BKL: Remove BKL from fat
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / block / blk-settings.c
bloba234f4bf1d6ffb7dda8a71593c3f777aa66baec0
1 /*
2 * Functions related to setting various queue properties from drivers
3 */
4 #include <linux/kernel.h>
5 #include <linux/module.h>
6 #include <linux/init.h>
7 #include <linux/bio.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>
15 #include "blk.h"
17 unsigned long blk_max_low_pfn;
18 EXPORT_SYMBOL(blk_max_low_pfn);
20 unsigned long blk_max_pfn;
22 /**
23 * blk_queue_prep_rq - set a prepare_request function for queue
24 * @q: 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)
35 q->prep_rq_fn = pfn;
37 EXPORT_SYMBOL(blk_queue_prep_rq);
39 /**
40 * blk_queue_unprep_rq - set an unprepare_request function for queue
41 * @q: 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);
56 /**
57 * blk_queue_merge_bvec - set a merge_bvec function for queue
58 * @q: 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
70 * honored.
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)
98 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
106 * Description:
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->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
115 lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
116 lim->max_sectors = BLK_DEF_MAX_SECTORS;
117 lim->max_hw_sectors = INT_MAX;
118 lim->max_discard_sectors = 0;
119 lim->discard_granularity = 0;
120 lim->discard_alignment = 0;
121 lim->discard_misaligned = 0;
122 lim->discard_zeroes_data = -1;
123 lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;
124 lim->bounce_pfn = (unsigned long)(BLK_BOUNCE_ANY >> PAGE_SHIFT);
125 lim->alignment_offset = 0;
126 lim->io_opt = 0;
127 lim->misaligned = 0;
128 lim->no_cluster = 0;
130 EXPORT_SYMBOL(blk_set_default_limits);
133 * blk_queue_make_request - define an alternate make_request function for a device
134 * @q: the request queue for the device to be affected
135 * @mfn: the alternate make_request function
137 * Description:
138 * The normal way for &struct bios to be passed to a device
139 * driver is for them to be collected into requests on a request
140 * queue, and then to allow the device driver to select requests
141 * off that queue when it is ready. This works well for many block
142 * devices. However some block devices (typically virtual devices
143 * such as md or lvm) do not benefit from the processing on the
144 * request queue, and are served best by having the requests passed
145 * directly to them. This can be achieved by providing a function
146 * to blk_queue_make_request().
148 * Caveat:
149 * The driver that does this *must* be able to deal appropriately
150 * with buffers in "highmemory". This can be accomplished by either calling
151 * __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
152 * blk_queue_bounce() to create a buffer in normal memory.
154 void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
157 * set defaults
159 q->nr_requests = BLKDEV_MAX_RQ;
161 q->make_request_fn = mfn;
162 blk_queue_dma_alignment(q, 511);
163 blk_queue_congestion_threshold(q);
164 q->nr_batching = BLK_BATCH_REQ;
166 q->unplug_thresh = 4; /* hmm */
167 q->unplug_delay = msecs_to_jiffies(3); /* 3 milliseconds */
168 if (q->unplug_delay == 0)
169 q->unplug_delay = 1;
171 q->unplug_timer.function = blk_unplug_timeout;
172 q->unplug_timer.data = (unsigned long)q;
174 blk_set_default_limits(&q->limits);
175 blk_queue_max_hw_sectors(q, BLK_SAFE_MAX_SECTORS);
178 * If the caller didn't supply a lock, fall back to our embedded
179 * per-queue locks
181 if (!q->queue_lock)
182 q->queue_lock = &q->__queue_lock;
185 * by default assume old behaviour and bounce for any highmem page
187 blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
189 EXPORT_SYMBOL(blk_queue_make_request);
192 * blk_queue_bounce_limit - set bounce buffer limit for queue
193 * @q: the request queue for the device
194 * @dma_mask: the maximum address the device can handle
196 * Description:
197 * Different hardware can have different requirements as to what pages
198 * it can do I/O directly to. A low level driver can call
199 * blk_queue_bounce_limit to have lower memory pages allocated as bounce
200 * buffers for doing I/O to pages residing above @dma_mask.
