From: Pekka Enberg <penberg@cs.helsinki.fi>

Add generic functions for obtaining the hidden object (superblock, inode,
dentry, and dentry mount-point) in a stacked filesystem.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
---

 include/linux/stack_fs.h |   93 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)

Index: 2.6/include/linux/stack_fs.h
===================================================================
--- /dev/null
+++ 2.6/include/linux/stack_fs.h
@@ -0,0 +1,93 @@
+#ifndef __LINUX_STACK_FS_H
+#define __LINUX_STACK_FS_H
+
+#include <linux/dcache.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+
+#define STACKFS_MAX_BRANCHES (8)
+
+struct stackfs_sb_info {
+	struct super_block *hidden_sbs[STACKFS_MAX_BRANCHES];
+};
+
+struct stackfs_inode_info {
+	struct inode *hidden_inodes[STACKFS_MAX_BRANCHES];
+};
+
+struct stackfs_dentry_info {
+	struct dentry *hidden_dentrys[STACKFS_MAX_BRANCHES];
+	struct vfsmount *hidden_mnts[STACKFS_MAX_BRANCHES];
+};
+
+struct stackfs_file_info {
+	struct file *hidden_files[STACKFS_MAX_BRANCHES];
+};
+
+/*
+ * The functions expect struct stackfs_*_info to be the first member in the
+ * filesystem-specific info structures and that inode->i_private points at
+ * the beginning of the inode container.
+ */
+
+static inline struct super_block *
+__stackfs_hidden_sb(struct super_block *sb, unsigned long branch_idx)
+{
+	struct stackfs_sb_info *info = sb->s_fs_info;
+	return info->hidden_sbs[branch_idx];
+}
+
+static inline struct super_block *stackfs_hidden_sb(struct super_block *sb)
+{
+	return __stackfs_hidden_sb(sb, 0);
+}
+
+static inline struct inode *
+__stackfs_hidden_inode(struct inode *inode, unsigned long branch_idx)
+{
+	struct stackfs_inode_info *info = inode->i_private;
+	return info->hidden_inodes[branch_idx];
+}
+
+static inline struct inode *stackfs_hidden_inode(struct inode *inode)
+{
+	return __stackfs_hidden_inode(inode, 0);
+}
+
+static inline struct dentry *
+__stackfs_hidden_dentry(struct dentry *dentry, unsigned long branch_idx)
+{
+	struct stackfs_dentry_info *info = dentry->d_fsdata;
+	return info->hidden_dentrys[branch_idx];
+}
+
+static inline struct dentry *stackfs_hidden_dentry(struct dentry *dentry)
+{
+	return __stackfs_hidden_dentry(dentry, 0);
+}
+
+static inline struct vfsmount *
+__stackfs_hidden_dentry_mnt(struct dentry *dentry, unsigned long branch_idx)
+{
+	struct stackfs_dentry_info *info = dentry->d_fsdata;
+	return info->hidden_mnts[branch_idx];
+}
+
+static inline struct vfsmount *stackfs_hidden_dentry_mnt(struct dentry *dentry)
+{
+	return __stackfs_hidden_dentry_mnt(dentry, 0);
+}
+
+static inline struct file *
+__stackfs_hidden_file(struct file *file, unsigned long branch_idx)
+{
+	struct stackfs_file_info *info = file->private_data;
+	return info->hidden_files[branch_idx];
+}
+
+static inline struct file *stackfs_hidden_file(struct file *file)
+{
+	return __stackfs_hidden_file(file, 0);
+}
+
+#endif