_context(*ctx, "time_ns")) {
 137                 ret = -EEXIST;
 138                 goto error_find_context;
 139         }
 140         field->event_field->name = strdup("time_ns");
 141         if (!field->event_field->name) {
 142                 ret = -ENOMEM;
 143                 goto error_name;
 144         }
 145         field->event_field->type = type;
 146         field->get_size = time_ns_get_size;
 147         field->record = time_ns_record;
 148         field->get_value = time_ns_get_value;
 149         lttng_context_update(*ctx);
 150         return 0;
 151
 152 error_name:
 153 error_find_context:
 154         lttng_remove_context_field(ctx, field);
 155 error_context:
 156         lttng_ust_destroy_type(type);
 157         return ret;
 158 }
 159
 160 /*
 161  *  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 162  *   */
 163 void lttng_fixup_time_ns_tls(void)
 164 {
 165         asm volatile ("" : : "m" (URCU_TLS(cached_time_ns)));
 166 }