60e64091de1b34df8b5a0cd27c9a952b6b33ac86
[linux-3.10.git] / drivers / block / ll_rw_blk.c
1 /*
2  *  linux/drivers/block/ll_rw_blk.c
3  *
4  * Copyright (C) 1991, 1992 Linus Torvalds
5  * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
6  * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
7  * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>
8  * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au> -  July2000
9  * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - may 2001
10  */
11
12 /*
13  * This handles all read/write requests to block devices
14  */
15 #include <linux/config.h>
16 #include <linux/kernel.h>
17 #include <linux/module.h>
18 #include <linux/backing-dev.h>
19 #include <linux/bio.h>
20 #include <linux/blkdev.h>
21 #include <linux/highmem.h>
22 #include <linux/mm.h>
23 #include <linux/kernel_stat.h>
24 #include <linux/string.h>
25 #include <linux/init.h>
26 #include <linux/bootmem.h>      /* for max_pfn/max_low_pfn */
27 #include <linux/completion.h>
28 #include <linux/slab.h>
29 #include <linux/swap.h>
30 #include <linux/writeback.h>
31 #include <linux/blkdev.h>
32
33 /*
34  * for max sense size
35  */
36 #include <scsi/scsi_cmnd.h>
37
38 static void blk_unplug_work(void *data);
39 static void blk_unplug_timeout(unsigned long data);
40 static void drive_stat_acct(struct request *rq, int nr_sectors, int new_io);
41
42 /*
43  * For the allocated request tables
44  */
45 static kmem_cache_t *request_cachep;
46
47 /*
48  * For queue allocation
49  */
50 static kmem_cache_t *requestq_cachep;
51
52 /*
53  * For io context allocations
54  */
55 static kmem_cache_t *iocontext_cachep;
56
57 static wait_queue_head_t congestion_wqh[2] = {
58                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
59                 __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
60         };
61
62 /*
63  * Controlling structure to kblockd
64  */
65 static struct workqueue_struct *kblockd_workqueue; 
66
67 unsigned long blk_max_low_pfn, blk_max_pfn;
68
69 EXPORT_SYMBOL(blk_max_low_pfn);
70 EXPORT_SYMBOL(blk_max_pfn);
71
72 /* Amount of time in which a process may batch requests */
73 #define BLK_BATCH_TIME  (HZ/50UL)
74
75 /* Number of requests a "batching" process may submit */
76 #define BLK_BATCH_REQ   32
77
78 /*
79  * Return the threshold (number of used requests) at which the queue is
80  * considered to be congested.  It include a little hysteresis to keep the
81  * context switch rate down.
82  */
83 static inline int queue_congestion_on_threshold(struct request_queue *q)
84 {
85         return q->nr_congestion_on;
86 }
87
88 /*
89  * The threshold at which a queue is considered to be uncongested
90  */
91 static inline int queue_congestion_off_threshold(struct request_queue *q)
92 {
93         return q->nr_congestion_off;
94 }
95
96 static void blk_queue_congestion_threshold(struct request_queue *q)
97 {
98         int nr;
99
100         nr = q->nr_requests - (q->nr_requests / 8) + 1;
101         if (nr > q->nr_requests)
102                 nr = q->nr_requests;
103         q->nr_congestion_on = nr;
104
105         nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests / 16) - 1;
106         if (nr < 1)
107                 nr = 1;
108         q->nr_congestion_off = nr;
109 }
110
111 /*
112  * A queue has just exitted congestion.  Note this in the global counter of
113  * congested queues, and wake up anyone who was waiting for requests to be
114  * put back.
115  */
116 static void clear_queue_congested(request_queue_t *q, int rw)
117 {
118         enum bdi_state bit;
119         wait_queue_head_t *wqh = &congestion_wqh[rw];
120
121         bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
122         clear_bit(bit, &q->backing_dev_info.state);
123         smp_mb__after_clear_bit();
124         if (waitqueue_active(wqh))
125                 wake_up(wqh);
126 }
127
128 /*
129  * A queue has just entered congestion.  Flag that in the queue's VM-visible
130  * state flags and increment the global gounter of congested queues.
131  */
132 static void set_queue_congested(request_queue_t *q, int rw)
133 {
134         enum bdi_state bit;
135
136         bit = (rw == WRITE) ? BDI_write_congested : BDI_read_congested;
137         set_bit(bit, &q->backing_dev_info.state);
138 }
139
140 /**
141  * blk_get_backing_dev_info - get the address of a queue's backing_dev_info
142  * @bdev:       device
143  *
144  * Locates the passed device's request queue and returns the address of its
145  * backing_dev_info
146  *
147  * Will return NULL if the request queue cannot be located.
148  */
149 struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev)
150 {
151         struct backing_dev_info *ret = NULL;
152         request_queue_t *q = bdev_get_queue(bdev);
153
154         if (q)
155                 ret = &q->backing_dev_info;
156         return ret;
157 }
158
159 EXPORT_SYMBOL(blk_get_backing_dev_info);
160
161 void blk_queue_activity_fn(request_queue_t *q, activity_fn *fn, void *data)
162 {
163         q->activity_fn = fn;
164         q->activity_data = data;
165 }
166
167 EXPORT_SYMBOL(blk_queue_activity_fn);
168
169 /**
170  * blk_queue_prep_rq - set a prepare_request function for queue
171  * @q:          queue
172  * @pfn:        prepare_request function
173  *
174  * It's possible for a queue to register a prepare_request callback which
175  * is invoked before the request is handed to the request_fn. The goal of
176  * the function is to prepare a request for I/O, it can be used to build a
177  * cdb from the request data for instance.
178  *
179  */
180 void blk_queue_prep_rq(request_queue_t *q, prep_rq_fn *pfn)
181 {
182         q->prep_rq_fn = pfn;
183 }
184
185 EXPORT_SYMBOL(blk_queue_prep_rq);
186
187 /**
188  * blk_queue_merge_bvec - set a merge_bvec function for queue
189  * @q:          queue
190  * @mbfn:       merge_bvec_fn
191  *
192  * Usually queues have static limitations on the max sectors or segments that
193  * we can put in a request. Stacking drivers may have some settings that
194  * are dynamic, and thus we have to query the queue whether it is ok to
195  * add a new bio_vec to a bio at a given offset or not. If the block device
196  * has such limitations, it needs to register a merge_bvec_fn to control
197  * the size of bio's sent to it. Note that a block device *must* allow a
198  * single page to be added to an empty bio. The block device driver may want
199  * to use the bio_split() function to deal with these bio's. By default
200  * no merge_bvec_fn is defined for a queue, and only the fixed limits are
201  * honored.
202  */
203 void blk_queue_merge_bvec(request_queue_t *q, merge_bvec_fn *mbfn)
204 {
205         q->merge_bvec_fn = mbfn;
206 }
207
208 EXPORT_SYMBOL(blk_queue_merge_bvec);
209
210 /**
211  * blk_queue_make_request - define an alternate make_request function for a device
212  * @q:  the request queue for the device to be affected
213  * @mfn: the alternate make_request function
214  *
215  * Description:
216  *    The normal way for &struct bios to be passed to a device
217  *    driver is for them to be collected into requests on a request
218  *    queue, and then to allow the device driver to select requests
219  *    off that queue when it is ready.  This works well for many block
220  *    devices. However some block devices (typically virtual devices
221  *    such as md or lvm) do not benefit from the processing on the
222  *    request queue, and are served best by having the requests passed
223  *    directly to them.  This can be achieved by providing a function
224  *    to blk_queue_make_request().
225  *
226  * Caveat:
227  *    The driver that does this *must* be able to deal appropriately
228  *    with buffers in "highmemory". This can be accomplished by either calling
229  *    __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
230  *    blk_queue_bounce() to create a buffer in normal memory.
