/* General filesystem caching interface
   *
   * Copyright (C) 2004-2007 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * 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.
   *
   * NOTE!!! See:
   *
   *	Documentation/filesystems/caching/netfs-api.txt
   *
   * for a description of the network filesystem interface declared here.
   */
  
  #ifndef _LINUX_FSCACHE_H
  #define _LINUX_FSCACHE_H
  
  #include <linux/fs.h>
  #include <linux/list.h>
  #include <linux/pagemap.h>
  #include <linux/pagevec.h>
  
  #if defined(CONFIG_FSCACHE) || defined(CONFIG_FSCACHE_MODULE)
  #define fscache_available() (1)
  #define fscache_cookie_valid(cookie) (cookie)
  #else
  #define fscache_available() (0)
  #define fscache_cookie_valid(cookie) (0)
  #endif
  
  
  /*
   * overload PG_private_2 to give us PG_fscache - this is used to indicate that
   * a page is currently backed by a local disk cache
   */
  #define PageFsCache(page)		PagePrivate2((page))
  #define SetPageFsCache(page)		SetPagePrivate2((page))
  #define ClearPageFsCache(page)		ClearPagePrivate2((page))
  #define TestSetPageFsCache(page)	TestSetPagePrivate2((page))
  #define TestClearPageFsCache(page)	TestClearPagePrivate2((page))
  
  /* pattern used to fill dead space in an index entry */
  #define FSCACHE_INDEX_DEADFILL_PATTERN 0x79
  
  struct pagevec;
  struct fscache_cache_tag;
  struct fscache_cookie;
  struct fscache_netfs;
  
  typedef void (*fscache_rw_complete_t)(struct page *page,
  				      void *context,
  				      int error);
  
  /* result of index entry consultation */
  enum fscache_checkaux {
  	FSCACHE_CHECKAUX_OKAY,		/* entry okay as is */
  	FSCACHE_CHECKAUX_NEEDS_UPDATE,	/* entry requires update */
  	FSCACHE_CHECKAUX_OBSOLETE,	/* entry requires deletion */
  };
  
  /*
   * fscache cookie definition
   */
  struct fscache_cookie_def {
  	/* name of cookie type */
  	char name[16];
  
  	/* cookie type */
  	uint8_t type;
  #define FSCACHE_COOKIE_TYPE_INDEX	0
  #define FSCACHE_COOKIE_TYPE_DATAFILE	1
  
  	/* select the cache into which to insert an entry in this index
  	 * - optional
  	 * - should return a cache identifier or NULL to cause the cache to be
  	 *   inherited from the parent if possible or the first cache picked
  	 *   for a non-index file if not
  	 */
  	struct fscache_cache_tag *(*select_cache)(
  		const void *parent_netfs_data,
  		const void *cookie_netfs_data);
  
  	/* get an index key
  	 * - should store the key data in the buffer

  	 * - should return the amount of data stored

  	 * - not permitted to return an error
  	 * - the netfs data from the cookie being used as the source is
  	 *   presented
  	 */
  	uint16_t (*get_key)(const void *cookie_netfs_data,
  			    void *buffer,
  			    uint16_t bufmax);
  
  	/* get certain file attributes from the netfs data
  	 * - this function can be absent for an index
  	 * - not permitted to return an error
  	 * - the netfs data from the cookie being used as the source is
  	 *   presented
  	 */
  	void (*get_attr)(const void *cookie_netfs_data, uint64_t *size);

  	/* get the auxiliary data from netfs data

  	 * - this function can be absent if the index carries no state data

  	 * - should store the auxiliary data in the buffer

  	 * - should return the amount of amount stored
  	 * - not permitted to return an error
  	 * - the netfs data from the cookie being used as the source is
  	 *   presented
  	 */
  	uint16_t (*get_aux)(const void *cookie_netfs_data,
  			    void *buffer,
  			    uint16_t bufmax);
  
