2 * Functions related to setting various queue properties from drivers
4 #include <linux/kernel.h>
5 #include <linux/module.h>
6 #include <linux/init.h>
8 #include <linux/blkdev.h>
9 #include <linux/bootmem.h> /* for max_pfn/max_low_pfn */
10 #include <linux/gcd.h>
11 #include <linux/jiffies.h>
15 unsigned long blk_max_low_pfn
;
16 EXPORT_SYMBOL(blk_max_low_pfn
);
18 unsigned long blk_max_pfn
;
21 * blk_queue_prep_rq - set a prepare_request function for queue
23 * @pfn: prepare_request function
25 * It's possible for a queue to register a prepare_request callback which
26 * is invoked before the request is handed to the request_fn. The goal of
27 * the function is to prepare a request for I/O, it can be used to build a
28 * cdb from the request data for instance.
31 void blk_queue_prep_rq(struct request_queue
*q
, prep_rq_fn
*pfn
)
35 EXPORT_SYMBOL(blk_queue_prep_rq
);
38 * blk_queue_merge_bvec - set a merge_bvec function for queue
40 * @mbfn: merge_bvec_fn
42 * Usually queues have static limitations on the max sectors or segments that
43 * we can put in a request. Stacking drivers may have some settings that
44 * are dynamic, and thus we have to query the queue whether it is ok to
45 * add a new bio_vec to a bio at a given offset or not. If the block device
46 * has such limitations, it needs to register a merge_bvec_fn to control
47 * the size of bio's sent to it. Note that a block device *must* allow a
48 * single page to be added to an empty bio. The block device driver may want
49 * to use the bio_split() function to deal with these bio's. By default
50 * no merge_bvec_fn is defined for a queue, and only the fixed limits are
53 void blk_queue_merge_bvec(struct request_queue
*q
, merge_bvec_fn
*mbfn
)
55 q
->merge_bvec_fn
= mbfn
;
57 EXPORT_SYMBOL(blk_queue_merge_bvec
);
59 void blk_queue_softirq_done(struct request_queue
*q
, softirq_done_fn
*fn
)
61 q
->softirq_done_fn
= fn
;
63 EXPORT_SYMBOL(blk_queue_softirq_done
);
65 void blk_queue_rq_timeout(struct request_queue
*q
, unsigned int timeout
)
67 q
->rq_timeout
= timeout
;
69 EXPORT_SYMBOL_GPL(blk_queue_rq_timeout
);
71 void blk_queue_rq_timed_out(struct request_queue
*q
, rq_timed_out_fn
*fn
)
73 q
->rq_timed_out_fn
= fn
;
75 EXPORT_SYMBOL_GPL(blk_queue_rq_timed_out
);
77 void blk_queue_lld_busy(struct request_queue
*q
, lld_busy_fn
*fn
)
81 EXPORT_SYMBOL_GPL(blk_queue_lld_busy
);
84 * blk_set_default_limits - reset limits to default values
85 * @lim: the queue_limits structure to reset
88 * Returns a queue_limit struct to its default state. Can be used by
89 * stacking drivers like DM that stage table swaps and reuse an
90 * existing device queue.
92 void blk_set_default_limits(struct queue_limits
*lim
)
94 lim
->max_phys_segments
= MAX_PHYS_SEGMENTS
;
95 lim
->max_hw_segments
= MAX_HW_SEGMENTS
;
96 lim
->seg_boundary_mask
= BLK_SEG_BOUNDARY_MASK
;
97 lim
->max_segment_size
= MAX_SEGMENT_SIZE
;
98 lim
->max_sectors
= BLK_DEF_MAX_SECTORS
;
99 lim
->max_hw_sectors
= INT_MAX
;
100 lim
->max_discard_sectors
= 0;
101 lim
->discard_granularity
= 0;
102 lim
->discard_alignment
= 0;
103 lim
->discard_misaligned
= 0;
104 lim
->logical_block_size
= lim
->physical_block_size
= lim
->io_min
= 512;
105 lim
->bounce_pfn
= (unsigned long)(BLK_BOUNCE_ANY
>> PAGE_SHIFT
);
106 lim
->alignment_offset
= 0;
111 EXPORT_SYMBOL(blk_set_default_limits
);
114 * blk_queue_make_request - define an alternate make_request function for a device
115 * @q: the request queue for the device to be affected
116 * @mfn: the alternate make_request function
119 * The normal way for &struct bios to be passed to a device
120 * driver is for them to be collected into requests on a request
121 * queue, and then to allow the device driver to select requests
122 * off that queue when it is ready. This works well for many block
123 * devices. However some block devices (typically virtual devices
124 * such as md or lvm) do not benefit from the processing on the
125 * request queue, and are served best by having the requests passed
126 * directly to them. This can be achieved by providing a function
127 * to blk_queue_make_request().
