busybox/util-linux/switch_root.c

/* 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 "busybox.h"
#include <sys/vfs.h>


// Make up for header deficiencies.

#ifndef RAMFS_MAGIC
#define RAMFS_MAGIC		0x858458f6
#endif

#ifndef TMPFS_MAGIC
#define TMPFS_MAGIC		0x01021994
#endif

#ifndef MS_MOVE
#define MS_MOVE			8192
#endif

dev_t rootdev;

// Recursively delete contents of rootfs.

static void delete_contents(char *directory)
{
	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)) {
		if((dir = opendir(directory))) {
			while ((d = readdir(dir))) {
				char *newdir=d->d_name;

				// Skip . and ..
				if(*newdir=='.' && (!newdir[1] || (newdir[1]=='.' && !newdir[2])))
					continue;

				// Recurse to delete contents
				newdir = alloca(strlen(directory) + strlen(d->d_name) + 2);
				sprintf(newdir, "%s/%s", directory, d->d_name);
				delete_contents(newdir);
			}
			closedir(dir);

			// Directory should now be empty.  Zap it.
			rmdir(directory);
		}

	// It wasn't a directory.  Zap it.

	} else unlink(directory);
}

int switch_root_main(int argc, char *argv[])
{
	char *newroot, *console=NULL;
	struct stat st1, st2;
	struct statfs stfs;

	// Parse args (-c console)

	opt_complementary = "-2";
	getopt32(argc, argv, "c:", &console);

	// Change to new root directory and verify it's a different fs.

	newroot=argv[optind++];

	if (chdir(newroot) || lstat(".", &st1) || lstat("/", &st2) ||
		st1.st_dev == st2.st_dev)
	{
		bb_error_msg_and_die("bad newroot %s", newroot);
	}
	rootdev=st2.st_dev;

	// 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 eat their filesystemss.)

	if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs) ||
		(stfs.f_type != RAMFS_MAGIC && stfs.f_type != TMPFS_MAGIC) ||
		getpid() != 1)
	{
		bb_error_msg_and_die("not rootfs");
	}

	// Zap everything out of rootdev

	delete_contents("/");

	// Overmount / with newdir and chroot into it.  The chdir is needed to
	// recalculate "." and ".." links.

	if (mount(".", "/", NULL, MS_MOVE, NULL) || chroot(".") || chdir("/"))
		bb_error_msg_and_die("moving root");

	// If a new console specified, redirect stdin/stdout/stderr to that.

	if (console) {
		close(0);
		if(open(console, O_RDWR) < 0)
			bb_error_msg_and_die("bad console '%s'", console);
		dup2(0, 1);
		dup2(0, 2);
	}

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