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
13// Make up for header deficiencies.
14
15#ifndef RAMFS_MAGIC
16#define RAMFS_MAGIC		0x858458f6
17#endif
18
19#ifndef TMPFS_MAGIC
20#define TMPFS_MAGIC		0x01021994
21#endif
22
23#ifndef MS_MOVE
24#define MS_MOVE			8192
25#endif
26
27static dev_t rootdev;
28
29// Recursively delete contents of rootfs.
30
31static void delete_contents(const char *directory)
32{
33	DIR *dir;
34	struct dirent *d;
35	struct stat st;
36
37	// Don't descend into other filesystems
38	if (lstat(directory, &st) || st.st_dev != rootdev) return;
39
40	// Recursively delete the contents of directories.
41	if (S_ISDIR(st.st_mode)) {
42		dir = opendir(directory);
43		if (dir) {
44			while ((d = readdir(dir))) {
45				char *newdir = d->d_name;
46
47				// Skip . and ..
48				if (*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2])))
49					continue;
50
51				// Recurse to delete contents
52				newdir = alloca(strlen(directory) + strlen(d->d_name) + 2);
53				sprintf(newdir, "%s/%s", directory, d->d_name);
54				delete_contents(newdir);
55			}
56			closedir(dir);
57
58			// Directory should now be empty.  Zap it.
59			rmdir(directory);
60		}
61
62	// It wasn't a directory.  Zap it.
63
64	} else unlink(directory);
65}
66
67int switch_root_main(int argc, char **argv);
68int switch_root_main(int argc, char **argv)
69{
70	char *newroot, *console = NULL;
71	struct stat st1, st2;
72	struct statfs stfs;
73
74	// Parse args (-c console)
75
76	opt_complementary = "-2";
77	getopt32(argv, "c:", &console);
78	argv += optind;
79
80	// Change to new root directory and verify it's a different fs.
81
82	newroot = *argv++;
83
84	xchdir(newroot);
85	if (lstat(".", &st1) || lstat("/", &st2) || st1.st_dev == st2.st_dev) {
86		bb_error_msg_and_die("bad newroot %s", newroot);
87	}
88	rootdev = st2.st_dev;
89
90	// Additional sanity checks: we're about to rm -rf /,  so be REALLY SURE
91	// we mean it.  (I could make this a CONFIG option, but I would get email
92	// from all the people who WILL eat their filesystems.)
93
94	if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) ||
95		(stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) ||
96		getpid() != 1)
97	{
98		bb_error_msg_and_die("not rootfs");
99	}
100
101	// Zap everything out of rootdev
102
103	delete_contents("/");
104
105	// Overmount / with newdir and chroot into it.  The chdir is needed to
106	// recalculate "." and ".." links.
107
108	if (mount(".", "/", NULL, MS_MOVE, NULL) || chroot("."))
109		bb_error_msg_and_die("error moving root");
110	xchdir("/");
111
112	// If a new console specified, redirect stdin/stdout/stderr to that.
113
114	if (console) {
115		close(0);
116		xopen(console, O_RDWR);
117		dup2(0, 1);
118		dup2(0, 2);
119	}
120
121	// Exec real init.  (This is why we must be pid 1.)
122	execv(argv[0], argv);
123	bb_perror_msg_and_die("bad init %s", argv[0]);
124}
125