  	/* consult the netfs about the state of an object
  	 * - this function can be absent if the index carries no state data
  	 * - the netfs data from the cookie being used as the target is

  	 *   presented, as is the auxiliary data

  	 */
  	enum fscache_checkaux (*check_aux)(void *cookie_netfs_data,
  					   const void *data,
  					   uint16_t datalen);
  
  	/* get an extra reference on a read context
  	 * - this function can be absent if the completion function doesn't
  	 *   require a context
  	 */
  	void (*get_context)(void *cookie_netfs_data, void *context);
  
  	/* release an extra reference on a read context
  	 * - this function can be absent if the completion function doesn't
  	 *   require a context
  	 */
  	void (*put_context)(void *cookie_netfs_data, void *context);

  	/* indicate page that now have cache metadata retained
  	 * - this function should mark the specified page as now being cached
  	 * - the page will have been marked with PG_fscache before this is

  	 *   called, so this is optional
  	 */

  	void (*mark_page_cached)(void *cookie_netfs_data,
  				 struct address_space *mapping,
  				 struct page *page);

  
  	/* indicate the cookie is no longer cached
  	 * - this function is called when the backing store currently caching
  	 *   a cookie is removed
  	 * - the netfs should use this to clean up any markers indicating
  	 *   cached pages
  	 * - this is mandatory for any object that may have data
  	 */
  	void (*now_uncached)(void *cookie_netfs_data);
  };
  
  /*
   * fscache cached network filesystem type
   * - name, version and ops must be filled in before registration
   * - all other fields will be set during registration
   */
  struct fscache_netfs {
  	uint32_t			version;	/* indexing version */
  	const char			*name;		/* filesystem name */
  	struct fscache_cookie		*primary_index;
  	struct list_head		link;		/* internal link */
  };
  
  /*

   * data file or index object cookie
   * - a file will only appear in one cache
   * - a request to cache a file may or may not be honoured, subject to
   *   constraints such as disk space
   * - indices are created on disk just-in-time
   */
  struct fscache_cookie {
  	atomic_t			usage;		/* number of users of this cookie */
  	atomic_t			n_children;	/* number of children of this cookie */
  	atomic_t			n_active;	/* number of active users of netfs ptrs */
  	spinlock_t			lock;
  	spinlock_t			stores_lock;	/* lock on page store tree */
  	struct hlist_head		backing_objects; /* object(s) backing this file/index */
  	const struct fscache_cookie_def	*def;		/* definition */
  	struct fscache_cookie		*parent;	/* parent of this entry */
  	void				*netfs_data;	/* back pointer to netfs */
  	struct radix_tree_root		stores;		/* pages to be stored on this cookie */
  #define FSCACHE_COOKIE_PENDING_TAG	0		/* pages tag: pending write to cache */
  #define FSCACHE_COOKIE_STORING_TAG	1		/* pages tag: writing to cache */
  
  	unsigned long			flags;
  #define FSCACHE_COOKIE_LOOKING_UP	0	/* T if non-index cookie being looked up still */
  #define FSCACHE_COOKIE_NO_DATA_YET	1	/* T if new object with no cached data yet */
  #define FSCACHE_COOKIE_UNAVAILABLE	2	/* T if cookie is unavailable (error, etc) */
  #define FSCACHE_COOKIE_INVALIDATING	3	/* T if cookie is being invalidated */
  #define FSCACHE_COOKIE_RELINQUISHED	4	/* T if cookie has been relinquished */
  #define FSCACHE_COOKIE_ENABLED		5	/* T if cookie is enabled */
  #define FSCACHE_COOKIE_ENABLEMENT_LOCK	6	/* T if cookie is being en/disabled */
  };
  
  static inline bool fscache_cookie_enabled(struct fscache_cookie *cookie)
  {
  	return test_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);
  }
  
