include/linux/kernfs.h - kernel/msm-5.4 - Gitiles

 /*
  * kernfs.h - pseudo filesystem decoupled from vfs locking
  *
  * This file is released under the GPLv2.
  */

 #ifndef __LINUX_KERNFS_H
 #define __LINUX_KERNFS_H

 #include <linux/kernel.h>
 #include <linux/err.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
 #include <linux/idr.h>
 #include <linux/lockdep.h>
 #include <linux/rbtree.h>
 #include <linux/atomic.h>
 #include <linux/uidgid.h>
 #include <linux/wait.h>

 struct file;
 struct dentry;
 struct iattr;
 struct seq_file;
 struct vm_area_struct;
 struct super_block;
 struct file_system_type;

 struct kernfs_open_node;
 struct kernfs_iattrs;

 enum kernfs_node_type {
 	KERNFS_DIR		= 0x0001,
 	KERNFS_FILE		= 0x0002,
 	KERNFS_LINK		= 0x0004,
 };

 #define KERNFS_TYPE_MASK	0x000f
 #define KERNFS_FLAG_MASK	~KERNFS_TYPE_MASK

 enum kernfs_node_flag {
 	KERNFS_ACTIVATED	= 0x0010,
 	KERNFS_NS		= 0x0020,
 	KERNFS_HAS_SEQ_SHOW	= 0x0040,
 	KERNFS_HAS_MMAP		= 0x0080,
 	KERNFS_LOCKDEP		= 0x0100,
 	KERNFS_SUICIDAL		= 0x0400,
 	KERNFS_SUICIDED		= 0x0800,
 	KERNFS_EMPTY_DIR	= 0x1000,
 	KERNFS_HAS_RELEASE	= 0x2000,
 };

 /* @flags for kernfs_create_root() */
 enum kernfs_root_flag {
 	/*
 	 * kernfs_nodes are created in the deactivated state and invisible.
 	 * They require explicit kernfs_activate() to become visible.  This
 	 * can be used to make related nodes become visible atomically
 	 * after all nodes are created successfully.
 	 */
 	KERNFS_ROOT_CREATE_DEACTIVATED		= 0x0001,

 	/*
 	 * For regular flies, if the opener has CAP_DAC_OVERRIDE, open(2)
 	 * succeeds regardless of the RW permissions.  sysfs had an extra
 	 * layer of enforcement where open(2) fails with -EACCES regardless
 	 * of CAP_DAC_OVERRIDE if the permission doesn't have the
 	 * respective read or write access at all (none of S_IRUGO or
 	 * S_IWUGO) or the respective operation isn't implemented.  The
 	 * following flag enables that behavior.
 	 */
 	KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK	= 0x0002,

 	/*
 	 * The filesystem supports exportfs operation, so userspace can use
 	 * fhandle to access nodes of the fs.
 	 */
 	KERNFS_ROOT_SUPPORT_EXPORTOP		= 0x0004,
 };

 /* type-specific structures for kernfs_node union members */
 struct kernfs_elem_dir {
 	unsigned long		subdirs;
 	/* children rbtree starts here and goes through kn->rb */
 	struct rb_root		children;

 	/*
 	 * The kernfs hierarchy this directory belongs to.  This fits
 	 * better directly in kernfs_node but is here to save space.
 	 */
 	struct kernfs_root	*root;
 };

 struct kernfs_elem_symlink {
 	struct kernfs_node	*target_kn;
 };

 struct kernfs_elem_attr {
 	const struct kernfs_ops	*ops;
 	struct kernfs_open_node	*open;
 	loff_t			size;
 	struct kernfs_node	*notify_next;	/* for kernfs_notify() */
 };

 /* represent a kernfs node */
 union kernfs_node_id {
 	struct {
 		/*
 		 * blktrace will export this struct as a simplified 'struct
 		 * fid' (which is a big data struction), so userspace can use
 		 * it to find kernfs node. The layout must match the first two
 		 * fields of 'struct fid' exactly.
 		 */
 		u32		ino;
 		u32		generation;
 	};
 	u64			id;
 };

 /*
  * kernfs_node - the building block of kernfs hierarchy.  Each and every
  * kernfs node is represented by single kernfs_node.  Most fields are
  * private to kernfs and shouldn't be accessed directly by kernfs users.
  *
  * As long as s_count reference is held, the kernfs_node itself is
  * accessible.  Dereferencing elem or any other outer entity requires
  * active reference.
  */
 struct kernfs_node {
 	atomic_t		count;
 	atomic_t		active;
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map	dep_map;
 #endif
 	/*
 	 * Use kernfs_get_parent() and kernfs_name/path() instead of
 	 * accessing the following two fields directly.  If the node is
 	 * never moved to a different parent, it is safe to access the
 	 * parent directly.
 	 */
 	struct kernfs_node	*parent;
 	const char		*name;

 	struct rb_node		rb;

 	const void		*ns;	/* namespace tag */
 	unsigned int		hash;	/* ns + name hash */
 	union {
 		struct kernfs_elem_dir		dir;
 		struct kernfs_elem_symlink	symlink;
 		struct kernfs_elem_attr		attr;
 	};

 	void			*priv;

 	union kernfs_node_id	id;
 	unsigned short		flags;
 	umode_t			mode;
 	struct kernfs_iattrs	*iattr;
 };