202 void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)
204 unsigned long b_pfn = dma_mask >> PAGE_SHIFT;
205 int dma = 0;
207 q->bounce_gfp = GFP_NOIO;
208 #if BITS_PER_LONG == 64
210 * Assume anything <= 4GB can be handled by IOMMU. Actually
211 * some IOMMUs can handle everything, but I don't know of a
212 * way to test this here.
214 if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
215 dma = 1;
216 q->limits.bounce_pfn = max_low_pfn;
217 #else
218 if (b_pfn < blk_max_low_pfn)
219 dma = 1;
220 q->limits.bounce_pfn = b_pfn;
221 #endif
222 if (dma) {
223 init_emergency_isa_pool();
224 q->bounce_gfp = GFP_NOIO | GFP_DMA;
225 q->limits.bounce_pfn = b_pfn;
228 EXPORT_SYMBOL(blk_queue_bounce_limit);
231 * blk_queue_max_hw_sectors - set max sectors for a request for this queue
232 * @q: the request queue for the device
233 * @max_hw_sectors: max hardware sectors in the usual 512b unit
235 * Description:
236 * Enables a low level driver to set a hard upper limit,
237 * max_hw_sectors, on the size of requests. max_hw_sectors is set by
238 * the device driver based upon the combined capabilities of I/O
239 * controller and storage device.
241 * max_sectors is a soft limit imposed by the block layer for
242 * filesystem type requests. This value can be overridden on a
243 * per-device basis in /sys/block/<device>/queue/max_sectors_kb.
244 * The soft limit can not exceed max_hw_sectors.
246 void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)
248 if ((max_hw_sectors << 9) < PAGE_CACHE_SIZE) {
249 max_hw_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
250 printk(KERN_INFO "%s: set to minimum %d\n",
251 __func__, max_hw_sectors);
254 q->limits.max_hw_sectors = max_hw_sectors;
255 q->limits.max_sectors = min_t(unsigned int, max_hw_sectors,
256 BLK_DEF_MAX_SECTORS);
258 EXPORT_SYMBOL(blk_queue_max_hw_sectors);
261 * blk_queue_max_discard_sectors - set max sectors for a single discard
262 * @q: the request queue for the device
263 * @max_discard_sectors: maximum number of sectors to discard
265 void blk_queue_max_discard_sectors(struct request_queue *q,
266 unsigned int max_discard_sectors)
268 q->limits.max_discard_sectors = max_discard_sectors;
270 EXPORT_SYMBOL(blk_queue_max_discard_sectors);
273 * blk_queue_max_segments - set max hw segments for a request for this queue
274 * @q: the request queue for the device
275 * @max_segments: max number of segments
277 * Description:
278 * Enables a low level driver to set an upper limit on the number of
279 * hw data segments in a request.
281 void blk_queue_max_segments(struct request_queue *q, unsigned short max_segments)
283 if (!max_segments) {
284 max_segments = 1;
285 printk(KERN_INFO "%s: set to minimum %d\n",
286 __func__, max_segments);
289 q->limits.max_segments = max_segments;
291 EXPORT_SYMBOL(blk_queue_max_segments);
294 * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
295 * @q: the request queue for the device
296 * @max_size: max size of segment in bytes
298 * Description:
299 * Enables a low level driver to set an upper limit on the size of a
300 * coalesced segment
302 void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
304 if (max_size < PAGE_CACHE_SIZE) {
305 max_size = PAGE_CACHE_SIZE;
306 printk(KERN_INFO "%s: set to minimum %d\n",
307 __func__, max_size);
310 q->limits.max_segment_size = max_size;
312 EXPORT_SYMBOL(blk_queue_max_segment_size);
315 * blk_queue_logical_block_size - set logical block size for the queue
316 * @q: the request queue for the device
317 * @size: the logical block size, in bytes
319 * Description:
320 * This should be set to the lowest possible block size that the
321 * storage device can address. The default of 512 covers most
322 * hardware.
