linux/block/blk-settings.c
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   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_unprep_rq - set an unprepare_request function for queue
  41 * @q:          queue
  42 * @ufn:        unprepare_request function
  43 *
  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.
  48 *
  49 */
  50void blk_queue_unprep_rq(struct request_queue *q, unprep_rq_fn *ufn)
  51{
  52        q->unprep_rq_fn = ufn;
  53}
  54EXPORT_SYMBOL(blk_queue_unprep_rq);
  55
  56/**
  57 * blk_queue_merge_bvec - set a merge_bvec function for queue
  58 * @q:          queue
  59 * @mbfn:       merge_bvec_fn
  60 *
  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.
  71 */
  72void blk_queue_merge_bvec(struct request_queue *q, merge_bvec_fn *mbfn)
  73{
  74        q->merge_bvec_fn = mbfn;
  75}
  76EXPORT_SYMBOL(blk_queue_merge_bvec);
  77
  78void blk_queue_softirq_done(struct request_queue *q, softirq_done_fn *fn)
  79{
  80        q->softirq_done_fn = fn;
  81}
  82EXPORT_SYMBOL(blk_queue_softirq_done);
  83
  84void blk_queue_rq_timeout(struct request_queue *q, unsigned int timeout)
  85{
  86        q->rq_timeout = timeout;
  87}
  88EXPORT_SYMBOL_GPL(blk_queue_rq_timeout);
  89
  90void blk_queue_rq_timed_out(struct request_queue *q, rq_timed_out_fn *fn)
  91{
  92        q->rq_timed_out_fn = fn;
  93}
  94EXPORT_SYMBOL_GPL(blk_queue_rq_timed_out);
  95
  96void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
  97{
  98        q->lld_busy_fn = fn;
  99}
 100EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
 101
 102/**
 103 * blk_set_default_limits - reset limits to default values
 104 * @lim:  the queue_limits structure to reset
 105 *
 106 * Description:
 107 *   Returns a queue_limit struct to its default state.
 108 */
 109void blk_set_default_limits(struct queue_limits *lim)
 110{
 111        lim->max_segments = BLK_MAX_SEGMENTS;
 112        lim->max_integrity_segments = 0;
 113        lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
 114        lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
 115        lim->max_sectors = lim->max_hw_sectors = BLK_SAFE_MAX_SECTORS;
 116        lim->max_discard_sectors = 0;
 117        lim->discard_granularity = 0;
 118        lim->discard_alignment = 0;
 119        lim->discard_misaligned = 0;
 120        lim->discard_zeroes_data = 0;
 121        lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;
 122        lim->bounce_pfn = (unsigned long)(BLK_BOUNCE_ANY >> PAGE_SHIFT);
 123        lim->alignment_offset = 0;
 124        lim->io_opt = 0;
 125        lim->misaligned = 0;
 126        lim->cluster = 1;
 127}
 128EXPORT_SYMBOL(blk_set_default_limits);
 129
 130/**
 131 * blk_set_stacking_limits - set default limits for stacking devices
 132 * @lim:  the queue_limits structure to reset
 133 *
 134 * Description:
 135 *   Returns a queue_limit struct to its default state. Should be used
 136 *   by stacking drivers like DM that have no internal limits.
 137 */
 138void blk_set_stacking_limits(struct queue_limits *lim)
 139{
 140        blk_set_default_limits(lim);
 141
 142        /* Inherit limits from component devices */
 143        lim->discard_zeroes_data = 1;
 144        lim->max_segments = USHRT_MAX;
 145        lim->max_hw_sectors = UINT_MAX;
 146        lim->max_sectors = UINT_MAX;
 147}
 148EXPORT_SYMBOL(blk_set_stacking_limits);
 149
 150/**
 151 * blk_queue_make_request - define an alternate make_request function for a device
 152 * @q:  the request queue for the device to be affected
 153 * @mfn: the alternate make_request function
 154 *
 155 * Description:
 156 *    The normal way for &struct bios to be passed to a device
 157 *    driver is for them to be collected into requests on a request
 158 *    queue, and then to allow the device driver to select requests
 159 *    off that queue when it is ready.  This works well for many block
 160 *    devices. However some block devices (typically virtual devices
 161 *    such as md or lvm) do not benefit from the processing on the
 162 *    request queue, and are served best by having the requests passed
 163 *    directly to them.  This can be achieved by providing a function
 164 *    to blk_queue_make_request().
