From: Jan Blunck <jblunck@xxxxxxx>
This adds follow_union_up() to travers from one layer to the next overlayed
mountpoint if given an union mounted mountpoint. This is basically the invert
of what follow_mount() is doing.
Signed-off-by: Jan Blunck <jblunck@xxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
fs/Kconfig | 8 ++++++++
fs/Makefile | 2 ++
fs/union.c | 34 ++++++++++++++++++++++++++++++++++
fs/union.h | 25 +++++++++++++++++++++++++
4 files changed, 69 insertions(+)
Index: linux-2.6/fs/Kconfig
===================================================================
--- linux-2.6.orig/fs/Kconfig 2009-05-20 15:05:15.000000000 +0200
+++ linux-2.6/fs/Kconfig 2009-05-20 15:09:52.000000000 +0200
@@ -62,6 +62,14 @@ source "fs/autofs/Kconfig"
source "fs/autofs4/Kconfig"
source "fs/fuse/Kconfig"
+config UNION_MOUNT
+ bool "Union mount support (EXPERIMENTAL)"
+ depends on EXPERIMENTAL
+ ---help---
+ If you say Y here, you will be able to mount file systems as
+ union mount stacks. This is a VFS based implementation and
+ should work with all file systems. If unsure, say N.
+
config GENERIC_ACL
bool
select FS_POSIX_ACL
Index: linux-2.6/fs/Makefile
===================================================================
--- linux-2.6.orig/fs/Makefile 2009-05-20 15:05:15.000000000 +0200
+++ linux-2.6/fs/Makefile 2009-05-20 15:09:52.000000000 +0200
@@ -51,6 +51,8 @@ obj-$(CONFIG_FS_POSIX_ACL) += posix_acl.
obj-$(CONFIG_NFS_COMMON) += nfs_common/
obj-$(CONFIG_GENERIC_ACL) += generic_acl.o
+obj-$(CONFIG_UNION_MOUNT) += union.o
+
obj-y += quota/
obj-$(CONFIG_PROC_FS) += proc/
Index: linux-2.6/fs/union.c
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/fs/union.c 2009-05-20 15:09:52.000000000 +0200
@@ -0,0 +1,34 @@
+/*
+ * VFS based union mount for Linux
+ *
+ * Copyright (C) 2004-2007 IBM Corporation, IBM Deutschland Entwicklung GmbH.
+ * Copyright (C) 2007 Novell Inc.
+ *
+ * Author(s): Jan Blunck (j.blunck@xxxxxxxxxxxxx)
+ *
+ * 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.
+ */
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include "union.h"
+
+/*
+ * follow_union_up - follow the union stack one layer "up"
+ *
+ * This is called to traverse the union stack from one layer to the next
+ * overlayed one. follow_union_up() is called by various lookup functions
+ * that are aware of union mounts.
+ *
+ * Returns non zero if followed to the next layer, zero otherwise.
+ */
+int follow_union_up(struct path *path)
+{
+ if (IS_MNT_UNION(path->mnt) && path->dentry == path->mnt->mnt_root)
+ return follow_up(&path->mnt, &path->dentry);
+
+ return 0;
+}
Index: linux-2.6/fs/union.h
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/fs/union.h 2009-05-20 15:09:52.000000000 +0200
@@ -0,0 +1,25 @@
+/*
+ * VFS based union mount for Linux
+ *
+ * Copyright (C) 2004-2007 IBM Corporation, IBM Deutschland Entwicklung GmbH.
+ * Copyright (C) 2007 Novell Inc.
+ * Author(s): Jan Blunck (j.blunck@xxxxxxxxxxxxx)
+ *
+ * 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.
+ *
+ */
+
+#include <linux/mount.h>
+
+struct path;
+
+extern int follow_union_up(struct path *path);
+
+#ifdef CONFIG_UNION_MOUNT
+#define IS_MNT_UNION(mnt) ((mnt)->mnt_flags & MNT_UNION)
+#else
+#define IS_MNT_UNION(x) (0)
+#endif
--
--
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