130 * The driver that does this *must* be able to deal appropriately
131 * with buffers in "highmemory". This can be accomplished by either calling
132 * __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
133 * blk_queue_bounce() to create a buffer in normal memory.
135 void blk_queue_make_request(struct request_queue
*q
, make_request_fn
*mfn
)
140 q
->nr_requests
= BLKDEV_MAX_RQ
;
142 q
->make_request_fn
= mfn
;
143 blk_queue_dma_alignment(q
, 511);
144 blk_queue_congestion_threshold(q
);
145 q
->nr_batching
= BLK_BATCH_REQ
;
147 q
->unplug_thresh
= 4; /* hmm */
148 q
->unplug_delay
= msecs_to_jiffies(3); /* 3 milliseconds */
149 if (q
->unplug_delay
== 0)
152 q
->unplug_timer
.function
= blk_unplug_timeout
;
153 q
->unplug_timer
.data
= (unsigned long)q
;
155 blk_set_default_limits(&q
->limits
);
156 blk_queue_max_sectors(q
, SAFE_MAX_SECTORS
);
159 * If the caller didn't supply a lock, fall back to our embedded
163 q
->queue_lock
= &q
->__queue_lock
;
166 * by default assume old behaviour and bounce for any highmem page
168 blk_queue_bounce_limit(q
, BLK_BOUNCE_HIGH
);
170 EXPORT_SYMBOL(blk_queue_make_request
);
173 * blk_queue_bounce_limit - set bounce buffer limit for queue
174 * @q: the request queue for the device
175 * @dma_mask: the maximum address the device can handle
178 * Different hardware can have different requirements as to what pages
179 * it can do I/O directly to. A low level driver can call
180 * blk_queue_bounce_limit to have lower memory pages allocated as bounce
181 * buffers for doing I/O to pages residing above @dma_mask.
183 void blk_queue_bounce_limit(struct request_queue
*q
, u64 dma_mask
)
185 unsigned long b_pfn
= dma_mask
>> PAGE_SHIFT
;
188 q
->bounce_gfp
= GFP_NOIO
;
189 #if BITS_PER_LONG == 64
191 * Assume anything <= 4GB can be handled by IOMMU. Actually
192 * some IOMMUs can handle everything, but I don't know of a
193 * way to test this here.
195 if (b_pfn
< (min_t(u64
, 0xffffffffUL
, BLK_BOUNCE_HIGH
) >> PAGE_SHIFT
))
197 q
->limits
.bounce_pfn
= max_low_pfn
;
199 if (b_pfn
< blk_max_low_pfn
)
201 q
->limits
.bounce_pfn
= b_pfn
;
204 init_emergency_isa_pool();
205 q
->bounce_gfp
= GFP_NOIO
| GFP_DMA
;
206 q
->limits
.bounce_pfn
= b_pfn
;
209 EXPORT_SYMBOL(blk_queue_bounce_limit
);
212 * blk_queue_max_sectors - set max sectors for a request for this queue
213 * @q: the request queue for the device
214 * @max_sectors: max sectors in the usual 512b unit
217 * Enables a low level driver to set an upper limit on the size of
220 void blk_queue_max_sectors(struct request_queue
*q
, unsigned int max_sectors
)
222 if ((max_sectors
<< 9) < PAGE_CACHE_SIZE
) {
223 max_sectors
= 1 << (PAGE_CACHE_SHIFT
- 9);
224 printk(KERN_INFO
"%s: set to minimum %d\n",
225 __func__
, max_sectors
);
228 if (BLK_DEF_MAX_SECTORS
> max_sectors
)
229 q
->limits
.max_hw_sectors
= q
->limits
.max_sectors
= max_sectors
;
231 q
->limits
.max_sectors
= BLK_DEF_MAX_SECTORS
;
232 q
->limits
.max_hw_sectors
= max_sectors
;
235 EXPORT_SYMBOL(blk_queue_max_sectors
);
237 void blk_queue_max_hw_sectors(struct request_queue
*q
, unsigned int max_sectors
)
239 if (BLK_DEF_MAX_SECTORS
> max_sectors
)
240 q
->limits
.max_hw_sectors
= BLK_DEF_MAX_SECTORS
;
242 q
->limits
.max_hw_sectors
= max_sectors
;
244 EXPORT_SYMBOL(blk_queue_max_hw_sectors
);
247 * blk_queue_max_discard_sectors - set max sectors for a single discard
248 * @q: the request queue for the device
249 * @max_discard_sectors: maximum number of sectors to discard
251 void blk_queue_max_discard_sectors(struct request_queue
*q
,
252 unsigned int max_discard_sectors
)
254 q
->limits
.max_discard_sectors
= max_discard_sectors
;
256 EXPORT_SYMBOL(blk_queue_max_discard_sectors
);
259 * blk_queue_max_phys_segments - set max phys segments for a request for this queue
260 * @q: the request queue for the device
261 * @max_segments: max number of segments
264 * Enables a low level driver to set an upper limit on the number of
265 * physical data segments in a request. This would be the largest sized
266 * scatter list the driver could handle.
