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/lcm.h>
12 #include <linux/jiffies.h>
13 #include <linux/gfp.h>
17 unsigned long blk_max_low_pfn;
18 EXPORT_SYMBOL(blk_max_low_pfn);
20 unsigned long blk_max_pfn;
23 * blk_queue_prep_rq - set a prepare_request function for queue
25 * @pfn: prepare_request function
27 * It's possible for a queue to register a prepare_request callback which
28 * is invoked before the request is handed to the request_fn. The goal of
29 * the function is to prepare a request for I/O, it can be used to build a
30 * cdb from the request data for instance.
33 void blk_queue_prep_rq(struct request_queue *q, prep_rq_fn *pfn)
37 EXPORT_SYMBOL(blk_queue_prep_rq);
40 * blk_queue_unprep_rq - set an unprepare_request function for queue
42 * @ufn: unprepare_request function
44 * It's possible for a queue to register an unprepare_request callback
45 * which is invoked before the request is finally completed. The goal
46 * of the function is to deallocate any data that was allocated in the
47 * prepare_request callback.
50 void blk_queue_unprep_rq(struct request_queue *q, unprep_rq_fn *ufn)
52 q->unprep_rq_fn = ufn;
54 EXPORT_SYMBOL(blk_queue_unprep_rq);
57 * blk_queue_merge_bvec - set a merge_bvec function for queue
59 * @mbfn: merge_bvec_fn
61 * Usually queues have static limitations on the max sectors or segments that
62 * we can put in a request. Stacking drivers may have some settings that
63 * are dynamic, and thus we have to query the queue whether it is ok to
64 * add a new bio_vec to a bio at a given offset or not. If the block device
65 * has such limitations, it needs to register a merge_bvec_fn to control
66 * the size of bio's sent to it. Note that a block device *must* allow a
67 * single page to be added to an empty bio. The block device driver may want
68 * to use the bio_split() function to deal with these bio's. By default
69 * no merge_bvec_fn is defined for a queue, and only the fixed limits are
72 void blk_queue_merge_bvec(struct request_queue *q, merge_bvec_fn *mbfn)
74 q->merge_bvec_fn = mbfn;
76 EXPORT_SYMBOL(blk_queue_merge_bvec);
78 void blk_queue_softirq_done(struct request_queue *q, softirq_done_fn *fn)
80 q->softirq_done_fn = fn;
82 EXPORT_SYMBOL(blk_queue_softirq_done);
84 void blk_queue_rq_timeout(struct request_queue *q, unsigned int timeout)
86 q->rq_timeout = timeout;
88 EXPORT_SYMBOL_GPL(blk_queue_rq_timeout);
90 void blk_queue_rq_timed_out(struct request_queue *q, rq_timed_out_fn *fn)
92 q->rq_timed_out_fn = fn;
94 EXPORT_SYMBOL_GPL(blk_queue_rq_timed_out);
96 void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
100 EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
103 * blk_set_default_limits - reset limits to default values
104 * @lim: the queue_limits structure to reset
107 * Returns a queue_limit struct to its default state. Can be used by
108 * stacking drivers like DM that stage table swaps and reuse an
109 * existing device queue.
111 void blk_set_default_limits(struct queue_limits *lim)
113 lim->max_segments = BLK_MAX_SEGMENTS;
114 lim->max_integrity_segments = 0;
115 lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
116 lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
117 lim->max_sectors = BLK_DEF_MAX_SECTORS;
118 lim->max_hw_sectors = INT_MAX;
119 lim->max_discard_sectors = 0;
120 lim->discard_granularity = 0;
121 lim->discard_alignment = 0;
122 lim->discard_misaligned = 0;
123 lim->discard_zeroes_data = -1;
124 lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;
125 lim->bounce_pfn = (unsigned long)(BLK_BOUNCE_ANY >> PAGE_SHIFT);
126 lim->alignment_offset = 0;
131 EXPORT_SYMBOL(blk_set_default_limits);
134 * blk_queue_make_request - define an alternate make_request function for a device
135 * @q: the request queue for the device to be affected
136 * @mfn: the alternate make_request function
139 * The normal way for &struct bios to be passed to a device
140 * driver is for them to be collected into requests on a request
141 * queue, and then to allow the device driver to select requests
142 * off that queue when it is ready. This works well for many block
143 * devices. However some block devices (typically virtual devices
144 * such as md or lvm) do not benefit from the processing on the
145 * request queue, and are served best by having the requests passed
146 * directly to them. This can be achieved by providing a function
147 * to blk_queue_make_request().