 165 *
 166 * Caveat:
 167 *    The driver that does this *must* be able to deal appropriately
 168 *    with buffers in "highmemory". This can be accomplished by either calling
 169 *    __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
 170 *    blk_queue_bounce() to create a buffer in normal memory.
 171 **/
 172void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
 173{
 174        /*
 175         * set defaults
 176         */
 177        q->nr_requests = BLKDEV_MAX_RQ;
 178
 179        q->make_request_fn = mfn;
 180        blk_queue_dma_alignment(q, 511);
 181        blk_queue_congestion_threshold(q);
 182        q->nr_batching = BLK_BATCH_REQ;
 183
 184        blk_set_default_limits(&q->limits);
 185
 186        /*
 187         * by default assume old behaviour and bounce for any highmem page
 188         */
 189        blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
 190}
 191EXPORT_SYMBOL(blk_queue_make_request);
 192
 193/**
 194 * blk_queue_bounce_limit - set bounce buffer limit for queue
 195 * @q: the request queue for the device
 196 * @dma_mask: the maximum address the device can handle
 197 *
 198 * Description:
 199 *    Different hardware can have different requirements as to what pages
 200 *    it can do I/O directly to. A low level driver can call
 201 *    blk_queue_bounce_limit to have lower memory pages allocated as bounce
 202 *    buffers for doing I/O to pages residing above @dma_mask.
 203 **/
 204void blk_queue_bounce_limit(struct request_queue *q, u64 dma_mask)
 205{
 206        unsigned long b_pfn = dma_mask >> PAGE_SHIFT;
 207        int dma = 0;
 208
 209        q->bounce_gfp = GFP_NOIO;
 210#if BITS_PER_LONG == 64
 211        /*
 212         * Assume anything <= 4GB can be handled by IOMMU.  Actually
 213         * some IOMMUs can handle everything, but I don't know of a
 214         * way to test this here.
 215         */
 216        if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
 217                dma = 1;
 218        q->limits.bounce_pfn = max(max_low_pfn, b_pfn);
 219#else
 220        if (b_pfn < blk_max_low_pfn)
 221                dma = 1;
 222        q->limits.bounce_pfn = b_pfn;
 223#endif
 224        if (dma) {
 225                init_emergency_isa_pool();
 226                q->bounce_gfp = GFP_NOIO | GFP_DMA;
 227                q->limits.bounce_pfn = b_pfn;
 228        }
 229}
 230EXPORT_SYMBOL(blk_queue_bounce_limit);
 231
 232/**
 233 * blk_limits_max_hw_sectors - set hard and soft limit of max sectors for request
 234 * @limits: the queue limits
 235 * @max_hw_sectors:  max hardware sectors in the usual 512b unit
 236 *
 237 * Description:
 238 *    Enables a low level driver to set a hard upper limit,
 239 *    max_hw_sectors, on the size of requests.  max_hw_sectors is set by
 240 *    the device driver based upon the combined capabilities of I/O
 241 *    controller and storage device.
 242 *
 243 *    max_sectors is a soft limit imposed by the block layer for
 244 *    filesystem type requests.  This value can be overridden on a
 245 *    per-device basis in /sys/block/<device>/queue/max_sectors_kb.
 246 *    The soft limit can not exceed max_hw_sectors.
 247 **/
 248void blk_limits_max_hw_sectors(struct queue_limits *limits, unsigned int max_hw_sectors)
 249{
 250        if ((max_hw_sectors << 9) < PAGE_CACHE_SIZE) {
 251                max_hw_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
 252                printk(KERN_INFO "%s: set to minimum %d\n",
 253                       __func__, max_hw_sectors);
 254        }
 255
 256        limits->max_hw_sectors = max_hw_sectors;
 257        limits->max_sectors = min_t(unsigned int, max_hw_sectors,
 258                                    BLK_DEF_MAX_SECTORS);
 259}
 260EXPORT_SYMBOL(blk_limits_max_hw_sectors);
 261
 262/**
 263 * blk_queue_max_hw_sectors - set max sectors for a request for this queue
 264 * @q:  the request queue for the device
 265 * @max_hw_sectors:  max hardware sectors in the usual 512b unit
 266 *
 267 * Description:
 268 *    See description for blk_limits_max_hw_sectors().