 /*
  * kernfs_syscall_ops may be specified on kernfs_create_root() to support
  * syscalls.  These optional callbacks are invoked on the matching syscalls
  * and can perform any kernfs operations which don't necessarily have to be
  * the exact operation requested.  An active reference is held for each
  * kernfs_node parameter.
  */
 struct kernfs_syscall_ops {
 	int (*remount_fs)(struct kernfs_root *root, int *flags, char *data);
 	int (*show_options)(struct seq_file *sf, struct kernfs_root *root);

 	int (*mkdir)(struct kernfs_node *parent, const char *name,
 		     umode_t mode);
 	int (*rmdir)(struct kernfs_node *kn);
 	int (*rename)(struct kernfs_node *kn, struct kernfs_node *new_parent,
 		      const char *new_name);
 	int (*show_path)(struct seq_file *sf, struct kernfs_node *kn,
 			 struct kernfs_root *root);
 };

 struct kernfs_root {
 	/* published fields */
 	struct kernfs_node	*kn;
 	unsigned int		flags;	/* KERNFS_ROOT_* flags */

 	/* private fields, do not use outside kernfs proper */
 	struct idr		ino_idr;
 	u32			next_generation;
 	struct kernfs_syscall_ops *syscall_ops;

 	/* list of kernfs_super_info of this root, protected by kernfs_mutex */
 	struct list_head	supers;

 	wait_queue_head_t	deactivate_waitq;
 };

 struct kernfs_open_file {
 	/* published fields */
 	struct kernfs_node	*kn;
 	struct file		*file;
 	struct seq_file		*seq_file;
 	void			*priv;

 	/* private fields, do not use outside kernfs proper */
 	struct mutex		mutex;
 	struct mutex		prealloc_mutex;
 	int			event;
 	struct list_head	list;
 	char			*prealloc_buf;

 	size_t			atomic_write_len;
 	bool			mmapped:1;
 	bool			released:1;
 	const struct vm_operations_struct *vm_ops;
 };

 struct kernfs_ops {
 	/*
 	 * Optional open/release methods.  Both are called with
 	 * @of->seq_file populated.
 	 */
 	int (*open)(struct kernfs_open_file *of);
 	void (*release)(struct kernfs_open_file *of);

 	/*
 	 * Read is handled by either seq_file or raw_read().
 	 *
 	 * If seq_show() is present, seq_file path is active.  Other seq
 	 * operations are optional and if not implemented, the behavior is
 	 * equivalent to single_open().  @sf->private points to the
 	 * associated kernfs_open_file.
 	 *
 	 * read() is bounced through kernel buffer and a read larger than
 	 * PAGE_SIZE results in partial operation of PAGE_SIZE.
 	 */
 	int (*seq_show)(struct seq_file *sf, void *v);

 	void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
 	void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
 	void (*seq_stop)(struct seq_file *sf, void *v);

 	ssize_t (*read)(struct kernfs_open_file *of, char *buf, size_t bytes,
 			loff_t off);

 	/*
 	 * write() is bounced through kernel buffer.  If atomic_write_len
 	 * is not set, a write larger than PAGE_SIZE results in partial
 	 * operations of PAGE_SIZE chunks.  If atomic_write_len is set,
 	 * writes upto the specified size are executed atomically but
 	 * larger ones are rejected with -E2BIG.
 	 */
 	size_t atomic_write_len;
 	/*
 	 * "prealloc" causes a buffer to be allocated at open for
 	 * all read/write requests.  As ->seq_show uses seq_read()
 	 * which does its own allocation, it is incompatible with
 	 * ->prealloc.  Provide ->read and ->write with ->prealloc.
 	 */
 	bool prealloc;
 	ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
 			 loff_t off);

 	int (*mmap)(struct kernfs_open_file *of, struct vm_area_struct *vma);

 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lock_class_key	lockdep_key;
 #endif
 };

 #ifdef CONFIG_KERNFS

 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
 {
 	return kn->flags & KERNFS_TYPE_MASK;
 }

 /**
  * kernfs_enable_ns - enable namespace under a directory
  * @kn: directory of interest, should be empty
  *
  * This is to be called right after @kn is created to enable namespace
  * under it.  All children of @kn must have non-NULL namespace tags and
  * only the ones which match the super_block's tag will be visible.
  */
 static inline void kernfs_enable_ns(struct kernfs_node *kn)
 {
 	WARN_ON_ONCE(kernfs_type(kn) != KERNFS_DIR);
 	WARN_ON_ONCE(!RB_EMPTY_ROOT(&kn->dir.children));
 	kn->flags |= KERNFS_NS;
 }