324 void blk_queue_logical_block_size(struct request_queue *q, unsigned short size)
326 q->limits.logical_block_size = size;
328 if (q->limits.physical_block_size < size)
329 q->limits.physical_block_size = size;
331 if (q->limits.io_min < q->limits.physical_block_size)
332 q->limits.io_min = q->limits.physical_block_size;
334 EXPORT_SYMBOL(blk_queue_logical_block_size);
337 * blk_queue_physical_block_size - set physical block size for the queue
338 * @q: the request queue for the device
339 * @size: the physical block size, in bytes
341 * Description:
342 * This should be set to the lowest possible sector size that the
343 * hardware can operate on without reverting to read-modify-write
344 * operations.
346 void blk_queue_physical_block_size(struct request_queue *q, unsigned short size)
348 q->limits.physical_block_size = size;
350 if (q->limits.physical_block_size < q->limits.logical_block_size)
351 q->limits.physical_block_size = q->limits.logical_block_size;
353 if (q->limits.io_min < q->limits.physical_block_size)
354 q->limits.io_min = q->limits.physical_block_size;
356 EXPORT_SYMBOL(blk_queue_physical_block_size);
359 * blk_queue_alignment_offset - set physical block alignment offset
360 * @q: the request queue for the device
361 * @offset: alignment offset in bytes
363 * Description:
364 * Some devices are naturally misaligned to compensate for things like
365 * the legacy DOS partition table 63-sector offset. Low-level drivers
366 * should call this function for devices whose first sector is not
367 * naturally aligned.
369 void blk_queue_alignment_offset(struct request_queue *q, unsigned int offset)
371 q->limits.alignment_offset =
372 offset & (q->limits.physical_block_size - 1);
373 q->limits.misaligned = 0;
375 EXPORT_SYMBOL(blk_queue_alignment_offset);
378 * blk_limits_io_min - set minimum request size for a device
379 * @limits: the queue limits
380 * @min: smallest I/O size in bytes
382 * Description:
383 * Some devices have an internal block size bigger than the reported
384 * hardware sector size. This function can be used to signal the
385 * smallest I/O the device can perform without incurring a performance
386 * penalty.
388 void blk_limits_io_min(struct queue_limits *limits, unsigned int min)
390 limits->io_min = min;
392 if (limits->io_min < limits->logical_block_size)
393 limits->io_min = limits->logical_block_size;
395 if (limits->io_min < limits->physical_block_size)
396 limits->io_min = limits->physical_block_size;
398 EXPORT_SYMBOL(blk_limits_io_min);
401 * blk_queue_io_min - set minimum request size for the queue
402 * @q: the request queue for the device
403 * @min: smallest I/O size in bytes
405 * Description:
406 * Storage devices may report a granularity or preferred minimum I/O
407 * size which is the smallest request the device can perform without
408 * incurring a performance penalty. For disk drives this is often the
409 * physical block size. For RAID arrays it is often the stripe chunk
410 * size. A properly aligned multiple of minimum_io_size is the
411 * preferred request size for workloads where a high number of I/O
412 * operations is desired.
414 void blk_queue_io_min(struct request_queue *q, unsigned int min)
416 blk_limits_io_min(&q->limits, min);
418 EXPORT_SYMBOL(blk_queue_io_min);
421 * blk_limits_io_opt - set optimal request size for a device
422 * @limits: the queue limits
423 * @opt: smallest I/O size in bytes
425 * Description:
426 * Storage devices may report an optimal I/O size, which is the
427 * device's preferred unit for sustained I/O. This is rarely reported
428 * for disk drives. For RAID arrays it is usually the stripe width or
429 * the internal track size. A properly aligned multiple of
430 * optimal_io_size is the preferred request size for workloads where
431 * sustained throughput is desired.
