Root/block/blk-settings.c

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>
14
15#include "blk.h"
16
17unsigned long blk_max_low_pfn;
18EXPORT_SYMBOL(blk_max_low_pfn);
19
20unsigned long blk_max_pfn;
21
22/**
23 * blk_queue_prep_rq - set a prepare_request function for queue
24 * @q: queue
25 * @pfn: prepare_request function
26 *
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.
31 *
32 */
33void blk_queue_prep_rq(struct request_queue *q, prep_rq_fn *pfn)
34{
35    q->prep_rq_fn = pfn;
36}
37EXPORT_SYMBOL(blk_queue_prep_rq);
38
39/**
40 * blk_queue_merge_bvec - set a merge_bvec function for queue
41 * @q: queue
42 * @mbfn: merge_bvec_fn
43 *
44 * Usually queues have static limitations on the max sectors or segments that
45 * we can put in a request. Stacking drivers may have some settings that
46 * are dynamic, and thus we have to query the queue whether it is ok to
47 * add a new bio_vec to a bio at a given offset or not. If the block device
48 * has such limitations, it needs to register a merge_bvec_fn to control
49 * the size of bio's sent to it. Note that a block device *must* allow a
50 * single page to be added to an empty bio. The block device driver may want
51 * to use the bio_split() function to deal with these bio's. By default
52 * no merge_bvec_fn is defined for a queue, and only the fixed limits are
53 * honored.
54 */
55void blk_queue_merge_bvec(struct request_queue *q, merge_bvec_fn *mbfn)
56{
57    q->merge_bvec_fn = mbfn;
58}
59EXPORT_SYMBOL(blk_queue_merge_bvec);
60
61void blk_queue_softirq_done(struct request_queue *q, softirq_done_fn *fn)
62{
63    q->softirq_done_fn = fn;
64}
65EXPORT_SYMBOL(blk_queue_softirq_done);
66
67void blk_queue_rq_timeout(struct request_queue *q, unsigned int timeout)
68{
69    q->rq_timeout = timeout;
70}
71EXPORT_SYMBOL_GPL(blk_queue_rq_timeout);
72
73void blk_queue_rq_timed_out(struct request_queue *q, rq_timed_out_fn *fn)
74{
75    q->rq_timed_out_fn = fn;
76}
77EXPORT_SYMBOL_GPL(blk_queue_rq_timed_out);
78
79void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
80{
81    q->lld_busy_fn = fn;
82}
83EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
84
85/**
86 * blk_set_default_limits - reset limits to default values
87 * @lim: the queue_limits structure to reset
88 *
89 * Description:
90 * Returns a queue_limit struct to its default state. Can be used by
91 * stacking drivers like DM that stage table swaps and reuse an
92 * existing device queue.
93 */
94void blk_set_default_limits(struct queue_limits *lim)
95{
96    lim->max_segments = BLK_MAX_SEGMENTS;
97    lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
98    lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
99    lim->max_sectors = BLK_DEF_MAX_SECTORS;
100    lim->max_hw_sectors = INT_MAX;
101    lim->max_discard_sectors = 0;
102    lim->discard_granularity = 0;
103    lim->discard_alignment = 0;
104    lim->discard_misaligned = 0;
105    lim->discard_zeroes_data = -1;
106    lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;
107    lim->bounce_pfn = (unsigned long)(BLK_BOUNCE_ANY >> PAGE_SHIFT);
108    lim->alignment_offset = 0;
109    lim->io_opt = 0;
110    lim->misaligned = 0;
111    lim->no_cluster = 0;
112}
113EXPORT_SYMBOL(blk_set_default_limits);
114
115/**
116 * blk_queue_make_request - define an alternate make_request function for a device
117 * @q: the request queue for the device to be affected
118 * @mfn: the alternate make_request function
119 *
120 * Description:
121 * The normal way for &struct bios to be passed to a device
122 * driver is for them to be collected into requests on a request
123 * queue, and then to allow the device driver to select requests
124 * off that queue when it is ready. This works well for many block
125 * devices. However some block devices (typically virtual devices
126 * such as md or lvm) do not benefit from the processing on the
127 * request queue, and are served best by having the requests passed
128 * directly to them. This can be achieved by providing a function
129 * to blk_queue_make_request().