 /**
  * kernfs_ns_enabled - test whether namespace is enabled
  * @kn: the node to test
  *
  * Test whether namespace filtering is enabled for the children of @ns.
  */
 static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 {
 	return kn->flags & KERNFS_NS;
 }

 int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen);
 int kernfs_path_from_node(struct kernfs_node *root_kn, struct kernfs_node *kn,
 			  char *buf, size_t buflen);
 void pr_cont_kernfs_name(struct kernfs_node *kn);
 void pr_cont_kernfs_path(struct kernfs_node *kn);
 struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn);
 struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
 					   const char *name, const void *ns);
 struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
 					   const char *path, const void *ns);
 void kernfs_get(struct kernfs_node *kn);
 void kernfs_put(struct kernfs_node *kn);

 struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry);
 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb);
 struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn);

 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 				  struct super_block *sb);
 struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
 				       unsigned int flags, void *priv);
 void kernfs_destroy_root(struct kernfs_root *root);

 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
 					 const char *name, umode_t mode,
 					 kuid_t uid, kgid_t gid,
 					 void *priv, const void *ns);
 struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
 					    const char *name);
 struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 					 const char *name, umode_t mode,
 					 kuid_t uid, kgid_t gid,
 					 loff_t size,
 					 const struct kernfs_ops *ops,
 					 void *priv, const void *ns,
 					 struct lock_class_key *key);
 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
 				       const char *name,
 				       struct kernfs_node *target);
 void kernfs_activate(struct kernfs_node *kn);
 void kernfs_remove(struct kernfs_node *kn);
 void kernfs_break_active_protection(struct kernfs_node *kn);
 void kernfs_unbreak_active_protection(struct kernfs_node *kn);
 bool kernfs_remove_self(struct kernfs_node *kn);
 int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
 			     const void *ns);
 int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
 		     const char *new_name, const void *new_ns);
 int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
 void kernfs_notify(struct kernfs_node *kn);

 const void *kernfs_super_ns(struct super_block *sb);
 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
 			       struct kernfs_root *root, unsigned long magic,
 			       bool *new_sb_created, const void *ns);
 void kernfs_kill_sb(struct super_block *sb);
 struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns);

 void kernfs_init(void);

 struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
 	const union kernfs_node_id *id);
 #else	/* CONFIG_KERNFS */

 static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
 { return 0; }	/* whatever */

 static inline void kernfs_enable_ns(struct kernfs_node *kn) { }

 static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
 { return false; }

 static inline int kernfs_name(struct kernfs_node *kn, char *buf, size_t buflen)
 { return -ENOSYS; }

 static inline int kernfs_path_from_node(struct kernfs_node *root_kn,
 					struct kernfs_node *kn,
 					char *buf, size_t buflen)
 { return -ENOSYS; }

 static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }
 static inline void pr_cont_kernfs_path(struct kernfs_node *kn) { }

 static inline struct kernfs_node *kernfs_get_parent(struct kernfs_node *kn)
 { return NULL; }

 static inline struct kernfs_node *
 kernfs_find_and_get_ns(struct kernfs_node *parent, const char *name,
 		       const void *ns)
 { return NULL; }
 static inline struct kernfs_node *
 kernfs_walk_and_get_ns(struct kernfs_node *parent, const char *path,
 		       const void *ns)
 { return NULL; }

 static inline void kernfs_get(struct kernfs_node *kn) { }
 static inline void kernfs_put(struct kernfs_node *kn) { }

 static inline struct kernfs_node *kernfs_node_from_dentry(struct dentry *dentry)
 { return NULL; }

 static inline struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
 { return NULL; }

 static inline struct inode *
 kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn)
 { return NULL; }

 static inline struct kernfs_root *
 kernfs_create_root(struct kernfs_syscall_ops *scops, unsigned int flags,
 		   void *priv)
 { return ERR_PTR(-ENOSYS); }

 static inline void kernfs_destroy_root(struct kernfs_root *root) { }

 static inline struct kernfs_node *
 kernfs_create_dir_ns(struct kernfs_node *parent, const char *name,
 		     umode_t mode, kuid_t uid, kgid_t gid,
 		     void *priv, const void *ns)
 { return ERR_PTR(-ENOSYS); }

 static inline struct kernfs_node *
 __kernfs_create_file(struct kernfs_node *parent, const char *name,
 		     umode_t mode, kuid_t uid, kgid_t gid,
 		     loff_t size, const struct kernfs_ops *ops,
 		     void *priv, const void *ns, struct lock_class_key *key)
 { return ERR_PTR(-ENOSYS); }