 269 **/
 270void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)
 271{
 272        blk_limits_max_hw_sectors(&q->limits, max_hw_sectors);
 273}
 274EXPORT_SYMBOL(blk_queue_max_hw_sectors);
 275
 276/**
 277 * blk_queue_max_discard_sectors - set max sectors for a single discard
 278 * @q:  the request queue for the device
 279 * @max_discard_sectors: maximum number of sectors to discard
 280 **/
 281void blk_queue_max_discard_sectors(struct request_queue *q,
 282                unsigned int max_discard_sectors)
 283{
 284        q->limits.max_discard_sectors = max_discard_sectors;
 285}
 286EXPORT_SYMBOL(blk_queue_max_discard_sectors);
 287
 288/**
 289 * blk_queue_max_segments - set max hw segments for a request for this queue
 290 * @q:  the request queue for the device
 291 * @max_segments:  max number of segments
 292 *
 293 * Description:
 294 *    Enables a low level driver to set an upper limit on the number of
 295 *    hw data segments in a request.
 296 **/
 297void blk_queue_max_segments(struct request_queue *q, unsigned short max_segments)
 298{
 299        if (!max_segments) {
 300                max_segments = 1;
 301                printk(KERN_INFO "%s: set to minimum %d\n",
 302                       __func__, max_segments);
 303        }
 304
 305        q->limits.max_segments = max_segments;
 306}
 307EXPORT_SYMBOL(blk_queue_max_segments);
 308
 309/**
 310 * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
 311 * @q:  the request queue for the device
 312 * @max_size:  max size of segment in bytes
 313 *
 314 * Description:
 315 *    Enables a low level driver to set an upper limit on the size of a
 316 *    coalesced segment
 317 **/
 318void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
 319{
 320        if (max_size < PAGE_CACHE_SIZE) {
 321                max_size = PAGE_CACHE_SIZE;
 322                printk(KERN_INFO "%s: set to minimum %d\n",
 323                       __func__, max_size);
 324        }
 325
 326        q->limits.max_segment_size = max_size;
 327}
 328EXPORT_SYMBOL(blk_queue_max_segment_size);
 329
 330/**
 331 * blk_queue_logical_block_size - set logical block size for the queue
 332 * @q:  the request queue for the device
 333 * @size:  the logical block size, in bytes
 334 *
 335 * Description:
 336 *   This should be set to the lowest possible block size that the
 337 *   storage device can address.  The default of 512 covers most
 338 *   hardware.
 339 **/
 340void blk_queue_logical_block_size(struct request_queue *q, unsigned short size)
 341{
 342        q->limits.logical_block_size = size;
 343
 344        if (q->limits.physical_block_size < size)
 345                q->limits.physical_block_size = size;
 346
 347        if (q->limits.io_min < q->limits.physical_block_size)
 348                q->limits.io_min = q->limits.physical_block_size;
 349}
 350EXPORT_SYMBOL(blk_queue_logical_block_size);
 351
 352/**
 353 * blk_queue_physical_block_size - set physical block size for the queue
 354 * @q:  the request queue for the device
 355 * @size:  the physical block size, in bytes
 356 *
 357 * Description:
 358 *   This should be set to the lowest possible sector size that the
 359 *   hardware can operate on without reverting to read-modify-write
 360 *   operations.
 361 */
 362void blk_queue_physical_block_size(struct request_queue *q, unsigned int size)
 363{
 364        q->limits.physical_block_size = size;
 365
 366        if (q->limits.physical_block_size < q->limits.logical_block_size)
 367                q->limits.physical_block_size = q->limits.logical_block_size;
 368
 369        if (q->limits.io_min < q->limits.physical_block_size)
 370                q->limits.io_min = q->limits.physical_block_size;
 371}
 372EXPORT_SYMBOL(blk_queue_physical_block_size);
 373
 374/**
 375 * blk_queue_alignment_offset - set physical block alignment offset
 376 * @q:  the request queue for the device
 377 * @offset: alignment offset in bytes
 378 *
 379 * Description:
 380 *   Some devices are naturally misaligned to compensate for things like
 381 *   the legacy DOS partition table 63-sector offset.  Low-level drivers
 382 *   should call this function for devices whose first sector is not
 383 *   naturally aligned.
