1 /*
2 * Copyright 2011, 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 <unistd.h>
18 #include <sys/reboot.h>
19 #include <sys/syscall.h>
20 #include <sys/types.h>
21 #include <sys/stat.h>
22 #include <fcntl.h>
23 #include <stdio.h>
24 #include <string.h>
25
26 #include <cutils/android_reboot.h>
27
28 #define UNUSED __attribute__((unused))
29
30 /* Check to see if /proc/mounts contains any writeable filesystems
31 * backed by a block device.
32 * Return true if none found, else return false.
33 */
remount_ro_done(void)34 static int remount_ro_done(void)
35 {
36 FILE *f;
37 char mount_dev[256];
38 char mount_dir[256];
39 char mount_type[256];
40 char mount_opts[256];
41 int mount_freq;
42 int mount_passno;
43 int match;
44 int found_rw_fs = 0;
45
46 f = fopen("/proc/mounts", "r");
47 if (! f) {
48 /* If we can't read /proc/mounts, just give up */
49 return 1;
50 }
51
52 do {
53 match = fscanf(f, "%255s %255s %255s %255s %d %d\n",
54 mount_dev, mount_dir, mount_type,
55 mount_opts, &mount_freq, &mount_passno);
56 mount_dev[255] = 0;
57 mount_dir[255] = 0;
58 mount_type[255] = 0;
59 mount_opts[255] = 0;
60 if ((match == 6) && !strncmp(mount_dev, "/dev/block", 10) && strstr(mount_opts, "rw,")) {
61 found_rw_fs = 1;
62 break;
63 }
64 } while (match != EOF);
65
66 fclose(f);
67
68 return !found_rw_fs;
69 }
70
71 /* Remounting filesystems read-only is difficult when there are files
72 * opened for writing or pending deletes on the filesystem. There is
73 * no way to force the remount with the mount(2) syscall. The magic sysrq
74 * 'u' command does an emergency remount read-only on all writable filesystems
75 * that have a block device (i.e. not tmpfs filesystems) by calling
76 * emergency_remount(), which knows how to force the remount to read-only.
77 * Unfortunately, that is asynchronous, and just schedules the work and
78 * returns. The best way to determine if it is done is to read /proc/mounts
79 * repeatedly until there are no more writable filesystems mounted on
80 * block devices.
81 */
remount_ro(void)82 static void remount_ro(void)
83 {
84 int fd, cnt = 0;
85
86 /* Trigger the remount of the filesystems as read-only,
87 * which also marks them clean.
88 */
89 fd = open("/proc/sysrq-trigger", O_WRONLY);
90 if (fd < 0) {
91 return;
92 }
93 write(fd, "u", 1);
94 close(fd);
95
96
97 /* Now poll /proc/mounts till it's done */
98 while (!remount_ro_done() && (cnt < 50)) {
99 usleep(100000);
100 cnt++;
101 }
102
103 return;
104 }
105
106
android_reboot(int cmd,int flags UNUSED,char * arg)107 int android_reboot(int cmd, int flags UNUSED, char *arg)
108 {
109 int ret;
110
111 sync();
112 remount_ro();
113
114 switch (cmd) {
115 case ANDROID_RB_RESTART:
116 ret = reboot(RB_AUTOBOOT);
117 break;
118
119 case ANDROID_RB_POWEROFF:
120 ret = reboot(RB_POWER_OFF);
121 break;
122
123 case ANDROID_RB_RESTART2:
124 ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
125 LINUX_REBOOT_CMD_RESTART2, arg);
126 break;
127
128 default:
129 ret = -1;
130 }
131
132 return ret;
133 }
134
135