231  **/
232 void blk_queue_make_request(request_queue_t * q, make_request_fn * mfn)
233 {
234         /*
235          * set defaults
236          */
237         q->nr_requests = BLKDEV_MAX_RQ;
238         q->max_phys_segments = MAX_PHYS_SEGMENTS;
239         q->max_hw_segments = MAX_HW_SEGMENTS;
240         q->make_request_fn = mfn;
241         q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
242         q->backing_dev_info.state = 0;
243         q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
244         blk_queue_max_sectors(q, MAX_SECTORS);
245         blk_queue_hardsect_size(q, 512);
246         blk_queue_dma_alignment(q, 511);
247         blk_queue_congestion_threshold(q);
248         q->nr_batching = BLK_BATCH_REQ;
249
250         q->unplug_thresh = 4;           /* hmm */
251         q->unplug_delay = (3 * HZ) / 1000;      /* 3 milliseconds */
252         if (q->unplug_delay == 0)
253                 q->unplug_delay = 1;
254
255         INIT_WORK(&q->unplug_work, blk_unplug_work, q);
256
257         q->unplug_timer.function = blk_unplug_timeout;
258         q->unplug_timer.data = (unsigned long)q;
259
260         /*
261          * by default assume old behaviour and bounce for any highmem page
262          */
263         blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
264
265         blk_queue_activity_fn(q, NULL, NULL);
266
267         INIT_LIST_HEAD(&q->drain_list);
268 }
269
270 EXPORT_SYMBOL(blk_queue_make_request);
271
272 static inline void rq_init(request_queue_t *q, struct request *rq)
273 {
274         INIT_LIST_HEAD(&rq->queuelist);
275
276         rq->errors = 0;
277         rq->rq_status = RQ_ACTIVE;
278         rq->bio = rq->biotail = NULL;
279         rq->buffer = NULL;
280         rq->ref_count = 1;
281         rq->q = q;
282         rq->waiting = NULL;
283         rq->special = NULL;
284         rq->data_len = 0;
285         rq->data = NULL;
286         rq->sense = NULL;
287         rq->end_io = NULL;
288         rq->end_io_data = NULL;
289 }
290
291 /**
292  * blk_queue_ordered - does this queue support ordered writes
293  * @q:     the request queue
294  * @flag:  see below
295  *
296  * Description:
297  *   For journalled file systems, doing ordered writes on a commit
298  *   block instead of explicitly doing wait_on_buffer (which is bad
299  *   for performance) can be a big win. Block drivers supporting this
300  *   feature should call this function and indicate so.
301  *
302  **/
303 void blk_queue_ordered(request_queue_t *q, int flag)
304 {
305         switch (flag) {
306                 case QUEUE_ORDERED_NONE:
307                         if (q->flush_rq)
308                                 kmem_cache_free(request_cachep, q->flush_rq);
309                         q->flush_rq = NULL;
310                         q->ordered = flag;
311                         break;
312                 case QUEUE_ORDERED_TAG:
313                         q->ordered = flag;
314                         break;
315                 case QUEUE_ORDERED_FLUSH:
316                         q->ordered = flag;
317                         if (!q->flush_rq)
318                                 q->flush_rq = kmem_cache_alloc(request_cachep,
319                                                                 GFP_KERNEL);
320                         break;
321                 default:
322                         printk("blk_queue_ordered: bad value %d\n", flag);
323                         break;
324         }
325 }
326
327 EXPORT_SYMBOL(blk_queue_ordered);
328
329 /**
330  * blk_queue_issue_flush_fn - set function for issuing a flush
331  * @q:     the request queue
332  * @iff:   the function to be called issuing the flush
333  *
334  * Description:
335  *   If a driver supports issuing a flush command, the support is notified
336  *   to the block layer by defining it through this call.
337  *
338  **/
339 void blk_queue_issue_flush_fn(request_queue_t *q, issue_flush_fn *iff)
340 {
341         q->issue_flush_fn = iff;
342 }
343
344 EXPORT_SYMBOL(blk_queue_issue_flush_fn);
345
346 /*
347  * Cache flushing for ordered writes handling
348  */
349 static void blk_pre_flush_end_io(struct request *flush_rq)
350 {
351         struct request *rq = flush_rq->end_io_data;
352         request_queue_t *q = rq->q;
353
354         rq->flags |= REQ_BAR_PREFLUSH;
355
356         if (!flush_rq->errors)
357                 elv_requeue_request(q, rq);
358         else {
359                 q->end_flush_fn(q, flush_rq);
360                 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
361                 q->request_fn(q);
362         }
363 }
364
365 static void blk_post_flush_end_io(struct request *flush_rq)
366 {
367         struct request *rq = flush_rq->end_io_data;
368         request_queue_t *q = rq->q;
369
370         rq->flags |= REQ_BAR_POSTFLUSH;
371
372         q->end_flush_fn(q, flush_rq);
373         clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
374         q->request_fn(q);
375 }
376
377 struct request *blk_start_pre_flush(request_queue_t *q, struct request *rq)
378 {
379         struct request *flush_rq = q->flush_rq;
380
381         BUG_ON(!blk_barrier_rq(rq));
382
383         if (test_and_set_bit(QUEUE_FLAG_FLUSH, &q->queue_flags))
384                 return NULL;
385
386         rq_init(q, flush_rq);
387         flush_rq->elevator_private = NULL;
388         flush_rq->flags = REQ_BAR_FLUSH;
389         flush_rq->rq_disk = rq->rq_disk;
390         flush_rq->rl = NULL;
391
392         /*
393          * prepare_flush returns 0 if no flush is needed, just mark both
394          * pre and post flush as done in that case
395          */
396         if (!q->prepare_flush_fn(q, flush_rq)) {
397                 rq->flags |= REQ_BAR_PREFLUSH | REQ_BAR_POSTFLUSH;
398                 clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
399                 return rq;
400         }
401
402         /*
403          * some drivers dequeue requests right away, some only after io
404          * completion. make sure the request is dequeued.
405          */
406         if (!list_empty(&rq->queuelist))
407                 blkdev_dequeue_request(rq);
408
409         elv_deactivate_request(q, rq);
410
411         flush_rq->end_io_data = rq;
412         flush_rq->end_io = blk_pre_flush_end_io;
413
414         __elv_add_request(q, flush_rq, ELEVATOR_INSERT_FRONT, 0);
415         return flush_rq;
416 }
417
418 static void blk_start_post_flush(request_queue_t *q, struct request *rq)
419 {
420         struct request *flush_rq = q->flush_rq;
421
422         BUG_ON(!blk_barrier_rq(rq));
423
424         rq_init(q, flush_rq);
425         flush_rq->elevator_private = NULL;
426         flush_rq->flags = REQ_BAR_FLUSH;
427         flush_rq->rq_disk = rq->rq_disk;
428         flush_rq->rl = NULL;
429
430         if (q->prepare_flush_fn(q, flush_rq)) {
431                 flush_rq->end_io_data = rq;
432                 flush_rq->end_io = blk_post_flush_end_io;
433
434                 __elv_add_request(q, flush_rq, ELEVATOR_INSERT_FRONT, 0);
435                 q->request_fn(q);
436         }
437 }
438
439 static inline int blk_check_end_barrier(request_queue_t *q, struct request *rq,
440                                         int sectors)
441 {
442         if (sectors > rq->nr_sectors)
443                 sectors = rq->nr_sectors;
444
445         rq->nr_sectors -= sectors;
446         return rq->nr_sectors;
447 }
448
449 static int __blk_complete_barrier_rq(request_queue_t *q, struct request *rq,
450                                      int sectors, int queue_locked)
451 {
452         if (q->ordered != QUEUE_ORDERED_FLUSH)
453                 return 0;
454         if (!blk_fs_request(rq) || !blk_barrier_rq(rq))
455                 return 0;
456         if (blk_barrier_postflush(rq))
457                 return 0;
458
459         if (!blk_check_end_barrier(q, rq, sectors)) {
460                 unsigned long flags = 0;
461
462                 if (!queue_locked)
463                         spin_lock_irqsave(q->queue_lock, flags);
464
465                 blk_start_post_flush(q, rq);
466
467                 if (!queue_locked)
468                         spin_unlock_irqrestore(q->queue_lock, flags);
469         }
470
471         return 1;
472 }
473
474 /**
475  * blk_complete_barrier_rq - complete possible barrier request
476  * @q:  the request queue for the device
477  * @rq:  the request
478  * @sectors:  number of sectors to complete
479  *
480  * Description:
481  *   Used in driver end_io handling to determine whether to postpone
482  *   completion of a barrier request until a post flush has been done. This
483  *   is the unlocked variant, used if the caller doesn't already hold the
484  *   queue lock.
485  **/
486 int blk_complete_barrier_rq(request_queue_t *q, struct request *rq, int sectors)
487 {
488         return __blk_complete_barrier_rq(q, rq, sectors, 0);
489 }
490 EXPORT_SYMBOL(blk_complete_barrier_rq);
491
492 /**
493  * blk_complete_barrier_rq_locked - complete possible barrier request
494  * @q:  the request queue for the device
495  * @rq:  the request
496  * @sectors:  number of sectors to complete
497  *
498  * Description:
499  *   See blk_complete_barrier_rq(). This variant must be used if the caller
500  *   holds the queue lock.
501  **/
502 int blk_complete_barrier_rq_locked(request_queue_t *q, struct request *rq,
503                                    int sectors)
504 {
505         return __blk_complete_barrier_rq(q, rq, sectors, 1);
506 }
507 EXPORT_SYMBOL(blk_complete_barrier_rq_locked);
508
509 /**
510  * blk_queue_bounce_limit - set bounce buffer limit for queue
511  * @q:  the request queue for the device
512  * @dma_addr:   bus address limit
513  *
514  * Description:
515  *    Different hardware can have different requirements as to what pages
516  *    it can do I/O directly to. A low level driver can call
517  *    blk_queue_bounce_limit to have lower memory pages allocated as bounce
518  *    buffers for doing I/O to pages residing above @page. By default
519  *    the block layer sets this to the highest numbered "low" memory page.