  /*

   * slow-path functions for when there is actually caching available, and the
   * netfs does actually have a valid token
   * - these are not to be called directly
   * - these are undefined symbols when FS-Cache is not configured and the
   *   optimiser takes care of not using them
   */

  extern int __fscache_register_netfs(struct fscache_netfs *);
  extern void __fscache_unregister_netfs(struct fscache_netfs *);

  extern struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *);
  extern void __fscache_release_cache_tag(struct fscache_cache_tag *);

  extern struct fscache_cookie *__fscache_acquire_cookie(
  	struct fscache_cookie *,
  	const struct fscache_cookie_def *,

  	void *, bool);
  extern void __fscache_relinquish_cookie(struct fscache_cookie *, bool);

  extern int __fscache_check_consistency(struct fscache_cookie *);

  extern void __fscache_update_cookie(struct fscache_cookie *);

  extern int __fscache_attr_changed(struct fscache_cookie *);

  extern void __fscache_invalidate(struct fscache_cookie *);
  extern void __fscache_wait_on_invalidate(struct fscache_cookie *);

  extern int __fscache_read_or_alloc_page(struct fscache_cookie *,
  					struct page *,
  					fscache_rw_complete_t,
  					void *,
  					gfp_t);
  extern int __fscache_read_or_alloc_pages(struct fscache_cookie *,
  					 struct address_space *,
  					 struct list_head *,
  					 unsigned *,
  					 fscache_rw_complete_t,
  					 void *,
  					 gfp_t);
  extern int __fscache_alloc_page(struct fscache_cookie *, struct page *, gfp_t);
  extern int __fscache_write_page(struct fscache_cookie *, struct page *, gfp_t);
  extern void __fscache_uncache_page(struct fscache_cookie *, struct page *);
  extern bool __fscache_check_page_write(struct fscache_cookie *, struct page *);
  extern void __fscache_wait_on_page_write(struct fscache_cookie *, struct page *);

  extern bool __fscache_maybe_release_page(struct fscache_cookie *, struct page *,
  					 gfp_t);

  extern void __fscache_uncache_all_inode_pages(struct fscache_cookie *,
  					      struct inode *);

  extern void __fscache_readpages_cancel(struct fscache_cookie *cookie,
  				       struct list_head *pages);

  extern void __fscache_disable_cookie(struct fscache_cookie *, bool);
  extern void __fscache_enable_cookie(struct fscache_cookie *,
  				    bool (*)(void *), void *);

  /**
   * fscache_register_netfs - Register a filesystem as desiring caching services
   * @netfs: The description of the filesystem
   *
   * Register a filesystem as desiring caching services if they're available.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  int fscache_register_netfs(struct fscache_netfs *netfs)
  {

  	if (fscache_available())
  		return __fscache_register_netfs(netfs);
  	else
  		return 0;

  }
  
  /**
   * fscache_unregister_netfs - Indicate that a filesystem no longer desires
   * caching services
   * @netfs: The description of the filesystem
   *
   * Indicate that a filesystem no longer desires caching services for the
   * moment.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  void fscache_unregister_netfs(struct fscache_netfs *netfs)
  {

  	if (fscache_available())
  		__fscache_unregister_netfs(netfs);

  }
  
  /**
   * fscache_lookup_cache_tag - Look up a cache tag
   * @name: The name of the tag to search for
   *
   * Acquire a specific cache referral tag that can be used to select a specific
   * cache in which to cache an index.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name)
  {

  	if (fscache_available())
  		return __fscache_lookup_cache_tag(name);
  	else
  		return NULL;

  }
  
  /**
   * fscache_release_cache_tag - Release a cache tag
   * @tag: The tag to release
   *
   * Release a reference to a cache referral tag previously looked up.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  void fscache_release_cache_tag(struct fscache_cache_tag *tag)
  {

  	if (fscache_available())
  		__fscache_release_cache_tag(tag);

