/*
   * Functions related to setting various queue properties from drivers
   */
  #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/gcd.h>

  #include <linux/lcm.h>

  #include <linux/jiffies.h>

  #include <linux/gfp.h>

  
  #include "blk.h"

  unsigned long blk_max_low_pfn;

  EXPORT_SYMBOL(blk_max_low_pfn);

  
  unsigned long blk_max_pfn;

  
  /**
   * blk_queue_prep_rq - set a prepare_request function for queue
   * @q:		queue
   * @pfn:	prepare_request function
   *
   * It's possible for a queue to register a prepare_request callback which
   * is invoked before the request is handed to the request_fn. The goal of
   * the function is to prepare a request for I/O, it can be used to build a
   * cdb from the request data for instance.
   *
   */
  void blk_queue_prep_rq(struct request_queue *q, prep_rq_fn *pfn)
  {
  	q->prep_rq_fn = pfn;
  }

  EXPORT_SYMBOL(blk_queue_prep_rq);
  
  /**

   * blk_queue_unprep_rq - set an unprepare_request function for queue
   * @q:		queue
   * @ufn:	unprepare_request function
   *
   * It's possible for a queue to register an unprepare_request callback
   * which is invoked before the request is finally completed. The goal
   * of the function is to deallocate any data that was allocated in the
   * prepare_request callback.
   *
   */
  void blk_queue_unprep_rq(struct request_queue *q, unprep_rq_fn *ufn)
  {
  	q->unprep_rq_fn = ufn;
  }
  EXPORT_SYMBOL(blk_queue_unprep_rq);
  
  /**

   * blk_queue_merge_bvec - set a merge_bvec function for queue
   * @q:		queue
   * @mbfn:	merge_bvec_fn
   *
   * Usually queues have static limitations on the max sectors or segments that
   * we can put in a request. Stacking drivers may have some settings that
   * are dynamic, and thus we have to query the queue whether it is ok to
   * add a new bio_vec to a bio at a given offset or not. If the block device
   * has such limitations, it needs to register a merge_bvec_fn to control
   * the size of bio's sent to it. Note that a block device *must* allow a
   * single page to be added to an empty bio. The block device driver may want
   * to use the bio_split() function to deal with these bio's. By default
   * no merge_bvec_fn is defined for a queue, and only the fixed limits are
   * honored.
   */
  void blk_queue_merge_bvec(struct request_queue *q, merge_bvec_fn *mbfn)
  {
  	q->merge_bvec_fn = mbfn;
  }

  EXPORT_SYMBOL(blk_queue_merge_bvec);
  
  void blk_queue_softirq_done(struct request_queue *q, softirq_done_fn *fn)
  {
  	q->softirq_done_fn = fn;
  }

  EXPORT_SYMBOL(blk_queue_softirq_done);

  void blk_queue_rq_timeout(struct request_queue *q, unsigned int timeout)
  {
  	q->rq_timeout = timeout;
  }
  EXPORT_SYMBOL_GPL(blk_queue_rq_timeout);
  
  void blk_queue_rq_timed_out(struct request_queue *q, rq_timed_out_fn *fn)
  {
  	q->rq_timed_out_fn = fn;
  }
  EXPORT_SYMBOL_GPL(blk_queue_rq_timed_out);

  void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
  {
  	q->lld_busy_fn = fn;
  }
  EXPORT_SYMBOL_GPL(blk_queue_lld_busy);

  /**

   * blk_set_default_limits - reset limits to default values

   * @lim:  the queue_limits structure to reset

   *
   * Description:
   *   Returns a queue_limit struct to its default state.  Can be used by
   *   stacking drivers like DM that stage table swaps and reuse an
   *   existing device queue.
   */
  void blk_set_default_limits(struct queue_limits *lim)
  {

  	lim->max_segments = BLK_MAX_SEGMENTS;

  	lim->max_integrity_segments = 0;

  	lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;

  	lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;

  	lim->max_sectors = BLK_DEF_MAX_SECTORS;
  	lim->max_hw_sectors = INT_MAX;

  	lim->max_discard_sectors = 0;
  	lim->discard_granularity = 0;
  	lim->discard_alignment = 0;
  	lim->discard_misaligned = 0;

  	lim->discard_zeroes_data = -1;

  	lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;

  	lim->bounce_pfn = (unsigned long)(BLK_BOUNCE_ANY >> PAGE_SHIFT);

  	lim->alignment_offset = 0;
  	lim->io_opt = 0;
  	lim->misaligned = 0;

  	lim->cluster = 1;

