src/lib/lttng-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/ust-ringbuffer-context.h>
  19
  20 #include "context-internal.h"
  21 #include "common/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(void *priv __attribute__((unused)),
  80                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
  81                 size_t offset)
  82 {
  83         size_t size = 0;
  84
  85         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(ino_t));
  86         size += sizeof(ino_t);
  87         return size;
  88 }
  89
  90 static
  91 void pid_ns_record(void *priv __attribute__((unused)),
  92                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
  93                 struct lttng_ust_ring_buffer_ctx *ctx,
  94                 struct lttng_ust_channel_buffer *chan)
  95 {
  96         ino_t pid_ns;
  97
  98         pid_ns = get_pid_ns();
  99         chan->ops->event_write(ctx, &pid_ns, sizeof(pid_ns), lttng_ust_rb_alignof(pid_ns));
 100 }
 101
 102 static
 103 void pid_ns_get_value(void *priv __attribute__((unused)),
 104                 struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)),
 105                 struct lttng_ust_ctx_value *value)
 106 {
 107         value->u.u64 = get_pid_ns();
 108 }
 109
 110 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
 111         lttng_ust_static_event_field("pid_ns",
 112                 lttng_ust_static_type_integer(sizeof(ino_t) * CHAR_BIT,
 113                                 lttng_ust_rb_alignof(ino_t) * CHAR_BIT,
 114                                 lttng_ust_is_signed_type(ino_t),
 115                                 LTTNG_UST_BYTE_ORDER, 10),
 116                 false, false),
 117         pid_ns_get_size,
 118         pid_ns_record,
 119         pid_ns_get_value,
 120         NULL, NULL);
 121
 122 int lttng_add_pid_ns_to_ctx(struct lttng_ust_ctx **ctx)
 123 {
 124         int ret;
 125
 126         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
 127                 ret = -EEXIST;
 128                 goto error_find_context;
 129         }
 130         ret = lttng_ust_context_append(ctx, ctx_field);
 131         if (ret)
 132                 return ret;
 133         return 0;
 134
 135 error_find_context:
 136         return ret;
 137 }