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/*
* Copyright 2011, The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <unistd.h>
#include <sys/reboot.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <mntent.h>
#include <stdio.h>
#include <string.h>
#include <cutils/android_reboot.h>
#define UNUSED __attribute__((unused))
/* Check to see if /proc/mounts contains any writeable filesystems
* backed by a block device.
* Return true if none found, else return false.
*/
static int remount_ro_done(void)
{
FILE* fp;
struct mntent* mentry;
int found_rw_fs = 0;
if ((fp = setmntent("/proc/mounts", "r")) == NULL) {
/* If we can't read /proc/mounts, just give up. */
return 1;
}
while ((mentry = getmntent(fp)) != NULL) {
if (!strncmp(mentry->mnt_fsname, "/dev/block", 10) && strstr(mentry->mnt_opts, "rw,")) {
found_rw_fs = 1;
break;
}
}
endmntent(fp);
return !found_rw_fs;
}
/* Remounting filesystems read-only is difficult when there are files
* opened for writing or pending deletes on the filesystem. There is
* no way to force the remount with the mount(2) syscall. The magic sysrq
* 'u' command does an emergency remount read-only on all writable filesystems
* that have a block device (i.e. not tmpfs filesystems) by calling
* emergency_remount(), which knows how to force the remount to read-only.
* Unfortunately, that is asynchronous, and just schedules the work and
* returns. The best way to determine if it is done is to read /proc/mounts
* repeatedly until there are no more writable filesystems mounted on
* block devices.
*/
static void remount_ro(void)
{
int fd, cnt = 0;
/* Trigger the remount of the filesystems as read-only,
* which also marks them clean.
*/
fd = open("/proc/sysrq-trigger", O_WRONLY);
if (fd < 0) {
return;
}
write(fd, "u", 1);
close(fd);
/* Now poll /proc/mounts till it's done */
while (!remount_ro_done() && (cnt < 50)) {
usleep(100000);
cnt++;
}
return;
}
int android_reboot(int cmd, int flags UNUSED, const char *arg)
{
int ret;
sync();
remount_ro();
switch (cmd) {
case ANDROID_RB_RESTART:
ret = reboot(RB_AUTOBOOT);
break;
case ANDROID_RB_POWEROFF:
ret = reboot(RB_POWER_OFF);
break;
case ANDROID_RB_RESTART2:
ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
LINUX_REBOOT_CMD_RESTART2, arg);
break;
default:
ret = -1;
}
return ret;
}
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