520  **/
521 void blk_queue_bounce_limit(request_queue_t *q, u64 dma_addr)
522 {
523         unsigned long bounce_pfn = dma_addr >> PAGE_SHIFT;
524
525         /*
526          * set appropriate bounce gfp mask -- unfortunately we don't have a
527          * full 4GB zone, so we have to resort to low memory for any bounces.
528          * ISA has its own < 16MB zone.
529          */
530         if (bounce_pfn < blk_max_low_pfn) {
531                 BUG_ON(dma_addr < BLK_BOUNCE_ISA);
532                 init_emergency_isa_pool();
533                 q->bounce_gfp = GFP_NOIO | GFP_DMA;
534         } else
535                 q->bounce_gfp = GFP_NOIO;
536
537         q->bounce_pfn = bounce_pfn;
538 }
539
540 EXPORT_SYMBOL(blk_queue_bounce_limit);
541
542 /**
543  * blk_queue_max_sectors - set max sectors for a request for this queue
544  * @q:  the request queue for the device
545  * @max_sectors:  max sectors in the usual 512b unit
546  *
547  * Description:
548  *    Enables a low level driver to set an upper limit on the size of
549  *    received requests.
550  **/
551 void blk_queue_max_sectors(request_queue_t *q, unsigned short max_sectors)
552 {
553         if ((max_sectors << 9) < PAGE_CACHE_SIZE) {
554                 max_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
555                 printk("%s: set to minimum %d\n", __FUNCTION__, max_sectors);
556         }
557
558         q->max_sectors = q->max_hw_sectors = max_sectors;
559 }
560
561 EXPORT_SYMBOL(blk_queue_max_sectors);
562
563 /**
564  * blk_queue_max_phys_segments - set max phys segments for a request for this queue
565  * @q:  the request queue for the device
566  * @max_segments:  max number of segments
567  *
568  * Description:
569  *    Enables a low level driver to set an upper limit on the number of
570  *    physical data segments in a request.  This would be the largest sized
571  *    scatter list the driver could handle.
572  **/
573 void blk_queue_max_phys_segments(request_queue_t *q, unsigned short max_segments)
574 {
575         if (!max_segments) {
576                 max_segments = 1;
577                 printk("%s: set to minimum %d\n", __FUNCTION__, max_segments);
578         }
579
580         q->max_phys_segments = max_segments;
581 }
582
583 EXPORT_SYMBOL(blk_queue_max_phys_segments);
584
585 /**
586  * blk_queue_max_hw_segments - set max hw segments for a request for this queue
587  * @q:  the request queue for the device
588  * @max_segments:  max number of segments
589  *
590  * Description:
591  *    Enables a low level driver to set an upper limit on the number of
592  *    hw data segments in a request.  This would be the largest number of
593  *    address/length pairs the host adapter can actually give as once
594  *    to the device.
595  **/
596 void blk_queue_max_hw_segments(request_queue_t *q, unsigned short max_segments)
597 {
598         if (!max_segments) {
599                 max_segments = 1;
600                 printk("%s: set to minimum %d\n", __FUNCTION__, max_segments);
601         }
602
603         q->max_hw_segments = max_segments;
604 }
605
606 EXPORT_SYMBOL(blk_queue_max_hw_segments);
607
608 /**
609  * blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
610  * @q:  the request queue for the device
611  * @max_size:  max size of segment in bytes
612  *
613  * Description:
614  *    Enables a low level driver to set an upper limit on the size of a
615  *    coalesced segment
616  **/
617 void blk_queue_max_segment_size(request_queue_t *q, unsigned int max_size)
618 {
619         if (max_size < PAGE_CACHE_SIZE) {
620                 max_size = PAGE_CACHE_SIZE;
621                 printk("%s: set to minimum %d\n", __FUNCTION__, max_size);
622         }
623
624         q->max_segment_size = max_size;
625 }
626
627 EXPORT_SYMBOL(blk_queue_max_segment_size);
628
629 /**
630  * blk_queue_hardsect_size - set hardware sector size for the queue
631  * @q:  the request queue for the device
632  * @size:  the hardware sector size, in bytes
633  *
634  * Description:
635  *   This should typically be set to the lowest possible sector size
636  *   that the hardware can operate on (possible without reverting to
637  *   even internal read-modify-write operations). Usually the default
638  *   of 512 covers most hardware.
639  **/
640 void blk_queue_hardsect_size(request_queue_t *q, unsigned short size)
641 {
642         q->hardsect_size = size;
643 }
644
645 EXPORT_SYMBOL(blk_queue_hardsect_size);
646
647 /*
648  * Returns the minimum that is _not_ zero, unless both are zero.
649  */
650 #define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
651
652 /**
653  * blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
654  * @t:  the stacking driver (top)
655  * @b:  the underlying device (bottom)
656  **/
657 void blk_queue_stack_limits(request_queue_t *t, request_queue_t *b)
658 {
659         /* zero is "infinity" */
660         t->max_sectors = t->max_hw_sectors =
661                 min_not_zero(t->max_sectors,b->max_sectors);
662
663         t->max_phys_segments = min(t->max_phys_segments,b->max_phys_segments);
664         t->max_hw_segments = min(t->max_hw_segments,b->max_hw_segments);
665         t->max_segment_size = min(t->max_segment_size,b->max_segment_size);
666         t->hardsect_size = max(t->hardsect_size,b->hardsect_size);
667 }
668
669 EXPORT_SYMBOL(blk_queue_stack_limits);
670
671 /**
672  * blk_queue_segment_boundary - set boundary rules for segment merging
673  * @q:  the request queue for the device
674  * @mask:  the memory boundary mask
675  **/
676 void blk_queue_segment_boundary(request_queue_t *q, unsigned long mask)
677 {
678         if (mask < PAGE_CACHE_SIZE - 1) {
679                 mask = PAGE_CACHE_SIZE - 1;
680                 printk("%s: set to minimum %lx\n", __FUNCTION__, mask);
681         }
682
683         q->seg_boundary_mask = mask;
684 }
685
686 EXPORT_SYMBOL(blk_queue_segment_boundary);
687
688 /**
689  * blk_queue_dma_alignment - set dma length and memory alignment
690  * @q:     the request queue for the device
691  * @mask:  alignment mask
692  *
693  * description:
694  *    set required memory and length aligment for direct dma transactions.
695  *    this is used when buiding direct io requests for the queue.
696  *
697  **/
698 void blk_queue_dma_alignment(request_queue_t *q, int mask)
699 {
700         q->dma_alignment = mask;
701 }
702
703 EXPORT_SYMBOL(blk_queue_dma_alignment);
704
705 /**
706  * blk_queue_find_tag - find a request by its tag and queue
707  *
708  * @q:   The request queue for the device
709  * @tag: The tag of the request
710  *
711  * Notes:
712  *    Should be used when a device returns a tag and you want to match
713  *    it with a request.
714  *
715  *    no locks need be held.
716  **/
717 struct request *blk_queue_find_tag(request_queue_t *q, int tag)
718 {
719         struct blk_queue_tag *bqt = q->queue_tags;
720
721         if (unlikely(bqt == NULL || tag >= bqt->max_depth))
722                 return NULL;
723
724         return bqt->tag_index[tag];
725 }
726
727 EXPORT_SYMBOL(blk_queue_find_tag);
728
729 /**
730  * __blk_queue_free_tags - release tag maintenance info
731  * @q:  the request queue for the device
732  *
733  *  Notes:
734  *    blk_cleanup_queue() will take care of calling this function, if tagging
735  *    has been used. So there's no need to call this directly.
736  **/
737 static void __blk_queue_free_tags(request_queue_t *q)
738 {
739         struct blk_queue_tag *bqt = q->queue_tags;
740
741         if (!bqt)
742                 return;
743
744         if (atomic_dec_and_test(&bqt->refcnt)) {
745                 BUG_ON(bqt->busy);
746                 BUG_ON(!list_empty(&bqt->busy_list));
747
748                 kfree(bqt->tag_index);
749                 bqt->tag_index = NULL;
750
751                 kfree(bqt->tag_map);
752                 bqt->tag_map = NULL;
753
754                 kfree(bqt);
755         }
756
757         q->queue_tags = NULL;
758         q->queue_flags &= ~(1 << QUEUE_FLAG_QUEUED);
759 }
760
761 /**
762  * blk_queue_free_tags - release tag maintenance info
763  * @q:  the request queue for the device
764  *
765  *  Notes:
766  *      This is used to disabled tagged queuing to a device, yet leave
767  *      queue in function.
