/* General filesystem caching backing cache 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/backend-api.txt
   *
   * for a description of the cache backend interface declared here.
   */
  
  #ifndef _LINUX_FSCACHE_CACHE_H
  #define _LINUX_FSCACHE_CACHE_H
  
  #include <linux/fscache.h>
  #include <linux/sched.h>
  #include <linux/workqueue.h>
  
  #define NR_MAXCACHES BITS_PER_LONG
  
  struct fscache_cache;
  struct fscache_cache_ops;
  struct fscache_object;
  struct fscache_operation;
  
  /*
   * cache tag definition
   */
  struct fscache_cache_tag {
  	struct list_head	link;
  	struct fscache_cache	*cache;		/* cache referred to by this tag */
  	unsigned long		flags;
  #define FSCACHE_TAG_RESERVED	0		/* T if tag is reserved for a cache */
  	atomic_t		usage;
  	char			name[0];	/* tag name */
  };
  
  /*
   * cache definition
   */
  struct fscache_cache {
  	const struct fscache_cache_ops *ops;
  	struct fscache_cache_tag *tag;		/* tag representing this cache */
  	struct kobject		*kobj;		/* system representation of this cache */
  	struct list_head	link;		/* link in list of caches */
  	size_t			max_index_size;	/* maximum size of index data */
  	char			identifier[36];	/* cache label */
  
  	/* node management */
  	struct work_struct	op_gc;		/* operation garbage collector */
  	struct list_head	object_list;	/* list of data/index objects */
  	struct list_head	op_gc_list;	/* list of ops to be deleted */
  	spinlock_t		object_list_lock;
  	spinlock_t		op_gc_list_lock;
  	atomic_t		object_count;	/* no. of live objects in this cache */
  	struct fscache_object	*fsdef;		/* object for the fsdef index */
  	unsigned long		flags;
  #define FSCACHE_IOERROR		0	/* cache stopped on I/O error */
  #define FSCACHE_CACHE_WITHDRAWN	1	/* cache has been withdrawn */
  };
  
  extern wait_queue_head_t fscache_cache_cleared_wq;
  
  /*
   * operation to be applied to a cache object
   * - retrieval initiation operations are done in the context of the process
   *   that issued them, and not in an async thread pool
   */
  typedef void (*fscache_operation_release_t)(struct fscache_operation *op);
  typedef void (*fscache_operation_processor_t)(struct fscache_operation *op);
  
  enum fscache_operation_state {
  	FSCACHE_OP_ST_BLANK,		/* Op is not yet submitted */
  	FSCACHE_OP_ST_INITIALISED,	/* Op is initialised */
  	FSCACHE_OP_ST_PENDING,		/* Op is blocked from running */
  	FSCACHE_OP_ST_IN_PROGRESS,	/* Op is in progress */
  	FSCACHE_OP_ST_COMPLETE,		/* Op is complete */
  	FSCACHE_OP_ST_CANCELLED,	/* Op has been cancelled */
  	FSCACHE_OP_ST_DEAD		/* Op is now dead */
  };
  
  struct fscache_operation {
  	struct work_struct	work;		/* record for async ops */
  	struct list_head	pend_link;	/* link in object->pending_ops */
  	struct fscache_object	*object;	/* object to be operated upon */
  
  	unsigned long		flags;
  #define FSCACHE_OP_TYPE		0x000f	/* operation type */
  #define FSCACHE_OP_ASYNC	0x0001	/* - async op, processor may sleep for disk */
  #define FSCACHE_OP_MYTHREAD	0x0002	/* - processing is done be issuing thread, not pool */
  #define FSCACHE_OP_WAITING	4	/* cleared when op is woken */
  #define FSCACHE_OP_EXCLUSIVE	5	/* exclusive op, other ops must wait */
  #define FSCACHE_OP_DEC_READ_CNT	6	/* decrement object->n_reads on destruction */
  #define FSCACHE_OP_UNUSE_COOKIE	7	/* call fscache_unuse_cookie() on completion */
  #define FSCACHE_OP_KEEP_FLAGS	0x00f0	/* flags to keep when repurposing an op */
  
  	enum fscache_operation_state state;
  	atomic_t		usage;
  	unsigned		debug_id;	/* debugging ID */
  