130 *
131 * Caveat:
132 * The driver that does this *must* be able to deal appropriately
133 * with buffers in "highmemory". This can be accomplished by either calling
134 * __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
135 * blk_queue_bounce() to create a buffer in normal memory.
136 **/
137void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
138{
139    /*
140     * set defaults
141     */
142    q->nr_requests = BLKDEV_MAX_RQ;
143
144    q->make_request_fn = mfn;
145    blk_queue_dma_alignment(q, 511);
146    blk_queue_congestion_threshold(q);
147    q->nr_batching = BLK_BATCH_REQ;
148
149    q->unplug_thresh = 4; /* hmm */
150    q->unplug_delay = msecs_to_jiffies(3); /* 3 milliseconds */
151    if (q->unplug_delay == 0)
152        q->unplug_delay = 1;
153
154    q->unplug_timer.function = blk_unplug_timeout;
155    q->unplug_timer.data = (unsigned long)q;
156
157    blk_set_default_limits(&q->limits);
158    blk_queue_max_hw_sectors(q, BLK_SAFE_MAX_SECTORS);
159
160    /*
161     * If the caller didn't supply a lock, fall back to our embedded
162     * per-queue locks
163     */
164    if (!q->queue_lock)
165        q->queue_lock = &q->__queue_lock;
166
167    /*
168     * by default assume old behaviour and bounce for any highmem page
169     */
170    blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
171}
172EXPORT_SYMBOL(blk_queue_make_request);
173
174/**
175 * blk_queue_bounce_limit - set bounce buffer limit for queue
176 * @q: the request queue for the device
177 * @dma_mask: the maximum address the device can handle
178 *
179 * Description:
180 * Different hardware can have different requirements as to what pages
181 * it can do I/O directly to. A low level driver can call
182 * blk_queue_bounce_limit to have lower memory pages allocated as bounce
183 * buffers for doing I/O to pages residing above @dma_mask.
184 **/
185void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)
186{
187    unsigned long b_pfn = dma_mask >> PAGE_SHIFT;
188    int dma = 0;
189
190    q->bounce_gfp = GFP_NOIO;
191#if BITS_PER_LONG == 64
192    /*
193     * Assume anything <= 4GB can be handled by IOMMU. Actually
194     * some IOMMUs can handle everything, but I don't know of a
195     * way to test this here.
196     */
197    if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
198        dma = 1;
199    q->limits.bounce_pfn = max_low_pfn;
200#else
201    if (b_pfn < blk_max_low_pfn)
202        dma = 1;
203    q->limits.bounce_pfn = b_pfn;
204#endif
205    if (dma) {
206        init_emergency_isa_pool();
207        q->bounce_gfp = GFP_NOIO | GFP_DMA;
208        q->limits.bounce_pfn = b_pfn;
209    }
210}
211EXPORT_SYMBOL(blk_queue_bounce_limit);
212
213/**
214 * blk_queue_max_hw_sectors - set max sectors for a request for this queue
215 * @q: the request queue for the device
216 * @max_hw_sectors: max hardware sectors in the usual 512b unit
217 *
218 * Description:
219 * Enables a low level driver to set a hard upper limit,
220 * max_hw_sectors, on the size of requests. max_hw_sectors is set by
221 * the device driver based upon the combined capabilities of I/O
222 * controller and storage device.
223 *
224 * max_sectors is a soft limit imposed by the block layer for
225 * filesystem type requests. This value can be overridden on a
226 * per-device basis in /sys/block/<device>/queue/max_sectors_kb.
227 * The soft limit can not exceed max_hw_sectors.
228 **/
229void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)
230{
231    if ((max_hw_sectors << 9) < PAGE_CACHE_SIZE) {
232        max_hw_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
233        printk(KERN_INFO "%s: set to minimum %d\n",
234               __func__, max_hw_sectors);
235    }
236
237    q->limits.max_hw_sectors = max_hw_sectors;
238    q->limits.max_sectors = min_t(unsigned int, max_hw_sectors,
239                      BLK_DEF_MAX_SECTORS);
240}
241EXPORT_SYMBOL(blk_queue_max_hw_sectors);
242
243/**
244 * blk_queue_max_discard_sectors - set max sectors for a single discard
245 * @q: the request queue for the device
246 * @max_discard_sectors: maximum number of sectors to discard
247 **/
248void blk_queue_max_discard_sectors(struct request_queue *q,
249        unsigned int max_discard_sectors)
250{
251    q->limits.max_discard_sectors = max_discard_sectors;
252}
253EXPORT_SYMBOL(blk_queue_max_discard_sectors);
254
255/**
256 * blk_queue_max_segments - set max hw segments for a request for this queue
257 * @q: the request queue for the device
258 * @max_segments: max number of segments
259 *
260 * Description:
261 * Enables a low level driver to set an upper limit on the number of
262 * hw data segments in a request.