  }
  EXPORT_SYMBOL(blk_set_default_limits);
  
  /**

   * blk_queue_make_request - define an alternate make_request function for a device
   * @q:  the request queue for the device to be affected
   * @mfn: the alternate make_request function
   *
   * Description:
   *    The normal way for &struct bios to be passed to a device
   *    driver is for them to be collected into requests on a request
   *    queue, and then to allow the device driver to select requests
   *    off that queue when it is ready.  This works well for many block
   *    devices. However some block devices (typically virtual devices
   *    such as md or lvm) do not benefit from the processing on the
   *    request queue, and are served best by having the requests passed
   *    directly to them.  This can be achieved by providing a function
   *    to blk_queue_make_request().
   *
   * Caveat:
   *    The driver that does this *must* be able to deal appropriately
   *    with buffers in "highmemory". This can be accomplished by either calling
   *    __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
   *    blk_queue_bounce() to create a buffer in normal memory.
   **/

  void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)

  {
  	/*
  	 * set defaults
  	 */
  	q->nr_requests = BLKDEV_MAX_RQ;

  	q->make_request_fn = mfn;

  	blk_queue_dma_alignment(q, 511);
  	blk_queue_congestion_threshold(q);
  	q->nr_batching = BLK_BATCH_REQ;

  	blk_set_default_limits(&q->limits);

  	blk_queue_max_hw_sectors(q, BLK_SAFE_MAX_SECTORS);

  	/*
  	 * by default assume old behaviour and bounce for any highmem page
  	 */
  	blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
  }

  EXPORT_SYMBOL(blk_queue_make_request);
  
  /**
   * blk_queue_bounce_limit - set bounce buffer limit for queue

   * @q: the request queue for the device
   * @dma_mask: the maximum address the device can handle

   *
   * Description:
   *    Different hardware can have different requirements as to what pages
   *    it can do I/O directly to. A low level driver can call
   *    blk_queue_bounce_limit to have lower memory pages allocated as bounce

   *    buffers for doing I/O to pages residing above @dma_mask.

   **/

  void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)

  {

  	unsigned long b_pfn = dma_mask >> PAGE_SHIFT;

  	int dma = 0;
  
  	q->bounce_gfp = GFP_NOIO;
  #if BITS_PER_LONG == 64

  	/*
  	 * Assume anything <= 4GB can be handled by IOMMU.  Actually
  	 * some IOMMUs can handle everything, but I don't know of a
  	 * way to test this here.
  	 */
  	if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))

  		dma = 1;

  	q->limits.bounce_pfn = max(max_low_pfn, b_pfn);

  #else

  	if (b_pfn < blk_max_low_pfn)

  		dma = 1;

  	q->limits.bounce_pfn = b_pfn;

  #endif

  	if (dma) {
  		init_emergency_isa_pool();
  		q->bounce_gfp = GFP_NOIO | GFP_DMA;

  		q->limits.bounce_pfn = b_pfn;

  	}
  }

  EXPORT_SYMBOL(blk_queue_bounce_limit);
  
  /**

   * blk_limits_max_hw_sectors - set hard and soft limit of max sectors for request
   * @limits: the queue limits

   * @max_hw_sectors:  max hardware sectors in the usual 512b unit

   *
   * Description:

   *    Enables a low level driver to set a hard upper limit,
   *    max_hw_sectors, on the size of requests.  max_hw_sectors is set by
   *    the device driver based upon the combined capabilities of I/O
   *    controller and storage device.
   *
   *    max_sectors is a soft limit imposed by the block layer for
   *    filesystem type requests.  This value can be overridden on a
   *    per-device basis in /sys/block/<device>/queue/max_sectors_kb.
   *    The soft limit can not exceed max_hw_sectors.