 384 */
 385void blk_queue_alignment_offset(struct request_queue *q, unsigned int offset)
 386{
 387        q->limits.alignment_offset =
 388                offset & (q->limits.physical_block_size - 1);
 389        q->limits.misaligned = 0;
 390}
 391EXPORT_SYMBOL(blk_queue_alignment_offset);
 392
 393/**
 394 * blk_limits_io_min - set minimum request size for a device
 395 * @limits: the queue limits
 396 * @min:  smallest I/O size in bytes
 397 *
 398 * Description:
 399 *   Some devices have an internal block size bigger than the reported
 400 *   hardware sector size.  This function can be used to signal the
 401 *   smallest I/O the device can perform without incurring a performance
 402 *   penalty.
 403 */
 404void blk_limits_io_min(struct queue_limits *limits, unsigned int min)
 405{
 406        limits->io_min = min;
 407
 408        if (limits->io_min < limits->logical_block_size)
 409                limits->io_min = limits->logical_block_size;
 410
 411        if (limits->io_min < limits->physical_block_size)
 412                limits->io_min = limits->physical_block_size;
 413}
 414EXPORT_SYMBOL(blk_limits_io_min);
 415
 416/**
 417 * blk_queue_io_min - set minimum request size for the queue
 418 * @q:  the request queue for the device
 419 * @min:  smallest I/O size in bytes
 420 *
 421 * Description:
 422 *   Storage devices may report a granularity or preferred minimum I/O
 423 *   size which is the smallest request the device can perform without
 424 *   incurring a performance penalty.  For disk drives this is often the
 425 *   physical block size.  For RAID arrays it is often the stripe chunk
 426 *   size.  A properly aligned multiple of minimum_io_size is the
 427 *   preferred request size for workloads where a high number of I/O
 428 *   operations is desired.
 429 */
 430void blk_queue_io_min(struct request_queue *q, unsigned int min)
 431{
 432        blk_limits_io_min(&q->limits, min);
 433}
 434EXPORT_SYMBOL(blk_queue_io_min);
 435
 436/**
 437 * blk_limits_io_opt - set optimal request size for a device
 438 * @limits: the queue limits
 439 * @opt:  smallest I/O size in bytes
 440 *
 441 * Description:
 442 *   Storage devices may report an optimal I/O size, which is the
 443 *   device's preferred unit for sustained I/O.  This is rarely reported
 444 *   for disk drives.  For RAID arrays it is usually the stripe width or
 445 *   the internal track size.  A properly aligned multiple of
 446 *   optimal_io_size is the preferred request size for workloads where
 447 *   sustained throughput is desired.
 448 */
 449void blk_limits_io_opt(struct queue_limits *limits, unsigned int opt)
 450{
 451        limits->io_opt = opt;
 452}
 453EXPORT_SYMBOL(blk_limits_io_opt);
 454
 455/**
 456 * blk_queue_io_opt - set optimal request size for the queue
 457 * @q:  the request queue for the device
 458 * @opt:  optimal request size in bytes
 459 *
 460 * Description:
 461 *   Storage devices may report an optimal I/O size, which is the
 462 *   device's preferred unit for sustained I/O.  This is rarely reported
 463 *   for disk drives.  For RAID arrays it is usually the stripe width or
 464 *   the internal track size.  A properly aligned multiple of
 465 *   optimal_io_size is the preferred request size for workloads where
 466 *   sustained throughput is desired.
 467 */
 468void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
 469{
 470        blk_limits_io_opt(&q->limits, opt);
 471}
 472EXPORT_SYMBOL(blk_queue_io_opt);
 473
 474/**
 475 * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
 476 * @t:  the stacking driver (top)
 477 * @b:  the underlying device (bottom)
 478 **/
 479void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
 480{
 481        blk_stack_limits(&t->limits, &b->limits, 0);
 482}
 483EXPORT_SYMBOL(blk_queue_stack_limits);
 484
 485/**
 486 * blk_stack_limits - adjust queue_limits for stacked devices
 487 * @t:  the stacking driver limits (top device)
 488 * @b:  the underlying queue limits (bottom, component device)
 489 * @start:  first data sector within component device
 490 *
 491 * Description:
 492 *    This function is used by stacking drivers like MD and DM to ensure
 493 *    that all component devices have compatible block sizes and
 494 *    alignments.  The stacking driver must provide a queue_limits
 495 *    struct (top) and then iteratively call the stacking function for
 496 *    all component (bottom) devices.  The stacking function will
 497 *    attempt to combine the values and ensure proper alignment.