263 **/
264void blk_queue_max_segments(struct request_queue *q, unsigned short max_segments)
265{
266    if (!max_segments) {
267        max_segments = 1;
268        printk(KERN_INFO "%s: set to minimum %d\n",
269               __func__, max_segments);
270    }
271
272    q->limits.max_segments = max_segments;
273}
274EXPORT_SYMBOL(blk_queue_max_segments);
275
276/**
277 * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
278 * @q: the request queue for the device
279 * @max_size: max size of segment in bytes
280 *
281 * Description:
282 * Enables a low level driver to set an upper limit on the size of a
283 * coalesced segment
284 **/
285void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
286{
287    if (max_size < PAGE_CACHE_SIZE) {
288        max_size = PAGE_CACHE_SIZE;
289        printk(KERN_INFO "%s: set to minimum %d\n",
290               __func__, max_size);
291    }
292
293    q->limits.max_segment_size = max_size;
294}
295EXPORT_SYMBOL(blk_queue_max_segment_size);
296
297/**
298 * blk_queue_logical_block_size - set logical block size for the queue
299 * @q: the request queue for the device
300 * @size: the logical block size, in bytes
301 *
302 * Description:
303 * This should be set to the lowest possible block size that the
304 * storage device can address. The default of 512 covers most
305 * hardware.
306 **/
307void blk_queue_logical_block_size(struct request_queue *q, unsigned short size)
308{
309    q->limits.logical_block_size = size;
310
311    if (q->limits.physical_block_size < size)
312        q->limits.physical_block_size = size;
313
314    if (q->limits.io_min < q->limits.physical_block_size)
315        q->limits.io_min = q->limits.physical_block_size;
316}
317EXPORT_SYMBOL(blk_queue_logical_block_size);
318
319/**
320 * blk_queue_physical_block_size - set physical block size for the queue
321 * @q: the request queue for the device
322 * @size: the physical block size, in bytes
323 *
324 * Description:
325 * This should be set to the lowest possible sector size that the
326 * hardware can operate on without reverting to read-modify-write
327 * operations.
328 */
329void blk_queue_physical_block_size(struct request_queue *q, unsigned short size)
330{
331    q->limits.physical_block_size = size;
332
333    if (q->limits.physical_block_size < q->limits.logical_block_size)
334        q->limits.physical_block_size = q->limits.logical_block_size;
335
336    if (q->limits.io_min < q->limits.physical_block_size)
337        q->limits.io_min = q->limits.physical_block_size;
338}
339EXPORT_SYMBOL(blk_queue_physical_block_size);
340
341/**
342 * blk_queue_alignment_offset - set physical block alignment offset
343 * @q: the request queue for the device
344 * @offset: alignment offset in bytes
345 *
346 * Description:
347 * Some devices are naturally misaligned to compensate for things like
348 * the legacy DOS partition table 63-sector offset. Low-level drivers
349 * should call this function for devices whose first sector is not
350 * naturally aligned.
351 */
352void blk_queue_alignment_offset(struct request_queue *q, unsigned int offset)
353{
354    q->limits.alignment_offset =
355        offset & (q->limits.physical_block_size - 1);
356    q->limits.misaligned = 0;
357}
358EXPORT_SYMBOL(blk_queue_alignment_offset);
359
360/**
361 * blk_limits_io_min - set minimum request size for a device
362 * @limits: the queue limits
363 * @min: smallest I/O size in bytes
364 *
365 * Description:
366 * Some devices have an internal block size bigger than the reported
367 * hardware sector size. This function can be used to signal the
368 * smallest I/O the device can perform without incurring a performance
369 * penalty.