268 void blk_queue_max_phys_segments(struct request_queue
*q
,
269 unsigned short max_segments
)
273 printk(KERN_INFO
"%s: set to minimum %d\n",
274 __func__
, max_segments
);
277 q
->limits
.max_phys_segments
= max_segments
;
279 EXPORT_SYMBOL(blk_queue_max_phys_segments
);
282 * blk_queue_max_hw_segments - set max hw segments for a request for this queue
283 * @q: the request queue for the device
284 * @max_segments: max number of segments
287 * Enables a low level driver to set an upper limit on the number of
288 * hw data segments in a request. This would be the largest number of
289 * address/length pairs the host adapter can actually give at once
292 void blk_queue_max_hw_segments(struct request_queue
*q
,
293 unsigned short max_segments
)
297 printk(KERN_INFO
"%s: set to minimum %d\n",
298 __func__
, max_segments
);
301 q
->limits
.max_hw_segments
= max_segments
;
303 EXPORT_SYMBOL(blk_queue_max_hw_segments
);
306 * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
307 * @q: the request queue for the device
308 * @max_size: max size of segment in bytes
311 * Enables a low level driver to set an upper limit on the size of a
314 void blk_queue_max_segment_size(struct request_queue
*q
, unsigned int max_size
)
316 if (max_size
< PAGE_CACHE_SIZE
) {
317 max_size
= PAGE_CACHE_SIZE
;
318 printk(KERN_INFO
"%s: set to minimum %d\n",
322 q
->limits
.max_segment_size
= max_size
;
324 EXPORT_SYMBOL(blk_queue_max_segment_size
);
327 * blk_queue_logical_block_size - set logical block size for the queue
328 * @q: the request queue for the device
329 * @size: the logical block size, in bytes
332 * This should be set to the lowest possible block size that the
333 * storage device can address. The default of 512 covers most
336 void blk_queue_logical_block_size(struct request_queue
*q
, unsigned short size
)
338 q
->limits
.logical_block_size
= size
;
340 if (q
->limits
.physical_block_size
< size
)
341 q
->limits
.physical_block_size
= size
;
343 if (q
->limits
.io_min
< q
->limits
.physical_block_size
)
344 q
->limits
.io_min
= q
->limits
.physical_block_size
;
346 EXPORT_SYMBOL(blk_queue_logical_block_size
);
349 * blk_queue_physical_block_size - set physical block size for the queue
350 * @q: the request queue for the device
351 * @size: the physical block size, in bytes
354 * This should be set to the lowest possible sector size that the
355 * hardware can operate on without reverting to read-modify-write
358 void blk_queue_physical_block_size(struct request_queue
*q
, unsigned short size
)
360 q
->limits
.physical_block_size
= size
;
362 if (q
->limits
.physical_block_size
< q
->limits
.logical_block_size
)
363 q
->limits
.physical_block_size
= q
->limits
.logical_block_size
;
365 if (q
->limits
.io_min
< q
->limits
.physical_block_size
)
366 q
->limits
.io_min
= q
->limits
.physical_block_size
;
368 EXPORT_SYMBOL(blk_queue_physical_block_size
);
371 * blk_queue_alignment_offset - set physical block alignment offset
372 * @q: the request queue for the device
373 * @offset: alignment offset in bytes
376 * Some devices are naturally misaligned to compensate for things like
377 * the legacy DOS partition table 63-sector offset. Low-level drivers