 498 *
 499 *    Returns 0 if the top and bottom queue_limits are compatible.  The
 500 *    top device's block sizes and alignment offsets may be adjusted to
 501 *    ensure alignment with the bottom device. If no compatible sizes
 502 *    and alignments exist, -1 is returned and the resulting top
 503 *    queue_limits will have the misaligned flag set to indicate that
 504 *    the alignment_offset is undefined.
 505 */
 506int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 507                     sector_t start)
 508{
 509        unsigned int top, bottom, alignment, ret = 0;
 510
 511        t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
 512        t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
 513        t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
 514
 515        t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
 516                                            b->seg_boundary_mask);
 517
 518        t->max_segments = min_not_zero(t->max_segments, b->max_segments);
 519        t->max_integrity_segments = min_not_zero(t->max_integrity_segments,
 520                                                 b->max_integrity_segments);
 521
 522        t->max_segment_size = min_not_zero(t->max_segment_size,
 523                                           b->max_segment_size);
 524
 525        t->misaligned |= b->misaligned;
 526
 527        alignment = queue_limit_alignment_offset(b, start);
 528
 529        /* Bottom device has different alignment.  Check that it is
 530         * compatible with the current top alignment.
 531         */
 532        if (t->alignment_offset != alignment) {
 533
 534                top = max(t->physical_block_size, t->io_min)
 535                        + t->alignment_offset;
 536                bottom = max(b->physical_block_size, b->io_min) + alignment;
 537
 538                /* Verify that top and bottom intervals line up */
 539                if (max(top, bottom) & (min(top, bottom) - 1)) {
 540                        t->misaligned = 1;
 541                        ret = -1;
 542                }
 543        }
 544
 545        t->logical_block_size = max(t->logical_block_size,
 546                                    b->logical_block_size);
 547
 548        t->physical_block_size = max(t->physical_block_size,
 549                                     b->physical_block_size);
 550
 551        t->io_min = max(t->io_min, b->io_min);
 552        t->io_opt = lcm(t->io_opt, b->io_opt);
 553
 554        t->cluster &= b->cluster;
 555        t->discard_zeroes_data &= b->discard_zeroes_data;
 556
 557        /* Physical block size a multiple of the logical block size? */
 558        if (t->physical_block_size & (t->logical_block_size - 1)) {
 559                t->physical_block_size = t->logical_block_size;
 560                t->misaligned = 1;
 561                ret = -1;
 562        }
 563
 564        /* Minimum I/O a multiple of the physical block size? */
 565        if (t->io_min & (t->physical_block_size - 1)) {
 566                t->io_min = t->physical_block_size;
 567                t->misaligned = 1;
 568                ret = -1;
 569        }
 570
 571        /* Optimal I/O a multiple of the physical block size? */
 572        if (t->io_opt & (t->physical_block_size - 1)) {
 573                t->io_opt = 0;
 574                t->misaligned = 1;
 575                ret = -1;
 576        }
 577
 578        /* Find lowest common alignment_offset */
 579        t->alignment_offset = lcm(t->alignment_offset, alignment)
 580                & (max(t->physical_block_size, t->io_min) - 1);
 581
 582        /* Verify that new alignment_offset is on a logical block boundary */
 583        if (t->alignment_offset & (t->logical_block_size - 1)) {
 584                t->misaligned = 1;
 585                ret = -1;
 586        }
 587
 588        /* Discard alignment and granularity */
 589        if (b->discard_granularity) {
 590                alignment = queue_limit_discard_alignment(b, start);
 591
 592                if (t->discard_granularity != 0 &&
 593                    t->discard_alignment != alignment) {
 594                        top = t->discard_granularity + t->discard_alignment;
 595                        bottom = b->discard_granularity + alignment;
 596
 597                        /* Verify that top and bottom intervals line up */
 598                        if (max(top, bottom) & (min(top, bottom) - 1))
 599                                t->discard_misaligned = 1;
 600                }
 601
 602                t->max_discard_sectors = min_not_zero(t->max_discard_sectors,
 603                                                      b->max_discard_sectors);
 604                t->discard_granularity = max(t->discard_granularity,
 605                                             b->discard_granularity);
 606                t->discard_alignment = lcm(t->discard_alignment, alignment) &
 607                        (t->discard_granularity - 1);
 608        }
 609
 610        return ret;
 611}
 612EXPORT_SYMBOL(blk_stack_limits);
 613
 614/**
 615 * bdev_stack_limits - adjust queue limits for stacked drivers
 616 * @t:  the stacking driver limits (top device)
 617 * @bdev:  the component block_device (bottom)
 618 * @start:  first data sector within component device
 619 *
 620 * Description:
 621 *    Merges queue limits for a top device and a block_device.  Returns
 622 *    0 if alignment didn't change.  Returns -1 if adding the bottom
 623 *    device caused misalignment.