  }
  
  /**
   * fscache_acquire_cookie - Acquire a cookie to represent a cache object
   * @parent: The cookie that's to be the parent of this one
   * @def: A description of the cache object, including callback operations
   * @netfs_data: An arbitrary piece of data to be kept in the cookie to
   * represent the cache object to the netfs

   * @enable: Whether or not to enable a data cookie immediately

   *
   * This function is used to inform FS-Cache about part of an index hierarchy
   * that can be used to locate files.  This is done by requesting a cookie for
   * each index in the path to the file.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  struct fscache_cookie *fscache_acquire_cookie(
  	struct fscache_cookie *parent,
  	const struct fscache_cookie_def *def,

  	void *netfs_data,
  	bool enable)

  {

  	if (fscache_cookie_valid(parent) && fscache_cookie_enabled(parent))
  		return __fscache_acquire_cookie(parent, def, netfs_data,
  						enable);

  	else
  		return NULL;

  }
  
  /**
   * fscache_relinquish_cookie - Return the cookie to the cache, maybe discarding
   * it
   * @cookie: The cookie being returned
   * @retire: True if the cache object the cookie represents is to be discarded
   *
   * This function returns a cookie to the cache, forcibly discarding the
   * associated cache object if retire is set to true.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline

  void fscache_relinquish_cookie(struct fscache_cookie *cookie, bool retire)

  {

  	if (fscache_cookie_valid(cookie))
  		__fscache_relinquish_cookie(cookie, retire);

  }
  
  /**

   * fscache_check_consistency - Request that if the cache is updated
   * @cookie: The cookie representing the cache object
   *
   * Request an consistency check from fscache, which passes the request
   * to the backing cache.
   *
   * Returns 0 if consistent and -ESTALE if inconsistent.  May also
   * return -ENOMEM and -ERESTARTSYS.
   */
  static inline
  int fscache_check_consistency(struct fscache_cookie *cookie)
  {

  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))

  		return __fscache_check_consistency(cookie);
  	else
  		return 0;
  }
  
  /**

   * fscache_update_cookie - Request that a cache object be updated
   * @cookie: The cookie representing the cache object
   *
   * Request an update of the index data for the cache object associated with the
   * cookie.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  void fscache_update_cookie(struct fscache_cookie *cookie)
  {

  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))

  		__fscache_update_cookie(cookie);

  }
  
  /**
   * fscache_pin_cookie - Pin a data-storage cache object in its cache
   * @cookie: The cookie representing the cache object
   *
   * Permit data-storage cache objects to be pinned in the cache.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  int fscache_pin_cookie(struct fscache_cookie *cookie)
  {
  	return -ENOBUFS;
  }
  
  /**
   * fscache_pin_cookie - Unpin a data-storage cache object in its cache
   * @cookie: The cookie representing the cache object
   *
   * Permit data-storage cache objects to be unpinned from the cache.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  void fscache_unpin_cookie(struct fscache_cookie *cookie)
  {
  }
  
  /**
   * fscache_attr_changed - Notify cache that an object's attributes changed
   * @cookie: The cookie representing the cache object
   *
   * Send a notification to the cache indicating that an object's attributes have
   * changed.  This includes the data size.  These attributes will be obtained
   * through the get_attr() cookie definition op.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  int fscache_attr_changed(struct fscache_cookie *cookie)
  {

  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))

  		return __fscache_attr_changed(cookie);
  	else
  		return -ENOBUFS;

  }
  
  /**

   * fscache_invalidate - Notify cache that an object needs invalidation
   * @cookie: The cookie representing the cache object
   *
   * Notify the cache that an object is needs to be invalidated and that it
   * should abort any retrievals or stores it is doing on the cache.  The object
   * is then marked non-caching until such time as the invalidation is complete.
   *
   * This can be called with spinlocks held.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  void fscache_invalidate(struct fscache_cookie *cookie)
  {

  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))