768  **/
769 void blk_queue_free_tags(request_queue_t *q)
770 {
771         clear_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
772 }
773
774 EXPORT_SYMBOL(blk_queue_free_tags);
775
776 static int
777 init_tag_map(request_queue_t *q, struct blk_queue_tag *tags, int depth)
778 {
779         struct request **tag_index;
780         unsigned long *tag_map;
781         int nr_ulongs;
782
783         if (depth > q->nr_requests * 2) {
784                 depth = q->nr_requests * 2;
785                 printk(KERN_ERR "%s: adjusted depth to %d\n",
786                                 __FUNCTION__, depth);
787         }
788
789         tag_index = kmalloc(depth * sizeof(struct request *), GFP_ATOMIC);
790         if (!tag_index)
791                 goto fail;
792
793         nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
794         tag_map = kmalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
795         if (!tag_map)
796                 goto fail;
797
798         memset(tag_index, 0, depth * sizeof(struct request *));
799         memset(tag_map, 0, nr_ulongs * sizeof(unsigned long));
800         tags->max_depth = depth;
801         tags->tag_index = tag_index;
802         tags->tag_map = tag_map;
803
804         return 0;
805 fail:
806         kfree(tag_index);
807         return -ENOMEM;
808 }
809
810 /**
811  * blk_queue_init_tags - initialize the queue tag info
812  * @q:  the request queue for the device
813  * @depth:  the maximum queue depth supported
814  * @tags: the tag to use
815  **/
816 int blk_queue_init_tags(request_queue_t *q, int depth,
817                         struct blk_queue_tag *tags)
818 {
819         int rc;
820
821         BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
822
823         if (!tags && !q->queue_tags) {
824                 tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
825                 if (!tags)
826                         goto fail;
827
828                 if (init_tag_map(q, tags, depth))
829                         goto fail;
830
831                 INIT_LIST_HEAD(&tags->busy_list);
832                 tags->busy = 0;
833                 atomic_set(&tags->refcnt, 1);
834         } else if (q->queue_tags) {
835                 if ((rc = blk_queue_resize_tags(q, depth)))
836                         return rc;
837                 set_bit(QUEUE_FLAG_QUEUED, &q->queue_flags);
838                 return 0;
839         } else
840                 atomic_inc(&tags->refcnt);
841
842         /*
843          * assign it, all done
844          */
845         q->queue_tags = tags;
846         q->queue_flags |= (1 << QUEUE_FLAG_QUEUED);
847         return 0;
848 fail:
849         kfree(tags);
850         return -ENOMEM;
851 }
852
853 EXPORT_SYMBOL(blk_queue_init_tags);
854
855 /**
856  * blk_queue_resize_tags - change the queueing depth
857  * @q:  the request queue for the device
858  * @new_depth: the new max command queueing depth
859  *
860  *  Notes:
861  *    Must be called with the queue lock held.
862  **/
863 int blk_queue_resize_tags(request_queue_t *q, int new_depth)
864 {
865         struct blk_queue_tag *bqt = q->queue_tags;
866         struct request **tag_index;
867         unsigned long *tag_map;
868         int max_depth, nr_ulongs;
869
870         if (!bqt)
871                 return -ENXIO;
872
873         /*
874          * save the old state info, so we can copy it back
875          */
876         tag_index = bqt->tag_index;
877         tag_map = bqt->tag_map;
878         max_depth = bqt->max_depth;
879
880         if (init_tag_map(q, bqt, new_depth))
881                 return -ENOMEM;
882
883         memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
884         nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
885         memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
886
887         kfree(tag_index);
888         kfree(tag_map);
889         return 0;
890 }
891
892 EXPORT_SYMBOL(blk_queue_resize_tags);
893
894 /**
895  * blk_queue_end_tag - end tag operations for a request
896  * @q:  the request queue for the device
897  * @rq: the request that has completed
898  *
899  *  Description:
900  *    Typically called when end_that_request_first() returns 0, meaning
901  *    all transfers have been done for a request. It's important to call
902  *    this function before end_that_request_last(), as that will put the
903  *    request back on the free list thus corrupting the internal tag list.
904  *
905  *  Notes:
906  *   queue lock must be held.
907  **/
908 void blk_queue_end_tag(request_queue_t *q, struct request *rq)
909 {
910         struct blk_queue_tag *bqt = q->queue_tags;
911         int tag = rq->tag;
912
913         BUG_ON(tag == -1);
914
915         if (unlikely(tag >= bqt->max_depth))
916                 /*
917                  * This can happen after tag depth has been reduced.
918                  * FIXME: how about a warning or info message here?
919                  */
920                 return;
921
922         if (unlikely(!__test_and_clear_bit(tag, bqt->tag_map))) {
923                 printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
924                        __FUNCTION__, tag);
925                 return;
926         }
927
928         list_del_init(&rq->queuelist);
929         rq->flags &= ~REQ_QUEUED;
930         rq->tag = -1;
931
932         if (unlikely(bqt->tag_index[tag] == NULL))
933                 printk(KERN_ERR "%s: tag %d is missing\n",
934                        __FUNCTION__, tag);
935
936         bqt->tag_index[tag] = NULL;
937         bqt->busy--;
938 }
939
940 EXPORT_SYMBOL(blk_queue_end_tag);
941
942 /**
943  * blk_queue_start_tag - find a free tag and assign it
944  * @q:  the request queue for the device
945  * @rq:  the block request that needs tagging
946  *
947  *  Description:
948  *    This can either be used as a stand-alone helper, or possibly be
949  *    assigned as the queue &prep_rq_fn (in which case &struct request
950  *    automagically gets a tag assigned). Note that this function
951  *    assumes that any type of request can be queued! if this is not
952  *    true for your device, you must check the request type before
953  *    calling this function.  The request will also be removed from
954  *    the request queue, so it's the drivers responsibility to readd
955  *    it if it should need to be restarted for some reason.
956  *
957  *  Notes:
958  *   queue lock must be held.
959  **/
960 int blk_queue_start_tag(request_queue_t *q, struct request *rq)
961 {
962         struct blk_queue_tag *bqt = q->queue_tags;
963         int tag;
964
965         if (unlikely((rq->flags & REQ_QUEUED))) {
966                 printk(KERN_ERR 
967                        "%s: request %p for device [%s] already tagged %d",
968                        __FUNCTION__, rq,
969                        rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
970                 BUG();
971         }
972
973         tag = find_first_zero_bit(bqt->tag_map, bqt->max_depth);
974         if (tag >= bqt->max_depth)
975                 return 1;
976
977         __set_bit(tag, bqt->tag_map);
978
979         rq->flags |= REQ_QUEUED;
980         rq->tag = tag;
981         bqt->tag_index[tag] = rq;
982         blkdev_dequeue_request(rq);
983         list_add(&rq->queuelist, &bqt->busy_list);
984         bqt->busy++;
985         return 0;
986 }
987
988 EXPORT_SYMBOL(blk_queue_start_tag);
989
990 /**
991  * blk_queue_invalidate_tags - invalidate all pending tags
992  * @q:  the request queue for the device
993  *
994  *  Description:
995  *   Hardware conditions may dictate a need to stop all pending requests.
996  *   In this case, we will safely clear the block side of the tag queue and
997  *   readd all requests to the request queue in the right order.
998  *
999  *  Notes:
1000  *   queue lock must be held.
