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

   1 /*
   2  * lttng-context-ipc-ns.c
   3  *
   4  * LTTng UST ipc namespace context.
   5  *
   6  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *               2019 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 <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28 #include <lttng/ust-events.h>
  29 #include <lttng/ust-tracer.h>
  30 #include <lttng/ringbuffer-config.h>
  31 #include <lttng/ust-tid.h>
  32 #include <urcu/tls-compat.h>
  33 #include "lttng-tracer-core.h"
  34 #include "ns.h"
  35
  36 /*
  37  * We cache the result to ensure we don't stat(2) the proc filesystem on
  38  * each event.
  39  */
  40 #ifdef CONFIG_RCU_TLS
  41 static DEFINE_URCU_TLS(ino_t, cached_ipc_ns) = NS_INO_UNINITIALIZED;
  42 #else
  43 static DEFINE_URCU_TLS_INIT(ino_t, cached_ipc_ns, NS_INO_UNINITIALIZED);
  44 #endif
  45
  46 static
  47 ino_t get_ipc_ns(void)
  48 {
  49         struct stat sb;
  50         ino_t ipc_ns;
  51
  52         ipc_ns = CMM_LOAD_SHARED(URCU_TLS(cached_ipc_ns));
  53
  54         /*
  55          * If the cache is populated, do nothing and return the
  56          * cached inode number.
  57          */
  58         if (caa_likely(ipc_ns != NS_INO_UNINITIALIZED))
  59                 return ipc_ns;
  60
  61         /*
  62          * At this point we have to populate the cache, set the initial
  63          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  64          * number from the proc filesystem, this is the value we will
  65          * cache.
  66          */
  67         ipc_ns = NS_INO_UNAVAILABLE;
  68
  69         /*
  70          * /proc/thread-self was introduced in kernel v3.17
  71          */
  72         if (stat("/proc/thread-self/ns/ipc", &sb) == 0) {
  73                 ipc_ns = sb.st_ino;
  74         } else {
  75                 char proc_ns_path[LTTNG_PROC_NS_PATH_MAX];
  76
  77                 if (snprintf(proc_ns_path, LTTNG_PROC_NS_PATH_MAX,
  78                                 "/proc/self/task/%d/ns/ipc",
  79                                 lttng_gettid()) >= 0) {
  80
  81                         if (stat(proc_ns_path, &sb) == 0) {
  82                                 ipc_ns = sb.st_ino;
  83                         }
  84                 }
  85         }
  86
  87         /*
  88          * And finally, store the inode number in the cache.
  89          */
  90         CMM_STORE_SHARED(URCU_TLS(cached_ipc_ns), ipc_ns);
  91
  92         return ipc_ns;
  93 }
  94
  95 /*
  96  * The ipc namespace can change for 3 reasons
  97  *  * clone(2) called with CLONE_NEWIPC
  98  *  * setns(2) called with the fd of a different ipc ns
  99  *  * unshare(2) called with CLONE_NEWIPC
 100  */
 101 void lttng_context_ipc_ns_reset(void)
 102 {
 103         CMM_STORE_SHARED(URCU_TLS(cached_ipc_ns), NS_INO_UNINITIALIZED);
 104 }
 105
 106 static
 107 size_t ipc_ns_get_size(struct lttng_ctx_field *field, size_t offset)
 108 {
 109         size_t size = 0;
 110
 111         size += lib_ring_buffer_align(offset, lttng_alignof(ino_t));
 112         size += sizeof(ino_t);
 113         return size;
 114 }
 115
 116 static
 117 void ipc_ns_record(struct lttng_ctx_field *field,
 118                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
 119                  struct lttng_channel *chan)
 120 {
 121         ino_t ipc_ns;
 122
 123         ipc_ns = get_ipc_ns();
 124         lib_ring_buffer_align_ctx(ctx, lttng_alignof(ipc_ns));
 125         chan->ops->event_write(ctx, &ipc_ns, sizeof(ipc_ns));
 126 }
 127
 128 static
 129 void ipc_ns_get_value(struct lttng_ctx_field *field,
 130                 struct lttng_ctx_value *value)
 131 {
 132         value->u.s64 = get_ipc_ns();
 133 }
 134
 135 int lttng_add_ipc_ns_to_ctx(struct lttng_ctx **ctx)
 136 {
 137         struct lttng_ctx_field *field;
 138
 139         field = lttng_append_context(ctx);
 140         if (!field)
 141                 return -ENOMEM;
 142         if (lttng_find_context(*ctx, "ipc_ns")) {
 143                 lttng_remove_context_field(ctx, field);
 144                 return -EEXIST;
 145         }
 146         field->event_field.name = "ipc_ns";
 147         field->event_field.type.atype = atype_integer;
 148         field->event_field.type.u.basic.integer.size = sizeof(ino_t) * CHAR_BIT;
 149         field->event_field.type.u.basic.integer.alignment = lttng_alignof(ino_t) * CHAR_BIT;
 150         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(ino_t);
 151         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
 152         field->event_field.type.u.basic.integer.base = 10;
 153         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
 154         field->get_size = ipc_ns_get_size;
 155         field->record = ipc_ns_record;
 156         field->get_value = ipc_ns_get_value;
 157         lttng_context_update(*ctx);
 158         return 0;
 159 }
 160
 161 /*
 162  *  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 163  *   */
 164 void lttng_fixup_ipc_ns_tls(void)
 165 {
 166         asm volatile ("" : : "m" (URCU_TLS(cached_ipc_ns)));
 167 }