/*
   * Functions related to setting various queue properties from drivers
   */
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/bio.h>
  #include <linux/blkdev.h>
  
  #include "blk.h"
  
  /*
   * for max sense size
   */
  #include <scsi/scsi_cmnd.h>
  
  /**
   * blk_end_sync_rq - executes a completion event on a request
   * @rq: request to complete

   * @error: end I/O status of the request

   */

  static void blk_end_sync_rq(struct request *rq, int error)

  {
  	struct completion *waiting = rq->end_io_data;
  
  	rq->end_io_data = NULL;
  	__blk_put_request(rq->q, rq);
  
  	/*
  	 * complete last, if this is a stack request the process (and thus
  	 * the rq pointer) could be invalid right after this complete()
  	 */
  	complete(waiting);
  }

  
  /**
   * blk_execute_rq_nowait - insert a request into queue for execution
   * @q:		queue to insert the request in
   * @bd_disk:	matching gendisk
   * @rq:		request to insert
   * @at_head:    insert request at head or tail of queue
   * @done:	I/O completion handler
   *
   * Description:

   *    Insert a fully prepared request at the back of the I/O scheduler queue

   *    for execution.  Don't wait for completion.
   */
  void blk_execute_rq_nowait(struct request_queue *q, struct gendisk *bd_disk,
  			   struct request *rq, int at_head,
  			   rq_end_io_fn *done)
  {
  	int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;

  	WARN_ON(irqs_disabled());
  	spin_lock_irq(q->queue_lock);

  	if (unlikely(blk_queue_dead(q))) {

  		spin_unlock_irq(q->queue_lock);

  		rq->errors = -ENXIO;
  		if (rq->end_io)
  			rq->end_io(rq, rq->errors);
  		return;
  	}

  	rq->rq_disk = bd_disk;

  	rq->end_io = done;

  	__elv_add_request(q, rq, where);

  	__blk_run_queue(q);

  	/* the queue is stopped so it won't be run */

  	if (rq->cmd_type == REQ_TYPE_PM_RESUME)

  		q->request_fn(q);

  	spin_unlock_irq(q->queue_lock);
  }
  EXPORT_SYMBOL_GPL(blk_execute_rq_nowait);
  
  /**
   * blk_execute_rq - insert a request into queue for execution
   * @q:		queue to insert the request in
   * @bd_disk:	matching gendisk
   * @rq:		request to insert
   * @at_head:    insert request at head or tail of queue
   *
   * Description:

   *    Insert a fully prepared request at the back of the I/O scheduler queue

   *    for execution and wait for completion.
   */
  int blk_execute_rq(struct request_queue *q, struct gendisk *bd_disk,
  		   struct request *rq, int at_head)
  {
  	DECLARE_COMPLETION_ONSTACK(wait);
  	char sense[SCSI_SENSE_BUFFERSIZE];
  	int err = 0;

  	unsigned long hang_check;

  
  	/*
  	 * we need an extra reference to the request, so we can look at
  	 * it after io completion
  	 */
  	rq->ref_count++;
  
  	if (!rq->sense) {
  		memset(sense, 0, sizeof(sense));
  		rq->sense = sense;
  		rq->sense_len = 0;
  	}
  
  	rq->end_io_data = &wait;
  	blk_execute_rq_nowait(q, bd_disk, rq, at_head, blk_end_sync_rq);

  
  	/* Prevent hang_check timer from firing at us during very long I/O */
  	hang_check = sysctl_hung_task_timeout_secs;
  	if (hang_check)
  		while (!wait_for_completion_timeout(&wait, hang_check * (HZ/2)));
  	else
  		wait_for_completion(&wait);

  
  	if (rq->errors)
  		err = -EIO;
  
  	return err;
  }

  EXPORT_SYMBOL(blk_execute_rq);