libfstools/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 #include <libgen.h>
  23
  24 #include "libfstools.h"
  25
  26 char const *extroot_prefix = NULL;
  27
  28 /*
  29  * This will execute "block extroot" and make use of mounted extroot or return
  30  * an error.
  31  */
  32 int mount_extroot(void)
  33 {
  34         char ldlib_path[32];
  35         char block_path[32];
  36         char kmod_loader[128];
  37         char *kmod_prefix;
  38         struct stat s;
  39         pid_t pid;
  40
  41         if (!extroot_prefix)
  42                 return -1;
  43
  44         /* try finding the library directory */
  45         snprintf(ldlib_path, sizeof(ldlib_path), "%s/upper/lib", extroot_prefix);
  46
  47         if (stat(ldlib_path, &s) || !S_ISDIR(s.st_mode))
  48                 snprintf(ldlib_path, sizeof(ldlib_path), "%s/lib", extroot_prefix);
  49
  50         /* try finding the block executable */
  51         snprintf(block_path, sizeof(block_path), "%s/upper/sbin/block", extroot_prefix);
  52
  53         if (stat(block_path, &s) || !S_ISREG(s.st_mode))
  54                 snprintf(block_path, sizeof(block_path), "%s/sbin/block", extroot_prefix);
  55
  56         if (stat(block_path, &s) || !S_ISREG(s.st_mode))
  57                 snprintf(block_path, sizeof(block_path), "/sbin/block");
  58
  59         if (stat(block_path, &s) || !S_ISREG(s.st_mode))
  60                 return -1;
  61
  62         /* set LD_LIBRARY_PATH env var and load kmods from overlay if we found a lib directory there */
  63         if (!stat(ldlib_path, &s) && S_ISDIR(s.st_mode)) {
  64                 setenv("LD_LIBRARY_PATH", ldlib_path, 1);
  65                 kmod_prefix = dirname(ldlib_path);
  66                 sprintf(kmod_loader, "/sbin/kmodloader %s/etc/modules-boot.d/ %s", kmod_prefix, kmod_prefix);
  67                 system(kmod_loader);
  68         }
  69
  70         pid = fork();
  71         if (!pid) {
  72                 mkdir("/tmp/extroot", 0755);
  73                 execl(block_path, block_path, "extroot", NULL);
  74                 exit(-1);
  75         } else if (pid > 0) {
  76                 int status;
  77
  78                 waitpid(pid, &status, 0);
  79                 if (!WEXITSTATUS(status)) {
  80                         if (find_mount("/tmp/extroot/mnt")) {
  81                                 mount("/dev/root", "/", NULL, MS_NOATIME | MS_REMOUNT | MS_RDONLY, 0);
  82
  83                                 mkdir("/tmp/extroot/mnt/proc", 0755);
  84                                 mkdir("/tmp/extroot/mnt/dev", 0755);
  85                                 mkdir("/tmp/extroot/mnt/sys", 0755);
  86                                 mkdir("/tmp/extroot/mnt/tmp", 0755);
  87                                 mkdir("/tmp/extroot/mnt/rom", 0755);
  88
  89                                 if (mount_move("/tmp/extroot", "", "/mnt")) {
  90                                         fprintf(stderr, "moving pivotroot failed - continue normal boot\n");
  91                                         umount("/tmp/extroot/mnt");
  92                                 } else if (pivot("/mnt", "/rom")) {
  93                                         fprintf(stderr, "switching to pivotroot failed - continue normal boot\n");
  94                                         umount("/mnt");
  95                                 } else {
  96                                         umount("/tmp/overlay");
  97                                         rmdir("/tmp/overlay");
  98                                         rmdir("/tmp/extroot/mnt");
  99                                         rmdir("/tmp/extroot");
 100                                         return 0;
 101                                 }
 102                         } else if (find_mount("/tmp/extroot/overlay")) {
 103                                 if (mount_move("/tmp/extroot", "", "/overlay")) {
 104                                         fprintf(stderr, "moving extroot failed - continue normal boot\n");
 105                                         umount("/tmp/extroot/overlay");
 106                                 } else if (fopivot("/overlay", "/rom")) {
 107                                         fprintf(stderr, "switching to extroot failed - continue normal boot\n");
 108                                         umount("/overlay");
 109                                 } else {
 110                                         umount("/tmp/overlay");
 111                                         rmdir("/tmp/overlay");
 112                                         rmdir("/tmp/extroot/overlay");
 113                                         rmdir("/tmp/extroot");
 114                                         return 0;
 115                                 }
 116                         }
 117                 }
 118         }
 119         return -1;
 120 }