  	/* operation processor callback
  	 * - can be NULL if FSCACHE_OP_WAITING is going to be used to perform
  	 *   the op in a non-pool thread */
  	fscache_operation_processor_t processor;
  
  	/* operation releaser */
  	fscache_operation_release_t release;
  };
  
  extern atomic_t fscache_op_debug_id;
  extern void fscache_op_work_func(struct work_struct *work);
  
  extern void fscache_enqueue_operation(struct fscache_operation *);
  extern void fscache_op_complete(struct fscache_operation *, bool);
  extern void fscache_put_operation(struct fscache_operation *);
  
  /**
   * fscache_operation_init - Do basic initialisation of an operation
   * @op: The operation to initialise
   * @release: The release function to assign
   *
   * Do basic initialisation of an operation.  The caller must still set flags,
   * object and processor if needed.
   */
  static inline void fscache_operation_init(struct fscache_operation *op,
  					fscache_operation_processor_t processor,
  					fscache_operation_release_t release)
  {
  	INIT_WORK(&op->work, fscache_op_work_func);
  	atomic_set(&op->usage, 1);
  	op->state = FSCACHE_OP_ST_INITIALISED;
  	op->debug_id = atomic_inc_return(&fscache_op_debug_id);
  	op->processor = processor;
  	op->release = release;
  	INIT_LIST_HEAD(&op->pend_link);
  }
  
  /*
   * data read operation
   */
  struct fscache_retrieval {
  	struct fscache_operation op;
  	struct address_space	*mapping;	/* netfs pages */
  	fscache_rw_complete_t	end_io_func;	/* function to call on I/O completion */
  	void			*context;	/* netfs read context (pinned) */
  	struct list_head	to_do;		/* list of things to be done by the backend */
  	unsigned long		start_time;	/* time at which retrieval started */
  	atomic_t		n_pages;	/* number of pages to be retrieved */
  };
  
  typedef int (*fscache_page_retrieval_func_t)(struct fscache_retrieval *op,
  					     struct page *page,
  					     gfp_t gfp);
  
  typedef int (*fscache_pages_retrieval_func_t)(struct fscache_retrieval *op,
  					      struct list_head *pages,
  					      unsigned *nr_pages,
  					      gfp_t gfp);
  
  /**
   * fscache_get_retrieval - Get an extra reference on a retrieval operation
   * @op: The retrieval operation to get a reference on
   *
   * Get an extra reference on a retrieval operation.
   */
  static inline
  struct fscache_retrieval *fscache_get_retrieval(struct fscache_retrieval *op)
  {
  	atomic_inc(&op->op.usage);
  	return op;
  }
  
  /**
   * fscache_enqueue_retrieval - Enqueue a retrieval operation for processing
   * @op: The retrieval operation affected
   *
   * Enqueue a retrieval operation for processing by the FS-Cache thread pool.
   */
  static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
  {
  	fscache_enqueue_operation(&op->op);
  }
  
  /**
   * fscache_retrieval_complete - Record (partial) completion of a retrieval
   * @op: The retrieval operation affected
   * @n_pages: The number of pages to account for
   */
  static inline void fscache_retrieval_complete(struct fscache_retrieval *op,
  					      int n_pages)
  {
  	atomic_sub(n_pages, &op->n_pages);
  	if (atomic_read(&op->n_pages) <= 0)
  		fscache_op_complete(&op->op, true);
  }
  
  /**
   * fscache_put_retrieval - Drop a reference to a retrieval operation
   * @op: The retrieval operation affected
   *
   * Drop a reference to a retrieval operation.
   */
  static inline void fscache_put_retrieval(struct fscache_retrieval *op)
  {
  	fscache_put_operation(&op->op);
  }
  
  /*
   * cached page storage work item
   * - used to do three things:
   *   - batch writes to the cache
   *   - do cache writes asynchronously
   *   - defer writes until cache object lookup completion
   */
  struct fscache_storage {
  	struct fscache_operation op;
  	pgoff_t			store_limit;	/* don't write more than this */
  };
  
  /*
   * cache operations
   */
  struct fscache_cache_ops {
  	/* name of cache provider */
  	const char *name;
  
