[hacktree] ostree_switch_root: New executable for use in initrd

[Colin Walters <walters src gnome org>]

commit 5098f1895c04c8208a4cfc954505ba83842de7cd
Author: Colin Walters <walters verbum org>
Date:   Wed Oct 19 12:22:42 2011 -0400

    ostree_switch_root: New executable for use in initrd
    
    Since Debian's initrd uses busybox which is super limited, let's
    fork util-linux's switch_root and add more there.

 parallel-debian/ostree_switch_root.c |  241 ++++++++++++++++++++++++++++++++++
 1 files changed, 241 insertions(+), 0 deletions(-)
---
diff --git a/parallel-debian/ostree_switch_root.c b/parallel-debian/ostree_switch_root.c
new file mode 100644
index 0000000..a9f34a0
--- /dev/null
+++ b/parallel-debian/ostree_switch_root.c
@@ -0,0 +1,241 @@
+/* -*- c-file-style: "linux" -*-
+ * ostree_switch_root.c - switch to new root directory and start init.
+ * Copyright 2011 Colin Walters <walters verbum org>
+ *
+ * Based of switch_root.c from util-linux.
+ * Copyright 2002-2009 Red Hat, Inc.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Authors:
+ *	Peter Jones <pjones redhat com>
+ *	Jeremy Katz <katzj redhat com>
+ *	Colin Walters <walters verbum org>
+ */
+#define _GNU_SOURCE
+#include <sys/mount.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/param.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <ctype.h>
+#include <dirent.h>
+
+static int
+perrorv (const char *format, ...)
+{
+	va_list args;
+	char buf[PATH_MAX];
+	char *p;
+
+	p = strerror_r (errno, buf, sizeof (buf));
+
+	va_start (args, format);
+
+	vfprintf (stderr, format, args);
+	fprintf (stderr, ": %s\n", p);
+
+	va_end (args);
+	
+	return 0;
+}
+
+/* remove all files/directories below dirName -- don't cross mountpoints */
+static int recursiveRemove(int fd)
+{
+	struct stat rb;
+	DIR *dir;
+	int rc = -1;
+	int dfd;
+
+	if (!(dir = fdopendir(fd))) {
+		perrorv("failed to open directory");
+		goto done;
+	}
+
+	/* fdopendir() precludes us from continuing to use the input fd */
+	dfd = dirfd(dir);
+
+	if (fstat(dfd, &rb)) {
+		perrorv("failed to stat directory");
+		goto done;
+	}
+
+	while(1) {
+		struct dirent *d;
+
+		errno = 0;
+		if (!(d = readdir(dir))) {
+			if (errno) {
+				perrorv("failed to read directory");
+				goto done;
+			}
+			break;	/* end of directory */
+		}
+
+		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
+			continue;
+
+		if (d->d_type == DT_DIR) {
+			struct stat sb;
+
+			if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
+				perrorv("failed to stat %s", d->d_name);
+				continue;
+			}
+
+			/* remove subdirectories if device is same as dir */
+			if (sb.st_dev == rb.st_dev) {
+				int cfd;
+
+				cfd = openat(dfd, d->d_name, O_RDONLY);
+				if (cfd >= 0) {
+					recursiveRemove(cfd);
+					close(cfd);
+				}
+			} else
+				continue;
+		}
+
+		if (unlinkat(dfd, d->d_name,
+			     d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
+			perrorv("failed to unlink %s", d->d_name);
+	}
+
+	rc = 0;	/* success */
+
+done:
+	if (dir)
+		closedir(dir);
+	return rc;
+}
+
+static int make_readonly(const char *tree)
+{
+	if (mount(tree, tree, NULL, MS_BIND, NULL) < 0) {
+		perrorv("Failed to do initial RO bind mount %s", tree);
+		return -1;
+	}
+	if (mount(tree, tree, NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL) < 0) {
+		perrorv("Failed to remount RO bind mount %s", tree);
+		return -1;
+	}
+	return 0;
+}
+
+
+static int switchroot(const char *newroot, const char *subroot)
+{
+	const char *root_bind_mounts[] = { "/home", "/root", "/var", NULL };
+	int i;
+	int orig_cfd;
+	int new_cfd;
+	pid_t pid;
+	char srcpath[PATH_MAX];
+	char destpath[PATH_MAX];
+
+	orig_cfd = open("/", O_RDONLY);
+	new_cfd = open(newroot, O_RDONLY);
+
+	/* For now just remount the rootfs r/w.  Should definitely
+	 * handle this better later... (famous last words)
+	 */
+	if (mount(newroot, newroot, NULL, MS_REMOUNT & ~MS_RDONLY, NULL) < 0) {
+		perrorv("failed to remount / read/write", newroot);
+		return -1;
+	}
+
+	for (i = 0; root_bind_mounts[i] != NULL; i++) {
+		snprintf(srcpath, sizeof(srcpath), "%s%s", newroot, root_bind_mounts[i]);
+		snprintf(destpath, sizeof(destpath), "%s/%s%s", newroot, subroot, root_bind_mounts[i]);
+		if (mount(srcpath, destpath, NULL, MS_BIND & ~MS_RDONLY, NULL) < 0) {
+			perrorv("failed to bind mount %s to %s", srcpath, destpath);
+			return -1;
+		}
+	}
+
+	if (chdir(newroot)) {
+		perrorv("failed to change directory to %s", newroot);
+		return -1;
+	}
+
+	if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
+		perrorv("failed to mount moving %s to /", newroot);
+		return -1;
+	}
+
+	if (fchdir (new_cfd) < 0) {
+		perrorv("failed to fchdir back to initrd");
+		return -1;
+	}
+
+	if (chroot(subroot) < 0) {
+		perrorv("failed to change root to %s", subroot);
+		return -1;
+	}
+
+	if (orig_cfd >= 0) {
+		pid = fork();
+		if (pid <= 0) {
+			recursiveRemove(orig_cfd);
+			if (pid == 0)
+				exit(EXIT_SUCCESS);
+		}
+		close(orig_cfd);
+	}
+	close(new_cfd);
+	return 0;
+}
+
+static void usage(FILE *output)
+{
+	fprintf(output, "usage: %s <newrootdir> <subroot> <init> <args to init>\n",
+			program_invocation_short_name);
+	exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
+}
+
+int main(int argc, char *argv[])
+{
+	char *newroot, *subroot, *init, **initargs;
+
+	if (argc < 3)
+		usage(stderr);
+
+	if ((!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
+		usage(stdout);
+
+	newroot = argv[1];
+	subroot = argv[2];
+	init = argv[3];
+	initargs = &argv[3];
+
+	if (!*newroot || !*init)
+		usage(stderr);
+
+	if (switchroot(newroot, subroot))
+		exit(1);
+
+	if (access(init, X_OK))
+		perrorv("cannot access %s", init);
+
+	execv(init, initargs);
+	exit(1);
+}
+