backend/extroot.c

   1 /*
   2  * Copyright (C) 2014 John Crispin <blogic@openwrt.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU Lesser General Public License version 2.1
   6  * as published by the Free Software Foundation
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  */
  13
  14 #include <unistd.h>
  15 #include <stdlib.h>
  16 #include <stdio.h>
  17 #include <string.h>
  18 #include <sys/mount.h>
  19 #include <sys/types.h>
  20 #include <sys/stat.h>
  21 #include <sys/wait.h>
  22
  23 #include "../fs-state.h"
  24
  25 char const *extroot_prefix = NULL;
  26
  27 static int mount_extroot(void)
  28 {
  29         char block_path[32];
  30         char kmod_loader[64];
  31         struct stat s;
  32         pid_t pid;
  33
  34         if (!extroot_prefix)
  35                 return -1;
  36
  37         sprintf(block_path, "%s/sbin/block", extroot_prefix);
  38
  39         if (stat(block_path, &s))
  40                 return -1;
  41
  42         sprintf(kmod_loader, "/sbin/kmodloader %s/etc/modules-boot.d/ %s", extroot_prefix, extroot_prefix);
  43         system(kmod_loader);
  44
  45         pid = fork();
  46         if (!pid) {
  47                 mkdir("/tmp/extroot", 0755);
  48                 execl(block_path, block_path, "extroot", NULL);
  49                 exit(-1);
  50         } else if (pid > 0) {
  51                 int status;
  52
  53                 waitpid(pid, &status, 0);
  54                 if (!WEXITSTATUS(status)) {
  55                         if (find_mount("/tmp/extroot/mnt")) {
  56                                 mount("/dev/root", "/", NULL, MS_NOATIME | MS_REMOUNT | MS_RDONLY, 0);
  57
  58                                 mkdir("/tmp/extroot/mnt/proc", 0755);
  59                                 mkdir("/tmp/extroot/mnt/dev", 0755);
  60                                 mkdir("/tmp/extroot/mnt/sys", 0755);
  61                                 mkdir("/tmp/extroot/mnt/tmp", 0755);
  62                                 mkdir("/tmp/extroot/mnt/rom", 0755);
  63
  64                                 if (mount_move("/tmp/extroot", "", "/mnt")) {
  65                                         fprintf(stderr, "moving pivotroot failed - continue normal boot\n");
  66                                         umount("/tmp/extroot/mnt");
  67                                 } else if (pivot("/mnt", "/rom")) {
  68                                         fprintf(stderr, "switching to pivotroot failed - continue normal boot\n");
  69                                         umount("/mnt");
  70                                 } else {
  71                                         umount("/tmp/overlay");
  72                                         rmdir("/tmp/overlay");
  73                                         rmdir("/tmp/extroot/mnt");
  74                                         rmdir("/tmp/extroot");
  75                                         return 0;
  76                                 }
  77                         } else if (find_mount("/tmp/extroot/overlay")) {
  78                                 if (mount_move("/tmp/extroot", "", "/overlay")) {
  79                                         fprintf(stderr, "moving extroot failed - continue normal boot\n");
  80                                         umount("/tmp/extroot/overlay");
  81                                 } else if (fopivot("/overlay", "/rom")) {
  82                                         fprintf(stderr, "switching to extroot failed - continue normal boot\n");
  83                                         umount("/overlay");
  84                                 } else {
  85                                         umount("/tmp/overlay");
  86                                         rmdir("/tmp/overlay");
  87                                         rmdir("/tmp/extroot/overlay");
  88                                         rmdir("/tmp/extroot");
  89                                         return 0;
  90                                 }
  91                         }
  92                 }
  93         }
  94         return -1;
  95 }
  96
  97 static struct backend extroot_backend = {
  98         .name = "extroot",
  99         .mount = mount_extroot,
 100 };
 101 BACKEND(extroot_backend);