/*
   * Functions related to io context handling
   */
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/bio.h>
  #include <linux/blkdev.h>

  #include <linux/slab.h>

  
  #include "blk.h"
  
  /*
   * For io context allocations
   */
  static struct kmem_cache *iocontext_cachep;

  /**
   * get_io_context - increment reference count to io_context
   * @ioc: io_context to get
   *
   * Increment reference count to @ioc.
   */
  void get_io_context(struct io_context *ioc)
  {
  	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
  	atomic_long_inc(&ioc->refcount);
  }
  EXPORT_SYMBOL(get_io_context);

  static void icq_free_icq_rcu(struct rcu_head *head)
  {
  	struct io_cq *icq = container_of(head, struct io_cq, __rcu_head);
  
  	kmem_cache_free(icq->__rcu_icq_cache, icq);
  }

  /* Exit an icq. Called with both ioc and q locked. */

  static void ioc_exit_icq(struct io_cq *icq)
  {

  	struct elevator_type *et = icq->q->elevator->type;
  
  	if (icq->flags & ICQ_EXITED)
  		return;
  
  	if (et->ops.elevator_exit_icq_fn)
  		et->ops.elevator_exit_icq_fn(icq);
  
  	icq->flags |= ICQ_EXITED;
  }
  
  /* Release an icq.  Called with both ioc and q locked. */
  static void ioc_destroy_icq(struct io_cq *icq)
  {

  	struct io_context *ioc = icq->ioc;
  	struct request_queue *q = icq->q;
  	struct elevator_type *et = q->elevator->type;
  
  	lockdep_assert_held(&ioc->lock);
  	lockdep_assert_held(q->queue_lock);
  
  	radix_tree_delete(&ioc->icq_tree, icq->q->id);
  	hlist_del_init(&icq->ioc_node);
  	list_del_init(&icq->q_node);
  
  	/*
  	 * Both setting lookup hint to and clearing it from @icq are done
  	 * under queue_lock.  If it's not pointing to @icq now, it never
  	 * will.  Hint assignment itself can race safely.
  	 */

  	if (rcu_access_pointer(ioc->icq_hint) == icq)

  		rcu_assign_pointer(ioc->icq_hint, NULL);

  	ioc_exit_icq(icq);

  
  	/*
  	 * @icq->q might have gone away by the time RCU callback runs
  	 * making it impossible to determine icq_cache.  Record it in @icq.
  	 */
  	icq->__rcu_icq_cache = et->icq_cache;
  	call_rcu(&icq->__rcu_head, icq_free_icq_rcu);
  }

  /*
   * Slow path for ioc release in put_io_context().  Performs double-lock

   * dancing to unlink all icq's and then frees ioc.

   */
  static void ioc_release_fn(struct work_struct *work)

  {

  	struct io_context *ioc = container_of(work, struct io_context,
  					      release_work);

  	unsigned long flags;

  	/*
  	 * Exiting icq may call into put_io_context() through elevator
  	 * which will trigger lockdep warning.  The ioc's are guaranteed to
  	 * be different, use a different locking subclass here.  Use
  	 * irqsave variant as there's no spin_lock_irq_nested().
  	 */
  	spin_lock_irqsave_nested(&ioc->lock, flags, 1);

  	while (!hlist_empty(&ioc->icq_list)) {
  		struct io_cq *icq = hlist_entry(ioc->icq_list.first,
  						struct io_cq, ioc_node);

  		struct request_queue *q = icq->q;
  
  		if (spin_trylock(q->queue_lock)) {

  			ioc_destroy_icq(icq);

  			spin_unlock(q->queue_lock);
  		} else {
  			spin_unlock_irqrestore(&ioc->lock, flags);
  			cpu_relax();
  			spin_lock_irqsave_nested(&ioc->lock, flags, 1);

  		}

  	}

  	spin_unlock_irqrestore(&ioc->lock, flags);

  
  	kmem_cache_free(iocontext_cachep, ioc);

  }

  /**
   * put_io_context - put a reference of io_context
   * @ioc: io_context to put
   *
   * Decrement reference count of @ioc and release it if the count reaches

   * zero.

   */

  void put_io_context(struct io_context *ioc)

  {

  	unsigned long flags;

  	bool free_ioc = false;

  	if (ioc == NULL)

  		return;

  	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);

  	/*

  	 * Releasing ioc requires reverse order double locking and we may
  	 * already be holding a queue_lock.  Do it asynchronously from wq.