   **/

  void blk_limits_max_hw_sectors(struct queue_limits *limits, unsigned int max_hw_sectors)

  {

  	if ((max_hw_sectors << 9) < PAGE_CACHE_SIZE) {
  		max_hw_sectors = 1 << (PAGE_CACHE_SHIFT - 9);

  		printk(KERN_INFO "%s: set to minimum %d
  ",

  		       __func__, max_hw_sectors);

  	}

  	limits->max_hw_sectors = max_hw_sectors;
  	limits->max_sectors = min_t(unsigned int, max_hw_sectors,
  				    BLK_DEF_MAX_SECTORS);
  }
  EXPORT_SYMBOL(blk_limits_max_hw_sectors);
  
  /**
   * blk_queue_max_hw_sectors - set max sectors for a request for this queue
   * @q:  the request queue for the device
   * @max_hw_sectors:  max hardware sectors in the usual 512b unit
   *
   * Description:
   *    See description for blk_limits_max_hw_sectors().
   **/
  void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)
  {
  	blk_limits_max_hw_sectors(&q->limits, max_hw_sectors);

  }

  EXPORT_SYMBOL(blk_queue_max_hw_sectors);

  
  /**

   * blk_queue_max_discard_sectors - set max sectors for a single discard
   * @q:  the request queue for the device

   * @max_discard_sectors: maximum number of sectors to discard

   **/
  void blk_queue_max_discard_sectors(struct request_queue *q,
  		unsigned int max_discard_sectors)
  {
  	q->limits.max_discard_sectors = max_discard_sectors;
  }
  EXPORT_SYMBOL(blk_queue_max_discard_sectors);
  
  /**

   * blk_queue_max_segments - set max hw segments for a request for this queue

   * @q:  the request queue for the device
   * @max_segments:  max number of segments
   *
   * Description:
   *    Enables a low level driver to set an upper limit on the number of

   *    hw data segments in a request.

   **/

  void blk_queue_max_segments(struct request_queue *q, unsigned short max_segments)

  {
  	if (!max_segments) {
  		max_segments = 1;

  		printk(KERN_INFO "%s: set to minimum %d
  ",
  		       __func__, max_segments);

  	}

  	q->limits.max_segments = max_segments;

  }

  EXPORT_SYMBOL(blk_queue_max_segments);

  
  /**
   * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
   * @q:  the request queue for the device
   * @max_size:  max size of segment in bytes
   *
   * Description:
   *    Enables a low level driver to set an upper limit on the size of a
   *    coalesced segment
   **/
  void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
  {
  	if (max_size < PAGE_CACHE_SIZE) {
  		max_size = PAGE_CACHE_SIZE;

  		printk(KERN_INFO "%s: set to minimum %d
  ",
  		       __func__, max_size);

  	}

  	q->limits.max_segment_size = max_size;

  }

  EXPORT_SYMBOL(blk_queue_max_segment_size);
  
  /**

   * blk_queue_logical_block_size - set logical block size for the queue

   * @q:  the request queue for the device

   * @size:  the logical block size, in bytes

   *
   * Description:

   *   This should be set to the lowest possible block size that the
   *   storage device can address.  The default of 512 covers most
   *   hardware.

   **/

  void blk_queue_logical_block_size(struct request_queue *q, unsigned short size)

  {

  	q->limits.logical_block_size = size;

  
  	if (q->limits.physical_block_size < size)
  		q->limits.physical_block_size = size;
  
  	if (q->limits.io_min < q->limits.physical_block_size)
  		q->limits.io_min = q->limits.physical_block_size;

  }

  EXPORT_SYMBOL(blk_queue_logical_block_size);

  /**
   * blk_queue_physical_block_size - set physical block size for the queue
   * @q:  the request queue for the device
   * @size:  the physical block size, in bytes
   *
   * Description:
   *   This should be set to the lowest possible sector size that the
   *   hardware can operate on without reverting to read-modify-write
   *   operations.
   */

  void blk_queue_physical_block_size(struct request_queue *q, unsigned int size)