  	/* allocate an object record for a cookie */
  	struct fscache_object *(*alloc_object)(struct fscache_cache *cache,
  					       struct fscache_cookie *cookie);
  
  	/* look up the object for a cookie
  	 * - return -ETIMEDOUT to be requeued
  	 */
  	int (*lookup_object)(struct fscache_object *object);
  
  	/* finished looking up */
  	void (*lookup_complete)(struct fscache_object *object);
  
  	/* increment the usage count on this object (may fail if unmounting) */
  	struct fscache_object *(*grab_object)(struct fscache_object *object);
  
  	/* pin an object in the cache */
  	int (*pin_object)(struct fscache_object *object);
  
  	/* unpin an object in the cache */
  	void (*unpin_object)(struct fscache_object *object);
  
  	/* check the consistency between the backing cache and the FS-Cache
  	 * cookie */
  	bool (*check_consistency)(struct fscache_operation *op);
  
  	/* store the updated auxiliary data on an object */
  	void (*update_object)(struct fscache_object *object);
  
  	/* Invalidate an object */
  	void (*invalidate_object)(struct fscache_operation *op);
  
  	/* discard the resources pinned by an object and effect retirement if
  	 * necessary */
  	void (*drop_object)(struct fscache_object *object);
  
  	/* dispose of a reference to an object */
  	void (*put_object)(struct fscache_object *object);
  
  	/* sync a cache */
  	void (*sync_cache)(struct fscache_cache *cache);
  
  	/* notification that the attributes of a non-index object (such as
  	 * i_size) have changed */
  	int (*attr_changed)(struct fscache_object *object);
  
  	/* reserve space for an object's data and associated metadata */
  	int (*reserve_space)(struct fscache_object *object, loff_t i_size);
  
  	/* request a backing block for a page be read or allocated in the
  	 * cache */
  	fscache_page_retrieval_func_t read_or_alloc_page;
  
  	/* request backing blocks for a list of pages be read or allocated in
  	 * the cache */
  	fscache_pages_retrieval_func_t read_or_alloc_pages;
  
  	/* request a backing block for a page be allocated in the cache so that
  	 * it can be written directly */
  	fscache_page_retrieval_func_t allocate_page;
  
  	/* request backing blocks for pages be allocated in the cache so that
  	 * they can be written directly */
  	fscache_pages_retrieval_func_t allocate_pages;
  
  	/* write a page to its backing block in the cache */
  	int (*write_page)(struct fscache_storage *op, struct page *page);
  
  	/* detach backing block from a page (optional)
  	 * - must release the cookie lock before returning
  	 * - may sleep
  	 */
  	void (*uncache_page)(struct fscache_object *object,
  			     struct page *page);
  
  	/* dissociate a cache from all the pages it was backing */
  	void (*dissociate_pages)(struct fscache_cache *cache);
  };
  
  extern struct fscache_cookie fscache_fsdef_index;
  
  /*
   * Event list for fscache_object::{event_mask,events}
   */
  enum {
  	FSCACHE_OBJECT_EV_NEW_CHILD,	/* T if object has a new child */
  	FSCACHE_OBJECT_EV_PARENT_READY,	/* T if object's parent is ready */
  	FSCACHE_OBJECT_EV_UPDATE,	/* T if object should be updated */
  	FSCACHE_OBJECT_EV_INVALIDATE,	/* T if cache requested object invalidation */
  	FSCACHE_OBJECT_EV_CLEARED,	/* T if accessors all gone */
  	FSCACHE_OBJECT_EV_ERROR,	/* T if fatal error occurred during processing */
  	FSCACHE_OBJECT_EV_KILL,		/* T if netfs relinquished or cache withdrew object */
  	NR_FSCACHE_OBJECT_EVENTS
  };
  
  #define FSCACHE_OBJECT_EVENTS_MASK ((1UL << NR_FSCACHE_OBJECT_EVENTS) - 1)
  
  /*
   * States for object state machine.
   */
  struct fscache_transition {
  	unsigned long events;
  	const struct fscache_state *transit_to;
  };
  
  struct fscache_state {
  	char name[24];
  	char short_name[8];
  	const struct fscache_state *(*work)(struct fscache_object *object,
  					    int event);
  	const struct fscache_transition transitions[];
  };
  