1001  **/
1002 void blk_queue_invalidate_tags(request_queue_t *q)
1003 {
1004         struct blk_queue_tag *bqt = q->queue_tags;
1005         struct list_head *tmp, *n;
1006         struct request *rq;
1007
1008         list_for_each_safe(tmp, n, &bqt->busy_list) {
1009                 rq = list_entry_rq(tmp);
1010
1011                 if (rq->tag == -1) {
1012                         printk(KERN_ERR
1013                                "%s: bad tag found on list\n", __FUNCTION__);
1014                         list_del_init(&rq->queuelist);
1015                         rq->flags &= ~REQ_QUEUED;
1016                 } else
1017                         blk_queue_end_tag(q, rq);
1018
1019                 rq->flags &= ~REQ_STARTED;
1020                 __elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
1021         }
1022 }
1023
1024 EXPORT_SYMBOL(blk_queue_invalidate_tags);
1025
1026 static char *rq_flags[] = {
1027         "REQ_RW",
1028         "REQ_FAILFAST",
1029         "REQ_SOFTBARRIER",
1030         "REQ_HARDBARRIER",
1031         "REQ_CMD",
1032         "REQ_NOMERGE",
1033         "REQ_STARTED",
1034         "REQ_DONTPREP",
1035         "REQ_QUEUED",
1036         "REQ_PC",
1037         "REQ_BLOCK_PC",
1038         "REQ_SENSE",
1039         "REQ_FAILED",
1040         "REQ_QUIET",
1041         "REQ_SPECIAL",
1042         "REQ_DRIVE_CMD",
1043         "REQ_DRIVE_TASK",
1044         "REQ_DRIVE_TASKFILE",
1045         "REQ_PREEMPT",
1046         "REQ_PM_SUSPEND",
1047         "REQ_PM_RESUME",
1048         "REQ_PM_SHUTDOWN",
1049 };
1050
1051 void blk_dump_rq_flags(struct request *rq, char *msg)
1052 {
1053         int bit;
1054
1055         printk("%s: dev %s: flags = ", msg,
1056                 rq->rq_disk ? rq->rq_disk->disk_name : "?");
1057         bit = 0;
1058         do {
1059                 if (rq->flags & (1 << bit))
1060                         printk("%s ", rq_flags[bit]);
1061                 bit++;
1062         } while (bit < __REQ_NR_BITS);
1063
1064         printk("\nsector %llu, nr/cnr %lu/%u\n", (unsigned long long)rq->sector,
1065                                                        rq->nr_sectors,
1066                                                        rq->current_nr_sectors);
1067         printk("bio %p, biotail %p, buffer %p, data %p, len %u\n", rq->bio, rq->biotail, rq->buffer, rq->data, rq->data_len);
1068
1069         if (rq->flags & (REQ_BLOCK_PC | REQ_PC)) {
1070                 printk("cdb: ");
1071                 for (bit = 0; bit < sizeof(rq->cmd); bit++)
1072                         printk("%02x ", rq->cmd[bit]);
1073                 printk("\n");
1074         }
1075 }
1076
1077 EXPORT_SYMBOL(blk_dump_rq_flags);
1078
1079 void blk_recount_segments(request_queue_t *q, struct bio *bio)
1080 {
1081         struct bio_vec *bv, *bvprv = NULL;
1082         int i, nr_phys_segs, nr_hw_segs, seg_size, hw_seg_size, cluster;
1083         int high, highprv = 1;
1084
1085         if (unlikely(!bio->bi_io_vec))
1086                 return;
1087
1088         cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
1089         hw_seg_size = seg_size = nr_phys_segs = nr_hw_segs = 0;
1090         bio_for_each_segment(bv, bio, i) {
1091                 /*
1092                  * the trick here is making sure that a high page is never
1093                  * considered part of another segment, since that might
1094                  * change with the bounce page.
1095                  */
1096                 high = page_to_pfn(bv->bv_page) >= q->bounce_pfn;
1097                 if (high || highprv)
1098                         goto new_hw_segment;
1099                 if (cluster) {
1100                         if (seg_size + bv->bv_len > q->max_segment_size)
1101                                 goto new_segment;
1102                         if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
1103                                 goto new_segment;
1104                         if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
1105                                 goto new_segment;
1106                         if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
1107                                 goto new_hw_segment;
1108
1109                         seg_size += bv->bv_len;
1110                         hw_seg_size += bv->bv_len;
1111                         bvprv = bv;
1112                         continue;
1113                 }
1114 new_segment:
1115                 if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
1116                     !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len)) {
1117                         hw_seg_size += bv->bv_len;
1118                 } else {
1119 new_hw_segment:
1120                         if (hw_seg_size > bio->bi_hw_front_size)
1121                                 bio->bi_hw_front_size = hw_seg_size;
1122                         hw_seg_size = BIOVEC_VIRT_START_SIZE(bv) + bv->bv_len;
1123                         nr_hw_segs++;
1124                 }
1125
1126                 nr_phys_segs++;
1127                 bvprv = bv;
1128                 seg_size = bv->bv_len;
1129                 highprv = high;
1130         }
1131         if (hw_seg_size > bio->bi_hw_back_size)
1132                 bio->bi_hw_back_size = hw_seg_size;
1133         if (nr_hw_segs == 1 && hw_seg_size > bio->bi_hw_front_size)
1134                 bio->bi_hw_front_size = hw_seg_size;
1135         bio->bi_phys_segments = nr_phys_segs;
1136         bio->bi_hw_segments = nr_hw_segs;
1137         bio->bi_flags |= (1 << BIO_SEG_VALID);
1138 }
1139
1140
1141 static int blk_phys_contig_segment(request_queue_t *q, struct bio *bio,
1142                                    struct bio *nxt)
1143 {
1144         if (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER)))
1145                 return 0;
1146
1147         if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
1148                 return 0;
1149         if (bio->bi_size + nxt->bi_size > q->max_segment_size)
1150                 return 0;
1151
1152         /*
1153          * bio and nxt are contigous in memory, check if the queue allows
1154          * these two to be merged into one
1155          */
1156         if (BIO_SEG_BOUNDARY(q, bio, nxt))
1157                 return 1;
1158
1159         return 0;
1160 }
1161
1162 static int blk_hw_contig_segment(request_queue_t *q, struct bio *bio,
1163                                  struct bio *nxt)
1164 {
1165         if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
1166                 blk_recount_segments(q, bio);
1167         if (unlikely(!bio_flagged(nxt, BIO_SEG_VALID)))
1168                 blk_recount_segments(q, nxt);
1169         if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
1170             BIOVEC_VIRT_OVERSIZE(bio->bi_hw_front_size + bio->bi_hw_back_size))
1171                 return 0;
1172         if (bio->bi_size + nxt->bi_size > q->max_segment_size)
1173                 return 0;
1174
1175         return 1;
1176 }
1177
1178 /*
1179  * map a request to scatterlist, return number of sg entries setup. Caller
1180  * must make sure sg can hold rq->nr_phys_segments entries
1181  */
1182 int blk_rq_map_sg(request_queue_t *q, struct request *rq, struct scatterlist *sg)
1183 {
1184         struct bio_vec *bvec, *bvprv;
1185         struct bio *bio;
1186         int nsegs, i, cluster;
1187
1188         nsegs = 0;
1189         cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
1190
1191         /*
1192          * for each bio in rq
1193          */
1194         bvprv = NULL;
1195         rq_for_each_bio(bio, rq) {
1196                 /*
1197                  * for each segment in bio
1198                  */
1199                 bio_for_each_segment(bvec, bio, i) {
1200                         int nbytes = bvec->bv_len;
1201
1202                         if (bvprv && cluster) {
1203                                 if (sg[nsegs - 1].length + nbytes > q->max_segment_size)
1204                                         goto new_segment;
1205
1206                                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
1207                                         goto new_segment;
1208                                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
1209                                         goto new_segment;
1210
1211                                 sg[nsegs - 1].length += nbytes;
1212                         } else {
1213 new_segment:
1214                                 memset(&sg[nsegs],0,sizeof(struct scatterlist));
1215                                 sg[nsegs].page = bvec->bv_page;
1216                                 sg[nsegs].length = nbytes;
1217                                 sg[nsegs].offset = bvec->bv_offset;
1218
1219                                 nsegs++;
1220                         }
1221                         bvprv = bvec;
1222                 } /* segments in bio */
1223         } /* bios in rq */
1224
1225         return nsegs;
1226 }
1227
1228 EXPORT_SYMBOL(blk_rq_map_sg);
1229
1230 /*
1231  * the standard queue merge functions, can be overridden with device
1232  * specific ones if so desired
1233  */
1234
1235 static inline int ll_new_mergeable(request_queue_t *q,
1236                                    struct request *req,
1237                                    struct bio *bio)
1238 {
1239         int nr_phys_segs = bio_phys_segments(q, bio);
1240
1241         if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
1242                 req->flags |= REQ_NOMERGE;
1243                 if (req == q->last_merge)
1244                         q->last_merge = NULL;
1245                 return 0;
1246         }
1247
1248         /*
1249          * A hw segment is just getting larger, bump just the phys
1250          * counter.
1251          */
1252         req->nr_phys_segments += nr_phys_segs;
1253         return 1;
1254 }
1255
1256 static inline int ll_new_hw_segment(request_queue_t *q,
1257                                     struct request *req,
1258                                     struct bio *bio)
1259 {
1260         int nr_hw_segs = bio_hw_segments(q, bio);
1261         int nr_phys_segs = bio_phys_segments(q, bio);
1262
1263         if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
1264             || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
1265                 req->flags |= REQ_NOMERGE;
1266                 if (req == q->last_merge)
1267                         q->last_merge = NULL;
1268                 return 0;
1269         }
1270
1271         /*
1272          * This will form the start of a new hw segment.  Bump both
1273          * counters.
