text: /*
   * 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 "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_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_phys_segments = MAX_PHYS_SEGMENTS;
  	lim->max_hw_segments = MAX_HW_SEGMENTS;
  	lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
  	lim->max_segment_size = MAX_SEGMENT_SIZE;
  	lim->max_sectors = BLK_DEF_MAX_SECTORS;
  	lim->max_hw_sectors = INT_MAX;
  	lim->max_discard_sectors = SAFE_MAX_SECTORS;
  	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->no_cluster = 0;
  }
  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;
  
  	q->unplug_thresh = 4;		/* hmm */
  	q->unplug_delay = (3 * HZ) / 1000;	/* 3 milliseconds */
  	if (q->unplug_delay == 0)
  		q->unplug_delay = 1;
  
  	q->unplug_timer.function = blk_unplug_timeout;
  	q->unplug_timer.data = (unsigned long)q;
  
  	blk_set_default_limits(&q->limits);
  	blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
  
  	/*
  	 * If the caller didn't supply a lock, fall back to our embedded
  	 * per-queue locks
  	 */
  	if (!q->queue_lock)
  		q->queue_lock = &q->__queue_lock;
  
  	/*
  	 * 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_low_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_queue_max_sectors - set max sectors for a request for this queue
   * @q:  the request queue for the device
   * @max_sectors:  max sectors in the usual 512b unit
   *
   * Description:
   *    Enables a low level driver to set an upper limit on the size of
   *    received requests.
   **/
  void blk_queue_max_sectors(struct request_queue *q, unsigned int max_sectors)
  {
  	if ((max_sectors << 9) < PAGE_CACHE_SIZE) {
  		max_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
  		printk(KERN_INFO "%s: set to minimum %d\n",
  		       __func__, max_sectors);
  	}
  
  	if (BLK_DEF_MAX_SECTORS > max_sectors)
  		q->limits.max_hw_sectors = q->limits.max_sectors = max_sectors;
  	else {
  		q->limits.max_sectors = BLK_DEF_MAX_SECTORS;
  		q->limits.max_hw_sectors = max_sectors;
  	}
  }
  EXPORT_SYMBOL(blk_queue_max_sectors);
  
  void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_sectors)
  {
  	if (BLK_DEF_MAX_SECTORS > max_sectors)
  		q->limits.max_hw_sectors = BLK_DEF_MAX_SECTORS;
  	else
  		q->limits.max_hw_sectors = max_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_phys_segments - set max phys 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
   *    physical data segments in a request.  This would be the largest sized
   *    scatter list the driver could handle.
   **/
  void blk_queue_max_phys_segments(struct request_queue *q,
  				 unsigned short max_segments)
  {
  	if (!max_segments) {
  		max_segments = 1;
  		printk(KERN_INFO "%s: set to minimum %d\n",
  		       __func__, max_segments);
  	}
  
  	q->limits.max_phys_segments = max_segments;
  }
  EXPORT_SYMBOL(blk_queue_max_phys_segments);
  
  /**
   * blk_queue_max_hw_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.  This would be the largest number of
   *    address/length pairs the host adapter can actually give at once
   *    to the device.
   **/
  void blk_queue_max_hw_segments(struct request_queue *q,
  			       unsigned short max_segments)
  {
  	if (!max_segments) {
  		max_segments = 1;
  		printk(KERN_INFO "%s: set to minimum %d\n",
  		       __func__, max_segments);
  	}
  
  	q->limits.max_hw_segments = max_segments;
  }
  EXPORT_SYMBOL(blk_queue_max_hw_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\n",
  		       __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 short 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);
  
  /*
   * Returns the minimum that is _not_ zero, unless both are zero.
   */
  #define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
  
  /**
   * 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);
  
  	if (!t->queue_lock)
  		WARN_ON_ONCE(1);
  	else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
  		unsigned long flags;
  		spin_lock_irqsave(t->queue_lock, flags);
  		queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
  		spin_unlock_irqrestore(t->queue_lock, flags);
  	}
  }
  EXPORT_SYMBOL(blk_queue_stack_limits);
  
  /**
   * blk_stack_limits - adjust queue_limits for stacked devices
   * @t:	the stacking driver limits (top)
   * @b:  the underlying queue limits (bottom)
   * @offset:  offset to beginning of data within component device
   *
   * Description:
   *    Merges two queue_limit structs.  Returns 0 if alignment didn't
   *    change.  Returns -1 if adding the bottom device caused
   *    misalignment.
   */
  int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
  		     sector_t offset)
  {
  	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_phys_segments = min_not_zero(t->max_phys_segments,
  					    b->max_phys_segments);
  
  	t->max_hw_segments = min_not_zero(t->max_hw_segments,
  					  b->max_hw_segments);
  
  	t->max_segment_size = min_not_zero(t->max_segment_size,
  					   b->max_segment_size);
  
  	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->no_cluster |= b->no_cluster;
  
  	/* Bottom device offset aligned? */
  	if (offset &&
  	    (offset & (b->physical_block_size - 1)) != b->alignment_offset) {
  		t->misaligned = 1;
  		return -1;
  	}
  
  	/* If top has no alignment offset, inherit from bottom */
  	if (!t->alignment_offset)
  		t->alignment_offset =
  			b->alignment_offset & (b->physical_block_size - 1);
  
  	/* Top device aligned on logical block boundary? */
  	if (t->alignment_offset & (t->logical_block_size - 1)) {
  		t->misaligned = 1;
  		return -1;
  	}
  
  	/* Find lcm() of optimal I/O size */
  	if (t->io_opt && b->io_opt)
  		t->io_opt = (t->io_opt * b->io_opt) / gcd(t->io_opt, b->io_opt);
  	else if (b->io_opt)
  		t->io_opt = b->io_opt;
  
  	/* Verify that optimal I/O size is a multiple of io_min */
  	if (t->io_min && t->io_opt % t->io_min)
  		return -1;
  
  	return 0;
  }
  EXPORT_SYMBOL(blk_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 two queues.  Returns 0 if alignment
   *    didn't change.  Returns -1 if adding the bottom device caused
   *    misalignment.
   */
  void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
  		       sector_t offset)
  {
  	struct request_queue *t = disk->queue;
  	struct request_queue *b = bdev_get_queue(bdev);
  
  	offset += get_start_sect(bdev) << 9;
  
  	if (blk_stack_limits(&t->limits, &b->limits, offset) < 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\n",
  		       top, bottom);
  	}
  
  	if (!t->queue_lock)
  		WARN_ON_ONCE(1);
  	else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
  		unsigned long flags;
  
  		spin_lock_irqsave(t->queue_lock, flags);
  		if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
  			queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
  		spin_unlock_irqrestore(t->queue_lock, flags);
  	}
  }
  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_hw_segments() or blk_queue_max_phys_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_hw_segments(q) < 2 || queue_max_phys_segments(q) < 2)
  		return -EINVAL;
  	/* make room for appending the drain */
  	blk_queue_max_hw_segments(q, queue_max_hw_segments(q) - 1);
  	blk_queue_max_phys_segments(q, queue_max_phys_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\n",
  		       __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);
  
  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);
  