block/blk-settings.c - maze/linux - Git at Google

 /*
  * 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 "blk.h"

 unsigned long blk_max_low_pfn;
 EXPORT_SYMBOL(blk_max_low_pfn);

 unsigned long blk_max_pfn;
 EXPORT_SYMBOL(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);

 /**
  * 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;
 	blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
 	blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
 	q->make_request_fn = mfn;
 	q->backing_dev_info.ra_pages =
 			(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
 	q->backing_dev_info.state = 0;
 	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
 	blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
 	blk_queue_hardsect_size(q, 512);
 	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;

 	INIT_WORK(&q->unplug_work, blk_unplug_work);

 	q->unplug_timer.function = blk_unplug_timeout;
 	q->unplug_timer.data = (unsigned long)q;

 	/*
 	 * 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_addr:   bus address limit
  *
  * 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 @page.
  **/
 void blk_queue_bounce_limit(struct request_queue *q, u64 dma_addr)
 {
 	unsigned long b_pfn = dma_addr >> 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, 0xffffffff, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
 		dma = 1;
 	q->bounce_pfn = max_low_pfn;
 #else
 	if (b_pfn < blk_max_low_pfn)
 		dma = 1;
 	q->bounce_pfn = b_pfn;
 #endif
 	if (dma) {
 		init_emergency_isa_pool();
 		q->bounce_gfp = GFP_NOIO | GFP_DMA;
 		q->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", __FUNCTION__,
 							max_sectors);
 	}

 	if (BLK_DEF_MAX_SECTORS > max_sectors)
 		q->max_hw_sectors = q->max_sectors = max_sectors;
 	else {
 		q->max_sectors = BLK_DEF_MAX_SECTORS;
 		q->max_hw_sectors = max_sectors;
 	}
 }
 EXPORT_SYMBOL(blk_queue_max_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", __FUNCTION__,
 							max_segments);
 	}

 	q->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 as 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", __FUNCTION__,
 							max_segments);
 	}

 	q->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", __FUNCTION__,
 							max_size);
 	}

 	q->max_segment_size = max_size;
 }
 EXPORT_SYMBOL(blk_queue_max_segment_size);

 /**
  * blk_queue_hardsect_size - set hardware sector size for the queue
  * @q:  the request queue for the device
  * @size:  the hardware sector size, in bytes
  *
  * Description:
  *   This should typically be set to the lowest possible sector size
  *   that the hardware can operate on (possible without reverting to
  *   even internal read-modify-write operations). Usually the default
  *   of 512 covers most hardware.
  **/
 void blk_queue_hardsect_size(struct request_queue *q, unsigned short size)
 {
 	q->hardsect_size = size;
 }
 EXPORT_SYMBOL(blk_queue_hardsect_size);

 /*
  * 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)
 {
 	/* zero is "infinity" */
 	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->max_phys_segments = min(t->max_phys_segments, b->max_phys_segments);
 	t->max_hw_segments = min(t->max_hw_segments, b->max_hw_segments);
 	t->max_segment_size = min(t->max_segment_size, b->max_segment_size);
 	t->hardsect_size = max(t->hardsect_size, b->hardsect_size);
 	if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
 		clear_bit(QUEUE_FLAG_CLUSTER, &t->queue_flags);
 }
 EXPORT_SYMBOL(blk_queue_stack_limits);

 /**
  * blk_queue_dma_drain - Set up a drain buffer for excess dma.
  *
  * @q:  the request queue for the device
  * @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, void *buf,
 				unsigned int size)
 {
 	if (q->max_hw_segments < 2 || q->max_phys_segments < 2)
 		return -EINVAL;
 	/* make room for appending the drain */
 	--q->max_hw_segments;
 	--q->max_phys_segments;
 	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", __FUNCTION__,
 							mask);
 	}

 	q->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 aligment for direct dma transactions.
  *    this is used when buiding 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 aligment 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);
	/*
	* 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 "blk.h"

	unsigned long blk_max_low_pfn;
	EXPORT_SYMBOL(blk_max_low_pfn);

	unsigned long blk_max_pfn;
	EXPORT_SYMBOL(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);

	/**
	* 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;
	blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
	blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
	q->make_request_fn = mfn;
	q->backing_dev_info.ra_pages =
	(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
	q->backing_dev_info.state = 0;
	q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
	blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
	blk_queue_hardsect_size(q, 512);
	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;

	INIT_WORK(&q->unplug_work, blk_unplug_work);

	q->unplug_timer.function = blk_unplug_timeout;
	q->unplug_timer.data = (unsigned long)q;

	/*
	* 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_addr: bus address limit
	*
	* 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 @page.
	**/
	void blk_queue_bounce_limit(struct request_queue *q, u64 dma_addr)
	{
	unsigned long b_pfn = dma_addr >> 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, 0xffffffff, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
	dma = 1;
	q->bounce_pfn = max_low_pfn;
	#else
	if (b_pfn < blk_max_low_pfn)
	dma = 1;
	q->bounce_pfn = b_pfn;
	#endif
	if (dma) {
	init_emergency_isa_pool();
	q->bounce_gfp = GFP_NOIO \| GFP_DMA;
	q->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", __FUNCTION__,
	max_sectors);
	}

	if (BLK_DEF_MAX_SECTORS > max_sectors)
	q->max_hw_sectors = q->max_sectors = max_sectors;
	else {
	q->max_sectors = BLK_DEF_MAX_SECTORS;
	q->max_hw_sectors = max_sectors;
	}
	}
	EXPORT_SYMBOL(blk_queue_max_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", __FUNCTION__,
	max_segments);
	}

	q->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 as 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", __FUNCTION__,
	max_segments);
	}

	q->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", __FUNCTION__,
	max_size);
	}

	q->max_segment_size = max_size;
	}
	EXPORT_SYMBOL(blk_queue_max_segment_size);

	/**
	* blk_queue_hardsect_size - set hardware sector size for the queue
	* @q: the request queue for the device
	* @size: the hardware sector size, in bytes
	*
	* Description:
	* This should typically be set to the lowest possible sector size
	* that the hardware can operate on (possible without reverting to
	* even internal read-modify-write operations). Usually the default
	* of 512 covers most hardware.
	**/
	void blk_queue_hardsect_size(struct request_queue *q, unsigned short size)
	{
	q->hardsect_size = size;
	}
	EXPORT_SYMBOL(blk_queue_hardsect_size);

	/*
	* 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)
	{
	/* zero is "infinity" */
	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->max_phys_segments = min(t->max_phys_segments, b->max_phys_segments);
	t->max_hw_segments = min(t->max_hw_segments, b->max_hw_segments);
	t->max_segment_size = min(t->max_segment_size, b->max_segment_size);
	t->hardsect_size = max(t->hardsect_size, b->hardsect_size);
	if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
	clear_bit(QUEUE_FLAG_CLUSTER, &t->queue_flags);
	}
	EXPORT_SYMBOL(blk_queue_stack_limits);

	/**
	* blk_queue_dma_drain - Set up a drain buffer for excess dma.
	*
	* @q: the request queue for the device
	* @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, void buf,
	unsigned int size)
	{
	if (q->max_hw_segments < 2 \|\| q->max_phys_segments < 2)
	return -EINVAL;
	/* make room for appending the drain */
	--q->max_hw_segments;
	--q->max_phys_segments;
	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", __FUNCTION__,
	mask);
	}

	q->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 aligment for direct dma transactions.
	* this is used when buiding 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 aligment 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);