150 * The driver that does this *must* be able to deal appropriately
151 * with buffers in "highmemory". This can be accomplished by either calling
152 * __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
153 * blk_queue_bounce() to create a buffer in normal memory.
155 void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
160 q->nr_requests = BLKDEV_MAX_RQ;
162 q->make_request_fn = mfn;
163 blk_queue_dma_alignment(q, 511);
164 blk_queue_congestion_threshold(q);
165 q->nr_batching = BLK_BATCH_REQ;
167 blk_set_default_limits(&q->limits);
168 blk_queue_max_hw_sectors(q, BLK_SAFE_MAX_SECTORS);
171 * If the caller didn't supply a lock, fall back to our embedded
175 q->queue_lock = &q->__queue_lock;
178 * by default assume old behaviour and bounce for any highmem page
180 blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
182 EXPORT_SYMBOL(blk_queue_make_request);
185 * blk_queue_bounce_limit - set bounce buffer limit for queue
186 * @q: the request queue for the device
187 * @dma_mask: the maximum address the device can handle
190 * Different hardware can have different requirements as to what pages
191 * it can do I/O directly to. A low level driver can call
192 * blk_queue_bounce_limit to have lower memory pages allocated as bounce
193 * buffers for doing I/O to pages residing above @dma_mask.
195 void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)
197 unsigned long b_pfn = dma_mask >> PAGE_SHIFT;
200 q->bounce_gfp = GFP_NOIO;
201 #if BITS_PER_LONG == 64
203 * Assume anything <= 4GB can be handled by IOMMU. Actually
204 * some IOMMUs can handle everything, but I don't know of a
205 * way to test this here.
207 if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
209 q->limits.bounce_pfn = max(max_low_pfn, b_pfn);
211 if (b_pfn < blk_max_low_pfn)
213 q->limits.bounce_pfn = b_pfn;
216 init_emergency_isa_pool();
217 q->bounce_gfp = GFP_NOIO | GFP_DMA;
218 q->limits.bounce_pfn = b_pfn;
221 EXPORT_SYMBOL(blk_queue_bounce_limit);
224 * blk_limits_max_hw_sectors - set hard and soft limit of max sectors for request
225 * @limits: the queue limits
226 * @max_hw_sectors: max hardware sectors in the usual 512b unit
229 * Enables a low level driver to set a hard upper limit,
230 * max_hw_sectors, on the size of requests. max_hw_sectors is set by
231 * the device driver based upon the combined capabilities of I/O
232 * controller and storage device.
234 * max_sectors is a soft limit imposed by the block layer for
235 * filesystem type requests. This value can be overridden on a
236 * per-device basis in /sys/block/<device>/queue/max_sectors_kb.
237 * The soft limit can not exceed max_hw_sectors.
239 void blk_limits_max_hw_sectors(struct queue_limits *limits, unsigned int max_hw_sectors)
241 if ((max_hw_sectors << 9) < PAGE_CACHE_SIZE) {
242 max_hw_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
243 printk(KERN_INFO "%s: set to minimum %d\n",
244 __func__, max_hw_sectors);
247 limits->max_hw_sectors = max_hw_sectors;
248 limits->max_sectors = min_t(unsigned int, max_hw_sectors,
249 BLK_DEF_MAX_SECTORS);
251 EXPORT_SYMBOL(blk_limits_max_hw_sectors);
254 * blk_queue_max_hw_sectors - set max sectors for a request for this queue
255 * @q: the request queue for the device
256 * @max_hw_sectors: max hardware sectors in the usual 512b unit
259 * See description for blk_limits_max_hw_sectors().