433 void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt)
435 limits->io_opt = opt;
437 EXPORT_SYMBOL(blk_limits_io_opt);
440 * blk_queue_io_opt - set optimal request size for the queue
441 * @q: the request queue for the device
442 * @opt: optimal request size in bytes
444 * Description:
445 * Storage devices may report an optimal I/O size, which is the
446 * device's preferred unit for sustained I/O. This is rarely reported
447 * for disk drives. For RAID arrays it is usually the stripe width or
448 * the internal track size. A properly aligned multiple of
449 * optimal_io_size is the preferred request size for workloads where
450 * sustained throughput is desired.
452 void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
454 blk_limits_io_opt(&q->limits, opt);
456 EXPORT_SYMBOL(blk_queue_io_opt);
459 * Returns the minimum that is _not_ zero, unless both are zero.
461 #define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
464 * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
465 * @t: the stacking driver (top)
466 * @b: the underlying device (bottom)
468 void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
470 blk_stack_limits(&t->limits, &b->limits, 0);
472 if (!t->queue_lock)
473 WARN_ON_ONCE(1);
474 else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
475 unsigned long flags;
476 spin_lock_irqsave(t->queue_lock, flags);
477 queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
478 spin_unlock_irqrestore(t->queue_lock, flags);
481 EXPORT_SYMBOL(blk_queue_stack_limits);
484 * blk_stack_limits - adjust queue_limits for stacked devices
485 * @t: the stacking driver limits (top device)
486 * @b: the underlying queue limits (bottom, component device)
487 * @start: first data sector within component device
489 * Description:
490 * This function is used by stacking drivers like MD and DM to ensure
491 * that all component devices have compatible block sizes and
492 * alignments. The stacking driver must provide a queue_limits
493 * struct (top) and then iteratively call the stacking function for
494 * all component (bottom) devices. The stacking function will
495 * attempt to combine the values and ensure proper alignment.
497 * Returns 0 if the top and bottom queue_limits are compatible. The
498 * top device's block sizes and alignment offsets may be adjusted to
499 * ensure alignment with the bottom device. If no compatible sizes
500 * and alignments exist, -1 is returned and the resulting top
501 * queue_limits will have the misaligned flag set to indicate that
502 * the alignment_offset is undefined.
504 int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
505 sector_t start)
507 unsigned int top, bottom, alignment, ret = 0;
509 t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
510 t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
511 t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
513 t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
514 b->seg_boundary_mask);
516 t->max_segments = min_not_zero(t->max_segments, b->max_segments);
518 t->max_segment_size = min_not_zero(t->max_segment_size,
519 b->max_segment_size);
521 t->misaligned |= b->misaligned;
523 alignment = queue_limit_alignment_offset(b, start);
525 /* Bottom device has different alignment. Check that it is
526 * compatible with the current top alignment.
