1 files changed, 122 insertions, 0 deletions
diff --git a/util-linux/switch_root.c b/util-linux/switch_root.c
new file mode 100644
index 000000000..4c23f69da
--- /dev/null
+++ b/util-linux/switch_root.c
@@ -0,0 +1,122 @@
+/* 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]);
+}