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 */ 31 static 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 */ 79 static 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 } 102 103 104 int android_reboot(int cmd, int flags, char *arg) 105 { 106 int ret; 107 108 sync(); 109 remount_ro(); 110 111 switch (cmd) { 112 case ANDROID_RB_RESTART: 113 ret = reboot(RB_AUTOBOOT); 114 break; 115 116 case ANDROID_RB_POWEROFF: 117 ret = reboot(RB_POWER_OFF); 118 break; 119 120 case ANDROID_RB_RESTART2: 121 ret = __reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 122 LINUX_REBOOT_CMD_RESTART2, arg); 123 break; 124 125 default: 126 ret = -1; 127 } 128 129 return ret; 130 } 131 132
