| 1 | /* |
| 2 | * lttng-context-mnt-ns.c |
| 3 | * |
| 4 | * LTTng UST mnt 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 <stddef.h> |
| 26 | #include <sys/types.h> |
| 27 | #include <sys/stat.h> |
| 28 | #include <unistd.h> |
| 29 | #include <lttng/ust-events.h> |
| 30 | #include <lttng/ust-tracer.h> |
| 31 | #include <lttng/ringbuffer-config.h> |
| 32 | |
| 33 | #include "ns.h" |
| 34 | |
| 35 | /* |
| 36 | * We cache the result to ensure we don't stat(2) the proc filesystem on |
| 37 | * each event. The mount namespace is global to the process. |
| 38 | */ |
| 39 | static ino_t cached_mnt_ns = NS_INO_UNINITIALIZED; |
| 40 | |
| 41 | static |
| 42 | ino_t get_mnt_ns(void) |
| 43 | { |
| 44 | struct stat sb; |
| 45 | ino_t mnt_ns; |
| 46 | |
| 47 | mnt_ns = CMM_LOAD_SHARED(cached_mnt_ns); |
| 48 | |
| 49 | /* |
| 50 | * If the cache is populated, do nothing and return the |
| 51 | * cached inode number. |
| 52 | */ |
| 53 | if (caa_likely(mnt_ns != NS_INO_UNINITIALIZED)) |
| 54 | return mnt_ns; |
| 55 | |
| 56 | /* |
| 57 | * At this point we have to populate the cache, set the initial |
| 58 | * value to NS_INO_UNAVAILABLE (0), if we fail to get the inode |
| 59 | * number from the proc filesystem, this is the value we will |
| 60 | * cache. |
| 61 | */ |
| 62 | mnt_ns = NS_INO_UNAVAILABLE; |
| 63 | |
| 64 | if (stat("/proc/self/ns/mnt", &sb) == 0) { |
| 65 | mnt_ns = sb.st_ino; |
| 66 | } |
| 67 | |
| 68 | /* |
| 69 | * And finally, store the inode number in the cache. |
| 70 | */ |
| 71 | CMM_STORE_SHARED(cached_mnt_ns, mnt_ns); |
| 72 | |
| 73 | return mnt_ns; |
| 74 | } |
| 75 | |
| 76 | /* |
| 77 | * The mnt namespace can change for 3 reasons |
| 78 | * * clone(2) called with CLONE_NEWNS |
| 79 | * * setns(2) called with the fd of a different mnt ns |
| 80 | * * unshare(2) called with CLONE_NEWNS |
| 81 | */ |
| 82 | void lttng_context_mnt_ns_reset(void) |
| 83 | { |
| 84 | CMM_STORE_SHARED(cached_mnt_ns, NS_INO_UNINITIALIZED); |
| 85 | } |
| 86 | |
| 87 | static |
| 88 | size_t mnt_ns_get_size(struct lttng_ctx_field *field, size_t offset) |
| 89 | { |
| 90 | size_t size = 0; |
| 91 | |
| 92 | size += lib_ring_buffer_align(offset, lttng_alignof(ino_t)); |
| 93 | size += sizeof(ino_t); |
| 94 | return size; |
| 95 | } |
| 96 | |
| 97 | static |
| 98 | void mnt_ns_record(struct lttng_ctx_field *field, |
| 99 | struct lttng_ust_lib_ring_buffer_ctx *ctx, |
| 100 | struct lttng_channel *chan) |
| 101 | { |
| 102 | ino_t mnt_ns; |
| 103 | |
| 104 | mnt_ns = get_mnt_ns(); |
| 105 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(mnt_ns)); |
| 106 | chan->ops->event_write(ctx, &mnt_ns, sizeof(mnt_ns)); |
| 107 | } |
| 108 | |
| 109 | static |
| 110 | void mnt_ns_get_value(struct lttng_ctx_field *field, |
| 111 | struct lttng_ctx_value *value) |
| 112 | { |
| 113 | value->u.s64 = get_mnt_ns(); |
| 114 | } |
| 115 | |
| 116 | int lttng_add_mnt_ns_to_ctx(struct lttng_ctx **ctx) |
| 117 | { |
| 118 | struct lttng_ctx_field *field; |
| 119 | |
| 120 | field = lttng_append_context(ctx); |
| 121 | if (!field) |
| 122 | return -ENOMEM; |
| 123 | if (lttng_find_context(*ctx, "mnt_ns")) { |
| 124 | lttng_remove_context_field(ctx, field); |
| 125 | return -EEXIST; |
| 126 | } |
| 127 | field->event_field.name = "mnt_ns"; |
| 128 | field->event_field.type.atype = atype_integer; |
| 129 | field->event_field.type.u.integer.size = sizeof(ino_t) * CHAR_BIT; |
| 130 | field->event_field.type.u.integer.alignment = lttng_alignof(ino_t) * CHAR_BIT; |
| 131 | field->event_field.type.u.integer.signedness = lttng_is_signed_type(ino_t); |
| 132 | field->event_field.type.u.integer.reverse_byte_order = 0; |
| 133 | field->event_field.type.u.integer.base = 10; |
| 134 | field->event_field.type.u.integer.encoding = lttng_encode_none; |
| 135 | field->get_size = mnt_ns_get_size; |
| 136 | field->record = mnt_ns_record; |
| 137 | field->get_value = mnt_ns_get_value; |
| 138 | lttng_context_update(*ctx); |
| 139 | return 0; |
| 140 | } |