  {
  	q->limits.physical_block_size = size;
  
  	if (q->limits.physical_block_size < q->limits.logical_block_size)
  		q->limits.physical_block_size = q->limits.logical_block_size;
  
  	if (q->limits.io_min < q->limits.physical_block_size)
  		q->limits.io_min = q->limits.physical_block_size;
  }
  EXPORT_SYMBOL(blk_queue_physical_block_size);
  
  /**
   * blk_queue_alignment_offset - set physical block alignment offset
   * @q:	the request queue for the device

   * @offset: alignment offset in bytes

   *
   * Description:
   *   Some devices are naturally misaligned to compensate for things like
   *   the legacy DOS partition table 63-sector offset.  Low-level drivers
   *   should call this function for devices whose first sector is not
   *   naturally aligned.
   */
  void blk_queue_alignment_offset(struct request_queue *q, unsigned int offset)
  {
  	q->limits.alignment_offset =
  		offset & (q->limits.physical_block_size - 1);
  	q->limits.misaligned = 0;
  }
  EXPORT_SYMBOL(blk_queue_alignment_offset);
  
  /**

   * blk_limits_io_min - set minimum request size for a device
   * @limits: the queue limits
   * @min:  smallest I/O size in bytes
   *
   * Description:
   *   Some devices have an internal block size bigger than the reported
   *   hardware sector size.  This function can be used to signal the
   *   smallest I/O the device can perform without incurring a performance
   *   penalty.
   */
  void blk_limits_io_min(struct queue_limits *limits, unsigned int min)
  {
  	limits->io_min = min;
  
  	if (limits->io_min < limits->logical_block_size)
  		limits->io_min = limits->logical_block_size;
  
  	if (limits->io_min < limits->physical_block_size)
  		limits->io_min = limits->physical_block_size;
  }
  EXPORT_SYMBOL(blk_limits_io_min);
  
  /**

   * blk_queue_io_min - set minimum request size for the queue
   * @q:	the request queue for the device

   * @min:  smallest I/O size in bytes

   *
   * Description:

   *   Storage devices may report a granularity or preferred minimum I/O
   *   size which is the smallest request the device can perform without
   *   incurring a performance penalty.  For disk drives this is often the
   *   physical block size.  For RAID arrays it is often the stripe chunk
   *   size.  A properly aligned multiple of minimum_io_size is the
   *   preferred request size for workloads where a high number of I/O
   *   operations is desired.

   */
  void blk_queue_io_min(struct request_queue *q, unsigned int min)
  {

  	blk_limits_io_min(&q->limits, min);

  }
  EXPORT_SYMBOL(blk_queue_io_min);
  
  /**

   * blk_limits_io_opt - set optimal request size for a device
   * @limits: the queue limits
   * @opt:  smallest I/O size in bytes
   *
   * Description:
   *   Storage devices may report an optimal I/O size, which is the
   *   device's preferred unit for sustained I/O.  This is rarely reported
   *   for disk drives.  For RAID arrays it is usually the stripe width or
   *   the internal track size.  A properly aligned multiple of
   *   optimal_io_size is the preferred request size for workloads where
   *   sustained throughput is desired.
   */
  void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt)
  {
  	limits->io_opt = opt;
  }
  EXPORT_SYMBOL(blk_limits_io_opt);
  
  /**

   * blk_queue_io_opt - set optimal request size for the queue
   * @q:	the request queue for the device

   * @opt:  optimal request size in bytes

   *
   * Description:

   *   Storage devices may report an optimal I/O size, which is the
   *   device's preferred unit for sustained I/O.  This is rarely reported
   *   for disk drives.  For RAID arrays it is usually the stripe width or
   *   the internal track size.  A properly aligned multiple of
   *   optimal_io_size is the preferred request size for workloads where
   *   sustained throughput is desired.

