liblttng-ust/lttng-context-pid-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 pid 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/ringbuffer-context.h>
  19
  20 #include "context-internal.h"
  21 #include "ns.h"
  22
  23 /*
  24  * We cache the result to ensure we don't stat(2) the proc filesystem on
  25  * each event. The PID namespace is global to the process.
  26  */
  27 static ino_t cached_pid_ns = NS_INO_UNINITIALIZED;
  28
  29 static
  30 ino_t get_pid_ns(void)
  31 {
  32         struct stat sb;
  33         ino_t pid_ns;
  34
  35         pid_ns = CMM_LOAD_SHARED(cached_pid_ns);
  36
  37         /*
  38          * If the cache is populated, do nothing and return the
  39          * cached inode number.
  40          */
  41         if (caa_likely(pid_ns != NS_INO_UNINITIALIZED))
  42                 return pid_ns;
  43
  44         /*
  45          * At this point we have to populate the cache, set the initial
  46          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  47          * number from the proc filesystem, this is the value we will
  48          * cache.
  49          */
  50         pid_ns = NS_INO_UNAVAILABLE;
  51
  52         if (stat("/proc/self/ns/pid", &sb) == 0) {
  53                 pid_ns = sb.st_ino;
  54         }
  55
  56         /*
  57          * And finally, store the inode number in the cache.
  58          */
  59         CMM_STORE_SHARED(cached_pid_ns, pid_ns);
  60
  61         return pid_ns;
  62 }
  63
  64 /*
  65  * A process's PID namespace membership is determined when the process is
  66  * created and cannot be changed thereafter.
  67  *
  68  * The pid namespace can change only on clone(2) / fork(2) :
  69  *  - clone(2) with the CLONE_NEWPID flag
  70  *  - clone(2) / fork(2) after a call to unshare(2) with the CLONE_NEWPID flag
  71  *  - clone(2) / fork(2) after a call to setns(2) with a PID namespace fd
  72  */
  73 void lttng_context_pid_ns_reset(void)
  74 {
  75         CMM_STORE_SHARED(cached_pid_ns, NS_INO_UNINITIALIZED);
  76 }
  77
  78 static
  79 size_t pid_ns_get_size(struct lttng_ust_ctx_field *field, size_t offset)
  80 {
  81         size_t size = 0;
  82
  83         size += lttng_ust_lib_ring_buffer_align(offset, lttng_alignof(ino_t));
  84         size += sizeof(ino_t);
  85         return size;
  86 }
  87
  88 static
  89 void pid_ns_record(struct lttng_ust_ctx_field *field,
  90                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  91                  struct lttng_ust_channel_buffer *chan)
  92 {
  93         ino_t pid_ns;
  94
  95         pid_ns = get_pid_ns();
  96         lttng_ust_lib_ring_buffer_align_ctx(ctx, lttng_alignof(pid_ns));
  97         chan->ops->event_write(ctx, &pid_ns, sizeof(pid_ns));
  98 }
  99
 100 static
 101 void pid_ns_get_value(struct lttng_ust_ctx_field *field,
 102                 struct lttng_ust_ctx_value *value)
 103 {
 104         value->u.s64 = get_pid_ns();
 105 }
 106
 107 int lttng_add_pid_ns_to_ctx(struct lttng_ust_ctx **ctx)
 108 {
 109         struct lttng_ust_ctx_field *field;
 110         struct lttng_ust_type_common *type;
 111         int ret;
 112
 113         type = lttng_ust_create_type_integer(sizeof(ino_t) * CHAR_BIT,
 114                         lttng_alignof(ino_t) * CHAR_BIT,
 115                         lttng_ust_is_signed_type(ino_t),
 116                         BYTE_ORDER, 10);
 117         if (!type)
 118                 return -ENOMEM;
 119         field = lttng_append_context(ctx);
 120         if (!field) {
 121                 ret = -ENOMEM;
 122                 goto error_context;
 123         }
 124         if (lttng_find_context(*ctx, "pid_ns")) {
 125                 ret = -EEXIST;
 126                 goto error_find_context;
 127         }
 128         field->event_field->name = strdup("pid_ns");
 129         if (!field->event_field->name) {
 130                 ret = -ENOMEM;
 131                 goto error_name;
 132         }
 133         field->event_field->type = type;
 134         field->get_size = pid_ns_get_size;
 135         field->record = pid_ns_record;
 136         field->get_value = pid_ns_get_value;
 137         lttng_context_update(*ctx);
 138         return 0;
 139
 140 error_name:
 141 error_find_context:
 142         lttng_remove_context_field(ctx, field);
 143 error_context:
 144         lttng_ust_destroy_type(type);
 145         return ret;
 146 }