378 * should call this function for devices whose first sector is not
381 void blk_queue_alignment_offset(struct request_queue
*q
, unsigned int offset
)
383 q
->limits
.alignment_offset
=
384 offset
& (q
->limits
.physical_block_size
- 1);
385 q
->limits
.misaligned
= 0;
387 EXPORT_SYMBOL(blk_queue_alignment_offset
);
390 * blk_limits_io_min - set minimum request size for a device
391 * @limits: the queue limits
392 * @min: smallest I/O size in bytes
395 * Some devices have an internal block size bigger than the reported
396 * hardware sector size. This function can be used to signal the
397 * smallest I/O the device can perform without incurring a performance
400 void blk_limits_io_min(struct queue_limits
*limits
, unsigned int min
)
402 limits
->io_min
= min
;
404 if (limits
->io_min
< limits
->logical_block_size
)
405 limits
->io_min
= limits
->logical_block_size
;
407 if (limits
->io_min
< limits
->physical_block_size
)
408 limits
->io_min
= limits
->physical_block_size
;
410 EXPORT_SYMBOL(blk_limits_io_min
);
413 * blk_queue_io_min - set minimum request size for the queue
414 * @q: the request queue for the device
415 * @min: smallest I/O size in bytes
418 * Storage devices may report a granularity or preferred minimum I/O
419 * size which is the smallest request the device can perform without
420 * incurring a performance penalty. For disk drives this is often the
421 * physical block size. For RAID arrays it is often the stripe chunk
422 * size. A properly aligned multiple of minimum_io_size is the
423 * preferred request size for workloads where a high number of I/O
424 * operations is desired.
426 void blk_queue_io_min(struct request_queue
*q
, unsigned int min
)
428 blk_limits_io_min(&q
->limits
, min
);
430 EXPORT_SYMBOL(blk_queue_io_min
);
433 * blk_limits_io_opt - set optimal request size for a device
434 * @limits: the queue limits
435 * @opt: smallest I/O size in bytes
438 * Storage devices may report an optimal I/O size, which is the
439 * device's preferred unit for sustained I/O. This is rarely reported
440 * for disk drives. For RAID arrays it is usually the stripe width or
441 * the internal track size. A properly aligned multiple of
442 * optimal_io_size is the preferred request size for workloads where
443 * sustained throughput is desired.
445 void blk_limits_io_opt(struct queue_limits
*limits
, unsigned int opt
)
447 limits
->io_opt
= opt
;
449 EXPORT_SYMBOL(blk_limits_io_opt
);
452 * blk_queue_io_opt - set optimal request size for the queue
453 * @q: the request queue for the device
454 * @opt: optimal request size in bytes
457 * Storage devices may report an optimal I/O size, which is the
458 * device's preferred unit for sustained I/O. This is rarely reported
459 * for disk drives. For RAID arrays it is usually the stripe width or
460 * the internal track size. A properly aligned multiple of
461 * optimal_io_size is the preferred request size for workloads where
462 * sustained throughput is desired.
464 void blk_queue_io_opt(struct request_queue
*q
, unsigned int opt
)
466 blk_limits_io_opt(&q
->limits
, opt
);
468 EXPORT_SYMBOL(blk_queue_io_opt
);
471 * Returns the minimum that is _not_ zero, unless both are zero.
