android_reboot.c revision ba02cd1e9bccee9b112ccbee06bc204381b5a215 
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 */
34static 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 */
82static 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
107int 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