261 void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)
263 blk_limits_max_hw_sectors(&q->limits, max_hw_sectors);
265 EXPORT_SYMBOL(blk_queue_max_hw_sectors);
268 * blk_queue_max_discard_sectors - set max sectors for a single discard
269 * @q: the request queue for the device
270 * @max_discard_sectors: maximum number of sectors to discard
272 void blk_queue_max_discard_sectors(struct request_queue *q,
273 unsigned int max_discard_sectors)
275 q->limits.max_discard_sectors = max_discard_sectors;
277 EXPORT_SYMBOL(blk_queue_max_discard_sectors);
280 * blk_queue_max_segments - set max hw segments for a request for this queue
281 * @q: the request queue for the device
282 * @max_segments: max number of segments
285 * Enables a low level driver to set an upper limit on the number of
286 * hw data segments in a request.
288 void blk_queue_max_segments(struct request_queue *q, unsigned short max_segments)
292 printk(KERN_INFO "%s: set to minimum %d\n",
293 __func__, max_segments);
296 q->limits.max_segments = max_segments;
298 EXPORT_SYMBOL(blk_queue_max_segments);
301 * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
302 * @q: the request queue for the device
303 * @max_size: max size of segment in bytes
306 * Enables a low level driver to set an upper limit on the size of a
309 void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
311 if (max_size < PAGE_CACHE_SIZE) {
312 max_size = PAGE_CACHE_SIZE;
313 printk(KERN_INFO "%s: set to minimum %d\n",
317 q->limits.max_segment_size = max_size;
319 EXPORT_SYMBOL(blk_queue_max_segment_size);
322 * blk_queue_logical_block_size - set logical block size for the queue
323 * @q: the request queue for the device
324 * @size: the logical block size, in bytes
327 * This should be set to the lowest possible block size that the
328 * storage device can address. The default of 512 covers most
331 void blk_queue_logical_block_size(struct request_queue *q, unsigned short size)
333 q->limits.logical_block_size = size;
335 if (q->limits.physical_block_size < size)
336 q->limits.physical_block_size = size;
338 if (q->limits.io_min < q->limits.physical_block_size)
339 q->limits.io_min = q->limits.physical_block_size;
341 EXPORT_SYMBOL(blk_queue_logical_block_size);
344 * blk_queue_physical_block_size - set physical block size for the queue
345 * @q: the request queue for the device
346 * @size: the physical block size, in bytes
349 * This should be set to the lowest possible sector size that the
350 * hardware can operate on without reverting to read-modify-write
353 void blk_queue_physical_block_size(struct request_queue *q, unsigned int size)
355 q->limits.physical_block_size = size;
357 if (q->limits.physical_block_size < q->limits.logical_block_size)
358 q->limits.physical_block_size = q->limits.logical_block_size;
360 if (q->limits.io_min < q->limits.physical_block_size)
361 q->limits.io_min = q->limits.physical_block_size;
363 EXPORT_SYMBOL(blk_queue_physical_block_size);
366 * blk_queue_alignment_offset - set physical block alignment offset
367 * @q: the request queue for the device
368 * @offset: alignment offset in bytes
371 * Some devices are naturally misaligned to compensate for things like
372 * the legacy DOS partition table 63-sector offset. Low-level drivers
373 * should call this function for devices whose first sector is not
376 void blk_queue_alignment_offset(struct request_queue *q, unsigned int offset)
378 q->limits.alignment_offset =
379 offset & (q->limits.physical_block_size - 1);
380 q->limits.misaligned = 0;
382 EXPORT_SYMBOL(blk_queue_alignment_offset);
385 * blk_limits_io_min - set minimum request size for a device
386 * @limits: the queue limits
387 * @min: smallest I/O size in bytes
390 * Some devices have an internal block size bigger than the reported
391 * hardware sector size. This function can be used to signal the
392 * smallest I/O the device can perform without incurring a performance
395 void blk_limits_io_min(struct queue_limits *limits, unsigned int min)
397 limits->io_min = min;
399 if (limits->io_min < limits->logical_block_size)
400 limits->io_min = limits->logical_block_size;
402 if (limits->io_min < limits->physical_block_size)
403 limits->io_min = limits->physical_block_size;
405 EXPORT_SYMBOL(blk_limits_io_min);
408 * blk_queue_io_min - set minimum request size for the queue
409 * @q: the request queue for the device
410 * @min: smallest I/O size in bytes
413 * Storage devices may report a granularity or preferred minimum I/O
414 * size which is the smallest request the device can perform without
415 * incurring a performance penalty. For disk drives this is often the
416 * physical block size. For RAID arrays it is often the stripe chunk
417 * size. A properly aligned multiple of minimum_io_size is the
418 * preferred request size for workloads where a high number of I/O
419 * operations is desired.