 624 */
 625int bdev_stack_limits(struct queue_limits *t, struct block_device *bdev,
 626                      sector_t start)
 627{
 628        struct request_queue *bq = bdev_get_queue(bdev);
 629
 630        start += get_start_sect(bdev);
 631
 632        return blk_stack_limits(t, &bq->limits, start);
 633}
 634EXPORT_SYMBOL(bdev_stack_limits);
 635
 636/**
 637 * disk_stack_limits - adjust queue limits for stacked drivers
 638 * @disk:  MD/DM gendisk (top)
 639 * @bdev:  the underlying block device (bottom)
 640 * @offset:  offset to beginning of data within component device
 641 *
 642 * Description:
 643 *    Merges the limits for a top level gendisk and a bottom level
 644 *    block_device.
 645 */
 646void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
 647                       sector_t offset)
 648{
 649        struct request_queue *t = disk->queue;
 650
 651        if (bdev_stack_limits(&t->limits, bdev, offset >> 9) < 0) {
 652                char top[BDEVNAME_SIZE], bottom[BDEVNAME_SIZE];
 653
 654                disk_name(disk, 0, top);
 655                bdevname(bdev, bottom);
 656
 657                printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
 658                       top, bottom);
 659        }
 660}
 661EXPORT_SYMBOL(disk_stack_limits);
 662
 663/**
 664 * blk_queue_dma_pad - set pad mask
 665 * @q:     the request queue for the device
 666 * @mask:  pad mask
 667 *
 668 * Set dma pad mask.
 669 *
 670 * Appending pad buffer to a request modifies the last entry of a
 671 * scatter list such that it includes the pad buffer.
 672 **/
 673void blk_queue_dma_pad(struct request_queue *q, unsigned int mask)
 674{
 675        q->dma_pad_mask = mask;
 676}
 677EXPORT_SYMBOL(blk_queue_dma_pad);
 678
 679/**
 680 * blk_queue_update_dma_pad - update pad mask
 681 * @q:     the request queue for the device
 682 * @mask:  pad mask
 683 *
 684 * Update dma pad mask.
 685 *
 686 * Appending pad buffer to a request modifies the last entry of a
 687 * scatter list such that it includes the pad buffer.
 688 **/
 689void blk_queue_update_dma_pad(struct request_queue *q, unsigned int mask)
 690{
 691        if (mask > q->dma_pad_mask)
 692                q->dma_pad_mask = mask;
 693}
 694EXPORT_SYMBOL(blk_queue_update_dma_pad);
 695
 696/**
 697 * blk_queue_dma_drain - Set up a drain buffer for excess dma.
 698 * @q:  the request queue for the device
 699 * @dma_drain_needed: fn which returns non-zero if drain is necessary
 700 * @buf:        physically contiguous buffer
 701 * @size:       size of the buffer in bytes
 702 *
 703 * Some devices have excess DMA problems and can't simply discard (or
 704 * zero fill) the unwanted piece of the transfer.  They have to have a
 705 * real area of memory to transfer it into.  The use case for this is
 706 * ATAPI devices in DMA mode.  If the packet command causes a transfer
 707 * bigger than the transfer size some HBAs will lock up if there
 708 * aren't DMA elements to contain the excess transfer.  What this API
 709 * does is adjust the queue so that the buf is always appended
 710 * silently to the scatterlist.
 711 *
 712 * Note: This routine adjusts max_hw_segments to make room for appending
 713 * the drain buffer.  If you call blk_queue_max_segments() after calling
 714 * this routine, you must set the limit to one fewer than your device
 715 * can support otherwise there won't be room for the drain buffer.
