linux_kernel/fs/overlayfs/ovl_entry.h

/*
 *
 * Copyright (C) 2011 Novell Inc.
 * Copyright (C) 2016 Red Hat, Inc.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published by
 * the Free Software Foundation.
 */

struct ovl_config {
	char *lowerdir;
	char *upperdir;
	char *workdir;
	bool default_permissions;
	bool redirect_dir;
	bool index;
};

/* private information held for overlayfs's superblock */
struct ovl_fs {
	struct vfsmount *upper_mnt;
	unsigned numlower;
	struct vfsmount **lower_mnt;
	/* workbasedir is the path at workdir= mount option */
	struct dentry *workbasedir;
	/* workdir is the 'work' directory under workbasedir */
	struct dentry *workdir;
	/* index directory listing overlay inodes by origin file handle */
	struct dentry *indexdir;
	long namelen;
	/* pathnames of lower and upper dirs, for show_options */
	struct ovl_config config;
	/* creds of process who forced instantiation of super block */
	const struct cred *creator_cred;
	bool tmpfile;
	bool noxattr;
	/* sb common to all layers */
	struct super_block *same_sb;
};

/* private information held for every overlayfs dentry */
struct ovl_entry {
	union {
		struct {
			unsigned long has_upper;
			bool opaque;
		};
		struct rcu_head rcu;
	};
	unsigned numlower;
	struct path lowerstack[];
};

struct ovl_entry *ovl_alloc_entry(unsigned int numlower);

struct ovl_inode {
	struct ovl_dir_cache *cache;
	const char *redirect;
	u64 version;
	unsigned long flags;
	struct inode vfs_inode;
	struct dentry *__upperdentry;
	struct inode *lower;

	/* synchronize copy up and more */
	struct mutex lock;
};

static inline struct ovl_inode *OVL_I(struct inode *inode)
{
	return container_of(inode, struct ovl_inode, vfs_inode);
}

static inline struct dentry *ovl_upperdentry_dereference(struct ovl_inode *oi)
{
	return lockless_dereference(oi->__upperdentry);
}