 static inline struct kernfs_node *
 kernfs_create_link(struct kernfs_node *parent, const char *name,
 		   struct kernfs_node *target)
 { return ERR_PTR(-ENOSYS); }

 static inline void kernfs_activate(struct kernfs_node *kn) { }

 static inline void kernfs_remove(struct kernfs_node *kn) { }

 static inline bool kernfs_remove_self(struct kernfs_node *kn)
 { return false; }

 static inline int kernfs_remove_by_name_ns(struct kernfs_node *kn,
 					   const char *name, const void *ns)
 { return -ENOSYS; }

 static inline int kernfs_rename_ns(struct kernfs_node *kn,
 				   struct kernfs_node *new_parent,
 				   const char *new_name, const void *new_ns)
 { return -ENOSYS; }

 static inline int kernfs_setattr(struct kernfs_node *kn,
 				 const struct iattr *iattr)
 { return -ENOSYS; }

 static inline void kernfs_notify(struct kernfs_node *kn) { }

 static inline const void *kernfs_super_ns(struct super_block *sb)
 { return NULL; }

 static inline struct dentry *
 kernfs_mount_ns(struct file_system_type *fs_type, int flags,
 		struct kernfs_root *root, unsigned long magic,
 		bool *new_sb_created, const void *ns)
 { return ERR_PTR(-ENOSYS); }

 static inline void kernfs_kill_sb(struct super_block *sb) { }

 static inline void kernfs_init(void) { }

 #endif	/* CONFIG_KERNFS */

 /**
  * kernfs_path - build full path of a given node
  * @kn: kernfs_node of interest
  * @buf: buffer to copy @kn's name into
  * @buflen: size of @buf
  *
  * If @kn is NULL result will be "(null)".
  *
  * Returns the length of the full path.  If the full length is equal to or
  * greater than @buflen, @buf contains the truncated path with the trailing
  * '\0'.  On error, -errno is returned.
  */
 static inline int kernfs_path(struct kernfs_node *kn, char *buf, size_t buflen)
 {
 	return kernfs_path_from_node(kn, NULL, buf, buflen);
 }

 static inline struct kernfs_node *
 kernfs_find_and_get(struct kernfs_node *kn, const char *name)
 {
 	return kernfs_find_and_get_ns(kn, name, NULL);
 }

 static inline struct kernfs_node *
 kernfs_walk_and_get(struct kernfs_node *kn, const char *path)
 {
 	return kernfs_walk_and_get_ns(kn, path, NULL);
 }

 static inline struct kernfs_node *
 kernfs_create_dir(struct kernfs_node *parent, const char *name, umode_t mode,
 		  void *priv)
 {
 	return kernfs_create_dir_ns(parent, name, mode,
 				    GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
 				    priv, NULL);
 }

 static inline struct kernfs_node *
 kernfs_create_file_ns(struct kernfs_node *parent, const char *name,
 		      umode_t mode, kuid_t uid, kgid_t gid,
 		      loff_t size, const struct kernfs_ops *ops,
 		      void *priv, const void *ns)
 {
 	struct lock_class_key *key = NULL;

 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	key = (struct lock_class_key *)&ops->lockdep_key;
 #endif
 	return __kernfs_create_file(parent, name, mode, uid, gid,
 				    size, ops, priv, ns, key);
 }

 static inline struct kernfs_node *
 kernfs_create_file(struct kernfs_node *parent, const char *name, umode_t mode,
 		   loff_t size, const struct kernfs_ops *ops, void *priv)
 {
 	return kernfs_create_file_ns(parent, name, mode,
 				     GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
 				     size, ops, priv, NULL);
 }

 static inline int kernfs_remove_by_name(struct kernfs_node *parent,
 					const char *name)
 {
 	return kernfs_remove_by_name_ns(parent, name, NULL);
 }

 static inline int kernfs_rename(struct kernfs_node *kn,
 				struct kernfs_node *new_parent,
 				const char *new_name)
 {
 	return kernfs_rename_ns(kn, new_parent, new_name, NULL);
 }

 static inline struct dentry *
 kernfs_mount(struct file_system_type *fs_type, int flags,
 		struct kernfs_root *root, unsigned long magic,
 		bool *new_sb_created)
 {
 	return kernfs_mount_ns(fs_type, flags, root,
 				magic, new_sb_created, NULL);
 }

 #endif	/* __LINUX_KERNFS_H */
	/*
	* kernfs.h - pseudo filesystem decoupled from vfs locking
	*
	* This file is released under the GPLv2.
	*/