370 */
371void blk_limits_io_min(struct queue_limits *limits, unsigned int min)
372{
373    limits->io_min = min;
374
375    if (limits->io_min < limits->logical_block_size)
376        limits->io_min = limits->logical_block_size;
377
378    if (limits->io_min < limits->physical_block_size)
379        limits->io_min = limits->physical_block_size;
380}
381EXPORT_SYMBOL(blk_limits_io_min);
382
383/**
384 * blk_queue_io_min - set minimum request size for the queue
385 * @q: the request queue for the device
386 * @min: smallest I/O size in bytes
387 *
388 * Description:
389 * Storage devices may report a granularity or preferred minimum I/O
390 * size which is the smallest request the device can perform without
391 * incurring a performance penalty. For disk drives this is often the
392 * physical block size. For RAID arrays it is often the stripe chunk
393 * size. A properly aligned multiple of minimum_io_size is the
394 * preferred request size for workloads where a high number of I/O
395 * operations is desired.
396 */
397void blk_queue_io_min(struct request_queue *q, unsigned int min)
398{
399    blk_limits_io_min(&q->limits, min);
400}
401EXPORT_SYMBOL(blk_queue_io_min);
402
403/**
404 * blk_limits_io_opt - set optimal request size for a device
405 * @limits: the queue limits
406 * @opt: smallest I/O size in bytes
407 *
408 * Description:
409 * Storage devices may report an optimal I/O size, which is the
410 * device's preferred unit for sustained I/O. This is rarely reported
411 * for disk drives. For RAID arrays it is usually the stripe width or
412 * the internal track size. A properly aligned multiple of
413 * optimal_io_size is the preferred request size for workloads where
414 * sustained throughput is desired.
415 */
416void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt)
417{
418    limits->io_opt = opt;
419}
420EXPORT_SYMBOL(blk_limits_io_opt);
421
422/**
423 * blk_queue_io_opt - set optimal request size for the queue
424 * @q: the request queue for the device
425 * @opt: optimal request size in bytes
426 *
427 * Description:
428 * Storage devices may report an optimal I/O size, which is the
429 * device's preferred unit for sustained I/O. This is rarely reported
430 * for disk drives. For RAID arrays it is usually the stripe width or
431 * the internal track size. A properly aligned multiple of
432 * optimal_io_size is the preferred request size for workloads where
433 * sustained throughput is desired.
434 */
435void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
436{
437    blk_limits_io_opt(&q->limits, opt);
438}
439EXPORT_SYMBOL(blk_queue_io_opt);
440
441/*
442 * Returns the minimum that is _not_ zero, unless both are zero.
443 */
444#define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
445
446/**
447 * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
448 * @t: the stacking driver (top)
449 * @b: the underlying device (bottom)
450 **/
451void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
452{
453    blk_stack_limits(&t->limits, &b->limits, 0);
454
455    if (!t->queue_lock)
456        WARN_ON_ONCE(1);
457    else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
458        unsigned long flags;
459        spin_lock_irqsave(t->queue_lock, flags);
460        queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
461        spin_unlock_irqrestore(t->queue_lock, flags);
462    }
463}
464EXPORT_SYMBOL(blk_queue_stack_limits);
465
466/**
467 * blk_stack_limits - adjust queue_limits for stacked devices
468 * @t: the stacking driver limits (top device)
469 * @b: the underlying queue limits (bottom, component device)
470 * @start: first data sector within component device
471 *
472 * Description:
473 * This function is used by stacking drivers like MD and DM to ensure
474 * that all component devices have compatible block sizes and
475 * alignments. The stacking driver must provide a queue_limits
476 * struct (top) and then iteratively call the stacking function for
477 * all component (bottom) devices. The stacking function will
478 * attempt to combine the values and ensure proper alignment.
479 *
480 * Returns 0 if the top and bottom queue_limits are compatible. The
481 * top device's block sizes and alignment offsets may be adjusted to
482 * ensure alignment with the bottom device. If no compatible sizes
483 * and alignments exist, -1 is returned and the resulting top
484 * queue_limits will have the misaligned flag set to indicate that
485 * the alignment_offset is undefined.
