1 files changed, 115 insertions, 0 deletions
diff --git a/util-linux/switch_root.c b/util-linux/switch_root.c
new file mode 100644
index 0000000..21cc992
--- /dev/null
+++ b/util-linux/switch_root.c
@@ -0,0 +1,115 @@
+/* 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);
+		}
+
+	// It wasn't a directory.  Zap it.
+	} else 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 st1, st2;
+	struct statfs stfs;
+	dev_t rootdev;
+
+	// Parse args (-c console)
+	opt_complementary = "-2"; // minimum 2 params
+	getopt32(argv, "+c:", &console); // '+': stop parsing at first non-option
+	argv += optind;
+
+	// Change to new root directory and verify it's a different fs.
+	newroot = *argv++;
+
+	xchdir(newroot);
+	if (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 filesystems.)
+	if (lstat("/init", &st1) || !S_ISREG(st1.st_mode) || statfs("/", &stfs)
+	 || (((unsigned)stfs.f_type != RAMFS_MAGIC) && ((unsigned)stfs.f_type != TMPFS_MAGIC))
+	 || (getpid() != 1)
+	) {
+		bb_error_msg_and_die("not rootfs");
+	}
+
+	// Zap everything out of rootdev
+	delete_contents("/", rootdev);
+
+	// Overmount / with newdir and chroot into it.  The chdir is needed to
+	// recalculate "." and ".." links.
+	if (mount(".", "/", NULL, MS_MOVE, NULL))
+		bb_error_msg_and_die("error moving root");
+	xchroot(".");
+	xchdir("/");
+
+	// If a new console specified, redirect stdin/stdout/stderr to that.
+	if (console) {
+		close(0);
+		xopen(console, O_RDWR);
+		xdup2(0, 1);
+		xdup2(0, 2);
+	}
+
+	// Exec real init.  (This is why we must be pid 1.)
+	execv(argv[0], argv);
+	bb_perror_msg_and_die("bad init %s", argv[0]);
+}