LXR busybox/util-linux/switch

   1/* vi: set sw=4 ts=4: */
   2/* Copyright 2005 Rob Landley <rob@landley.net>
   3 *
   4 * Switch from rootfs to another filesystem as the root of the mount tree.
   5 *
   6 * Licensed under GPL version 2, see file LICENSE in this tarball for details.
   7 */
   8
   9#include "libbb.h"
  10#include <sys/vfs.h>
  11
  12// Make up for header deficiencies.
  13#ifndef RAMFS_MAGIC
  14#define RAMFS_MAGIC ((unsigned)0x858458f6)
  15#endif
  16
  17#ifndef TMPFS_MAGIC
  18#define TMPFS_MAGIC ((unsigned)0x01021994)
  19#endif
  20
  21#ifndef MS_MOVE
  22#define MS_MOVE     8192
  23#endif
  24
  25// Recursively delete contents of rootfs.
  26static void delete_contents(const char *directory, dev_t rootdev)
  27{
  28        DIR *dir;
  29        struct dirent *d;
  30        struct stat st;
  31
  32        // Don't descend into other filesystems
  33        if (lstat(directory, &st) || st.st_dev != rootdev)
  34                return;
  35
  36        // Recursively delete the contents of directories.
  37        if (S_ISDIR(st.st_mode)) {
  38                dir = opendir(directory);
  39                if (dir) {
  40                        while ((d = readdir(dir))) {
  41                                char *newdir = d->d_name;
  42
  43                                // Skip . and ..
  44                                if (DOT_OR_DOTDOT(newdir))
  45                                        continue;
  46
  47                                // Recurse to delete contents
  48                                newdir = concat_path_file(directory, newdir);
  49                                delete_contents(newdir, rootdev);
  50                                free(newdir);
  51                        }
  52                        closedir(dir);
  53
  54                        // Directory should now be empty.  Zap it.
  55                        rmdir(directory);
  56                }
  57
  58        // It wasn't a directory.  Zap it.
  59        } else unlink(directory);
  60}
  61
  62int switch_root_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  63int switch_root_main(int argc UNUSED_PARAM, char **argv)
  64{
  65        char *newroot, *console = NULL;
  66        struct stat st1, st2;
  67        struct statfs stfs;
  68        dev_t rootdev;
  69
  70        // Parse args (-c console)
  71        opt_complementary = "-2"; // minimum 2 params
  72        getopt32(argv, "+c:", &console); // '+': stop parsing at first non-option
  73        argv += optind;
  74
  75        // Change to new root directory and verify it's a different fs.
  76        newroot = *argv++;
  77
  78        xchdir(newroot);
  79        if (lstat(".", &st1) || lstat("/", &st2) || st1.st_dev == st2.st_dev) {
  80                bb_error_msg_and_die("bad newroot %s", newroot);
  81        }
  82        rootdev = st2.st_dev;
  83
  84        // Additional sanity checks: we're about to rm -rf /,  so be REALLY SURE
  85        // we mean it.  (I could make this a CONFIG option, but I would get email
  86        // from all the people who WILL eat their filesystems.)
  87        if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs)
  88         || (((unsigned)stfs.f_type != RAMFS_MAGIC) && ((unsigned)stfs.f_type != TMPFS_MAGIC))
  89         || (getpid() != 1)
  90        ) {
  91                bb_error_msg_and_die("not rootfs");
  92        }
  93
  94        // Zap everything out of rootdev
  95        delete_contents("/", rootdev);
  96
  97        // Overmount / with newdir and chroot into it.  The chdir is needed to
  98        // recalculate "." and ".." links.
  99        if (mount(".", "/", NULL, MS_MOVE, NULL))
 100                bb_error_msg_and_die("error moving root");
 101        xchroot(".");
 102        xchdir("/");
 103
 104        // If a new console specified, redirect stdin/stdout/stderr to that.
 105        if (console) {
 106                close(0);
 107                xopen(console, O_RDWR);
 108                xdup2(0, 1);
 109                xdup2(0, 2);
 110        }
 111
 112        // Exec real init.  (This is why we must be pid 1.)
 113        execv(argv[0], argv);
 114        bb_perror_msg_and_die("bad init %s", argv[0]);
 115}
 116