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 */ 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 */ 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 } 105 106 107 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