	#ifndef __LINUX_KERNFS_H
	#define __LINUX_KERNFS_H

	#include <linux/kernel.h>
	#include <linux/err.h>
	#include <linux/list.h>
	#include <linux/mutex.h>
	#include <linux/idr.h>
	#include <linux/lockdep.h>
	#include <linux/rbtree.h>
	#include <linux/atomic.h>
	#include <linux/uidgid.h>
	#include <linux/wait.h>

	struct file;
	struct dentry;
	struct iattr;
	struct seq_file;
	struct vm_area_struct;
	struct super_block;
	struct file_system_type;

	struct kernfs_open_node;
	struct kernfs_iattrs;

	enum kernfs_node_type {
	KERNFS_DIR = 0x0001,
	KERNFS_FILE = 0x0002,
	KERNFS_LINK = 0x0004,
	};

	#define KERNFS_TYPE_MASK 0x000f
	#define KERNFS_FLAG_MASK ~KERNFS_TYPE_MASK

	enum kernfs_node_flag {
	KERNFS_ACTIVATED = 0x0010,
	KERNFS_NS = 0x0020,
	KERNFS_HAS_SEQ_SHOW = 0x0040,
	KERNFS_HAS_MMAP = 0x0080,
	KERNFS_LOCKDEP = 0x0100,
	KERNFS_SUICIDAL = 0x0400,
	KERNFS_SUICIDED = 0x0800,
	KERNFS_EMPTY_DIR = 0x1000,
	KERNFS_HAS_RELEASE = 0x2000,
	};

	/* @flags for kernfs_create_root() */
	enum kernfs_root_flag {
	/*
	* kernfs_nodes are created in the deactivated state and invisible.
	* They require explicit kernfs_activate() to become visible. This
	* can be used to make related nodes become visible atomically
	* after all nodes are created successfully.
	*/
	KERNFS_ROOT_CREATE_DEACTIVATED = 0x0001,

	/*
	* For regular flies, if the opener has CAP_DAC_OVERRIDE, open(2)
	* succeeds regardless of the RW permissions. sysfs had an extra
	* layer of enforcement where open(2) fails with -EACCES regardless
	* of CAP_DAC_OVERRIDE if the permission doesn't have the
	* respective read or write access at all (none of S_IRUGO or
	* S_IWUGO) or the respective operation isn't implemented. The
	* following flag enables that behavior.
	*/
	KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK = 0x0002,

	/*
	* The filesystem supports exportfs operation, so userspace can use
	* fhandle to access nodes of the fs.
	*/
	KERNFS_ROOT_SUPPORT_EXPORTOP = 0x0004,
	};

	/* type-specific structures for kernfs_node union members */
	struct kernfs_elem_dir {
	unsigned long subdirs;
	/* children rbtree starts here and goes through kn->rb */
	struct rb_root children;

	/*
	* The kernfs hierarchy this directory belongs to. This fits
	* better directly in kernfs_node but is here to save space.
	*/
	struct kernfs_root *root;
	};

	struct kernfs_elem_symlink {
	struct kernfs_node *target_kn;
	};

	struct kernfs_elem_attr {
	const struct kernfs_ops *ops;
	struct kernfs_open_node *open;
	loff_t size;
	struct kernfs_node notify_next; / for kernfs_notify() */
	};

	/* represent a kernfs node */
	union kernfs_node_id {
	struct {
	/*
	* blktrace will export this struct as a simplified 'struct
	* fid' (which is a big data struction), so userspace can use
	* it to find kernfs node. The layout must match the first two
	* fields of 'struct fid' exactly.
	*/
	u32 ino;
	u32 generation;
	};
	u64 id;
	};

	/*
	* kernfs_node - the building block of kernfs hierarchy. Each and every
	* kernfs node is represented by single kernfs_node. Most fields are
	* private to kernfs and shouldn't be accessed directly by kernfs users.
	*
	* As long as s_count reference is held, the kernfs_node itself is
	* accessible. Dereferencing elem or any other outer entity requires
	* active reference.
	*/
	struct kernfs_node {
	atomic_t count;
	atomic_t active;
	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map dep_map;
	#endif
	/*
	* Use kernfs_get_parent() and kernfs_name/path() instead of
	* accessing the following two fields directly. If the node is
	* never moved to a different parent, it is safe to access the
	* parent directly.
	*/
	struct kernfs_node *parent;
	const char *name;

	struct rb_node rb;

	const void ns; / namespace tag */
	unsigned int hash; /* ns + name hash */
	union {
	struct kernfs_elem_dir dir;
	struct kernfs_elem_symlink symlink;
	struct kernfs_elem_attr attr;
	};

	void *priv;

	union kernfs_node_id id;
	unsigned short flags;
	umode_t mode;
	struct kernfs_iattrs *iattr;
	};

