android_reboot.c revision e3aeeb4de34dbb93e832e6554f494122ba633f3b 
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/types.h>
20#include <sys/stat.h>
21#include <fcntl.h>
22#include <stdio.h>
23#include <string.h>
24
25#include <cutils/android_reboot.h>
26
27/* Check to see if /proc/mounts contains any writeable filesystems
28 * backed by a block device.
29 * Return true if none found, else return false.
30 */
31static int remount_ro_done(void)
32{
33    FILE *f;
34    char mount_dev[256];
35    char mount_dir[256];
36    char mount_type[256];
37    char mount_opts[256];
38    int mount_freq;
39    int mount_passno;
40    int match;
41    int found_rw_fs = 0;
42
43    f = fopen("/proc/mounts", "r");
44    if (! f) {
45        /* If we can't read /proc/mounts, just give up */
46        return 1;
47    }
48
49    do {
50        match = fscanf(f, "%255s %255s %255s %255s %d %d\n",
51                       mount_dev, mount_dir, mount_type,
52                       mount_opts, &mount_freq, &mount_passno);
53        mount_dev[255] = 0;
54        mount_dir[255] = 0;
55        mount_type[255] = 0;
56        mount_opts[255] = 0;
57        if ((match == 6) && !strncmp(mount_dev, "/dev/block", 10) && strstr(mount_opts, "rw")) {
58            found_rw_fs = 1;
59            break;
60        }
61    } while (match != EOF);
62
63    fclose(f);
64
65    return !found_rw_fs;
66}
67
68/* Remounting filesystems read-only is difficult when there are files
69 * opened for writing or pending deletes on the filesystem.  There is
70 * no way to force the remount with the mount(2) syscall.  The magic sysrq
71 * 'u' command does an emergency remount read-only on all writable filesystems
72 * that have a block device (i.e. not tmpfs filesystems) by calling
73 * emergency_remount(), which knows how to force the remount to read-only.
74 * Unfortunately, that is asynchronous, and just schedules the work and
75 * returns.  The best way to determine if it is done is to read /proc/mounts
76 * repeatedly until there are no more writable filesystems mounted on
77 * block devices.
78 */
79static void remount_ro(void)
80{
81    int fd, cnt = 0;
82
83    /* Trigger the remount of the filesystems as read-only,
84     * which also marks them clean.
85     */
86    fd = open("/proc/sysrq-trigger", O_WRONLY);
87    if (fd < 0) {
88        return;
89    }
90    write(fd, "u", 1);
91    close(fd);
92
93
94    /* Now poll /proc/mounts till it's done */
95    while (!remount_ro_done() && (cnt < 50)) {
96        usleep(100000);
97        cnt++;
98    }
99
100    return;
101}
102
103
104int android_reboot(int cmd, int flags, char *arg)
105{
106    int ret;
107
108    if (!(flags & ANDROID_RB_FLAG_NO_SYNC))
109        sync();
110
111    if (!(flags & ANDROID_RB_FLAG_NO_REMOUNT_RO))
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 = __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