486 */
487int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
488             sector_t start)
489{
490    unsigned int top, bottom, alignment, ret = 0;
491
492    t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
493    t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
494    t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
495
496    t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
497                        b->seg_boundary_mask);
498
499    t->max_segments = min_not_zero(t->max_segments, b->max_segments);
500
501    t->max_segment_size = min_not_zero(t->max_segment_size,
502                       b->max_segment_size);
503
504    t->misaligned |= b->misaligned;
505
506    alignment = queue_limit_alignment_offset(b, start);
507
508    /* Bottom device has different alignment. Check that it is
509     * compatible with the current top alignment.
510     */
511    if (t->alignment_offset != alignment) {
512
513        top = max(t->physical_block_size, t->io_min)
514            + t->alignment_offset;
515        bottom = max(b->physical_block_size, b->io_min) + alignment;
516
517        /* Verify that top and bottom intervals line up */
518        if (max(top, bottom) & (min(top, bottom) - 1)) {
519            t->misaligned = 1;
520            ret = -1;
521        }
522    }
523
524    t->logical_block_size = max(t->logical_block_size,
525                    b->logical_block_size);
526
527    t->physical_block_size = max(t->physical_block_size,
528                     b->physical_block_size);
529
530    t->io_min = max(t->io_min, b->io_min);
531    t->io_opt = lcm(t->io_opt, b->io_opt);
532
533    t->no_cluster |= b->no_cluster;
534    t->discard_zeroes_data &= b->discard_zeroes_data;
535
536    /* Physical block size a multiple of the logical block size? */
537    if (t->physical_block_size & (t->logical_block_size - 1)) {
538        t->physical_block_size = t->logical_block_size;
539        t->misaligned = 1;
540        ret = -1;
541    }
542
543    /* Minimum I/O a multiple of the physical block size? */
544    if (t->io_min & (t->physical_block_size - 1)) {
545        t->io_min = t->physical_block_size;
546        t->misaligned = 1;
547        ret = -1;
548    }
549
550    /* Optimal I/O a multiple of the physical block size? */
551    if (t->io_opt & (t->physical_block_size - 1)) {
552        t->io_opt = 0;
553        t->misaligned = 1;
554        ret = -1;
555    }
556
557    /* Find lowest common alignment_offset */
558    t->alignment_offset = lcm(t->alignment_offset, alignment)
559        & (max(t->physical_block_size, t->io_min) - 1);
560
561    /* Verify that new alignment_offset is on a logical block boundary */
562    if (t->alignment_offset & (t->logical_block_size - 1)) {
563        t->misaligned = 1;
564        ret = -1;
565    }
566
567    /* Discard alignment and granularity */
568    if (b->discard_granularity) {
569        alignment = queue_limit_discard_alignment(b, start);
570
571        if (t->discard_granularity != 0 &&
572            t->discard_alignment != alignment) {
573            top = t->discard_granularity + t->discard_alignment;
574            bottom = b->discard_granularity + alignment;
575
576            /* Verify that top and bottom intervals line up */
577            if (max(top, bottom) & (min(top, bottom) - 1))
578                t->discard_misaligned = 1;
579        }
580
581        t->max_discard_sectors = min_not_zero(t->max_discard_sectors,
582                              b->max_discard_sectors);
583        t->discard_granularity = max(t->discard_granularity,
584                         b->discard_granularity);
585        t->discard_alignment = lcm(t->discard_alignment, alignment) &
586            (t->discard_granularity - 1);
587    }
588
589    return ret;
590}
591EXPORT_SYMBOL(blk_stack_limits);
592
593/**
594 * bdev_stack_limits - adjust queue limits for stacked drivers
595 * @t: the stacking driver limits (top device)
596 * @bdev: the component block_device (bottom)
597 * @start: first data sector within component device
598 *
599 * Description:
600 * Merges queue limits for a top device and a block_device. Returns
601 * 0 if alignment didn't change. Returns -1 if adding the bottom
602 * device caused misalignment.
603 */
604int bdev_stack_limits(struct queue_limits *t, struct block_device *bdev,
605              sector_t start)
606{
607    struct request_queue *bq = bdev_get_queue(bdev);
608
609    start += get_start_sect(bdev);
610
611    return blk_stack_limits(t, &bq->limits, start);
612}
613EXPORT_SYMBOL(bdev_stack_limits);
614
615/**
616 * disk_stack_limits - adjust queue limits for stacked drivers
617 * @disk: MD/DM gendisk (top)
618 * @bdev: the underlying block device (bottom)
619 * @offset: offset to beginning of data within component device
620 *
621 * Description:
622 * Merges the limits for a top level gendisk and a bottom level
623 * block_device.