	/*
	* kernfs_syscall_ops may be specified on kernfs_create_root() to support
	* syscalls. These optional callbacks are invoked on the matching syscalls
	* and can perform any kernfs operations which don't necessarily have to be
	* the exact operation requested. An active reference is held for each
	* kernfs_node parameter.
	*/
	struct kernfs_syscall_ops {
	int (remount_fs)(struct kernfs_root root, int flags, char data);
	int (show_options)(struct seq_file sf, struct kernfs_root *root);

	int (mkdir)(struct kernfs_node parent, const char *name,
	umode_t mode);
	int (rmdir)(struct kernfs_node kn);
	int (rename)(struct kernfs_node kn, struct kernfs_node *new_parent,
	const char *new_name);
	int (show_path)(struct seq_file sf, struct kernfs_node *kn,
	struct kernfs_root *root);
	};

	struct kernfs_root {
	/* published fields */
	struct kernfs_node *kn;
	unsigned int flags; /* KERNFS_ROOT_* flags */

	/* private fields, do not use outside kernfs proper */
	struct idr ino_idr;
	u32 next_generation;
	struct kernfs_syscall_ops *syscall_ops;

	/* list of kernfs_super_info of this root, protected by kernfs_mutex */
	struct list_head supers;

	wait_queue_head_t deactivate_waitq;
	};

	struct kernfs_open_file {
	/* published fields */
	struct kernfs_node *kn;
	struct file *file;
	struct seq_file *seq_file;
	void *priv;

	/* private fields, do not use outside kernfs proper */
	struct mutex mutex;
	struct mutex prealloc_mutex;
	int event;
	struct list_head list;
	char *prealloc_buf;

	size_t atomic_write_len;
	bool mmapped:1;
	bool released:1;
	const struct vm_operations_struct *vm_ops;
	};

	struct kernfs_ops {
	/*
	* Optional open/release methods. Both are called with
	* @of->seq_file populated.
	*/
	int (open)(struct kernfs_open_file of);
	void (release)(struct kernfs_open_file of);

	/*
	* Read is handled by either seq_file or raw_read().
	*
	* If seq_show() is present, seq_file path is active. Other seq
	* operations are optional and if not implemented, the behavior is
	* equivalent to single_open(). @sf->private points to the
	* associated kernfs_open_file.
	*
	* read() is bounced through kernel buffer and a read larger than
	* PAGE_SIZE results in partial operation of PAGE_SIZE.
	*/
	int (seq_show)(struct seq_file sf, void *v);

	void (seq_start)(struct seq_file sf, loff_t ppos);
	void (seq_next)(struct seq_file sf, void v, loff_t *ppos);
	void (seq_stop)(struct seq_file sf, void *v);

	ssize_t (read)(struct kernfs_open_file of, char *buf, size_t bytes,
	loff_t off);

	/*
	* write() is bounced through kernel buffer. If atomic_write_len
	* is not set, a write larger than PAGE_SIZE results in partial
	* operations of PAGE_SIZE chunks. If atomic_write_len is set,
	* writes upto the specified size are executed atomically but
	* larger ones are rejected with -E2BIG.
	*/
	size_t atomic_write_len;
	/*
	* "prealloc" causes a buffer to be allocated at open for
	* all read/write requests. As ->seq_show uses seq_read()
	* which does its own allocation, it is incompatible with
	* ->prealloc. Provide ->read and ->write with ->prealloc.
	*/
	bool prealloc;
	ssize_t (write)(struct kernfs_open_file of, char *buf, size_t bytes,
	loff_t off);

	int (mmap)(struct kernfs_open_file of, struct vm_area_struct *vma);

	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lock_class_key lockdep_key;
	#endif
	};

	#ifdef CONFIG_KERNFS

	static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
	{
	return kn->flags & KERNFS_TYPE_MASK;
	}

	/**
	* kernfs_enable_ns - enable namespace under a directory
	* @kn: directory of interest, should be empty
	*
	* This is to be called right after @kn is created to enable namespace
	* under it. All children of @kn must have non-NULL namespace tags and
	* only the ones which match the super_block's tag will be visible.
	*/
	static inline void kernfs_enable_ns(struct kernfs_node *kn)
	{
	WARN_ON_ONCE(kernfs_type(kn) != KERNFS_DIR);
	WARN_ON_ONCE(!RB_EMPTY_ROOT(&kn->dir.children));
	kn->flags \|= KERNFS_NS;
	}