1274          */
1275         req->nr_hw_segments += nr_hw_segs;
1276         req->nr_phys_segments += nr_phys_segs;
1277         return 1;
1278 }
1279
1280 static int ll_back_merge_fn(request_queue_t *q, struct request *req, 
1281                             struct bio *bio)
1282 {
1283         int len;
1284
1285         if (req->nr_sectors + bio_sectors(bio) > q->max_sectors) {
1286                 req->flags |= REQ_NOMERGE;
1287                 if (req == q->last_merge)
1288                         q->last_merge = NULL;
1289                 return 0;
1290         }
1291         if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID)))
1292                 blk_recount_segments(q, req->biotail);
1293         if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
1294                 blk_recount_segments(q, bio);
1295         len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
1296         if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio)) &&
1297             !BIOVEC_VIRT_OVERSIZE(len)) {
1298                 int mergeable =  ll_new_mergeable(q, req, bio);
1299
1300                 if (mergeable) {
1301                         if (req->nr_hw_segments == 1)
1302                                 req->bio->bi_hw_front_size = len;
1303                         if (bio->bi_hw_segments == 1)
1304                                 bio->bi_hw_back_size = len;
1305                 }
1306                 return mergeable;
1307         }
1308
1309         return ll_new_hw_segment(q, req, bio);
1310 }
1311
1312 static int ll_front_merge_fn(request_queue_t *q, struct request *req, 
1313                              struct bio *bio)
1314 {
1315         int len;
1316
1317         if (req->nr_sectors + bio_sectors(bio) > q->max_sectors) {
1318                 req->flags |= REQ_NOMERGE;
1319                 if (req == q->last_merge)
1320                         q->last_merge = NULL;
1321                 return 0;
1322         }
1323         len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
1324         if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
1325                 blk_recount_segments(q, bio);
1326         if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID)))
1327                 blk_recount_segments(q, req->bio);
1328         if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
1329             !BIOVEC_VIRT_OVERSIZE(len)) {
1330                 int mergeable =  ll_new_mergeable(q, req, bio);
1331
1332                 if (mergeable) {
1333                         if (bio->bi_hw_segments == 1)
1334                                 bio->bi_hw_front_size = len;
1335                         if (req->nr_hw_segments == 1)
1336                                 req->biotail->bi_hw_back_size = len;
1337                 }
1338                 return mergeable;
1339         }
1340
1341         return ll_new_hw_segment(q, req, bio);
1342 }
1343
1344 static int ll_merge_requests_fn(request_queue_t *q, struct request *req,
1345                                 struct request *next)
1346 {
1347         int total_phys_segments;
1348         int total_hw_segments;
1349
1350         /*
1351          * First check if the either of the requests are re-queued
1352          * requests.  Can't merge them if they are.
1353          */
1354         if (req->special || next->special)
1355                 return 0;
1356
1357         /*
1358          * Will it become too large?
1359          */
1360         if ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
1361                 return 0;
1362
1363         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
1364         if (blk_phys_contig_segment(q, req->biotail, next->bio))
1365                 total_phys_segments--;
1366
1367         if (total_phys_segments > q->max_phys_segments)
1368                 return 0;
1369
1370         total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
1371         if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
1372                 int len = req->biotail->bi_hw_back_size + next->bio->bi_hw_front_size;
1373                 /*
1374                  * propagate the combined length to the end of the requests
1375                  */
1376                 if (req->nr_hw_segments == 1)
1377                         req->bio->bi_hw_front_size = len;
1378                 if (next->nr_hw_segments == 1)
1379                         next->biotail->bi_hw_back_size = len;
1380                 total_hw_segments--;
1381         }
1382
1383         if (total_hw_segments > q->max_hw_segments)
1384                 return 0;
1385
1386         /* Merge is OK... */
1387         req->nr_phys_segments = total_phys_segments;
1388         req->nr_hw_segments = total_hw_segments;
1389         return 1;
1390 }
1391
1392 /*
1393  * "plug" the device if there are no outstanding requests: this will
1394  * force the transfer to start only after we have put all the requests
1395  * on the list.
1396  *
1397  * This is called with interrupts off and no requests on the queue and
1398  * with the queue lock held.
1399  */
1400 void blk_plug_device(request_queue_t *q)
1401 {
1402         WARN_ON(!irqs_disabled());
1403
1404         /*
1405          * don't plug a stopped queue, it must be paired with blk_start_queue()
1406          * which will restart the queueing
1407          */
1408         if (test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags))
1409                 return;
1410
1411         if (!test_and_set_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
1412                 mod_timer(&q->unplug_timer, jiffies + q->unplug_delay);
1413 }
1414
1415 EXPORT_SYMBOL(blk_plug_device);
1416
1417 /*
1418  * remove the queue from the plugged list, if present. called with
1419  * queue lock held and interrupts disabled.
1420  */
1421 int blk_remove_plug(request_queue_t *q)
1422 {
1423         WARN_ON(!irqs_disabled());
1424
1425         if (!test_and_clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags))
1426                 return 0;
1427
1428         del_timer(&q->unplug_timer);
1429         return 1;
1430 }
1431
1432 EXPORT_SYMBOL(blk_remove_plug);
1433
1434 /*
1435  * remove the plug and let it rip..
1436  */
1437 void __generic_unplug_device(request_queue_t *q)
1438 {
1439         if (unlikely(test_bit(QUEUE_FLAG_STOPPED, &q->queue_flags)))
1440                 return;
1441
1442         if (!blk_remove_plug(q))
1443                 return;
1444
1445         /*
1446          * was plugged, fire request_fn if queue has stuff to do
1447          */
1448         if (elv_next_request(q))
1449                 q->request_fn(q);
1450 }
1451 EXPORT_SYMBOL(__generic_unplug_device);
1452
1453 /**
1454  * generic_unplug_device - fire a request queue
1455  * @q:    The &request_queue_t in question
1456  *
1457  * Description:
1458  *   Linux uses plugging to build bigger requests queues before letting
1459  *   the device have at them. If a queue is plugged, the I/O scheduler
1460  *   is still adding and merging requests on the queue. Once the queue
1461  *   gets unplugged, the request_fn defined for the queue is invoked and
1462  *   transfers started.
1463  **/
1464 void generic_unplug_device(request_queue_t *q)
1465 {
1466         spin_lock_irq(q->queue_lock);
1467         __generic_unplug_device(q);
1468         spin_unlock_irq(q->queue_lock);
1469 }
1470 EXPORT_SYMBOL(generic_unplug_device);
1471
1472 static void blk_backing_dev_unplug(struct backing_dev_info *bdi,
1473                                    struct page *page)
1474 {
1475         request_queue_t *q = bdi->unplug_io_data;
1476
1477         /*
1478          * devices don't necessarily have an ->unplug_fn defined
1479          */
1480         if (q->unplug_fn)
1481                 q->unplug_fn(q);
1482 }
1483
1484 static void blk_unplug_work(void *data)
1485 {
1486         request_queue_t *q = data;
1487
1488         q->unplug_fn(q);
1489 }
1490
1491 static void blk_unplug_timeout(unsigned long data)
1492 {
1493         request_queue_t *q = (request_queue_t *)data;
1494
1495         kblockd_schedule_work(&q->unplug_work);
1496 }
1497
1498 /**
1499  * blk_start_queue - restart a previously stopped queue
1500  * @q:    The &request_queue_t in question
1501  *
1502  * Description:
1503  *   blk_start_queue() will clear the stop flag on the queue, and call
1504  *   the request_fn for the queue if it was in a stopped state when
1505  *   entered. Also see blk_stop_queue(). Queue lock must be held.
1506  **/
1507 void blk_start_queue(request_queue_t *q)
1508 {
1509         clear_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
1510
1511         /*
1512          * one level of recursion is ok and is much faster than kicking
1513          * the unplug handling
1514          */
1515         if (!test_and_set_bit(QUEUE_FLAG_REENTER, &q->queue_flags)) {
1516                 q->request_fn(q);
1517                 clear_bit(QUEUE_FLAG_REENTER, &q->queue_flags);
1518         } else {
1519                 blk_plug_device(q);
1520                 kblockd_schedule_work(&q->unplug_work);
1521         }
1522 }
1523
1524 EXPORT_SYMBOL(blk_start_queue);
1525
1526 /**
1527  * blk_stop_queue - stop a queue
1528  * @q:    The &request_queue_t in question
1529  *
1530  * Description:
1531  *   The Linux block layer assumes that a block driver will consume all
1532  *   entries on the request queue when the request_fn strategy is called.
1533  *   Often this will not happen, because of hardware limitations (queue
1534  *   depth settings). If a device driver gets a 'queue full' response,
1535  *   or if it simply chooses not to queue more I/O at one point, it can
1536  *   call this function to prevent the request_fn from being called until
1537  *   the driver has signalled it's ready to go again. This happens by calling
1538  *   blk_start_queue() to restart queue operations. Queue lock must be held.