  		__fscache_invalidate(cookie);
  }
  
  /**
   * fscache_wait_on_invalidate - Wait for invalidation to complete
   * @cookie: The cookie representing the cache object
   *
   * Wait for the invalidation of an object to complete.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  void fscache_wait_on_invalidate(struct fscache_cookie *cookie)
  {
  	if (fscache_cookie_valid(cookie))
  		__fscache_wait_on_invalidate(cookie);
  }
  
  /**

   * fscache_reserve_space - Reserve data space for a cached object
   * @cookie: The cookie representing the cache object
   * @i_size: The amount of space to be reserved
   *
   * Reserve an amount of space in the cache for the cache object attached to a
   * cookie so that a write to that object within the space can always be
   * honoured.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  int fscache_reserve_space(struct fscache_cookie *cookie, loff_t size)
  {
  	return -ENOBUFS;
  }
  
  /**
   * fscache_read_or_alloc_page - Read a page from the cache or allocate a block
   * in which to store it
   * @cookie: The cookie representing the cache object
   * @page: The netfs page to fill if possible
   * @end_io_func: The callback to invoke when and if the page is filled
   * @context: An arbitrary piece of data to pass on to end_io_func()
   * @gfp: The conditions under which memory allocation should be made
   *
   * Read a page from the cache, or if that's not possible make a potential
   * one-block reservation in the cache into which the page may be stored once
   * fetched from the server.
   *
   * If the page is not backed by the cache object, or if it there's some reason
   * it can't be, -ENOBUFS will be returned and nothing more will be done for
   * that page.
   *
   * Else, if that page is backed by the cache, a read will be initiated directly
   * to the netfs's page and 0 will be returned by this function.  The
   * end_io_func() callback will be invoked when the operation terminates on a
   * completion or failure.  Note that the callback may be invoked before the
   * return.
   *
   * Else, if the page is unbacked, -ENODATA is returned and a block may have
   * been allocated in the cache.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  int fscache_read_or_alloc_page(struct fscache_cookie *cookie,
  			       struct page *page,
  			       fscache_rw_complete_t end_io_func,
  			       void *context,
  			       gfp_t gfp)
  {

  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))

  		return __fscache_read_or_alloc_page(cookie, page, end_io_func,
  						    context, gfp);
  	else
  		return -ENOBUFS;

  }
  
  /**
   * fscache_read_or_alloc_pages - Read pages from the cache and/or allocate
   * blocks in which to store them
   * @cookie: The cookie representing the cache object
   * @mapping: The netfs inode mapping to which the pages will be attached
   * @pages: A list of potential netfs pages to be filled

   * @nr_pages: Number of pages to be read and/or allocated

   * @end_io_func: The callback to invoke when and if each page is filled
   * @context: An arbitrary piece of data to pass on to end_io_func()
   * @gfp: The conditions under which memory allocation should be made
   *
   * Read a set of pages from the cache, or if that's not possible, attempt to
   * make a potential one-block reservation for each page in the cache into which
   * that page may be stored once fetched from the server.
   *
   * If some pages are not backed by the cache object, or if it there's some
   * reason they can't be, -ENOBUFS will be returned and nothing more will be
   * done for that pages.
   *
   * Else, if some of the pages are backed by the cache, a read will be initiated
   * directly to the netfs's page and 0 will be returned by this function.  The
   * end_io_func() callback will be invoked when the operation terminates on a
   * completion or failure.  Note that the callback may be invoked before the
   * return.
   *
   * Else, if a page is unbacked, -ENODATA is returned and a block may have
   * been allocated in the cache.
   *
   * Because the function may want to return all of -ENOBUFS, -ENODATA and 0 in
   * regard to different pages, the return values are prioritised in that order.
   * Any pages submitted for reading are removed from the pages list.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  int fscache_read_or_alloc_pages(struct fscache_cookie *cookie,
  				struct address_space *mapping,
  				struct list_head *pages,
  				unsigned *nr_pages,
  				fscache_rw_complete_t end_io_func,
  				void *context,
  				gfp_t gfp)
  {