  /*
   * on-disk cache file or index handle
   */
  struct fscache_object {
  	const struct fscache_state *state;	/* Object state machine state */
  	const struct fscache_transition *oob_table; /* OOB state transition table */
  	int			debug_id;	/* debugging ID */
  	int			n_children;	/* number of child objects */
  	int			n_ops;		/* number of extant ops on object */
  	int			n_obj_ops;	/* number of object ops outstanding on object */
  	int			n_in_progress;	/* number of ops in progress */
  	int			n_exclusive;	/* number of exclusive ops queued or in progress */
  	atomic_t		n_reads;	/* number of read ops in progress */
  	spinlock_t		lock;		/* state and operations lock */
  
  	unsigned long		lookup_jif;	/* time at which lookup started */
  	unsigned long		oob_event_mask;	/* OOB events this object is interested in */
  	unsigned long		event_mask;	/* events this object is interested in */
  	unsigned long		events;		/* events to be processed by this object
  						 * (order is important - using fls) */
  
  	unsigned long		flags;
  #define FSCACHE_OBJECT_LOCK		0	/* T if object is busy being processed */
  #define FSCACHE_OBJECT_PENDING_WRITE	1	/* T if object has pending write */
  #define FSCACHE_OBJECT_WAITING		2	/* T if object is waiting on its parent */
  #define FSCACHE_OBJECT_IS_LIVE		3	/* T if object is not withdrawn or relinquished */
  #define FSCACHE_OBJECT_IS_LOOKED_UP	4	/* T if object has been looked up */
  #define FSCACHE_OBJECT_IS_AVAILABLE	5	/* T if object has become active */
  #define FSCACHE_OBJECT_RETIRED		6	/* T if object was retired on relinquishment */
  
  	struct list_head	cache_link;	/* link in cache->object_list */
  	struct hlist_node	cookie_link;	/* link in cookie->backing_objects */
  	struct fscache_cache	*cache;		/* cache that supplied this object */
  	struct fscache_cookie	*cookie;	/* netfs's file/index object */
  	struct fscache_object	*parent;	/* parent object */
  	struct work_struct	work;		/* attention scheduling record */
  	struct list_head	dependents;	/* FIFO of dependent objects */
  	struct list_head	dep_link;	/* link in parent's dependents list */
  	struct list_head	pending_ops;	/* unstarted operations on this object */
  #ifdef CONFIG_FSCACHE_OBJECT_LIST
  	struct rb_node		objlist_link;	/* link in global object list */
  #endif
  	pgoff_t			store_limit;	/* current storage limit */
  	loff_t			store_limit_l;	/* current storage limit */
  };
  
  extern void fscache_object_init(struct fscache_object *, struct fscache_cookie *,
  				struct fscache_cache *);
  extern void fscache_object_destroy(struct fscache_object *);
  
  extern void fscache_object_lookup_negative(struct fscache_object *object);
  extern void fscache_obtained_object(struct fscache_object *object);
  
  static inline bool fscache_object_is_live(struct fscache_object *object)
  {
  	return test_bit(FSCACHE_OBJECT_IS_LIVE, &object->flags);
  }
  
  static inline bool fscache_object_is_dying(struct fscache_object *object)
  {
  	return !fscache_object_is_live(object);
  }
  
  static inline bool fscache_object_is_available(struct fscache_object *object)
  {
  	return test_bit(FSCACHE_OBJECT_IS_AVAILABLE, &object->flags);
  }
  
  static inline bool fscache_object_is_active(struct fscache_object *object)
  {
  	return fscache_object_is_available(object) &&
  		fscache_object_is_live(object) &&
  		!test_bit(FSCACHE_IOERROR, &object->cache->flags);
  }
  
  static inline bool fscache_object_is_dead(struct fscache_object *object)
  {
  	return fscache_object_is_dying(object) &&
  		test_bit(FSCACHE_IOERROR, &object->cache->flags);
  }
  
  /**
   * fscache_object_destroyed - Note destruction of an object in a cache
   * @cache: The cache from which the object came
   *
   * Note the destruction and deallocation of an object record in a cache.
   */
  static inline void fscache_object_destroyed(struct fscache_cache *cache)
  {
  	if (atomic_dec_and_test(&cache->object_count))
  		wake_up_all(&fscache_cache_cleared_wq);
  }
  