1539  **/
1540 void blk_stop_queue(request_queue_t *q)
1541 {
1542         blk_remove_plug(q);
1543         set_bit(QUEUE_FLAG_STOPPED, &q->queue_flags);
1544 }
1545 EXPORT_SYMBOL(blk_stop_queue);
1546
1547 /**
1548  * blk_sync_queue - cancel any pending callbacks on a queue
1549  * @q: the queue
1550  *
1551  * Description:
1552  *     The block layer may perform asynchronous callback activity
1553  *     on a queue, such as calling the unplug function after a timeout.
1554  *     A block device may call blk_sync_queue to ensure that any
1555  *     such activity is cancelled, thus allowing it to release resources
1556  *     the the callbacks might use. The caller must already have made sure
1557  *     that its ->make_request_fn will not re-add plugging prior to calling
1558  *     this function.
1559  *
1560  */
1561 void blk_sync_queue(struct request_queue *q)
1562 {
1563         del_timer_sync(&q->unplug_timer);
1564         kblockd_flush();
1565 }
1566 EXPORT_SYMBOL(blk_sync_queue);
1567
1568 /**
1569  * blk_run_queue - run a single device queue
1570  * @q:  The queue to run
1571  */
1572 void blk_run_queue(struct request_queue *q)
1573 {
1574         unsigned long flags;
1575
1576         spin_lock_irqsave(q->queue_lock, flags);
1577         blk_remove_plug(q);
1578         if (!elv_queue_empty(q))
1579                 q->request_fn(q);
1580         spin_unlock_irqrestore(q->queue_lock, flags);
1581 }
1582 EXPORT_SYMBOL(blk_run_queue);
1583
1584 /**
1585  * blk_cleanup_queue: - release a &request_queue_t when it is no longer needed
1586  * @q:    the request queue to be released
1587  *
1588  * Description:
1589  *     blk_cleanup_queue is the pair to blk_init_queue() or
1590  *     blk_queue_make_request().  It should be called when a request queue is
1591  *     being released; typically when a block device is being de-registered.
1592  *     Currently, its primary task it to free all the &struct request
1593  *     structures that were allocated to the queue and the queue itself.
1594  *
1595  * Caveat:
1596  *     Hopefully the low level driver will have finished any
1597  *     outstanding requests first...
1598  **/
1599 void blk_cleanup_queue(request_queue_t * q)
1600 {
1601         struct request_list *rl = &q->rq;
1602
1603         if (!atomic_dec_and_test(&q->refcnt))
1604                 return;
1605
1606         if (q->elevator)
1607                 elevator_exit(q->elevator);
1608
1609         blk_sync_queue(q);
1610
1611         if (rl->rq_pool)
1612                 mempool_destroy(rl->rq_pool);
1613
1614         if (q->queue_tags)
1615                 __blk_queue_free_tags(q);
1616
1617         blk_queue_ordered(q, QUEUE_ORDERED_NONE);
1618
1619         kmem_cache_free(requestq_cachep, q);
1620 }
1621
1622 EXPORT_SYMBOL(blk_cleanup_queue);
1623
1624 static int blk_init_free_list(request_queue_t *q)
1625 {
1626         struct request_list *rl = &q->rq;
1627
1628         rl->count[READ] = rl->count[WRITE] = 0;
1629         rl->starved[READ] = rl->starved[WRITE] = 0;
1630         init_waitqueue_head(&rl->wait[READ]);
1631         init_waitqueue_head(&rl->wait[WRITE]);
1632         init_waitqueue_head(&rl->drain);
1633
1634         rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
1635                                 mempool_free_slab, request_cachep, q->node);
1636
1637         if (!rl->rq_pool)
1638                 return -ENOMEM;
1639
1640         return 0;
1641 }
1642
1643 static int __make_request(request_queue_t *, struct bio *);
1644
1645 request_queue_t *blk_alloc_queue(int gfp_mask)
1646 {
1647         return blk_alloc_queue_node(gfp_mask, -1);
1648 }
1649 EXPORT_SYMBOL(blk_alloc_queue);
1650
1651 request_queue_t *blk_alloc_queue_node(int gfp_mask, int node_id)
1652 {
1653         request_queue_t *q;
1654
1655         q = kmem_cache_alloc_node(requestq_cachep, gfp_mask, node_id);
1656         if (!q)
1657                 return NULL;
1658
1659         memset(q, 0, sizeof(*q));
1660         init_timer(&q->unplug_timer);
1661         atomic_set(&q->refcnt, 1);
1662
1663         q->backing_dev_info.unplug_io_fn = blk_backing_dev_unplug;
1664         q->backing_dev_info.unplug_io_data = q;
1665
1666         return q;
1667 }
1668 EXPORT_SYMBOL(blk_alloc_queue_node);
1669
1670 /**
1671  * blk_init_queue  - prepare a request queue for use with a block device
1672  * @rfn:  The function to be called to process requests that have been
1673  *        placed on the queue.
1674  * @lock: Request queue spin lock
1675  *
1676  * Description:
1677  *    If a block device wishes to use the standard request handling procedures,
1678  *    which sorts requests and coalesces adjacent requests, then it must
1679  *    call blk_init_queue().  The function @rfn will be called when there
1680  *    are requests on the queue that need to be processed.  If the device
1681  *    supports plugging, then @rfn may not be called immediately when requests
1682  *    are available on the queue, but may be called at some time later instead.
1683  *    Plugged queues are generally unplugged when a buffer belonging to one
1684  *    of the requests on the queue is needed, or due to memory pressure.
1685  *
1686  *    @rfn is not required, or even expected, to remove all requests off the
1687  *    queue, but only as many as it can handle at a time.  If it does leave
1688  *    requests on the queue, it is responsible for arranging that the requests
1689  *    get dealt with eventually.
1690  *
1691  *    The queue spin lock must be held while manipulating the requests on the
1692  *    request queue.
1693  *
1694  *    Function returns a pointer to the initialized request queue, or NULL if
1695  *    it didn't succeed.
1696  *
1697  * Note:
1698  *    blk_init_queue() must be paired with a blk_cleanup_queue() call
1699  *    when the block device is deactivated (such as at module unload).
1700  **/
1701
1702 request_queue_t *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
1703 {
1704         return blk_init_queue_node(rfn, lock, -1);
1705 }
1706 EXPORT_SYMBOL(blk_init_queue);
1707
1708 request_queue_t *
1709 blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
1710 {
1711         request_queue_t *q = blk_alloc_queue_node(GFP_KERNEL, node_id);
1712
1713         if (!q)
1714                 return NULL;
1715
1716         q->node = node_id;
1717         if (blk_init_free_list(q))
1718                 goto out_init;
1719
1720         /*
1721          * if caller didn't supply a lock, they get per-queue locking with
1722          * our embedded lock
1723          */
1724         if (!lock) {
1725                 spin_lock_init(&q->__queue_lock);
1726                 lock = &q->__queue_lock;
1727         }
1728
1729         q->request_fn           = rfn;
1730         q->back_merge_fn        = ll_back_merge_fn;
1731         q->front_merge_fn       = ll_front_merge_fn;
1732         q->merge_requests_fn    = ll_merge_requests_fn;
1733         q->prep_rq_fn           = NULL;
1734         q->unplug_fn            = generic_unplug_device;
1735         q->queue_flags          = (1 << QUEUE_FLAG_CLUSTER);
1736         q->queue_lock           = lock;
1737
1738         blk_queue_segment_boundary(q, 0xffffffff);
1739
1740         blk_queue_make_request(q, __make_request);
1741         blk_queue_max_segment_size(q, MAX_SEGMENT_SIZE);
1742
1743         blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
1744         blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
1745
1746         /*
1747          * all done
1748          */
1749         if (!elevator_init(q, NULL)) {
1750                 blk_queue_congestion_threshold(q);
1751                 return q;
1752         }
1753
1754         blk_cleanup_queue(q);
1755 out_init:
1756         kmem_cache_free(requestq_cachep, q);
1757         return NULL;
1758 }
1759 EXPORT_SYMBOL(blk_init_queue_node);
1760
1761 int blk_get_queue(request_queue_t *q)
1762 {
1763         if (likely(!test_bit(QUEUE_FLAG_DEAD, &q->queue_flags))) {
1764                 atomic_inc(&q->refcnt);
1765                 return 0;
1766         }
1767
1768         return 1;
1769 }
1770
1771 EXPORT_SYMBOL(blk_get_queue);
1772
1773 static inline void blk_free_request(request_queue_t *q, struct request *rq)
1774 {
1775         elv_put_request(q, rq);
1776         mempool_free(rq, q->rq.rq_pool);
1777 }
1778
1779 static inline struct request *blk_alloc_request(request_queue_t *q, int rw,
1780                                                 int gfp_mask)
1781 {
1782         struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
1783
1784         if (!rq)
1785                 return NULL;
1786
1787         /*
1788          * first three bits are identical in rq->flags and bio->bi_rw,
1789          * see bio.h and blkdev.h
1790          */
1791         rq->flags = rw;
1792
1793         if (!elv_set_request(q, rq, gfp_mask))
1794                 return rq;
1795
1796         mempool_free(rq, q->rq.rq_pool);
1797         return NULL;
1798 }
1799
1800 /*
1801  * ioc_batching returns true if the ioc is a valid batching request and
1802  * should be given priority access to a request.
