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 <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 #include "context-internal.h"
  23
  24
  25 /*
  26  * We cache the result to ensure we don't stat(2) the proc filesystem on
  27  * each event.
  28  */
  29 static DEFINE_URCU_TLS_INIT(ino_t, cached_time_ns, NS_INO_UNINITIALIZED);
  30
  31 static
  32 ino_t get_time_ns(void)
  33 {
  34         struct stat sb;
  35         ino_t time_ns;
  36
  37         time_ns = CMM_LOAD_SHARED(URCU_TLS(cached_time_ns));
  38
  39         /*
  40          * If the cache is populated, do nothing and return the
  41          * cached inode number.
  42          */
  43         if (caa_likely(time_ns != NS_INO_UNINITIALIZED))
  44                 return time_ns;
  45
  46         /*
  47          * At this point we have to populate the cache, set the initial
  48          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  49          * number from the proc filesystem, this is the value we will
  50          * cache.
  51          */
  52         time_ns = NS_INO_UNAVAILABLE;
  53
  54         /*
  55          * /proc/thread-self was introduced in kernel v3.17
  56          */
  57         if (stat("/proc/thread-self/ns/time", &sb) == 0) {
  58                 time_ns = sb.st_ino;
  59         } else {
  60                 char proc_ns_path[LTTNG_PROC_NS_PATH_MAX];
  61
  62                 if (snprintf(proc_ns_path, LTTNG_PROC_NS_PATH_MAX,
  63                                 "/proc/self/task/%d/ns/time",
  64                                 lttng_gettid()) >= 0) {
  65
  66                         if (stat(proc_ns_path, &sb) == 0) {
  67                                 time_ns = sb.st_ino;
  68                         }
  69                 }
  70         }
  71
  72         /*
  73          * And finally, store the inode number in the cache.
  74          */
  75         CMM_STORE_SHARED(URCU_TLS(cached_time_ns), time_ns);
  76
  77         return time_ns;
  78 }
  79
  80 /*
  81  * The time namespace can change for 2 reasons
  82  *  * setns(2) called with the fd of a different time ns
  83  *  * clone(2) / fork(2) after a call to unshare(2) with the CLONE_NEWTIME flag
  84  */
  85 void lttng_context_time_ns_reset(void)
  86 {
  87         CMM_STORE_SHARED(URCU_TLS(cached_time_ns), NS_INO_UNINITIALIZED);
  88 }
  89
  90 static
  91 size_t time_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 time_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 time_ns;
 106
 107         time_ns = get_time_ns();
 108         lib_ring_buffer_align_ctx(ctx, lttng_alignof(time_ns));
 109         chan->ops->event_write(ctx, &time_ns, sizeof(time_ns));
 110 }
 111
 112 static
 113 void time_ns_get_value(struct lttng_ctx_field *field,
 114                 struct lttng_ctx_value *value)
 115 {
 116         value->u.s64 = get_time_ns();
 117 }
 118
 119 int lttng_add_time_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, "time_ns")) {
 127                 lttng_remove_context_field(ctx, field);
 128                 return -EEXIST;
 129         }
 130         field->event_field.name = "time_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 = time_ns_get_size;
 139         field->record = time_ns_record;
 140         field->get_value = time_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_time_ns_tls(void)
 149 {
 150         asm volatile ("" : : "m" (URCU_TLS(cached_time_ns)));
 151 }