528 if (t->alignment_offset != alignment) {
530 top = max(t->physical_block_size, t->io_min)
531 + t->alignment_offset;
532 bottom = max(b->physical_block_size, b->io_min) + alignment;
534 /* Verify that top and bottom intervals line up */
535 if (max(top, bottom) & (min(top, bottom) - 1)) {
536 t->misaligned = 1;
537 ret = -1;
541 t->logical_block_size = max(t->logical_block_size,
542 b->logical_block_size);
544 t->physical_block_size = max(t->physical_block_size,
545 b->physical_block_size);
547 t->io_min = max(t->io_min, b->io_min);
548 t->io_opt = lcm(t->io_opt, b->io_opt);
550 t->no_cluster |= b->no_cluster;
551 t->discard_zeroes_data &= b->discard_zeroes_data;
553 /* Physical block size a multiple of the logical block size? */
554 if (t->physical_block_size & (t->logical_block_size - 1)) {
555 t->physical_block_size = t->logical_block_size;
556 t->misaligned = 1;
557 ret = -1;
560 /* Minimum I/O a multiple of the physical block size? */
561 if (t->io_min & (t->physical_block_size - 1)) {
562 t->io_min = t->physical_block_size;
563 t->misaligned = 1;
564 ret = -1;
567 /* Optimal I/O a multiple of the physical block size? */
568 if (t->io_opt & (t->physical_block_size - 1)) {
569 t->io_opt = 0;
570 t->misaligned = 1;
571 ret = -1;
574 /* Find lowest common alignment_offset */
575 t->alignment_offset = lcm(t->alignment_offset, alignment)
576 & (max(t->physical_block_size, t->io_min) - 1);
578 /* Verify that new alignment_offset is on a logical block boundary */
579 if (t->alignment_offset & (t->logical_block_size - 1)) {
580 t->misaligned = 1;
581 ret = -1;
584 /* Discard alignment and granularity */
585 if (b->discard_granularity) {
586 alignment = queue_limit_discard_alignment(b, start);
588 if (t->discard_granularity != 0 &&
589 t->discard_alignment != alignment) {
590 top = t->discard_granularity + t->discard_alignment;
591 bottom = b->discard_granularity + alignment;
593 /* Verify that top and bottom intervals line up */
594 if (max(top, bottom) & (min(top, bottom) - 1))
595 t->discard_misaligned = 1;
598 t->max_discard_sectors = min_not_zero(t->max_discard_sectors,
599 b->max_discard_sectors);
600 t->discard_granularity = max(t->discard_granularity,
601 b->discard_granularity);
602 t->discard_alignment = lcm(t->discard_alignment, alignment) &
603 (t->discard_granularity - 1);
606 return ret;
608 EXPORT_SYMBOL(blk_stack_limits);
611 * bdev_stack_limits - adjust queue limits for stacked drivers
612 * @t: the stacking driver limits (top device)
613 * @bdev: the component block_device (bottom)
614 * @start: first data sector within component device
616 * Description:
617 * Merges queue limits for a top device and a block_device. Returns
618 * 0 if alignment didn't change. Returns -1 if adding the bottom
619 * device caused misalignment.
621 int bdev_stack_limits(struct queue_limits *t, struct block_device *bdev,
622 sector_t start)
624 struct request_queue *bq = bdev_get_queue(bdev);
626 start += get_start_sect(bdev);
628 return blk_stack_limits(t, &bq->limits, start);
630 EXPORT_SYMBOL(bdev_stack_limits);
633 * disk_stack_limits - adjust queue limits for stacked drivers
634 * @disk: MD/DM gendisk (top)
635 * @bdev: the underlying block device (bottom)
636 * @offset: offset to beginning of data within component device
638 * Description:
639 * Merges the limits for a top level gendisk and a bottom level
640 * block_device.
642 void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
643 sector_t offset)
645 struct request_queue *t = disk->queue;
646 struct request_queue *b = bdev_get_queue(bdev);
648 if (bdev_stack_limits(&t->limits, bdev, offset >> 9) < 0) {
649 char top[BDEVNAME_SIZE], bottom[BDEVNAME_SIZE];
651 disk_name(disk, 0, top);
652 bdevname(bdev, bottom);
654 printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
655 top, bottom);
658 if (!t->queue_lock)
659 WARN_ON_ONCE(1);
660 else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
661 unsigned long flags;
663 spin_lock_irqsave(t->queue_lock, flags);
664 if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
665 queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
666 spin_unlock_irqrestore(t->queue_lock, flags);
669 EXPORT_SYMBOL(disk_stack_limits);
672 * blk_queue_dma_pad - set pad mask
673 * @q: the request queue for the device
674 * @mask: pad mask
676 * Set dma pad mask.
678 * Appending pad buffer to a request modifies the last entry of a
679 * scatter list such that it includes the pad buffer.
681 void blk_queue_dma_pad(struct request_queue *q, unsigned int mask)
683 q->dma_pad_mask = mask;
685 EXPORT_SYMBOL(blk_queue_dma_pad);
688 * blk_queue_update_dma_pad - update pad mask
689 * @q: the request queue for the device
690 * @mask: pad mask
692 * Update dma pad mask.