  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))

  		return __fscache_read_or_alloc_pages(cookie, mapping, pages,
  						     nr_pages, end_io_func,
  						     context, gfp);
  	else
  		return -ENOBUFS;

  }
  
  /**
   * fscache_alloc_page - Allocate a block in which to store a page
   * @cookie: The cookie representing the cache object
   * @page: The netfs page to allocate a page for
   * @gfp: The conditions under which memory allocation should be made
   *
   * Request Allocation a block in the cache in which to store a netfs page
   * without retrieving any contents from the cache.
   *
   * If the page is not backed by a file then -ENOBUFS will be returned and
   * nothing more will be done, and no reservation will be made.
   *
   * Else, a block will be allocated if one wasn't already, and 0 will be
   * returned
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  int fscache_alloc_page(struct fscache_cookie *cookie,
  		       struct page *page,
  		       gfp_t gfp)
  {

  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))

  		return __fscache_alloc_page(cookie, page, gfp);
  	else
  		return -ENOBUFS;

  }
  
  /**

   * fscache_readpages_cancel - Cancel read/alloc on pages
   * @cookie: The cookie representing the inode's cache object.
   * @pages: The netfs pages that we canceled write on in readpages()
   *
   * Uncache/unreserve the pages reserved earlier in readpages() via
   * fscache_readpages_or_alloc() and similar.  In most successful caches in
   * readpages() this doesn't do anything.  In cases when the underlying netfs's
   * readahead failed we need to clean up the pagelist (unmark and uncache).
   *
   * This function may sleep as it may have to clean up disk state.
   */
  static inline
  void fscache_readpages_cancel(struct fscache_cookie *cookie,
  			      struct list_head *pages)
  {
  	if (fscache_cookie_valid(cookie))
  		__fscache_readpages_cancel(cookie, pages);
  }
  
  /**

   * fscache_write_page - Request storage of a page in the cache
   * @cookie: The cookie representing the cache object
   * @page: The netfs page to store
   * @gfp: The conditions under which memory allocation should be made
   *
   * Request the contents of the netfs page be written into the cache.  This
   * request may be ignored if no cache block is currently allocated, in which
   * case it will return -ENOBUFS.
   *
   * If a cache block was already allocated, a write will be initiated and 0 will
   * be returned.  The PG_fscache_write page bit is set immediately and will then
   * be cleared at the completion of the write to indicate the success or failure
   * of the operation.  Note that the completion may happen before the return.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  int fscache_write_page(struct fscache_cookie *cookie,
  		       struct page *page,
  		       gfp_t gfp)
  {

  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))

  		return __fscache_write_page(cookie, page, gfp);
  	else
  		return -ENOBUFS;

  }
  
  /**
   * fscache_uncache_page - Indicate that caching is no longer required on a page
   * @cookie: The cookie representing the cache object
   * @page: The netfs page that was being cached.
   *
   * Tell the cache that we no longer want a page to be cached and that it should
   * remove any knowledge of the netfs page it may have.
   *
   * Note that this cannot cancel any outstanding I/O operations between this
   * page and the cache.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  void fscache_uncache_page(struct fscache_cookie *cookie,
  			  struct page *page)
  {

  	if (fscache_cookie_valid(cookie))
  		__fscache_uncache_page(cookie, page);

  }
  
  /**
   * fscache_check_page_write - Ask if a page is being writing to the cache
   * @cookie: The cookie representing the cache object
   * @page: The netfs page that is being cached.
   *
   * Ask the cache if a page is being written to the cache.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  bool fscache_check_page_write(struct fscache_cookie *cookie,
  			      struct page *page)
  {

  	if (fscache_cookie_valid(cookie))
  		return __fscache_check_page_write(cookie, page);

  	return false;
  }
  
  /**
   * fscache_wait_on_page_write - Wait for a page to complete writing to the cache
   * @cookie: The cookie representing the cache object
   * @page: The netfs page that is being cached.
   *
   * Ask the cache to wake us up when a page is no longer being written to the
   * cache.
   *
   * See Documentation/filesystems/caching/netfs-api.txt for a complete
   * description.
   */
  static inline
  void fscache_wait_on_page_write(struct fscache_cookie *cookie,
  				struct page *page)
  {

  	if (fscache_cookie_valid(cookie))
  		__fscache_wait_on_page_write(cookie, page);

