liblttng-ust/lttng-context-cgroup-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) 2019 Michael Jeanson <mjeanson@efficios.com>
   6  *
   7  * LTTng UST cgroup 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 <ust-tid.h>
  19 #include <urcu/tls-compat.h>
  20 #include <lttng/ringbuffer-context.h>
  21
  22 #include "context-internal.h"
  23 #include "lttng-tracer-core.h"
  24 #include "ns.h"
  25
  26
  27 /*
  28  * We cache the result to ensure we don't stat(2) the proc filesystem on
  29  * each event.
  30  */
  31 static DEFINE_URCU_TLS_INIT(ino_t, cached_cgroup_ns, NS_INO_UNINITIALIZED);
  32
  33 static
  34 ino_t get_cgroup_ns(void)
  35 {
  36         struct stat sb;
  37         ino_t cgroup_ns;
  38
  39         cgroup_ns = CMM_LOAD_SHARED(URCU_TLS(cached_cgroup_ns));
  40
  41         /*
  42          * If the cache is populated, do nothing and return the
  43          * cached inode number.
  44          */
  45         if (caa_likely(cgroup_ns != NS_INO_UNINITIALIZED))
  46                 return cgroup_ns;
  47
  48         /*
  49          * At this point we have to populate the cache, set the initial
  50          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  51          * number from the proc filesystem, this is the value we will
  52          * cache.
  53          */
  54         cgroup_ns = NS_INO_UNAVAILABLE;
  55
  56         /*
  57          * /proc/thread-self was introduced in kernel v3.17
  58          */
  59         if (stat("/proc/thread-self/ns/cgroup", &sb) == 0) {
  60                 cgroup_ns = sb.st_ino;
  61         } else {
  62                 char proc_ns_path[LTTNG_PROC_NS_PATH_MAX];
  63
  64                 if (snprintf(proc_ns_path, LTTNG_PROC_NS_PATH_MAX,
  65                                 "/proc/self/task/%d/ns/cgroup",
  66                                 lttng_gettid()) >= 0) {
  67
  68                         if (stat(proc_ns_path, &sb) == 0) {
  69                                 cgroup_ns = sb.st_ino;
  70                         }
  71                 }
  72         }
  73
  74         /*
  75          * And finally, store the inode number in the cache.
  76          */
  77         CMM_STORE_SHARED(URCU_TLS(cached_cgroup_ns), cgroup_ns);
  78
  79         return cgroup_ns;
  80 }
  81
  82 /*
  83  * The cgroup namespace can change for 3 reasons
  84  *  * clone(2) called with CLONE_NEWCGROUP
  85  *  * setns(2) called with the fd of a different cgroup ns
  86  *  * unshare(2) called with CLONE_NEWCGROUP
  87  */
  88 void lttng_context_cgroup_ns_reset(void)
  89 {
  90         CMM_STORE_SHARED(URCU_TLS(cached_cgroup_ns), NS_INO_UNINITIALIZED);
  91 }
  92
  93 static
  94 size_t cgroup_ns_get_size(struct lttng_ust_ctx_field *field __attribute__((unused)),
  95                 size_t offset)
  96 {
  97         size_t size = 0;
  98
  99         size += lttng_ust_lib_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
 100         size += sizeof(ino_t);
 101         return size;
 102 }
 103
 104 static
 105 void cgroup_ns_record(struct lttng_ust_ctx_field *field __attribute__((unused)),
 106                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
 107                  struct lttng_ust_channel_buffer *chan)
 108 {
 109         ino_t cgroup_ns;
 110
 111         cgroup_ns = get_cgroup_ns();
 112         chan->ops->event_write(ctx, &cgroup_ns, sizeof(cgroup_ns),
 113                         lttng_ust_rb_alignof(cgroup_ns));
 114 }
 115
 116 static
 117 void cgroup_ns_get_value(struct lttng_ust_ctx_field *field __attribute__((unused)),
 118                 struct lttng_ust_ctx_value *value)
 119 {
 120         value->u.s64 = get_cgroup_ns();
 121 }
 122
 123 int lttng_add_cgroup_ns_to_ctx(struct lttng_ust_ctx **ctx)
 124 {
 125         struct lttng_ust_ctx_field *field;
 126         struct lttng_ust_type_common *type;
 127         int ret;
 128
 129         type = lttng_ust_create_type_integer(sizeof(ino_t) * CHAR_BIT,
 130                         lttng_ust_rb_alignof(ino_t) * CHAR_BIT,
 131                         lttng_ust_is_signed_type(ino_t),
 132                         BYTE_ORDER, 10);
 133         if (!type)
 134                 return -ENOMEM;
 135         field = lttng_append_context(ctx);
 136         if (!field) {
 137                 ret = -ENOMEM;
 138                 goto error_context;
 139         }
 140         if (lttng_find_context(*ctx, "cgroup_ns")) {
 141                 ret = -EEXIST;
 142                 goto error_find_context;
 143         }
 144         field->event_field->name = strdup("cgroup_ns");
 145         if (!field->event_field->name) {
 146                 ret = -ENOMEM;
 147                 goto error_name;
 148         }
 149         field->event_field->type = type;
 150         field->get_size = cgroup_ns_get_size;
 151         field->record = cgroup_ns_record;
 152         field->get_value = cgroup_ns_get_value;
 153         lttng_context_update(*ctx);
 154         return 0;
 155
 156 error_name:
 157 error_find_context:
 158         lttng_remove_context_field(ctx, field);
 159 error_context:
 160         lttng_ust_destroy_type(type);
 161         return ret;
 162 }
 163
 164 /*
 165  *  * Force a read (imply TLS fixup for dlopen) of TLS variables.
 166  *   */
 167 void lttng_fixup_cgroup_ns_tls(void)
 168 {
 169         asm volatile ("" : : "m" (URCU_TLS(cached_cgroup_ns)));
 170 }