   */
  void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
  {

  	blk_limits_io_opt(&q->limits, opt);

  }
  EXPORT_SYMBOL(blk_queue_io_opt);

  /**
   * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
   * @t:	the stacking driver (top)
   * @b:  the underlying device (bottom)
   **/
  void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
  {

  	blk_stack_limits(&t->limits, &b->limits, 0);

  }

  EXPORT_SYMBOL(blk_queue_stack_limits);
  
  /**

   * blk_stack_limits - adjust queue_limits for stacked devices

   * @t:	the stacking driver limits (top device)
   * @b:  the underlying queue limits (bottom, component device)

   * @start:  first data sector within component device

   *
   * Description:

   *    This function is used by stacking drivers like MD and DM to ensure
   *    that all component devices have compatible block sizes and
   *    alignments.  The stacking driver must provide a queue_limits
   *    struct (top) and then iteratively call the stacking function for
   *    all component (bottom) devices.  The stacking function will
   *    attempt to combine the values and ensure proper alignment.
   *
   *    Returns 0 if the top and bottom queue_limits are compatible.  The
   *    top device's block sizes and alignment offsets may be adjusted to
   *    ensure alignment with the bottom device. If no compatible sizes
   *    and alignments exist, -1 is returned and the resulting top
   *    queue_limits will have the misaligned flag set to indicate that
   *    the alignment_offset is undefined.

   */
  int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,

  		     sector_t start)

  {

  	unsigned int top, bottom, alignment, ret = 0;

  	t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
  	t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);

  	t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);

  
  	t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
  					    b->seg_boundary_mask);

  	t->max_segments = min_not_zero(t->max_segments, b->max_segments);

  	t->max_integrity_segments = min_not_zero(t->max_integrity_segments,
  						 b->max_integrity_segments);

  
  	t->max_segment_size = min_not_zero(t->max_segment_size,
  					   b->max_segment_size);

  	t->misaligned |= b->misaligned;

  	alignment = queue_limit_alignment_offset(b, start);

  	/* Bottom device has different alignment.  Check that it is
  	 * compatible with the current top alignment.
  	 */

  	if (t->alignment_offset != alignment) {
  
  		top = max(t->physical_block_size, t->io_min)
  			+ t->alignment_offset;

  		bottom = max(b->physical_block_size, b->io_min) + alignment;

  		/* Verify that top and bottom intervals line up */

  		if (max(top, bottom) & (min(top, bottom) - 1)) {

  			t->misaligned = 1;

  			ret = -1;
  		}

  	}

  	t->logical_block_size = max(t->logical_block_size,
  				    b->logical_block_size);
  
  	t->physical_block_size = max(t->physical_block_size,
  				     b->physical_block_size);
  
  	t->io_min = max(t->io_min, b->io_min);

  	t->io_opt = lcm(t->io_opt, b->io_opt);

  	t->cluster &= b->cluster;

  	t->discard_zeroes_data &= b->discard_zeroes_data;

  	/* Physical block size a multiple of the logical block size? */

  	if (t->physical_block_size & (t->logical_block_size - 1)) {
  		t->physical_block_size = t->logical_block_size;

  		t->misaligned = 1;

  		ret = -1;

  	}

  	/* Minimum I/O a multiple of the physical block size? */

  	if (t->io_min & (t->physical_block_size - 1)) {
  		t->io_min = t->physical_block_size;
  		t->misaligned = 1;

  		ret = -1;

  	}

  	/* Optimal I/O a multiple of the physical block size? */

  	if (t->io_opt & (t->physical_block_size - 1)) {
  		t->io_opt = 0;
  		t->misaligned = 1;

  		ret = -1;

  	}

  	/* Find lowest common alignment_offset */

  	t->alignment_offset = lcm(t->alignment_offset, alignment)
  		& (max(t->physical_block_size, t->io_min) - 1);

  	/* Verify that new alignment_offset is on a logical block boundary */

  	if (t->alignment_offset & (t->logical_block_size - 1)) {

  		t->misaligned = 1;

  		ret = -1;
  	}

  	/* Discard alignment and granularity */
  	if (b->discard_granularity) {

  		alignment = queue_limit_discard_alignment(b, start);

  
  		if (t->discard_granularity != 0 &&
  		    t->discard_alignment != alignment) {
  			top = t->discard_granularity + t->discard_alignment;
  			bottom = b->discard_granularity + alignment;