421 void blk_queue_io_min(struct request_queue *q, unsigned int min)
423 blk_limits_io_min(&q->limits, min);
425 EXPORT_SYMBOL(blk_queue_io_min);
428 * blk_limits_io_opt - set optimal request size for a device
429 * @limits: the queue limits
430 * @opt: smallest I/O size in bytes
433 * Storage devices may report an optimal I/O size, which is the
434 * device's preferred unit for sustained I/O. This is rarely reported
435 * for disk drives. For RAID arrays it is usually the stripe width or
436 * the internal track size. A properly aligned multiple of
437 * optimal_io_size is the preferred request size for workloads where
438 * sustained throughput is desired.
440 void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt)
442 limits->io_opt = opt;
444 EXPORT_SYMBOL(blk_limits_io_opt);
447 * blk_queue_io_opt - set optimal request size for the queue
448 * @q: the request queue for the device
449 * @opt: optimal request size in bytes
452 * Storage devices may report an optimal I/O size, which is the
453 * device's preferred unit for sustained I/O. This is rarely reported
454 * for disk drives. For RAID arrays it is usually the stripe width or
455 * the internal track size. A properly aligned multiple of
456 * optimal_io_size is the preferred request size for workloads where
457 * sustained throughput is desired.
459 void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
461 blk_limits_io_opt(&q->limits, opt);
463 EXPORT_SYMBOL(blk_queue_io_opt);
466 * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
467 * @t: the stacking driver (top)
468 * @b: the underlying device (bottom)
470 void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
472 blk_stack_limits(&t->limits, &b->limits, 0);
474 EXPORT_SYMBOL(blk_queue_stack_limits);
477 * blk_stack_limits - adjust queue_limits for stacked devices
478 * @t: the stacking driver limits (top device)
479 * @b: the underlying queue limits (bottom, component device)
480 * @start: first data sector within component device
483 * This function is used by stacking drivers like MD and DM to ensure
484 * that all component devices have compatible block sizes and
485 * alignments. The stacking driver must provide a queue_limits
486 * struct (top) and then iteratively call the stacking function for
487 * all component (bottom) devices. The stacking function will
488 * attempt to combine the values and ensure proper alignment.
490 * Returns 0 if the top and bottom queue_limits are compatible. The
491 * top device's block sizes and alignment offsets may be adjusted to
492 * ensure alignment with the bottom device. If no compatible sizes
493 * and alignments exist, -1 is returned and the resulting top
494 * queue_limits will have the misaligned flag set to indicate that
495 * the alignment_offset is undefined.
497 int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
500 unsigned int top, bottom, alignment, ret = 0;
502 t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
503 t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
504 t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
506 t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
507 b->seg_boundary_mask);
509 t->max_segments = min_not_zero(t->max_segments, b->max_segments);
510 t->max_integrity_segments = min_not_zero(t->max_integrity_segments,
511 b->max_integrity_segments);
513 t->max_segment_size = min_not_zero(t->max_segment_size,
514 b->max_segment_size);
516 t->misaligned |= b->misaligned;
518 alignment = queue_limit_alignment_offset(b, start);
520 /* Bottom device has different alignment. Check that it is
521 * compatible with the current top alignment.