624 */
625void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
626               sector_t offset)
627{
628    struct request_queue *t = disk->queue;
629    struct request_queue *b = bdev_get_queue(bdev);
630
631    if (bdev_stack_limits(&t->limits, bdev, offset >> 9) < 0) {
632        char top[BDEVNAME_SIZE], bottom[BDEVNAME_SIZE];
633
634        disk_name(disk, 0, top);
635        bdevname(bdev, bottom);
636
637        printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
638               top, bottom);
639    }
640
641    if (!t->queue_lock)
642        WARN_ON_ONCE(1);
643    else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
644        unsigned long flags;
645
646        spin_lock_irqsave(t->queue_lock, flags);
647        if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
648            queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
649        spin_unlock_irqrestore(t->queue_lock, flags);
650    }
651}
652EXPORT_SYMBOL(disk_stack_limits);
653
654/**
655 * blk_queue_dma_pad - set pad mask
656 * @q: the request queue for the device
657 * @mask: pad mask
658 *
659 * Set dma pad mask.
660 *
661 * Appending pad buffer to a request modifies the last entry of a
662 * scatter list such that it includes the pad buffer.
663 **/
664void blk_queue_dma_pad(struct request_queue *q, unsigned int mask)
665{
666    q->dma_pad_mask = mask;
667}
668EXPORT_SYMBOL(blk_queue_dma_pad);
669
670/**
671 * blk_queue_update_dma_pad - update pad mask
672 * @q: the request queue for the device
673 * @mask: pad mask
674 *
675 * Update dma pad mask.
676 *
677 * Appending pad buffer to a request modifies the last entry of a
678 * scatter list such that it includes the pad buffer.
679 **/
680void blk_queue_update_dma_pad(struct request_queue *q, unsigned int mask)
681{
682    if (mask > q->dma_pad_mask)
683        q->dma_pad_mask = mask;
684}
685EXPORT_SYMBOL(blk_queue_update_dma_pad);
686
687/**
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
693 *
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.
702 *
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.
707 */
708int blk_queue_dma_drain(struct request_queue *q,
709                   dma_drain_needed_fn *dma_drain_needed,
710                   void *buf, unsigned int size)
711{
712    if (queue_max_segments(q) < 2)
713        return -EINVAL;
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;
719
720    return 0;
721}
722EXPORT_SYMBOL_GPL(blk_queue_dma_drain);
723
724/**
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
728 **/
729void blk_queue_segment_boundary(struct request_queue *q, unsigned long mask)
730{
731    if (mask < PAGE_CACHE_SIZE - 1) {
732        mask = PAGE_CACHE_SIZE - 1;
733        printk(KERN_INFO "%s: set to minimum %lx\n",
734               __func__, mask);
735    }
736
737    q->limits.seg_boundary_mask = mask;
738}
739EXPORT_SYMBOL(blk_queue_segment_boundary);
740
741/**
742 * blk_queue_dma_alignment - set dma length and memory alignment
743 * @q: the request queue for the device
744 * @mask: alignment mask
745 *
746 * description:
747 * set required memory and length alignment for direct dma transactions.
748 * this is used when building direct io requests for the queue.
749 *
750 **/
751void blk_queue_dma_alignment(struct request_queue *q, int mask)
752{
753    q->dma_alignment = mask;
754}
755EXPORT_SYMBOL(blk_queue_dma_alignment);
756
757/**
758 * blk_queue_update_dma_alignment - update dma length and memory alignment
759 * @q: the request queue for the device
760 * @mask: alignment mask
761 *
762 * description:
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.
769 *
770 **/
771void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
772{
773    BUG_ON(mask > PAGE_SIZE);
774
775    if (mask > q->dma_alignment)
776        q->dma_alignment = mask;
777}
778EXPORT_SYMBOL(blk_queue_update_dma_alignment);
779
780static int __init blk_settings_init(void)
781{
782    blk_max_low_pfn = max_low_pfn - 1;
783    blk_max_pfn = max_pfn - 1;
784    return 0;
785}
786subsys_initcall(blk_settings_init);
787

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