#ifndef IOCONTEXT_H
  #define IOCONTEXT_H

  #include <linux/radix-tree.h>

  #include <linux/rcupdate.h>

  #include <linux/workqueue.h>

  enum {

  	ICQ_IOPRIO_CHANGED,
  	ICQ_CGROUP_CHANGED,

  };

  /*
   * An io_cq (icq) is association between an io_context (ioc) and a
   * request_queue (q).  This is used by elevators which need to track
   * information per ioc - q pair.
   *
   * Elevator can request use of icq by setting elevator_type->icq_size and
   * ->icq_align.  Both size and align must be larger than that of struct
   * io_cq and elevator can use the tail area for private information.  The
   * recommended way to do this is defining a struct which contains io_cq as
   * the first member followed by private members and using its size and
   * align.  For example,
   *
   *	struct snail_io_cq {
   *		struct io_cq	icq;
   *		int		poke_snail;
   *		int		feed_snail;
   *	};
   *
   *	struct elevator_type snail_elv_type {
   *		.ops =		{ ... },
   *		.icq_size =	sizeof(struct snail_io_cq),
   *		.icq_align =	__alignof__(struct snail_io_cq),
   *		...
   *	};
   *
   * If icq_size is set, block core will manage icq's.  All requests will
   * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
   * is called and be holding a reference to the associated io_context.
   *
   * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
   * called and, on destruction, ->elevator_exit_icq_fn().  Both functions
   * are called with both the associated io_context and queue locks held.
   *
   * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
   * queue lock but the returned icq is valid only until the queue lock is
   * released.  Elevators can not and should not try to create or destroy
   * icq's.
   *
   * As icq's are linked from both ioc and q, the locking rules are a bit
   * complex.
   *
   * - ioc lock nests inside q lock.
   *
   * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
   *   q->icq_list and icq->q_node by q lock.
   *
   * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
   *   itself is protected by q lock.  However, both the indexes and icq
   *   itself are also RCU managed and lookup can be performed holding only
   *   the q lock.
   *
   * - icq's are not reference counted.  They are destroyed when either the
   *   ioc or q goes away.  Each request with icq set holds an extra
   *   reference to ioc to ensure it stays until the request is completed.
   *
   * - Linking and unlinking icq's are performed while holding both ioc and q
   *   locks.  Due to the lock ordering, q exit is simple but ioc exit
   *   requires reverse-order double lock dance.
   */

  struct io_cq {
  	struct request_queue	*q;
  	struct io_context	*ioc;

  	/*
  	 * q_node and ioc_node link io_cq through icq_list of q and ioc
  	 * respectively.  Both fields are unused once ioc_exit_icq() is
  	 * called and shared with __rcu_icq_cache and __rcu_head which are
  	 * used for RCU free of io_cq.
  	 */
  	union {
  		struct list_head	q_node;
  		struct kmem_cache	*__rcu_icq_cache;
  	};
  	union {
  		struct hlist_node	ioc_node;
  		struct rcu_head		__rcu_head;
  	};

  	unsigned long		changed;

  };
  
  /*

   * I/O subsystem state of the associated processes.  It is refcounted
   * and kmalloc'ed. These could be shared between processes.

   */
  struct io_context {

  	atomic_long_t refcount;

  	atomic_t nr_tasks;
  
  	/* all the fields below are protected by this lock */
  	spinlock_t lock;

  
  	unsigned short ioprio;

  	/*
  	 * For request batching
  	 */

  	int nr_batch_requests;     /* Number of requests left in the batch */

  	unsigned long last_waited; /* Time last woken after wait for request */

  	struct radix_tree_root	icq_tree;
  	struct io_cq __rcu	*icq_hint;
  	struct hlist_head	icq_list;

  
  	struct work_struct release_work;

  };

  static inline struct io_context *ioc_task_link(struct io_context *ioc)
  {
  	/*
  	 * if ref count is zero, don't allow sharing (ioc is going away, it's
  	 * a race).
  	 */

  	if (ioc && atomic_long_inc_not_zero(&ioc->refcount)) {

  		atomic_inc(&ioc->nr_tasks);

  		return ioc;

  	}

  
  	return NULL;
  }

  struct task_struct;

  #ifdef CONFIG_BLOCK

  void put_io_context(struct io_context *ioc, struct request_queue *locked_q);

  void exit_io_context(struct task_struct *task);

  struct io_context *get_task_io_context(struct task_struct *task,
  				       gfp_t gfp_flags, int node);

  void ioc_ioprio_changed(struct io_context *ioc, int ioprio);
  void ioc_cgroup_changed(struct io_context *ioc);

  #else

  struct io_context;

  static inline void put_io_context(struct io_context *ioc,
  				  struct request_queue *locked_q) { }

  static inline void exit_io_context(struct task_struct *task) { }

  #endif

  #endif