523 if (t->alignment_offset != alignment) {
525 top = max(t->physical_block_size, t->io_min)
526 + t->alignment_offset;
527 bottom = max(b->physical_block_size, b->io_min) + alignment;
529 /* Verify that top and bottom intervals line up */
530 if (max(top, bottom) & (min(top, bottom) - 1)) {
536 t->logical_block_size = max(t->logical_block_size,
537 b->logical_block_size);
539 t->physical_block_size = max(t->physical_block_size,
540 b->physical_block_size);
542 t->io_min = max(t->io_min, b->io_min);
543 t->io_opt = lcm(t->io_opt, b->io_opt);
545 t->cluster &= b->cluster;
546 t->discard_zeroes_data &= b->discard_zeroes_data;
548 /* Physical block size a multiple of the logical block size? */
549 if (t->physical_block_size & (t->logical_block_size - 1)) {
550 t->physical_block_size = t->logical_block_size;
555 /* Minimum I/O a multiple of the physical block size? */
556 if (t->io_min & (t->physical_block_size - 1)) {
557 t->io_min = t->physical_block_size;
562 /* Optimal I/O a multiple of the physical block size? */
563 if (t->io_opt & (t->physical_block_size - 1)) {
569 /* Find lowest common alignment_offset */
570 t->alignment_offset = lcm(t->alignment_offset, alignment)
571 & (max(t->physical_block_size, t->io_min) - 1);
573 /* Verify that new alignment_offset is on a logical block boundary */
574 if (t->alignment_offset & (t->logical_block_size - 1)) {
579 /* Discard alignment and granularity */
580 if (b->discard_granularity) {
581 alignment = queue_limit_discard_alignment(b, start);
583 if (t->discard_granularity != 0 &&
584 t->discard_alignment != alignment) {
585 top = t->discard_granularity + t->discard_alignment;
586 bottom = b->discard_granularity + alignment;
588 /* Verify that top and bottom intervals line up */
589 if (max(top, bottom) & (min(top, bottom) - 1))
590 t->discard_misaligned = 1;
593 t->max_discard_sectors = min_not_zero(t->max_discard_sectors,
594 b->max_discard_sectors);
595 t->discard_granularity = max(t->discard_granularity,
596 b->discard_granularity);
597 t->discard_alignment = lcm(t->discard_alignment, alignment) &
598 (t->discard_granularity - 1);
603 EXPORT_SYMBOL(blk_stack_limits);
606 * bdev_stack_limits - adjust queue limits for stacked drivers
607 * @t: the stacking driver limits (top device)
608 * @bdev: the component block_device (bottom)
609 * @start: first data sector within component device
612 * Merges queue limits for a top device and a block_device. Returns
613 * 0 if alignment didn't change. Returns -1 if adding the bottom
614 * device caused misalignment.
616 int bdev_stack_limits(struct queue_limits *t, struct block_device *bdev,
619 struct request_queue *bq = bdev_get_queue(bdev);
621 start += get_start_sect(bdev);
623 return blk_stack_limits(t, &bq->limits, start);
625 EXPORT_SYMBOL(bdev_stack_limits);
628 * disk_stack_limits - adjust queue limits for stacked drivers
629 * @disk: MD/DM gendisk (top)
630 * @bdev: the underlying block device (bottom)
631 * @offset: offset to beginning of data within component device
634 * Merges the limits for a top level gendisk and a bottom level
637 void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
640 struct request_queue *t = disk->queue;
642 if (bdev_stack_limits(&t->limits, bdev, offset >> 9) < 0) {
643 char top[BDEVNAME_SIZE], bottom[BDEVNAME_SIZE];
645 disk_name(disk, 0, top);
646 bdevname(bdev, bottom);
648 printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
652 EXPORT_SYMBOL(disk_stack_limits);
655 * blk_queue_dma_pad - set pad mask
656 * @q: the request queue for the device
661 * Appending pad buffer to a request modifies the last entry of a
662 * scatter list such that it includes the pad buffer.
664 void blk_queue_dma_pad(struct request_queue *q, unsigned int mask)
666 q->dma_pad_mask = mask;
668 EXPORT_SYMBOL(blk_queue_dma_pad);
671 * blk_queue_update_dma_pad - update pad mask
672 * @q: the request queue for the device
675 * Update dma pad mask.
677 * Appending pad buffer to a request modifies the last entry of a
678 * scatter list such that it includes the pad buffer.
680 void blk_queue_update_dma_pad(struct request_queue *q, unsigned int mask)
682 if (mask > q->dma_pad_mask)
683 q->dma_pad_mask = mask;
685 EXPORT_SYMBOL(blk_queue_update_dma_pad);
688 * blk_queue_dma_drain - Set up a drain buffer for excess dma.
