/*
   * 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/bootmem.h>	/* for max_pfn/max_low_pfn */

  #include <linux/slab.h>

  
  #include "blk.h"
  
  /*
   * For io context allocations
   */
  static struct kmem_cache *iocontext_cachep;
  
  static void cfq_dtor(struct io_context *ioc)
  {

  	if (!hlist_empty(&ioc->cic_list)) {
  		struct cfq_io_context *cic;
  
  		cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
  								cic_list);
  		cic->dtor(ioc);
  	}

  }
  
  /*
   * IO Context helper functions. put_io_context() returns 1 if there are no
   * more users of this io context, 0 otherwise.
   */
  int put_io_context(struct io_context *ioc)
  {
  	if (ioc == NULL)
  		return 1;

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

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

  		rcu_read_lock();

  		cfq_dtor(ioc);

  		rcu_read_unlock();

  
  		kmem_cache_free(iocontext_cachep, ioc);
  		return 1;
  	}
  	return 0;
  }
  EXPORT_SYMBOL(put_io_context);
  
  static void cfq_exit(struct io_context *ioc)
  {

  	rcu_read_lock();

  	if (!hlist_empty(&ioc->cic_list)) {
  		struct cfq_io_context *cic;
  
  		cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
  								cic_list);
  		cic->exit(ioc);
  	}
  	rcu_read_unlock();

  }
  
  /* Called by the exitting 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);

  
  	if (atomic_dec_and_test(&ioc->nr_tasks)) {

  		cfq_exit(ioc);

  	}

  	put_io_context(ioc);

  }
  
  struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
  {
  	struct io_context *ret;
  
  	ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
  	if (ret) {

  		atomic_long_set(&ret->refcount, 1);

  		atomic_set(&ret->nr_tasks, 1);
  		spin_lock_init(&ret->lock);
  		ret->ioprio_changed = 0;
  		ret->ioprio = 0;

  		ret->last_waited = 0; /* doesn't matter... */

  		ret->nr_batch_requests = 0; /* because this is 0 */

  		INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH);

  		INIT_HLIST_HEAD(&ret->cic_list);

  		ret->ioc_data = NULL;
  	}
  
  	return ret;
  }
  
  /*
   * If the current task has no IO context then create one and initialise it.
   * Otherwise, return its existing IO context.
   *
   * This returned IO context doesn't have a specifically elevated refcount,
   * but since the current task itself holds a reference, the context can be
   * used in general code, so long as it stays within `current` context.
   */
  struct io_context *current_io_context(gfp_t gfp_flags, int node)
  {
  	struct task_struct *tsk = current;
  	struct io_context *ret;
  
  	ret = tsk->io_context;
  	if (likely(ret))
  		return ret;
  
  	ret = alloc_io_context(gfp_flags, node);
  	if (ret) {
  		/* make sure set_task_ioprio() sees the settings above */
  		smp_wmb();
  		tsk->io_context = ret;
  	}
  
  	return ret;
  }
  
  /*
   * If the current task has no IO context then create one and initialise it.
   * If it does have a context, take a ref on it.
   *
   * This is always called in the context of the task which submitted the I/O.
   */
  struct io_context *get_io_context(gfp_t gfp_flags, int node)
  {
  	struct io_context *ret = NULL;
  
  	/*
  	 * Check for unlikely race with exiting task. ioc ref count is
  	 * zero when ioc is being detached.
  	 */
  	do {
  		ret = current_io_context(gfp_flags, node);
  		if (unlikely(!ret))
  			break;

  	} while (!atomic_long_inc_not_zero(&ret->refcount));

  
  	return ret;
  }
  EXPORT_SYMBOL(get_io_context);
  
  void copy_io_context(struct io_context **pdst, struct io_context **psrc)
  {
  	struct io_context *src = *psrc;
  	struct io_context *dst = *pdst;
  
  	if (src) {

  		BUG_ON(atomic_long_read(&src->refcount) == 0);
  		atomic_long_inc(&src->refcount);

  		put_io_context(dst);
  		*pdst = src;
  	}
  }
  EXPORT_SYMBOL(copy_io_context);

  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);