/*
   * Functions related to softirq rq completions
   */
  #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 "blk.h"
  
  static DEFINE_PER_CPU(struct list_head, blk_cpu_done);

  /*
   * Softirq action handler - move entries to local list and loop over them
   * while passing them to the queue registered handler.
   */
  static void blk_done_softirq(struct softirq_action *h)
  {
  	struct list_head *cpu_list, local_list;
  
  	local_irq_disable();
  	cpu_list = &__get_cpu_var(blk_cpu_done);
  	list_replace_init(cpu_list, &local_list);
  	local_irq_enable();
  
  	while (!list_empty(&local_list)) {
  		struct request *rq;
  
  		rq = list_entry(local_list.next, struct request, csd.list);
  		list_del_init(&rq->csd.list);
  		rq->q->softirq_done_fn(rq);
  	}
  }
  
  #if defined(CONFIG_SMP) && defined(CONFIG_USE_GENERIC_SMP_HELPERS)
  static void trigger_softirq(void *data)
  {
  	struct request *rq = data;
  	unsigned long flags;
  	struct list_head *list;
  
  	local_irq_save(flags);
  	list = &__get_cpu_var(blk_cpu_done);
  	list_add_tail(&rq->csd.list, list);
  
  	if (list->next == &rq->csd.list)
  		raise_softirq_irqoff(BLOCK_SOFTIRQ);
  
  	local_irq_restore(flags);
  }
  
  /*
   * Setup and invoke a run of 'trigger_softirq' on the given cpu.
   */
  static int raise_blk_irq(int cpu, struct request *rq)
  {
  	if (cpu_online(cpu)) {
  		struct call_single_data *data = &rq->csd;
  
  		data->func = trigger_softirq;
  		data->info = rq;
  		data->flags = 0;

  		__smp_call_function_single(cpu, data, 0);

  		return 0;
  	}
  
  	return 1;
  }
  #else /* CONFIG_SMP && CONFIG_USE_GENERIC_SMP_HELPERS */
  static int raise_blk_irq(int cpu, struct request *rq)
  {
  	return 1;
  }
  #endif

  static int __cpuinit blk_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_done, cpu),
  				 &__get_cpu_var(blk_cpu_done));
  		raise_softirq_irqoff(BLOCK_SOFTIRQ);
  		local_irq_enable();
  	}
  
  	return NOTIFY_OK;
  }

  static struct notifier_block __cpuinitdata blk_cpu_notifier = {

  	.notifier_call	= blk_cpu_notify,
  };

  void __blk_complete_request(struct request *req)

  {

  	int ccpu, cpu, group_cpu = NR_CPUS;

  	struct request_queue *q = req->q;

  	unsigned long flags;

  	BUG_ON(!q->softirq_done_fn);

  
  	local_irq_save(flags);

  	cpu = smp_processor_id();

  	/*
  	 * Select completion CPU
  	 */

  	if (req->cpu != -1) {

  		ccpu = req->cpu;

  		if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags)) {

  			ccpu = blk_cpu_to_group(ccpu);

  			group_cpu = blk_cpu_to_group(cpu);
  		}

  	} else

  		ccpu = cpu;

  	/*
  	 * If current CPU and requested CPU are in the same group, running
  	 * softirq in current CPU. One might concern this is just like
  	 * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
  	 * running in interrupt handler, and currently I/O controller doesn't
  	 * support multiple interrupts, so current CPU is unique actually. This
  	 * avoids IPI sending from current CPU to the first CPU of a group.
  	 */
  	if (ccpu == cpu || ccpu == group_cpu) {

  		struct list_head *list;
  do_local:
  		list = &__get_cpu_var(blk_cpu_done);
  		list_add_tail(&req->csd.list, list);
  
  		/*
  		 * if the list only contains our just added request,
  		 * signal a raise of the softirq. If there are already
  		 * entries there, someone already raised the irq but it
  		 * hasn't run yet.
  		 */
  		if (list->next == &req->csd.list)
  			raise_softirq_irqoff(BLOCK_SOFTIRQ);
  	} else if (raise_blk_irq(ccpu, req))
  		goto do_local;

  
  	local_irq_restore(flags);
  }

  
  /**
   * blk_complete_request - end I/O on a request
   * @req:      the request being processed
   *
   * Description:
   *     Ends all I/O on a request. It does not handle partial completions,
   *     unless the driver actually implements this in its completion callback
   *     through requeueing. The actual completion happens out-of-order,
   *     through a softirq handler. The user must have registered a completion
   *     callback through blk_queue_softirq_done().
   **/
  void blk_complete_request(struct request *req)
  {

  	if (unlikely(blk_should_fake_timeout(req->q)))
  		return;

  	if (!blk_mark_rq_complete(req))
  		__blk_complete_request(req);
  }

  EXPORT_SYMBOL(blk_complete_request);

  static __init int blk_softirq_init(void)

  {
  	int i;
  
  	for_each_possible_cpu(i)
  		INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
  
  	open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
  	register_hotcpu_notifier(&blk_cpu_notifier);
  	return 0;
  }
  subsys_initcall(blk_softirq_init);