liblttng-ust/lttng-context-time-ns.c

   1 /*
   2  * lttng-context-time-ns.c
   3  *
   4  * LTTng UST time namespace context.
   5  *
   6  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *               2020 Michael Jeanson <mjeanson@efficios.com>
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; only
  12  * version 2.1 of the License.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  */
  23
  24 #define _LGPL_SOURCE
  25 #include <stddef.h>
  26 #include <sys/types.h>
  27 #include <sys/stat.h>
  28 #include <unistd.h>
  29 #include <lttng/ust-events.h>
  30 #include <lttng/ust-tracer.h>
  31 #include <lttng/ringbuffer-config.h>
  32 #include <lttng/ust-tid.h>
  33 #include <urcu/tls-compat.h>
  34 #include "lttng-tracer-core.h"
  35 #include "ns.h"
  36 #include "context-internal.h"
  37
  38
  39 /*
  40  * We cache the result to ensure we don't stat(2) the proc filesystem on
  41  * each event.
  42  */
  43 static DEFINE_URCU_TLS_INIT(ino_t, cached_time_ns, NS_INO_UNINITIALIZED);
  44
  45 static
  46 ino_t get_time_ns(void)
  47 {
  48         struct stat sb;
  49         ino_t time_ns;
  50
  51         time_ns = CMM_LOAD_SHARED(URCU_TLS(cached_time_ns));
  52
  53         /*
  54          * If the cache is populated, do nothing and return the
  55          * cached inode number.
  56          */
  57         if (caa_likely(time_ns != NS_INO_UNINITIALIZED))
  58                 return time_ns;
  59
  60         /*
  61          * At this point we have to populate the cache, set the initial
  62          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  63          * number from the proc filesystem, this is the value we will
  64          * cache.
  65          */
  66         time_ns = NS_INO_UNAVAILABLE;
  67
  68         /*
  69          * /proc/thread-self was introduced in kernel v3.17
  70          */
  71         if (stat("/proc/thread-self/ns/time", &sb) == 0) {
  72                 time_ns = sb.st_ino;
  73         } else {
  74                 char proc_ns_path[LTTNG_PROC_NS_PATH_MAX];
  75
  76                 if (snprintf(proc_ns_path, LTTNG_PROC_NS_PATH_MAX,
  77                                 "/proc/self/task/%d/ns/time",
  78                                 lttng_gettid()) >= 0) {
  79
  80                         if (stat(proc_ns_path, &sb) == 0) {
  81                                 time_ns = sb.st_ino;
  82                         }
  83                 }
  84         }
  85
  86         /*
  87          * And finally, store the inode number in the cache.
  88          */
  89         CMM_STORE_SHARED(URCU_TLS(cached_time_ns), time_ns);
  90
  91         return time_ns;
  92 }
  93
  94 /*
  95  * The time namespace can change for 2 reasons
  96  *  * setns(2) called with the fd of a different time ns
  97  *  * clone(2) / fork(2) after a call to unshare(2) with the CLONE_NEWTIME flag
  98  */
  99 void lttng_context_time_ns_reset(void)
 100 {
 101         CMM_STORE_SHARED(URCU_TLS(cached_time_ns), NS_INO_UNINITIALIZED);
 102 }
 103
 104 static
 105 size_t time_ns_get_size(struct lttng_ctx_field *field, size_t offset)
 106 {
 107         size_t size = 0;
 108
 109         size += lib_ring_buffer_align(offset, lttng_alignof(ino_t));
 110         size += sizeof(ino_t);
 111         return size;
 112 }
 113
 114 static
 115 void time_ns_record(struct lttng_ctx_field *field,
 116                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
 117                  struct lttng_channel *chan)
 118 {
 119         ino_t time_ns;
 120
 121         time_ns = get_time_ns();
 122         lib_ring_buffer_align_ctx(ctx, lttng_alignof(time_ns));
 123         chan->ops->event_write(ctx, &time_ns, sizeof(time_ns));
 124 }
 125
 126 static
 127 void time_ns_get_value(struct lttng_ctx_field *field,
 128                 struct lttng_ctx_value *value)
 129 {
 130         value->u.s64 = get_time_ns();
 131 }
 132
 133 int lttng_add_time_ns_to_ctx(struct lttng_ctx **ctx)
 134 {
 135         struct lttng_ctx_field *field;
 136
 137         field = lttng_append_context(ctx);
 138         if (!field)
 139                 return -ENOMEM;
 140         if (lttng_find_context(*ctx, "time_ns")) {
 141                 lttng_remove_context_field(ctx, field);
 142                 return -EEXIST;
 143         }
 144         field->event_field.name = "time_ns";
 145         field->event_field.type.atype = atype_integer;
 146         field->event_field.type.u.integer.size = sizeof(ino_t) * CHAR_BIT;
 147         field->event_field.type.u.integer.alignment = lttng_alignof(ino_t) * CHAR_BIT;
 148         field->event_field.type.u.integer.signedness = lttng_is_signed_type(ino_t);
 149         field->event_field.type.u.integer.reverse_byte_order = 0;
 150         field->event_field.type.u.integer.base = 10;
 151         field->event_field.type.u.integer.encoding = lttng_encode_none;
 152         field->get_size = time_ns_get_size;
 153         field->record = time_ns_record;
 154         field->get_value = time_ns_get_value;
 155         lttng_context_update(*ctx);
 156         return 0;
 157 }
 158
 159 /*
 160  *  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 161  *   */
 162 void lttng_fixup_time_ns_tls(void)
 163 {
 164         asm volatile ("" : : "m" (URCU_TLS(cached_time_ns)));
 165 }