src/lib/lttng-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/ust-ringbuffer-context.h>
  19 #include "common/compat/tid.h"
  20 #include <urcu/tls-compat.h>
  21 #include "lttng-tracer-core.h"
  22 #include "common/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(void *priv __attribute__((unused)),
  93                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
  94                 size_t offset)
  95 {
  96         size_t size = 0;
  97
  98         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
  99         size += sizeof(ino_t);
 100         return size;
 101 }
 102
 103 static
 104 void time_ns_record(void *priv __attribute__((unused)),
 105                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
 106                 struct lttng_ust_ring_buffer_ctx *ctx,
 107                 struct lttng_ust_channel_buffer *chan)
 108 {
 109         ino_t time_ns;
 110
 111         time_ns = get_time_ns();
 112         chan->ops->event_write(ctx, &time_ns, sizeof(time_ns), lttng_ust_rb_alignof(time_ns));
 113 }
 114
 115 static
 116 void time_ns_get_value(void *priv __attribute__((unused)),
 117                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
 118                 struct lttng_ust_ctx_value *value)
 119 {
 120         value->u.u64 = get_time_ns();
 121 }
 122
 123 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
 124         lttng_ust_static_event_field("time_ns",
 125                 lttng_ust_static_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                                 LTTNG_UST_BYTE_ORDER, 10),
 129                 false, false),
 130         time_ns_get_size,
 131         time_ns_record,
 132         time_ns_get_value,
 133         NULL, NULL);
 134
 135 int lttng_add_time_ns_to_ctx(struct lttng_ust_ctx **ctx)
 136 {
 137         int ret;
 138
 139         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
 140                 ret = -EEXIST;
 141                 goto error_find_context;
 142         }
 143         ret = lttng_ust_context_append(ctx, ctx_field);
 144         if (ret)
 145                 return ret;
 146         return 0;
 147
 148 error_find_context:
 149         return ret;
 150 }
 151
 152 /*
 153  * Force a read (imply TLS allocation for dlopen) of TLS variables.
 154  */
 155 void lttng_ust_time_ns_init_thread(int flags)
 156 {
 157         asm volatile ("" : : "m" (URCU_TLS(cached_time_ns)));
 158         if (flags & LTTNG_UST_INIT_THREAD_CONTEXT_CACHE)
 159                 (void)get_time_ns();
 160 }