1 /*
2 * Copyright (C) 2018 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "apexd_private.h"
18
19 #include <sys/mount.h>
20 #include <sys/stat.h>
21
22 #include <android-base/logging.h>
23 #include <android-base/macros.h>
24
25 #include "string_log.h"
26
27 using android::base::ErrnoError;
28 using android::base::Result;
29
30 namespace android {
31 namespace apex {
32 namespace apexd_private {
33
BindMount(const std::string & target,const std::string & source)34 Result<void> BindMount(const std::string& target, const std::string& source) {
35 LOG(VERBOSE) << "Creating bind-mount for " << target << " for " << source;
36 // Ensure the directory exists, try to unmount.
37 {
38 bool exists;
39 bool is_dir;
40 {
41 struct stat buf;
42 if (stat(target.c_str(), &buf) != 0) {
43 if (errno == ENOENT) {
44 exists = false;
45 is_dir = false;
46 } else {
47 PLOG(ERROR) << "Could not stat target directory " << target;
48 // Still attempt to bind-mount.
49 exists = true;
50 is_dir = true;
51 }
52 } else {
53 exists = true;
54 is_dir = S_ISDIR(buf.st_mode);
55 }
56 }
57
58 // Ensure that it is a folder.
59 if (exists && !is_dir) {
60 LOG(WARNING) << target << " is not a directory, attempting to fix";
61 if (unlink(target.c_str()) != 0) {
62 PLOG(ERROR) << "Failed to unlink " << target;
63 // Try mkdir, anyways.
64 }
65 exists = false;
66 }
67 // And create it if necessary.
68 if (!exists) {
69 LOG(VERBOSE) << "Creating mountpoint " << target;
70 if (mkdir(target.c_str(), kMkdirMode) != 0) {
71 return ErrnoError() << "Could not create mountpoint " << target;
72 }
73 };
74 // Unmount any active bind-mount.
75 if (exists) {
76 int rc = umount2(target.c_str(), UMOUNT_NOFOLLOW);
77 if (rc != 0 && errno != EINVAL) {
78 // Log error but ignore.
79 PLOG(ERROR) << "Could not unmount " << target;
80 }
81 }
82 }
83
84 LOG(VERBOSE) << "Bind-mounting " << source << " to " << target;
85 if (mount(source.c_str(), target.c_str(), nullptr, MS_BIND, nullptr) == 0) {
86 return {};
87 }
88 return ErrnoError() << "Could not bind-mount " << source << " to " << target;
89 }
90
91 } // namespace apexd_private
92 } // namespace apex
93 } // namespace android
94