	/**
	* kernfs_ns_enabled - test whether namespace is enabled
	* @kn: the node to test
	*
	* Test whether namespace filtering is enabled for the children of @ns.
	*/
	static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
	{
	return kn->flags & KERNFS_NS;
	}

	int kernfs_name(struct kernfs_node kn, char buf, size_t buflen);
	int kernfs_path_from_node(struct kernfs_node root_kn, struct kernfs_node kn,
	char *buf, size_t buflen);
	void pr_cont_kernfs_name(struct kernfs_node *kn);
	void pr_cont_kernfs_path(struct kernfs_node *kn);
	struct kernfs_node kernfs_get_parent(struct kernfs_node kn);
	struct kernfs_node kernfs_find_and_get_ns(struct kernfs_node parent,
	const char name, const void ns);
	struct kernfs_node kernfs_walk_and_get_ns(struct kernfs_node parent,
	const char path, const void ns);
	void kernfs_get(struct kernfs_node *kn);
	void kernfs_put(struct kernfs_node *kn);

	struct kernfs_node kernfs_node_from_dentry(struct dentry dentry);
	struct kernfs_root kernfs_root_from_sb(struct super_block sb);
	struct inode kernfs_get_inode(struct super_block sb, struct kernfs_node *kn);

	struct dentry kernfs_node_dentry(struct kernfs_node kn,
	struct super_block *sb);
	struct kernfs_root kernfs_create_root(struct kernfs_syscall_ops scops,
	unsigned int flags, void *priv);
	void kernfs_destroy_root(struct kernfs_root *root);

	struct kernfs_node kernfs_create_dir_ns(struct kernfs_node parent,
	const char *name, umode_t mode,
	kuid_t uid, kgid_t gid,
	void priv, const void ns);
	struct kernfs_node kernfs_create_empty_dir(struct kernfs_node parent,
	const char *name);
	struct kernfs_node __kernfs_create_file(struct kernfs_node parent,
	const char *name, umode_t mode,
	kuid_t uid, kgid_t gid,
	loff_t size,
	const struct kernfs_ops *ops,
	void priv, const void ns,
	struct lock_class_key *key);
	struct kernfs_node kernfs_create_link(struct kernfs_node parent,
	const char *name,
	struct kernfs_node *target);
	void kernfs_activate(struct kernfs_node *kn);
	void kernfs_remove(struct kernfs_node *kn);
	void kernfs_break_active_protection(struct kernfs_node *kn);
	void kernfs_unbreak_active_protection(struct kernfs_node *kn);
	bool kernfs_remove_self(struct kernfs_node *kn);
	int kernfs_remove_by_name_ns(struct kernfs_node parent, const char name,
	const void *ns);
	int kernfs_rename_ns(struct kernfs_node kn, struct kernfs_node new_parent,
	const char new_name, const void new_ns);
	int kernfs_setattr(struct kernfs_node kn, const struct iattr iattr);
	void kernfs_notify(struct kernfs_node *kn);

	const void kernfs_super_ns(struct super_block sb);
	struct dentry kernfs_mount_ns(struct file_system_type fs_type, int flags,
	struct kernfs_root *root, unsigned long magic,
	bool new_sb_created, const void ns);
	void kernfs_kill_sb(struct super_block *sb);
	struct super_block kernfs_pin_sb(struct kernfs_root root, const void *ns);

	void kernfs_init(void);

	struct kernfs_node kernfs_get_node_by_id(struct kernfs_root root,
	const union kernfs_node_id *id);
	#else /* CONFIG_KERNFS */

	static inline enum kernfs_node_type kernfs_type(struct kernfs_node *kn)
	{ return 0; } /* whatever */

	static inline void kernfs_enable_ns(struct kernfs_node *kn) { }

	static inline bool kernfs_ns_enabled(struct kernfs_node *kn)
	{ return false; }

	static inline int kernfs_name(struct kernfs_node kn, char buf, size_t buflen)
	{ return -ENOSYS; }

	static inline int kernfs_path_from_node(struct kernfs_node *root_kn,
	struct kernfs_node *kn,
	char *buf, size_t buflen)
	{ return -ENOSYS; }

	static inline void pr_cont_kernfs_name(struct kernfs_node *kn) { }
	static inline void pr_cont_kernfs_path(struct kernfs_node *kn) { }

	static inline struct kernfs_node kernfs_get_parent(struct kernfs_node kn)
	{ return NULL; }

	static inline struct kernfs_node *
	kernfs_find_and_get_ns(struct kernfs_node parent, const char name,
	const void *ns)
	{ return NULL; }
	static inline struct kernfs_node *
	kernfs_walk_and_get_ns(struct kernfs_node parent, const char path,
	const void *ns)
	{ return NULL; }

	static inline void kernfs_get(struct kernfs_node *kn) { }
	static inline void kernfs_put(struct kernfs_node *kn) { }

	static inline struct kernfs_node kernfs_node_from_dentry(struct dentry dentry)
	{ return NULL; }

	static inline struct kernfs_root kernfs_root_from_sb(struct super_block sb)
	{ return NULL; }

	static inline struct inode *
	kernfs_get_inode(struct super_block sb, struct kernfs_node kn)
	{ return NULL; }

	static inline struct kernfs_root *
	kernfs_create_root(struct kernfs_syscall_ops *scops, unsigned int flags,
	void *priv)
	{ return ERR_PTR(-ENOSYS); }