  			/* Verify that top and bottom intervals line up */
  			if (max(top, bottom) & (min(top, bottom) - 1))
  				t->discard_misaligned = 1;
  		}

  		t->max_discard_sectors = min_not_zero(t->max_discard_sectors,
  						      b->max_discard_sectors);

  		t->discard_granularity = max(t->discard_granularity,
  					     b->discard_granularity);
  		t->discard_alignment = lcm(t->discard_alignment, alignment) &
  			(t->discard_granularity - 1);
  	}

  	return ret;

  }

  EXPORT_SYMBOL(blk_stack_limits);

  
  /**

   * bdev_stack_limits - adjust queue limits for stacked drivers
   * @t:	the stacking driver limits (top device)
   * @bdev:  the component block_device (bottom)
   * @start:  first data sector within component device
   *
   * Description:
   *    Merges queue limits for a top device and a block_device.  Returns
   *    0 if alignment didn't change.  Returns -1 if adding the bottom
   *    device caused misalignment.
   */
  int bdev_stack_limits(struct queue_limits *t, struct block_device *bdev,
  		      sector_t start)
  {
  	struct request_queue *bq = bdev_get_queue(bdev);
  
  	start += get_start_sect(bdev);

  	return blk_stack_limits(t, &bq->limits, start);

  }
  EXPORT_SYMBOL(bdev_stack_limits);
  
  /**

   * disk_stack_limits - adjust queue limits for stacked drivers

   * @disk:  MD/DM gendisk (top)

   * @bdev:  the underlying block device (bottom)
   * @offset:  offset to beginning of data within component device
   *
   * Description:

   *    Merges the limits for a top level gendisk and a bottom level
   *    block_device.

   */
  void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
  		       sector_t offset)
  {
  	struct request_queue *t = disk->queue;

  	if (bdev_stack_limits(&t->limits, bdev, offset >> 9) < 0) {

  		char top[BDEVNAME_SIZE], bottom[BDEVNAME_SIZE];
  
  		disk_name(disk, 0, top);
  		bdevname(bdev, bottom);
  
  		printk(KERN_NOTICE "%s: Warning: Device %s is misaligned
  ",
  		       top, bottom);
  	}

  }
  EXPORT_SYMBOL(disk_stack_limits);
  
  /**

   * blk_queue_dma_pad - set pad mask
   * @q:     the request queue for the device
   * @mask:  pad mask
   *

   * Set dma pad mask.

   *

   * Appending pad buffer to a request modifies the last entry of a
   * scatter list such that it includes the pad buffer.

   **/
  void blk_queue_dma_pad(struct request_queue *q, unsigned int mask)
  {
  	q->dma_pad_mask = mask;
  }
  EXPORT_SYMBOL(blk_queue_dma_pad);
  
  /**

   * blk_queue_update_dma_pad - update pad mask
   * @q:     the request queue for the device
   * @mask:  pad mask
   *
   * Update dma pad mask.
   *
   * Appending pad buffer to a request modifies the last entry of a
   * scatter list such that it includes the pad buffer.
   **/
  void blk_queue_update_dma_pad(struct request_queue *q, unsigned int mask)
  {
  	if (mask > q->dma_pad_mask)
  		q->dma_pad_mask = mask;
  }
  EXPORT_SYMBOL(blk_queue_update_dma_pad);
  
  /**

   * blk_queue_dma_drain - Set up a drain buffer for excess dma.

   * @q:  the request queue for the device

   * @dma_drain_needed: fn which returns non-zero if drain is necessary

   * @buf:	physically contiguous buffer
   * @size:	size of the buffer in bytes
   *
   * Some devices have excess DMA problems and can't simply discard (or
   * zero fill) the unwanted piece of the transfer.  They have to have a
   * real area of memory to transfer it into.  The use case for this is
   * ATAPI devices in DMA mode.  If the packet command causes a transfer
   * bigger than the transfer size some HBAs will lock up if there
   * aren't DMA elements to contain the excess transfer.  What this API
   * does is adjust the queue so that the buf is always appended
   * silently to the scatterlist.
   *

   * Note: This routine adjusts max_hw_segments to make room for appending
   * the drain buffer.  If you call blk_queue_max_segments() after calling
   * this routine, you must set the limit to one fewer than your device
   * can support otherwise there won't be room for the drain buffer.