689 * @q: the request queue for the device
690 * @dma_drain_needed: fn which returns non-zero if drain is necessary
691 * @buf: physically contiguous buffer
692 * @size: size of the buffer in bytes
694 * Some devices have excess DMA problems and can't simply discard (or
695 * zero fill) the unwanted piece of the transfer. They have to have a
696 * real area of memory to transfer it into. The use case for this is
697 * ATAPI devices in DMA mode. If the packet command causes a transfer
698 * bigger than the transfer size some HBAs will lock up if there
699 * aren't DMA elements to contain the excess transfer. What this API
700 * does is adjust the queue so that the buf is always appended
701 * silently to the scatterlist.
703 * Note: This routine adjusts max_hw_segments to make room for appending
704 * the drain buffer. If you call blk_queue_max_segments() after calling
705 * this routine, you must set the limit to one fewer than your device
706 * can support otherwise there won't be room for the drain buffer.
708 int blk_queue_dma_drain(struct request_queue *q,
709 dma_drain_needed_fn *dma_drain_needed,
710 void *buf, unsigned int size)
712 if (queue_max_segments(q) < 2)
714 /* make room for appending the drain */
715 blk_queue_max_segments(q, queue_max_segments(q) - 1);
716 q->dma_drain_needed = dma_drain_needed;
717 q->dma_drain_buffer = buf;
718 q->dma_drain_size = size;
722 EXPORT_SYMBOL_GPL(blk_queue_dma_drain);
725 * blk_queue_segment_boundary - set boundary rules for segment merging
726 * @q: the request queue for the device
727 * @mask: the memory boundary mask
729 void blk_queue_segment_boundary(struct request_queue *q, unsigned long mask)
731 if (mask < PAGE_CACHE_SIZE - 1) {
732 mask = PAGE_CACHE_SIZE - 1;
733 printk(KERN_INFO "%s: set to minimum %lx\n",
737 q->limits.seg_boundary_mask = mask;
739 EXPORT_SYMBOL(blk_queue_segment_boundary);
742 * blk_queue_dma_alignment - set dma length and memory alignment
743 * @q: the request queue for the device
744 * @mask: alignment mask
747 * set required memory and length alignment for direct dma transactions.
748 * this is used when building direct io requests for the queue.
751 void blk_queue_dma_alignment(struct request_queue *q, int mask)
753 q->dma_alignment = mask;
755 EXPORT_SYMBOL(blk_queue_dma_alignment);
758 * blk_queue_update_dma_alignment - update dma length and memory alignment
759 * @q: the request queue for the device
760 * @mask: alignment mask
763 * update required memory and length alignment for direct dma transactions.
764 * If the requested alignment is larger than the current alignment, then
765 * the current queue alignment is updated to the new value, otherwise it
766 * is left alone. The design of this is to allow multiple objects
767 * (driver, device, transport etc) to set their respective
768 * alignments without having them interfere.
771 void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
773 BUG_ON(mask > PAGE_SIZE);
775 if (mask > q->dma_alignment)
776 q->dma_alignment = mask;
778 EXPORT_SYMBOL(blk_queue_update_dma_alignment);
781 * blk_queue_flush - configure queue's cache flush capability
782 * @q: the request queue for the device
783 * @flush: 0, REQ_FLUSH or REQ_FLUSH | REQ_FUA
785 * Tell block layer cache flush capability of @q. If it supports
786 * flushing, REQ_FLUSH should be set. If it supports bypassing
787 * write cache for individual writes, REQ_FUA should be set.
789 void blk_queue_flush(struct request_queue *q, unsigned int flush)
791 WARN_ON_ONCE(flush & ~(REQ_FLUSH | REQ_FUA));
793 if (WARN_ON_ONCE(!(flush & REQ_FLUSH) && (flush & REQ_FUA)))
796 q->flush_flags = flush & (REQ_FLUSH | REQ_FUA);
798 EXPORT_SYMBOL_GPL(blk_queue_flush);
800 static int __init blk_settings_init(void)
802 blk_max_low_pfn = max_low_pfn - 1;
803 blk_max_pfn = max_pfn - 1;
806 subsys_initcall(blk_settings_init);