  	 */

  	if (atomic_long_dec_and_test(&ioc->refcount)) {
  		spin_lock_irqsave(&ioc->lock, flags);
  		if (!hlist_empty(&ioc->icq_list))

  			queue_work(system_power_efficient_wq,
  					&ioc->release_work);

  		else
  			free_ioc = true;

  		spin_unlock_irqrestore(&ioc->lock, flags);

  	}

  
  	if (free_ioc)
  		kmem_cache_free(iocontext_cachep, ioc);

  }

  EXPORT_SYMBOL(put_io_context);

  /**
   * put_io_context_active - put active reference on ioc
   * @ioc: ioc of interest
   *
   * Undo get_io_context_active().  If active reference reaches zero after
   * put, @ioc can never issue further IOs and ioscheds are notified.
   */
  void put_io_context_active(struct io_context *ioc)

  {

  	unsigned long flags;

  	struct io_cq *icq;

  	if (!atomic_dec_and_test(&ioc->active_ref)) {

  		put_io_context(ioc);
  		return;
  	}
  
  	/*
  	 * Need ioc lock to walk icq_list and q lock to exit icq.  Perform
  	 * reverse double locking.  Read comment in ioc_release_fn() for
  	 * explanation on the nested locking annotation.
  	 */
  retry:
  	spin_lock_irqsave_nested(&ioc->lock, flags, 1);

  	hlist_for_each_entry(icq, &ioc->icq_list, ioc_node) {

  		if (icq->flags & ICQ_EXITED)
  			continue;
  		if (spin_trylock(icq->q->queue_lock)) {
  			ioc_exit_icq(icq);
  			spin_unlock(icq->q->queue_lock);
  		} else {
  			spin_unlock_irqrestore(&ioc->lock, flags);
  			cpu_relax();
  			goto retry;
  		}
  	}
  	spin_unlock_irqrestore(&ioc->lock, flags);

  	put_io_context(ioc);

  }

  /* Called by the exiting task */
  void exit_io_context(struct task_struct *task)
  {
  	struct io_context *ioc;
  
  	task_lock(task);
  	ioc = task->io_context;
  	task->io_context = NULL;
  	task_unlock(task);
  
  	atomic_dec(&ioc->nr_tasks);
  	put_io_context_active(ioc);
  }

  /**
   * ioc_clear_queue - break any ioc association with the specified queue
   * @q: request_queue being cleared
   *
   * Walk @q->icq_list and exit all io_cq's.  Must be called with @q locked.
   */
  void ioc_clear_queue(struct request_queue *q)
  {
  	lockdep_assert_held(q->queue_lock);
  
  	while (!list_empty(&q->icq_list)) {
  		struct io_cq *icq = list_entry(q->icq_list.next,
  					       struct io_cq, q_node);
  		struct io_context *ioc = icq->ioc;
  
  		spin_lock(&ioc->lock);

  		ioc_destroy_icq(icq);

  		spin_unlock(&ioc->lock);
  	}
  }

  int create_task_io_context(struct task_struct *task, gfp_t gfp_flags, int node)

  {

  	struct io_context *ioc;

  	int ret;

  	ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
  				    node);
  	if (unlikely(!ioc))

  		return -ENOMEM;

  
  	/* initialize */
  	atomic_long_set(&ioc->refcount, 1);

  	atomic_set(&ioc->nr_tasks, 1);

  	atomic_set(&ioc->active_ref, 1);

  	spin_lock_init(&ioc->lock);

  	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC | __GFP_HIGH);
  	INIT_HLIST_HEAD(&ioc->icq_list);

  	INIT_WORK(&ioc->release_work, ioc_release_fn);

  	/*
  	 * Try to install.  ioc shouldn't be installed if someone else
  	 * already did or @task, which isn't %current, is exiting.  Note
  	 * that we need to allow ioc creation on exiting %current as exit
  	 * path may issue IOs from e.g. exit_files().  The exit path is
  	 * responsible for not issuing IO after exit_io_context().
  	 */

  	task_lock(task);

  	if (!task->io_context &&
  	    (task == current || !(task->flags & PF_EXITING)))

  		task->io_context = ioc;

  	else

  		kmem_cache_free(iocontext_cachep, ioc);

  
  	ret = task->io_context ? 0 : -EBUSY;

  	task_unlock(task);

  	return ret;

  }

  /**
   * get_task_io_context - get io_context of a task
   * @task: task of interest
   * @gfp_flags: allocation flags, used if allocation is necessary
   * @node: allocation node, used if allocation is necessary
   *
   * Return io_context of @task.  If it doesn't exist, it is created with
   * @gfp_flags and @node.  The returned io_context has its reference count
   * incremented.