   */

  int blk_queue_dma_drain(struct request_queue *q,

  			       dma_drain_needed_fn *dma_drain_needed,
  			       void *buf, unsigned int size)

  {

  	if (queue_max_segments(q) < 2)

  		return -EINVAL;
  	/* make room for appending the drain */

  	blk_queue_max_segments(q, queue_max_segments(q) - 1);

  	q->dma_drain_needed = dma_drain_needed;

  	q->dma_drain_buffer = buf;
  	q->dma_drain_size = size;
  
  	return 0;
  }

  EXPORT_SYMBOL_GPL(blk_queue_dma_drain);
  
  /**
   * blk_queue_segment_boundary - set boundary rules for segment merging
   * @q:  the request queue for the device
   * @mask:  the memory boundary mask
   **/
  void blk_queue_segment_boundary(struct request_queue *q, unsigned long mask)
  {
  	if (mask < PAGE_CACHE_SIZE - 1) {
  		mask = PAGE_CACHE_SIZE - 1;

  		printk(KERN_INFO "%s: set to minimum %lx
  ",
  		       __func__, mask);

  	}

  	q->limits.seg_boundary_mask = mask;

  }

  EXPORT_SYMBOL(blk_queue_segment_boundary);
  
  /**
   * blk_queue_dma_alignment - set dma length and memory alignment
   * @q:     the request queue for the device
   * @mask:  alignment mask
   *
   * description:

   *    set required memory and length alignment for direct dma transactions.

   *    this is used when building direct io requests for the queue.

   *
   **/
  void blk_queue_dma_alignment(struct request_queue *q, int mask)
  {
  	q->dma_alignment = mask;
  }

  EXPORT_SYMBOL(blk_queue_dma_alignment);
  
  /**
   * blk_queue_update_dma_alignment - update dma length and memory alignment
   * @q:     the request queue for the device
   * @mask:  alignment mask
   *
   * description:

   *    update required memory and length alignment for direct dma transactions.

   *    If the requested alignment is larger than the current alignment, then
   *    the current queue alignment is updated to the new value, otherwise it
   *    is left alone.  The design of this is to allow multiple objects
   *    (driver, device, transport etc) to set their respective
   *    alignments without having them interfere.
   *
   **/
  void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
  {
  	BUG_ON(mask > PAGE_SIZE);
  
  	if (mask > q->dma_alignment)
  		q->dma_alignment = mask;
  }

  EXPORT_SYMBOL(blk_queue_update_dma_alignment);

  /**
   * blk_queue_flush - configure queue's cache flush capability
   * @q:		the request queue for the device
   * @flush:	0, REQ_FLUSH or REQ_FLUSH | REQ_FUA
   *
   * Tell block layer cache flush capability of @q.  If it supports
   * flushing, REQ_FLUSH should be set.  If it supports bypassing
   * write cache for individual writes, REQ_FUA should be set.
   */
  void blk_queue_flush(struct request_queue *q, unsigned int flush)
  {
  	WARN_ON_ONCE(flush & ~(REQ_FLUSH | REQ_FUA));
  
  	if (WARN_ON_ONCE(!(flush & REQ_FLUSH) && (flush & REQ_FUA)))
  		flush &= ~REQ_FUA;
  
  	q->flush_flags = flush & (REQ_FLUSH | REQ_FUA);
  }
  EXPORT_SYMBOL_GPL(blk_queue_flush);

  static int __init blk_settings_init(void)

  {
  	blk_max_low_pfn = max_low_pfn - 1;
  	blk_max_pfn = max_pfn - 1;
  	return 0;
  }
  subsys_initcall(blk_settings_init);