move files around

Signed-off-by: John Crispin <blogic@openwrt.org>

1 files changed, 110 insertions, 0 deletions

diff --git a/libfstools/mount.c b/libfstools/mount.c
new file mode 100644
index 0000000..e7b57f0
--- /dev/null
+++ b/libfstools/mount.c
@@ -0,0 +1,110 @@
+/*
+ * Copyright (C) 2014 John Crispin <blogic@openwrt.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License version 2.1
+ * as published by the Free Software Foundation
+ *
+ * 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.
+ */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mount.h>
+
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+
+#include "../fs-state.h"
+
+/* this is a raw syscall - man 2 pivot_root */
+extern int pivot_root(const char *new_root, const char *put_old);
+
+int
+mount_move(char *oldroot, char *newroot, char *dir)
+{
+#ifndef MS_MOVE
+#define MS_MOVE	(1 << 13)
+#endif
+	struct stat s;
+	char olddir[64];
+	char newdir[64];
+	int ret;
+
+	snprintf(olddir, sizeof(olddir), "%s%s", oldroot, dir);
+	snprintf(newdir, sizeof(newdir), "%s%s", newroot, dir);
+
+	if (stat(olddir, &s) || !S_ISDIR(s.st_mode))
+		return -1;
+
+	if (stat(newdir, &s) || !S_ISDIR(s.st_mode))
+		return -1;
+
+	ret = mount(olddir, newdir, NULL, MS_NOATIME | MS_MOVE, NULL);
+
+/*	if (ret)
+		fprintf(stderr, "failed %s %s: %s\n", olddir, newdir, strerror(errno));*/
+
+	return ret;
+}
+
+int
+pivot(char *new, char *old)
+{
+	char pivotdir[64];
+	int ret;
+
+	if (mount_move("", new, "/proc"))
+		return -1;
+
+	snprintf(pivotdir, sizeof(pivotdir), "%s%s", new, old);
+
+	ret = pivot_root(new, pivotdir);
+
+	if (ret < 0) {
+		fprintf(stderr, "pivot_root failed %s %s: %s\n", new, pivotdir, strerror(errno));
+		return -1;
+	}
+
+	mount_move(old, "", "/dev");
+	mount_move(old, "", "/tmp");
+	mount_move(old, "", "/sys");
+	mount_move(old, "", "/overlay");
+
+	return 0;
+}
+
+int
+fopivot(char *rw_root, char *ro_root)
+{
+	char overlay[64], lowerdir[64];
+
+	if (find_filesystem("overlay")) {
+		fprintf(stderr, "BUG: no suitable fs found\n");
+		return -1;
+	}
+
+	snprintf(overlay, sizeof(overlay), "overlayfs:%s", rw_root);
+	snprintf(lowerdir, sizeof(lowerdir), "lowerdir=/,upperdir=%s", rw_root);
+
+	if (mount(overlay, "/mnt", "overlayfs", MS_NOATIME, lowerdir)) {
+		fprintf(stderr, "mount failed: %s\n", strerror(errno));
+		return -1;
+	}
+
+	return pivot("/mnt", ro_root);
+}
+
+int
+ramoverlay(void)
+{
+	mkdir("/tmp/root", 0755);
+	mount("tmpfs", "/tmp/root", "tmpfs", MS_NOATIME, "mode=0755");
+
+	return fopivot("/tmp/root", "/rom");
+}