473 #define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
476 * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
477 * @t: the stacking driver (top)
478 * @b: the underlying device (bottom)
480 void blk_queue_stack_limits(struct request_queue
*t
, struct request_queue
*b
)
482 blk_stack_limits(&t
->limits
, &b
->limits
, 0);
486 else if (!test_bit(QUEUE_FLAG_CLUSTER
, &b
->queue_flags
)) {
488 spin_lock_irqsave(t
->queue_lock
, flags
);
489 queue_flag_clear(QUEUE_FLAG_CLUSTER
, t
);
490 spin_unlock_irqrestore(t
->queue_lock
, flags
);
493 EXPORT_SYMBOL(blk_queue_stack_limits
);
495 static unsigned int lcm(unsigned int a
, unsigned int b
)
498 return (a
* b
) / gcd(a
, b
);
506 * blk_stack_limits - adjust queue_limits for stacked devices
507 * @t: the stacking driver limits (top)
508 * @b: the underlying queue limits (bottom)
509 * @offset: offset to beginning of data within component device
512 * Merges two queue_limit structs. Returns 0 if alignment didn't
513 * change. Returns -1 if adding the bottom device caused
516 int blk_stack_limits(struct queue_limits
*t
, struct queue_limits
*b
,
523 t
->max_sectors
= min_not_zero(t
->max_sectors
, b
->max_sectors
);
524 t
->max_hw_sectors
= min_not_zero(t
->max_hw_sectors
, b
->max_hw_sectors
);
525 t
->bounce_pfn
= min_not_zero(t
->bounce_pfn
, b
->bounce_pfn
);
527 t
->seg_boundary_mask
= min_not_zero(t
->seg_boundary_mask
,
528 b
->seg_boundary_mask
);
530 t
->max_phys_segments
= min_not_zero(t
->max_phys_segments
,
531 b
->max_phys_segments
);
533 t
->max_hw_segments
= min_not_zero(t
->max_hw_segments
,
536 t
->max_segment_size
= min_not_zero(t
->max_segment_size
,
537 b
->max_segment_size
);
539 t
->logical_block_size
= max(t
->logical_block_size
,
540 b
->logical_block_size
);
542 t
->physical_block_size
= max(t
->physical_block_size
,
543 b
->physical_block_size
);
545 t
->io_min
= max(t
->io_min
, b
->io_min
);
546 t
->no_cluster
|= b
->no_cluster
;
548 /* Bottom device offset aligned? */
550 (offset
& (b
->physical_block_size
- 1)) != b
->alignment_offset
) {
556 (offset
& (b
->discard_granularity
- 1)) != b
->discard_alignment
) {
557 t
->discard_misaligned
= 1;
561 /* If top has no alignment offset, inherit from bottom */
562 if (!t
->alignment_offset
)
563 t
->alignment_offset
=
564 b
->alignment_offset
& (b
->physical_block_size
- 1);
566 if (!t
->discard_alignment
)
567 t
->discard_alignment
=
568 b
->discard_alignment
& (b
->discard_granularity
- 1);
570 /* Top device aligned on logical block boundary? */
571 if (t
->alignment_offset
& (t
->logical_block_size
- 1)) {
576 /* Find lcm() of optimal I/O size and granularity */
577 t
->io_opt
= lcm(t
->io_opt
, b
->io_opt
);
578 t
->discard_granularity
= lcm(t
->discard_granularity
,
579 b
->discard_granularity
);
581 /* Verify that optimal I/O size is a multiple of io_min */
582 if (t
->io_min
&& t
->io_opt
% t
->io_min
)
587 EXPORT_SYMBOL(blk_stack_limits
);
590 * disk_stack_limits - adjust queue limits for stacked drivers
591 * @disk: MD/DM gendisk (top)
592 * @bdev: the underlying block device (bottom)
593 * @offset: offset to beginning of data within component device
596 * Merges the limits for two queues. Returns 0 if alignment
597 * didn't change. Returns -1 if adding the bottom device caused
600 void disk_stack_limits(struct gendisk
*disk
, struct block_device
*bdev
,
603 struct request_queue
*t
= disk
->queue
;
604 struct request_queue
*b
= bdev_get_queue(bdev
);
606 offset
+= get_start_sect(bdev
) << 9;
608 if (blk_stack_limits(&t
->limits
, &b
->limits
, offset
) < 0) {
609 char top
[BDEVNAME_SIZE
], bottom
[BDEVNAME_SIZE
];
611 disk_name(disk
, 0, top
);
612 bdevname(bdev
, bottom
);
614 printk(KERN_NOTICE
"%s: Warning: Device %s is misaligned\n",
620 else if (!test_bit(QUEUE_FLAG_CLUSTER
, &b
->queue_flags
)) {
623 spin_lock_irqsave(t
->queue_lock
, flags
);
624 if (!test_bit(QUEUE_FLAG_CLUSTER
, &b
->queue_flags
))
625 queue_flag_clear(QUEUE_FLAG_CLUSTER
, t
);
626 spin_unlock_irqrestore(t
->queue_lock
, flags
);
629 EXPORT_SYMBOL(disk_stack_limits
);
632 * blk_queue_dma_pad - set pad mask
633 * @q: the request queue for the device
638 * Appending pad buffer to a request modifies the last entry of a
639 * scatter list such that it includes the pad buffer.