	static inline void kernfs_destroy_root(struct kernfs_root *root) { }

	static inline struct kernfs_node *
	kernfs_create_dir_ns(struct kernfs_node parent, const char name,
	umode_t mode, kuid_t uid, kgid_t gid,
	void priv, const void ns)
	{ return ERR_PTR(-ENOSYS); }

	static inline struct kernfs_node *
	__kernfs_create_file(struct kernfs_node parent, const char name,
	umode_t mode, kuid_t uid, kgid_t gid,
	loff_t size, const struct kernfs_ops *ops,
	void priv, const void ns, struct lock_class_key *key)
	{ return ERR_PTR(-ENOSYS); }

	static inline struct kernfs_node *
	kernfs_create_link(struct kernfs_node parent, const char name,
	struct kernfs_node *target)
	{ return ERR_PTR(-ENOSYS); }

	static inline void kernfs_activate(struct kernfs_node *kn) { }

	static inline void kernfs_remove(struct kernfs_node *kn) { }

	static inline bool kernfs_remove_self(struct kernfs_node *kn)
	{ return false; }

	static inline int kernfs_remove_by_name_ns(struct kernfs_node *kn,
	const char name, const void ns)
	{ return -ENOSYS; }

	static inline int kernfs_rename_ns(struct kernfs_node *kn,
	struct kernfs_node *new_parent,
	const char new_name, const void new_ns)
	{ return -ENOSYS; }

	static inline int kernfs_setattr(struct kernfs_node *kn,
	const struct iattr *iattr)
	{ return -ENOSYS; }

	static inline void kernfs_notify(struct kernfs_node *kn) { }

	static inline const void kernfs_super_ns(struct super_block sb)
	{ return NULL; }

	static inline struct dentry *
	kernfs_mount_ns(struct file_system_type *fs_type, int flags,
	struct kernfs_root *root, unsigned long magic,
	bool new_sb_created, const void ns)
	{ return ERR_PTR(-ENOSYS); }

	static inline void kernfs_kill_sb(struct super_block *sb) { }

	static inline void kernfs_init(void) { }

	#endif /* CONFIG_KERNFS */

	/**
	* kernfs_path - build full path of a given node
	* @kn: kernfs_node of interest
	* @buf: buffer to copy @kn's name into
	* @buflen: size of @buf
	*
	* If @kn is NULL result will be "(null)".
	*
	* Returns the length of the full path. If the full length is equal to or
	* greater than @buflen, @buf contains the truncated path with the trailing
	* '\0'. On error, -errno is returned.
	*/
	static inline int kernfs_path(struct kernfs_node kn, char buf, size_t buflen)
	{
	return kernfs_path_from_node(kn, NULL, buf, buflen);
	}

	static inline struct kernfs_node *
	kernfs_find_and_get(struct kernfs_node kn, const char name)
	{
	return kernfs_find_and_get_ns(kn, name, NULL);
	}

	static inline struct kernfs_node *
	kernfs_walk_and_get(struct kernfs_node kn, const char path)
	{
	return kernfs_walk_and_get_ns(kn, path, NULL);
	}

	static inline struct kernfs_node *
	kernfs_create_dir(struct kernfs_node parent, const char name, umode_t mode,
	void *priv)
	{
	return kernfs_create_dir_ns(parent, name, mode,
	GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
	priv, NULL);
	}

	static inline struct kernfs_node *
	kernfs_create_file_ns(struct kernfs_node parent, const char name,
	umode_t mode, kuid_t uid, kgid_t gid,
	loff_t size, const struct kernfs_ops *ops,
	void priv, const void ns)
	{
	struct lock_class_key *key = NULL;

	#ifdef CONFIG_DEBUG_LOCK_ALLOC
	key = (struct lock_class_key *)&ops->lockdep_key;
	#endif
	return __kernfs_create_file(parent, name, mode, uid, gid,
	size, ops, priv, ns, key);
	}

	static inline struct kernfs_node *
	kernfs_create_file(struct kernfs_node parent, const char name, umode_t mode,
	loff_t size, const struct kernfs_ops ops, void priv)
	{
	return kernfs_create_file_ns(parent, name, mode,
	GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
	size, ops, priv, NULL);
	}

	static inline int kernfs_remove_by_name(struct kernfs_node *parent,
	const char *name)
	{
	return kernfs_remove_by_name_ns(parent, name, NULL);
	}

	static inline int kernfs_rename(struct kernfs_node *kn,
	struct kernfs_node *new_parent,
	const char *new_name)
	{
	return kernfs_rename_ns(kn, new_parent, new_name, NULL);
	}

	static inline struct dentry *
	kernfs_mount(struct file_system_type *fs_type, int flags,
	struct kernfs_root *root, unsigned long magic,
	bool *new_sb_created)
	{
	return kernfs_mount_ns(fs_type, flags, root,
	magic, new_sb_created, NULL);
	}

	#endif /* __LINUX_KERNFS_H */