694 * Appending pad buffer to a request modifies the last entry of a
695 * scatter list such that it includes the pad buffer.
697 void blk_queue_update_dma_pad(struct request_queue *q, unsigned int mask)
699 if (mask > q->dma_pad_mask)
700 q->dma_pad_mask = mask;
702 EXPORT_SYMBOL(blk_queue_update_dma_pad);
705 * blk_queue_dma_drain - Set up a drain buffer for excess dma.
706 * @q: the request queue for the device
707 * @dma_drain_needed: fn which returns non-zero if drain is necessary
708 * @buf: physically contiguous buffer
709 * @size: size of the buffer in bytes
711 * Some devices have excess DMA problems and can't simply discard (or
712 * zero fill) the unwanted piece of the transfer. They have to have a
713 * real area of memory to transfer it into. The use case for this is
714 * ATAPI devices in DMA mode. If the packet command causes a transfer
715 * bigger than the transfer size some HBAs will lock up if there
716 * aren't DMA elements to contain the excess transfer. What this API
717 * does is adjust the queue so that the buf is always appended
718 * silently to the scatterlist.
720 * Note: This routine adjusts max_hw_segments to make room for appending
721 * the drain buffer. If you call blk_queue_max_segments() after calling
722 * this routine, you must set the limit to one fewer than your device
723 * can support otherwise there won't be room for the drain buffer.
725 int blk_queue_dma_drain(struct request_queue *q,
726 dma_drain_needed_fn *dma_drain_needed,
727 void *buf, unsigned int size)
729 if (queue_max_segments(q) < 2)
730 return -EINVAL;
731 /* make room for appending the drain */
732 blk_queue_max_segments(q, queue_max_segments(q) - 1);
733 q->dma_drain_needed = dma_drain_needed;
734 q->dma_drain_buffer = buf;
735 q->dma_drain_size = size;
737 return 0;
739 EXPORT_SYMBOL_GPL(blk_queue_dma_drain);
742 * blk_queue_segment_boundary - set boundary rules for segment merging
743 * @q: the request queue for the device
744 * @mask: the memory boundary mask
746 void blk_queue_segment_boundary(struct request_queue *q, unsigned long mask)
748 if (mask < PAGE_CACHE_SIZE - 1) {
749 mask = PAGE_CACHE_SIZE - 1;
750 printk(KERN_INFO "%s: set to minimum %lx\n",
751 __func__, mask);
754 q->limits.seg_boundary_mask = mask;
756 EXPORT_SYMBOL(blk_queue_segment_boundary);
759 * blk_queue_dma_alignment - set dma length and memory alignment
760 * @q: the request queue for the device
761 * @mask: alignment mask
763 * description:
764 * set required memory and length alignment for direct dma transactions.
765 * this is used when building direct io requests for the queue.
768 void blk_queue_dma_alignment(struct request_queue *q, int mask)
770 q->dma_alignment = mask;
772 EXPORT_SYMBOL(blk_queue_dma_alignment);
775 * blk_queue_update_dma_alignment - update dma length and memory alignment
776 * @q: the request queue for the device
777 * @mask: alignment mask
779 * description:
780 * update required memory and length alignment for direct dma transactions.
781 * If the requested alignment is larger than the current alignment, then
782 * the current queue alignment is updated to the new value, otherwise it
783 * is left alone. The design of this is to allow multiple objects
784 * (driver, device, transport etc) to set their respective
785 * alignments without having them interfere.
788 void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
790 BUG_ON(mask > PAGE_SIZE);
792 if (mask > q->dma_alignment)
793 q->dma_alignment = mask;
795 EXPORT_SYMBOL(blk_queue_update_dma_alignment);
797 static int __init blk_settings_init(void)
799 blk_max_low_pfn = max_low_pfn - 1;
800 blk_max_pfn = max_pfn - 1;
801 return 0;
803 subsys_initcall(blk_settings_init);