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/* vi: set sw=4 ts=4: */
/* Copyright 2005 Rob Landley <rob@landley.net>
*
* Switch from rootfs to another filesystem as the root of the mount tree.
*
* Licensed under GPL version 2, see file LICENSE in this tarball for details.
*/
#include "libbb.h"
#include <sys/vfs.h>
// Make up for header deficiencies
#ifndef RAMFS_MAGIC
#define RAMFS_MAGIC ((unsigned)0x858458f6)
#endif
#ifndef TMPFS_MAGIC
#define TMPFS_MAGIC ((unsigned)0x01021994)
#endif
#ifndef MS_MOVE
#define MS_MOVE 8192
#endif
// Recursively delete contents of rootfs
static void delete_contents(const char *directory, dev_t rootdev)
{
DIR *dir;
struct dirent *d;
struct stat st;
// Don't descend into other filesystems
if (lstat(directory, &st) || st.st_dev != rootdev)
return;
// Recursively delete the contents of directories
if (S_ISDIR(st.st_mode)) {
dir = opendir(directory);
if (dir) {
while ((d = readdir(dir))) {
char *newdir = d->d_name;
// Skip . and ..
if (DOT_OR_DOTDOT(newdir))
continue;
// Recurse to delete contents
newdir = concat_path_file(directory, newdir);
delete_contents(newdir, rootdev);
free(newdir);
}
closedir(dir);
// Directory should now be empty, zap it
rmdir(directory);
}
} else {
// It wasn't a directory, zap it
unlink(directory);
}
}
int switch_root_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int switch_root_main(int argc UNUSED_PARAM, char **argv)
{
char *newroot, *console = NULL;
struct stat st;
struct statfs stfs;
dev_t rootdev;
// Parse args (-c console)
opt_complementary = "-2"; // minimum 2 params
getopt32(argv, "+c:", &console); // '+': stop at first non-option
argv += optind;
newroot = *argv++;
// Change to new root directory and verify it's a different fs
xchdir(newroot);
xstat("/", &st);
rootdev = st.st_dev;
xstat(".", &st);
if (st.st_dev == rootdev || getpid() != 1) {
// Show usage, it says new root must be a mountpoint
// and we must be PID 1
bb_show_usage();
}
// Additional sanity checks: we're about to rm -rf /, so be REALLY SURE
// we mean it. I could make this a CONFIG option, but I would get email
// from all the people who WILL destroy their filesystems.
statfs("/", &stfs); // this never fails
if (lstat("/init", &st) != 0 || !S_ISREG(st.st_mode)
|| ((unsigned)stfs.f_type != RAMFS_MAGIC
&& (unsigned)stfs.f_type != TMPFS_MAGIC)
) {
bb_error_msg_and_die("not rootfs");
}
// Zap everything out of rootdev
delete_contents("/", rootdev);
// Overmount / with newdir and chroot into it
if (mount(".", "/", NULL, MS_MOVE, NULL)) {
// For example, fails when newroot is not a mountpoint
bb_perror_msg_and_die("error moving root");
}
// The chdir is needed to recalculate "." and ".." links
xchroot(".");
xchdir("/");
// If a new console specified, redirect stdin/stdout/stderr to it
if (console) {
close(0);
xopen(console, O_RDWR);
xdup2(0, 1);
xdup2(0, 2);
}
// Exec real init
execv(argv[0], argv);
bb_perror_msg_and_die("can't execute '%s'", argv[0]);
}
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