/*
   * Functions related to interrupt-poll handling in the block layer. This
   * is similar to NAPI for network devices.
   */
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/bio.h>
  #include <linux/blkdev.h>
  #include <linux/interrupt.h>
  #include <linux/cpu.h>
  #include <linux/blk-iopoll.h>
  #include <linux/delay.h>
  
  #include "blk.h"
  
  int blk_iopoll_enabled = 1;
  EXPORT_SYMBOL(blk_iopoll_enabled);
  
  static unsigned int blk_iopoll_budget __read_mostly = 256;
  
  static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
  
  /**
   * blk_iopoll_sched - Schedule a run of the iopoll handler
   * @iop:      The parent iopoll structure
   *
   * Description:
   *     Add this blk_iopoll structure to the pending poll list and trigger the
   *     raise of the blk iopoll softirq. The driver must already have gotten a
   *     successful return from blk_iopoll_sched_prep() before calling this.
   **/
  void blk_iopoll_sched(struct blk_iopoll *iop)
  {
  	unsigned long flags;
  
  	local_irq_save(flags);
  	list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
  	__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
  	local_irq_restore(flags);
  }
  EXPORT_SYMBOL(blk_iopoll_sched);
  
  /**
   * __blk_iopoll_complete - Mark this @iop as un-polled again
   * @iop:      The parent iopoll structure
   *
   * Description:
   *     See blk_iopoll_complete(). This function must be called with interrupts
   *     disabled.
   **/
  void __blk_iopoll_complete(struct blk_iopoll *iop)
  {
  	list_del(&iop->list);
  	smp_mb__before_clear_bit();
  	clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
  }
  EXPORT_SYMBOL(__blk_iopoll_complete);
  
  /**
   * blk_iopoll_complete - Mark this @iop as un-polled again
   * @iop:      The parent iopoll structure
   *
   * Description:
   *     If a driver consumes less than the assigned budget in its run of the
   *     iopoll handler, it'll end the polled mode by calling this function. The
   *     iopoll handler will not be invoked again before blk_iopoll_sched_prep()
   *     is called.
   **/
  void blk_iopoll_complete(struct blk_iopoll *iopoll)
  {
  	unsigned long flags;
  
  	local_irq_save(flags);
  	__blk_iopoll_complete(iopoll);
  	local_irq_restore(flags);
  }
  EXPORT_SYMBOL(blk_iopoll_complete);
  
  static void blk_iopoll_softirq(struct softirq_action *h)
  {
  	struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
  	int rearm = 0, budget = blk_iopoll_budget;
  	unsigned long start_time = jiffies;
  
  	local_irq_disable();
  
  	while (!list_empty(list)) {
  		struct blk_iopoll *iop;
  		int work, weight;
  
  		/*
  		 * If softirq window is exhausted then punt.
  		 */
  		if (budget <= 0 || time_after(jiffies, start_time)) {
  			rearm = 1;
  			break;
  		}
  
  		local_irq_enable();
  
  		/* Even though interrupts have been re-enabled, this
  		 * access is safe because interrupts can only add new
  		 * entries to the tail of this list, and only ->poll()
  		 * calls can remove this head entry from the list.
  		 */
  		iop = list_entry(list->next, struct blk_iopoll, list);
  
  		weight = iop->weight;
  		work = 0;
  		if (test_bit(IOPOLL_F_SCHED, &iop->state))
  			work = iop->poll(iop, weight);
  
  		budget -= work;
  
  		local_irq_disable();
  
  		/*
  		 * Drivers must not modify the iopoll state, if they
  		 * consume their assigned weight (or more, some drivers can't
  		 * easily just stop processing, they have to complete an
  		 * entire mask of commands).In such cases this code
  		 * still "owns" the iopoll instance and therefore can
  		 * move the instance around on the list at-will.
  		 */
  		if (work >= weight) {
  			if (blk_iopoll_disable_pending(iop))
  				__blk_iopoll_complete(iop);
  			else
  				list_move_tail(&iop->list, list);
  		}
  	}
  
  	if (rearm)
  		__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
  
  	local_irq_enable();
  }
  
  /**
   * blk_iopoll_disable - Disable iopoll on this @iop
   * @iop:      The parent iopoll structure
   *
   * Description:
   *     Disable io polling and wait for any pending callbacks to have completed.
   **/
  void blk_iopoll_disable(struct blk_iopoll *iop)
  {
  	set_bit(IOPOLL_F_DISABLE, &iop->state);
  	while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
  		msleep(1);
  	clear_bit(IOPOLL_F_DISABLE, &iop->state);
  }
  EXPORT_SYMBOL(blk_iopoll_disable);
  
  /**
   * blk_iopoll_enable - Enable iopoll on this @iop
   * @iop:      The parent iopoll structure
   *
   * Description:
   *     Enable iopoll on this @iop. Note that the handler run will not be
   *     scheduled, it will only mark it as active.
   **/
  void blk_iopoll_enable(struct blk_iopoll *iop)
  {
  	BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
  	smp_mb__before_clear_bit();
  	clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
  }
  EXPORT_SYMBOL(blk_iopoll_enable);
  
  /**
   * blk_iopoll_init - Initialize this @iop
   * @iop:      The parent iopoll structure
   * @weight:   The default weight (or command completion budget)
   * @poll_fn:  The handler to invoke
   *
   * Description:
   *     Initialize this blk_iopoll structure. Before being actively used, the
   *     driver must call blk_iopoll_enable().
   **/
  void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
  {
  	memset(iop, 0, sizeof(*iop));
  	INIT_LIST_HEAD(&iop->list);
  	iop->weight = weight;
  	iop->poll = poll_fn;
  	set_bit(IOPOLL_F_SCHED, &iop->state);
  }
  EXPORT_SYMBOL(blk_iopoll_init);
  
  static int blk_iopoll_cpu_notify(struct notifier_block *self,
  				 unsigned long action, void *hcpu)
  {
  	/*
  	 * If a CPU goes away, splice its entries to the current CPU
  	 * and trigger a run of the softirq
  	 */
  	if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
  		int cpu = (unsigned long) hcpu;
  
  		local_irq_disable();
  		list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
  				 this_cpu_ptr(&blk_cpu_iopoll));
  		__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
  		local_irq_enable();
  	}
  
  	return NOTIFY_OK;
  }
  
  static struct notifier_block blk_iopoll_cpu_notifier = {
  	.notifier_call	= blk_iopoll_cpu_notify,
  };
  
  static __init int blk_iopoll_setup(void)
  {
  	int i;
  
  	for_each_possible_cpu(i)
  		INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
  
  	open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
  	register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
  	return 0;
  }
  subsys_initcall(blk_iopoll_setup);