  /**
   * fscache_object_lookup_error - Note an object encountered an error
   * @object: The object on which the error was encountered
   *
   * Note that an object encountered a fatal error (usually an I/O error) and
   * that it should be withdrawn as soon as possible.
   */
  static inline void fscache_object_lookup_error(struct fscache_object *object)
  {
  	set_bit(FSCACHE_OBJECT_EV_ERROR, &object->events);
  }
  
  /**
   * fscache_set_store_limit - Set the maximum size to be stored in an object
   * @object: The object to set the maximum on
   * @i_size: The limit to set in bytes
   *
   * Set the maximum size an object is permitted to reach, implying the highest
   * byte that may be written.  Intended to be called by the attr_changed() op.
   *
   * See Documentation/filesystems/caching/backend-api.txt for a complete
   * description.
   */
  static inline
  void fscache_set_store_limit(struct fscache_object *object, loff_t i_size)
  {
  	object->store_limit_l = i_size;
  	object->store_limit = i_size >> PAGE_SHIFT;
  	if (i_size & ~PAGE_MASK)
  		object->store_limit++;
  }
  
  /**
   * fscache_end_io - End a retrieval operation on a page
   * @op: The FS-Cache operation covering the retrieval
   * @page: The page that was to be fetched
   * @error: The error code (0 if successful)
   *
   * Note the end of an operation to retrieve a page, as covered by a particular
   * operation record.
   */
  static inline void fscache_end_io(struct fscache_retrieval *op,
  				  struct page *page, int error)
  {
  	op->end_io_func(page, op->context, error);
  }
  
  static inline void __fscache_use_cookie(struct fscache_cookie *cookie)
  {
  	atomic_inc(&cookie->n_active);
  }
  
  /**
   * fscache_use_cookie - Request usage of cookie attached to an object
   * @object: Object description
   * 
   * Request usage of the cookie attached to an object.  NULL is returned if the
   * relinquishment had reduced the cookie usage count to 0.
   */
  static inline bool fscache_use_cookie(struct fscache_object *object)
  {
  	struct fscache_cookie *cookie = object->cookie;
  	return atomic_inc_not_zero(&cookie->n_active) != 0;
  }
  
  static inline bool __fscache_unuse_cookie(struct fscache_cookie *cookie)
  {
  	return atomic_dec_and_test(&cookie->n_active);
  }
  
  static inline void __fscache_wake_unused_cookie(struct fscache_cookie *cookie)
  {
  	wake_up_atomic_t(&cookie->n_active);
  }
  
  /**
   * fscache_unuse_cookie - Cease usage of cookie attached to an object
   * @object: Object description
   * 
   * Cease usage of the cookie attached to an object.  When the users count
   * reaches zero then the cookie relinquishment will be permitted to proceed.
   */
  static inline void fscache_unuse_cookie(struct fscache_object *object)
  {
  	struct fscache_cookie *cookie = object->cookie;
  	if (__fscache_unuse_cookie(cookie))
  		__fscache_wake_unused_cookie(cookie);
  }
  
  /*
   * out-of-line cache backend functions
   */
  extern __printf(3, 4)
  void fscache_init_cache(struct fscache_cache *cache,
  			const struct fscache_cache_ops *ops,
  			const char *idfmt, ...);
  
  extern int fscache_add_cache(struct fscache_cache *cache,
  			     struct fscache_object *fsdef,
  			     const char *tagname);
  extern void fscache_withdraw_cache(struct fscache_cache *cache);
  
  extern void fscache_io_error(struct fscache_cache *cache);
  
  extern void fscache_mark_page_cached(struct fscache_retrieval *op,
  				     struct page *page);
  
  extern void fscache_mark_pages_cached(struct fscache_retrieval *op,
  				      struct pagevec *pagevec);
  
  extern bool fscache_object_sleep_till_congested(signed long *timeoutp);
  
  extern enum fscache_checkaux fscache_check_aux(struct fscache_object *object,
  					       const void *data,
  					       uint16_t datalen);
  
  #endif /* _LINUX_FSCACHE_CACHE_H */