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 <stddef.h>
  12 #include <sys/types.h>
  13 #include <sys/stat.h>
  14 #include <unistd.h>
  15 #include <lttng/ust-events.h>
  16 #include <lttng/ust-tracer.h>
  17 #include <lttng/ringbuffer-context.h>
  18
  19 #include "context-internal.h"
  20 #include "ns.h"
  21
  22 /*
  23  * We cache the result to ensure we don't stat(2) the proc filesystem on
  24  * each event. The PID namespace is global to the process.
  25  */
  26 static ino_t cached_pid_ns = NS_INO_UNINITIALIZED;
  27
  28 static
  29 ino_t get_pid_ns(void)
  30 {
  31         struct stat sb;
  32         ino_t pid_ns;
  33
  34         pid_ns = CMM_LOAD_SHARED(cached_pid_ns);
  35
  36         /*
  37          * If the cache is populated, do nothing and return the
  38          * cached inode number.
  39          */
  40         if (caa_likely(pid_ns != NS_INO_UNINITIALIZED))
  41                 return pid_ns;
  42
  43         /*
  44          * At this point we have to populate the cache, set the initial
  45          * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode
  46          * number from the proc filesystem, this is the value we will
  47          * cache.
  48          */
  49         pid_ns = NS_INO_UNAVAILABLE;
  50
  51         if (stat("/proc/self/ns/pid", &sb) == 0) {
  52                 pid_ns = sb.st_ino;
  53         }
  54
  55         /*
  56          * And finally, store the inode number in the cache.
  57          */
  58         CMM_STORE_SHARED(cached_pid_ns, pid_ns);
  59
  60         return pid_ns;
  61 }
  62
  63 /*
  64  * A process's PID namespace membership is determined when the process is
  65  * created and cannot be changed thereafter.
  66  *
  67  * The pid namespace can change only on clone(2) / fork(2) :
  68  *  - clone(2) with the CLONE_NEWPID flag
  69  *  - clone(2) / fork(2) after a call to unshare(2) with the CLONE_NEWPID flag
  70  *  - clone(2) / fork(2) after a call to setns(2) with a PID namespace fd
  71  */
  72 void lttng_context_pid_ns_reset(void)
  73 {
  74         CMM_STORE_SHARED(cached_pid_ns, NS_INO_UNINITIALIZED);
  75 }
  76
  77 static
  78 size_t pid_ns_get_size(struct lttng_ust_ctx_field *field, size_t offset)
  79 {
  80         size_t size = 0;
  81
  82         size += lib_ring_buffer_align(offset, lttng_alignof(ino_t));
  83         size += sizeof(ino_t);
  84         return size;
  85 }
  86
  87 static
  88 void pid_ns_record(struct lttng_ust_ctx_field *field,
  89                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  90                  struct lttng_channel *chan)
  91 {
  92         ino_t pid_ns;
  93
  94         pid_ns = get_pid_ns();
  95         lib_ring_buffer_align_ctx(ctx, lttng_alignof(pid_ns));
  96         chan->ops->event_write(ctx, &pid_ns, sizeof(pid_ns));
  97 }
  98
  99 static
 100 void pid_ns_get_value(struct lttng_ust_ctx_field *field,
 101                 struct lttng_ust_ctx_value *value)
 102 {
 103         value->u.s64 = get_pid_ns();
 104 }
 105
 106 int lttng_add_pid_ns_to_ctx(struct lttng_ust_ctx **ctx)
 107 {
 108         struct lttng_ust_ctx_field *field;
 109         struct lttng_ust_type_common *type;
 110         int ret;
 111
 112         type = lttng_ust_create_type_integer(sizeof(ino_t) * CHAR_BIT,
 113                         lttng_alignof(ino_t) * CHAR_BIT,
 114                         lttng_is_signed_type(ino_t),
 115                         BYTE_ORDER, 10);
 116         if (!type)
 117                 return -ENOMEM;
 118         field = lttng_append_context(ctx);
 119         if (!field) {
 120                 ret = -ENOMEM;
 121                 goto error_context;
 122         }
 123         if (lttng_find_context(*ctx, "pid_ns")) {
 124                 ret = -EEXIST;
 125                 goto error_find_context;
 126         }
 127         field->event_field->name = strdup("pid_ns");
 128         if (!field->event_field->name) {
 129                 ret = -ENOMEM;
 130                 goto error_name;
 131         }
 132         field->event_field->type = type;
 133         field->get_size = pid_ns_get_size;
 134         field->record = pid_ns_record;
 135         field->get_value = pid_ns_get_value;
 136         lttng_context_update(*ctx);
 137         return 0;
 138
 139 error_name:
 140 error_find_context:
 141         lttng_remove_context_field(ctx, field);
 142 error_context:
 143         lttng_ust_destroy_type(type);
 144         return ret;
 145 }