641 void blk_queue_dma_pad(struct request_queue
*q
, unsigned int mask
)
643 q
->dma_pad_mask
= mask
;
645 EXPORT_SYMBOL(blk_queue_dma_pad
);
648 * blk_queue_update_dma_pad - update pad mask
649 * @q: the request queue for the device
652 * Update dma pad mask.
654 * Appending pad buffer to a request modifies the last entry of a
655 * scatter list such that it includes the pad buffer.
657 void blk_queue_update_dma_pad(struct request_queue
*q
, unsigned int mask
)
659 if (mask
> q
->dma_pad_mask
)
660 q
->dma_pad_mask
= mask
;
662 EXPORT_SYMBOL(blk_queue_update_dma_pad
);
665 * blk_queue_dma_drain - Set up a drain buffer for excess dma.
666 * @q: the request queue for the device
667 * @dma_drain_needed: fn which returns non-zero if drain is necessary
668 * @buf: physically contiguous buffer
669 * @size: size of the buffer in bytes
671 * Some devices have excess DMA problems and can't simply discard (or
672 * zero fill) the unwanted piece of the transfer. They have to have a
673 * real area of memory to transfer it into. The use case for this is
674 * ATAPI devices in DMA mode. If the packet command causes a transfer
675 * bigger than the transfer size some HBAs will lock up if there
676 * aren't DMA elements to contain the excess transfer. What this API
677 * does is adjust the queue so that the buf is always appended
678 * silently to the scatterlist.
680 * Note: This routine adjusts max_hw_segments to make room for
681 * appending the drain buffer. If you call
682 * blk_queue_max_hw_segments() or blk_queue_max_phys_segments() after
683 * calling this routine, you must set the limit to one fewer than your
684 * device can support otherwise there won't be room for the drain
687 int blk_queue_dma_drain(struct request_queue
*q
,
688 dma_drain_needed_fn
*dma_drain_needed
,
689 void *buf
, unsigned int size
)
691 if (queue_max_hw_segments(q
) < 2 || queue_max_phys_segments(q
) < 2)
693 /* make room for appending the drain */
694 blk_queue_max_hw_segments(q
, queue_max_hw_segments(q
) - 1);
695 blk_queue_max_phys_segments(q
, queue_max_phys_segments(q
) - 1);
696 q
->dma_drain_needed
= dma_drain_needed
;
697 q
->dma_drain_buffer
= buf
;
698 q
->dma_drain_size
= size
;
702 EXPORT_SYMBOL_GPL(blk_queue_dma_drain
);
705 * blk_queue_segment_boundary - set boundary rules for segment merging
706 * @q: the request queue for the device
707 * @mask: the memory boundary mask
709 void blk_queue_segment_boundary(struct request_queue
*q
, unsigned long mask
)
711 if (mask
< PAGE_CACHE_SIZE
- 1) {
712 mask
= PAGE_CACHE_SIZE
- 1;
713 printk(KERN_INFO
"%s: set to minimum %lx\n",
717 q
->limits
.seg_boundary_mask
= mask
;
719 EXPORT_SYMBOL(blk_queue_segment_boundary
);
722 * blk_queue_dma_alignment - set dma length and memory alignment
723 * @q: the request queue for the device
724 * @mask: alignment mask
727 * set required memory and length alignment for direct dma transactions.
728 * this is used when building direct io requests for the queue.
731 void blk_queue_dma_alignment(struct request_queue
*q
, int mask
)
733 q
->dma_alignment
= mask
;
735 EXPORT_SYMBOL(blk_queue_dma_alignment
);
738 * blk_queue_update_dma_alignment - update dma length and memory alignment
739 * @q: the request queue for the device
740 * @mask: alignment mask
743 * update required memory and length alignment for direct dma transactions.
744 * If the requested alignment is larger than the current alignment, then
745 * the current queue alignment is updated to the new value, otherwise it
746 * is left alone. The design of this is to allow multiple objects
747 * (driver, device, transport etc) to set their respective
748 * alignments without having them interfere.
751 void blk_queue_update_dma_alignment(struct request_queue
*q
, int mask
)
753 BUG_ON(mask
> PAGE_SIZE
);
755 if (mask
> q
->dma_alignment
)
756 q
->dma_alignment
= mask
;
758 EXPORT_SYMBOL(blk_queue_update_dma_alignment
);
760 static int __init
blk_settings_init(void)
762 blk_max_low_pfn
= max_low_pfn
- 1;
763 blk_max_pfn
= max_pfn
- 1;
766 subsys_initcall(blk_settings_init
);