  }

  /**
   * fscache_maybe_release_page - Consider releasing a page, cancelling a store
   * @cookie: The cookie representing the cache object
   * @page: The netfs page that is being cached.
   * @gfp: The gfp flags passed to releasepage()
   *
   * Consider releasing a page for the vmscan algorithm, on behalf of the netfs's
   * releasepage() call.  A storage request on the page may cancelled if it is
   * not currently being processed.
   *
   * The function returns true if the page no longer has a storage request on it,
   * and false if a storage request is left in place.  If true is returned, the
   * page will have been passed to fscache_uncache_page().  If false is returned
   * the page cannot be freed yet.
   */
  static inline
  bool fscache_maybe_release_page(struct fscache_cookie *cookie,
  				struct page *page,
  				gfp_t gfp)
  {
  	if (fscache_cookie_valid(cookie) && PageFsCache(page))
  		return __fscache_maybe_release_page(cookie, page, gfp);
  	return false;
  }

  /**
   * fscache_uncache_all_inode_pages - Uncache all an inode's pages
   * @cookie: The cookie representing the inode's cache object.
   * @inode: The inode to uncache pages from.
   *
   * Uncache all the pages in an inode that are marked PG_fscache, assuming them
   * to be associated with the given cookie.
   *
   * This function may sleep.  It will wait for pages that are being written out
   * and will wait whilst the PG_fscache mark is removed by the cache.
   */
  static inline
  void fscache_uncache_all_inode_pages(struct fscache_cookie *cookie,
  				     struct inode *inode)
  {
  	if (fscache_cookie_valid(cookie))
  		__fscache_uncache_all_inode_pages(cookie, inode);
  }

  /**
   * fscache_disable_cookie - Disable a cookie
   * @cookie: The cookie representing the cache object
   * @invalidate: Invalidate the backing object
   *
   * Disable a cookie from accepting further alloc, read, write, invalidate,
   * update or acquire operations.  Outstanding operations can still be waited
   * upon and pages can still be uncached and the cookie relinquished.
   *
   * This will not return until all outstanding operations have completed.
   *
   * If @invalidate is set, then the backing object will be invalidated and
   * detached, otherwise it will just be detached.
   */
  static inline
  void fscache_disable_cookie(struct fscache_cookie *cookie, bool invalidate)
  {
  	if (fscache_cookie_valid(cookie) && fscache_cookie_enabled(cookie))
  		__fscache_disable_cookie(cookie, invalidate);
  }
  
  /**
   * fscache_enable_cookie - Reenable a cookie
   * @cookie: The cookie representing the cache object
   * @can_enable: A function to permit enablement once lock is held
   * @data: Data for can_enable()
   *
   * Reenable a previously disabled cookie, allowing it to accept further alloc,
   * read, write, invalidate, update or acquire operations.  An attempt will be
   * made to immediately reattach the cookie to a backing object.
   *
   * The can_enable() function is called (if not NULL) once the enablement lock
   * is held to rule on whether enablement is still permitted to go ahead.
   */
  static inline
  void fscache_enable_cookie(struct fscache_cookie *cookie,
  			   bool (*can_enable)(void *data),
  			   void *data)
  {
  	if (fscache_cookie_valid(cookie) && !fscache_cookie_enabled(cookie))
  		__fscache_enable_cookie(cookie, can_enable, data);
  }

  #endif /* _LINUX_FSCACHE_H */