   *

   * This function always goes through task_lock() and it's better to use

   * %current->io_context + get_io_context() for %current.

   */

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

  {

  	struct io_context *ioc;

  	might_sleep_if(gfpflags_allow_blocking(gfp_flags));

  	do {
  		task_lock(task);
  		ioc = task->io_context;
  		if (likely(ioc)) {
  			get_io_context(ioc);
  			task_unlock(task);
  			return ioc;
  		}

  		task_unlock(task);

  	} while (!create_task_io_context(task, gfp_flags, node));

  	return NULL;

  }

  EXPORT_SYMBOL(get_task_io_context);

  /**
   * ioc_lookup_icq - lookup io_cq from ioc
   * @ioc: the associated io_context
   * @q: the associated request_queue
   *
   * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
   * with @q->queue_lock held.
   */
  struct io_cq *ioc_lookup_icq(struct io_context *ioc, struct request_queue *q)
  {
  	struct io_cq *icq;
  
  	lockdep_assert_held(q->queue_lock);
  
  	/*
  	 * icq's are indexed from @ioc using radix tree and hint pointer,
  	 * both of which are protected with RCU.  All removals are done
  	 * holding both q and ioc locks, and we're holding q lock - if we
  	 * find a icq which points to us, it's guaranteed to be valid.
  	 */
  	rcu_read_lock();
  	icq = rcu_dereference(ioc->icq_hint);
  	if (icq && icq->q == q)
  		goto out;
  
  	icq = radix_tree_lookup(&ioc->icq_tree, q->id);
  	if (icq && icq->q == q)
  		rcu_assign_pointer(ioc->icq_hint, icq);	/* allowed to race */
  	else
  		icq = NULL;
  out:
  	rcu_read_unlock();
  	return icq;
  }
  EXPORT_SYMBOL(ioc_lookup_icq);

  /**
   * ioc_create_icq - create and link io_cq

   * @ioc: io_context of interest

   * @q: request_queue of interest
   * @gfp_mask: allocation mask
   *

   * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
   * will be created using @gfp_mask.

   *
   * The caller is responsible for ensuring @ioc won't go away and @q is
   * alive and will stay alive until this function returns.
   */

  struct io_cq *ioc_create_icq(struct io_context *ioc, struct request_queue *q,
  			     gfp_t gfp_mask)

  {
  	struct elevator_type *et = q->elevator->type;

  	struct io_cq *icq;
  
  	/* allocate stuff */

  	icq = kmem_cache_alloc_node(et->icq_cache, gfp_mask | __GFP_ZERO,
  				    q->node);
  	if (!icq)
  		return NULL;

  	if (radix_tree_maybe_preload(gfp_mask) < 0) {

  		kmem_cache_free(et->icq_cache, icq);
  		return NULL;
  	}
  
  	icq->ioc = ioc;
  	icq->q = q;
  	INIT_LIST_HEAD(&icq->q_node);
  	INIT_HLIST_NODE(&icq->ioc_node);
  
  	/* lock both q and ioc and try to link @icq */
  	spin_lock_irq(q->queue_lock);
  	spin_lock(&ioc->lock);
  
  	if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
  		hlist_add_head(&icq->ioc_node, &ioc->icq_list);
  		list_add(&icq->q_node, &q->icq_list);
  		if (et->ops.elevator_init_icq_fn)
  			et->ops.elevator_init_icq_fn(icq);
  	} else {
  		kmem_cache_free(et->icq_cache, icq);
  		icq = ioc_lookup_icq(ioc, q);
  		if (!icq)
  			printk(KERN_ERR "cfq: icq link failed!
  ");
  	}
  
  	spin_unlock(&ioc->lock);
  	spin_unlock_irq(q->queue_lock);
  	radix_tree_preload_end();
  	return icq;
  }

  static int __init blk_ioc_init(void)

  {
  	iocontext_cachep = kmem_cache_create("blkdev_ioc",
  			sizeof(struct io_context), 0, SLAB_PANIC, NULL);
  	return 0;
  }
  subsys_initcall(blk_ioc_init);