 716 */
 717int blk_queue_dma_drain(struct request_queue *q,
 718                               dma_drain_needed_fn *dma_drain_needed,
 719                               void *buf, unsigned int size)
 720{
 721        if (queue_max_segments(q) < 2)
 722                return -EINVAL;
 723        /* make room for appending the drain */
 724        blk_queue_max_segments(q, queue_max_segments(q) - 1);
 725        q->dma_drain_needed = dma_drain_needed;
 726        q->dma_drain_buffer = buf;
 727        q->dma_drain_size = size;
 728
 729        return 0;
 730}
 731EXPORT_SYMBOL_GPL(blk_queue_dma_drain);
 732
 733/**
 734 * blk_queue_segment_boundary - set boundary rules for segment merging
 735 * @q:  the request queue for the device
 736 * @mask:  the memory boundary mask
 737 **/
 738void blk_queue_segment_boundary(struct request_queue *q, unsigned long mask)
 739{
 740        if (mask < PAGE_CACHE_SIZE - 1) {
 741                mask = PAGE_CACHE_SIZE - 1;
 742                printk(KERN_INFO "%s: set to minimum %lx\n",
 743                       __func__, mask);
 744        }
 745
 746        q->limits.seg_boundary_mask = mask;
 747}
 748EXPORT_SYMBOL(blk_queue_segment_boundary);
 749
 750/**
 751 * blk_queue_dma_alignment - set dma length and memory alignment
 752 * @q:     the request queue for the device
 753 * @mask:  alignment mask
 754 *
 755 * description:
 756 *    set required memory and length alignment for direct dma transactions.
 757 *    this is used when building direct io requests for the queue.
 758 *
 759 **/
 760void blk_queue_dma_alignment(struct request_queue *q, int mask)
 761{
 762        q->dma_alignment = mask;
 763}
 764EXPORT_SYMBOL(blk_queue_dma_alignment);
 765
 766/**
 767 * blk_queue_update_dma_alignment - update dma length and memory alignment
 768 * @q:     the request queue for the device
 769 * @mask:  alignment mask
 770 *
 771 * description:
 772 *    update required memory and length alignment for direct dma transactions.
 773 *    If the requested alignment is larger than the current alignment, then
 774 *    the current queue alignment is updated to the new value, otherwise it
 775 *    is left alone.  The design of this is to allow multiple objects
 776 *    (driver, device, transport etc) to set their respective
 777 *    alignments without having them interfere.
 778 *
 779 **/
 780void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
 781{
 782        BUG_ON(mask > PAGE_SIZE);
 783
 784        if (mask > q->dma_alignment)
 785                q->dma_alignment = mask;
 786}
 787EXPORT_SYMBOL(blk_queue_update_dma_alignment);
 788
 789/**
 790 * blk_queue_flush - configure queue's cache flush capability
 791 * @q:          the request queue for the device
 792 * @flush:      0, REQ_FLUSH or REQ_FLUSH | REQ_FUA
 793 *
 794 * Tell block layer cache flush capability of @q.  If it supports
 795 * flushing, REQ_FLUSH should be set.  If it supports bypassing
 796 * write cache for individual writes, REQ_FUA should be set.
 797 */
 798void blk_queue_flush(struct request_queue *q, unsigned int flush)
 799{
 800        WARN_ON_ONCE(flush & ~(REQ_FLUSH | REQ_FUA));
 801
 802        if (WARN_ON_ONCE(!(flush & REQ_FLUSH) && (flush & REQ_FUA)))
 803                flush &= ~REQ_FUA;
 804
 805        q->flush_flags = flush & (REQ_FLUSH | REQ_FUA);
 806}
 807EXPORT_SYMBOL_GPL(blk_queue_flush);
 808
 809void blk_queue_flush_queueable(struct request_queue *q, bool queueable)
 810{
 811        q->flush_not_queueable = !queueable;
 812}
 813EXPORT_SYMBOL_GPL(blk_queue_flush_queueable);
 814
 815static int __init blk_settings_init(void)
 816{
 817        blk_max_low_pfn = max_low_pfn - 1;
 818        blk_max_pfn = max_pfn - 1;
 819        return 0;
 820}
 821subsys_initcall(blk_settings_init);
 822
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