• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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