1803  */
1804 static inline int ioc_batching(request_queue_t *q, struct io_context *ioc)
1805 {
1806         if (!ioc)
1807                 return 0;
1808
1809         /*
1810          * Make sure the process is able to allocate at least 1 request
1811          * even if the batch times out, otherwise we could theoretically
1812          * lose wakeups.
1813          */
1814         return ioc->nr_batch_requests == q->nr_batching ||
1815                 (ioc->nr_batch_requests > 0
1816                 && time_before(jiffies, ioc->last_waited + BLK_BATCH_TIME));
1817 }
1818
1819 /*
1820  * ioc_set_batching sets ioc to be a new "batcher" if it is not one. This
1821  * will cause the process to be a "batcher" on all queues in the system. This
1822  * is the behaviour we want though - once it gets a wakeup it should be given
1823  * a nice run.
1824  */
1825 static void ioc_set_batching(request_queue_t *q, struct io_context *ioc)
1826 {
1827         if (!ioc || ioc_batching(q, ioc))
1828                 return;
1829
1830         ioc->nr_batch_requests = q->nr_batching;
1831         ioc->last_waited = jiffies;
1832 }
1833
1834 static void __freed_request(request_queue_t *q, int rw)
1835 {
1836         struct request_list *rl = &q->rq;
1837
1838         if (rl->count[rw] < queue_congestion_off_threshold(q))
1839                 clear_queue_congested(q, rw);
1840
1841         if (rl->count[rw] + 1 <= q->nr_requests) {
1842                 if (waitqueue_active(&rl->wait[rw]))
1843                         wake_up(&rl->wait[rw]);
1844
1845                 blk_clear_queue_full(q, rw);
1846         }
1847 }
1848
1849 /*
1850  * A request has just been released.  Account for it, update the full and
1851  * congestion status, wake up any waiters.   Called under q->queue_lock.
1852  */
1853 static void freed_request(request_queue_t *q, int rw)
1854 {
1855         struct request_list *rl = &q->rq;
1856
1857         rl->count[rw]--;
1858
1859         __freed_request(q, rw);
1860
1861         if (unlikely(rl->starved[rw ^ 1]))
1862                 __freed_request(q, rw ^ 1);
1863
1864         if (!rl->count[READ] && !rl->count[WRITE]) {
1865                 smp_mb();
1866                 if (unlikely(waitqueue_active(&rl->drain)))
1867                         wake_up(&rl->drain);
1868         }
1869 }
1870
1871 #define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
1872 /*
1873  * Get a free request, queue_lock must not be held
1874  */
1875 static struct request *get_request(request_queue_t *q, int rw, int gfp_mask)
1876 {
1877         struct request *rq = NULL;
1878         struct request_list *rl = &q->rq;
1879         struct io_context *ioc = get_io_context(gfp_mask);
1880
1881         if (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)))
1882                 goto out;
1883
1884         spin_lock_irq(q->queue_lock);
1885         if (rl->count[rw]+1 >= q->nr_requests) {
1886                 /*
1887                  * The queue will fill after this allocation, so set it as
1888                  * full, and mark this process as "batching". This process
1889                  * will be allowed to complete a batch of requests, others
1890                  * will be blocked.
1891                  */
1892                 if (!blk_queue_full(q, rw)) {
1893                         ioc_set_batching(q, ioc);
1894                         blk_set_queue_full(q, rw);
1895                 }
1896         }
1897
1898         switch (elv_may_queue(q, rw)) {
1899                 case ELV_MQUEUE_NO:
1900                         goto rq_starved;
1901                 case ELV_MQUEUE_MAY:
1902                         break;
1903                 case ELV_MQUEUE_MUST:
1904                         goto get_rq;
1905         }
1906
1907         if (blk_queue_full(q, rw) && !ioc_batching(q, ioc)) {
1908                 /*
1909                  * The queue is full and the allocating process is not a
1910                  * "batcher", and not exempted by the IO scheduler
1911                  */
1912                 spin_unlock_irq(q->queue_lock);
1913                 goto out;
1914         }
1915
1916 get_rq:
1917         rl->count[rw]++;
1918         rl->starved[rw] = 0;
1919         if (rl->count[rw] >= queue_congestion_on_threshold(q))
1920                 set_queue_congested(q, rw);
1921         spin_unlock_irq(q->queue_lock);
1922
1923         rq = blk_alloc_request(q, rw, gfp_mask);
1924         if (!rq) {
1925                 /*
1926                  * Allocation failed presumably due to memory. Undo anything
1927                  * we might have messed up.
1928                  *
1929                  * Allocating task should really be put onto the front of the
1930                  * wait queue, but this is pretty rare.
1931                  */
1932                 spin_lock_irq(q->queue_lock);
1933                 freed_request(q, rw);
1934
1935                 /*
1936                  * in the very unlikely event that allocation failed and no
1937                  * requests for this direction was pending, mark us starved
1938                  * so that freeing of a request in the other direction will
1939                  * notice us. another possible fix would be to split the
1940                  * rq mempool into READ and WRITE
1941                  */
1942 rq_starved:
1943                 if (unlikely(rl->count[rw] == 0))
1944                         rl->starved[rw] = 1;
1945
1946                 spin_unlock_irq(q->queue_lock);
1947                 goto out;
1948         }
1949
1950         if (ioc_batching(q, ioc))
1951                 ioc->nr_batch_requests--;
1952         
1953         rq_init(q, rq);
1954         rq->rl = rl;
1955 out:
1956         put_io_context(ioc);
1957         return rq;
1958 }
1959
1960 /*
1961  * No available requests for this queue, unplug the device and wait for some
1962  * requests to become available.
1963  */
1964 static struct request *get_request_wait(request_queue_t *q, int rw)
1965 {
1966         DEFINE_WAIT(wait);
1967         struct request *rq;
1968
1969         do {
1970                 struct request_list *rl = &q->rq;
1971
1972                 prepare_to_wait_exclusive(&rl->wait[rw], &wait,
1973                                 TASK_UNINTERRUPTIBLE);
1974
1975                 rq = get_request(q, rw, GFP_NOIO);
1976
1977                 if (!rq) {
1978                         struct io_context *ioc;
1979
1980                         generic_unplug_device(q);
1981                         io_schedule();
1982
1983                         /*
1984                          * After sleeping, we become a "batching" process and
1985                          * will be able to allocate at least one request, and
1986                          * up to a big batch of them for a small period time.
1987                          * See ioc_batching, ioc_set_batching
1988                          */
1989                         ioc = get_io_context(GFP_NOIO);
1990                         ioc_set_batching(q, ioc);
1991                         put_io_context(ioc);
1992                 }
1993                 finish_wait(&rl->wait[rw], &wait);
1994         } while (!rq);
1995
1996         return rq;
1997 }
1998
1999 struct request *blk_get_request(request_queue_t *q, int rw, int gfp_mask)
2000 {
2001         struct request *rq;
2002
2003         BUG_ON(rw != READ && rw != WRITE);
2004
2005         if (gfp_mask & __GFP_WAIT)
2006                 rq = get_request_wait(q, rw);
2007         else
2008                 rq = get_request(q, rw, gfp_mask);
2009
2010         return rq;
2011 }
2012
2013 EXPORT_SYMBOL(blk_get_request);
2014
2015 /**
2016  * blk_requeue_request - put a request back on queue
2017  * @q:          request queue where request should be inserted
2018  * @rq:         request to be inserted
2019  *
2020  * Description:
2021  *    Drivers often keep queueing requests until the hardware cannot accept
2022  *    more, when that condition happens we need to put the request back
2023  *    on the queue. Must be called with queue lock held.
2024  */
2025 void blk_requeue_request(request_queue_t *q, struct request *rq)
2026 {
2027         if (blk_rq_tagged(rq))
2028                 blk_queue_end_tag(q, rq);
2029
2030         elv_requeue_request(q, rq);
2031 }
2032
2033 EXPORT_SYMBOL(blk_requeue_request);
2034
2035 /**
2036  * blk_insert_request - insert a special request in to a request queue
2037  * @q:          request queue where request should be inserted
2038  * @rq:         request to be inserted
2039  * @at_head:    insert request at head or tail of queue
2040  * @data:       private data
2041  *
2042  * Description:
2043  *    Many block devices need to execute commands asynchronously, so they don't
2044  *    block the whole kernel from preemption during request execution.  This is
2045  *    accomplished normally by inserting aritficial requests tagged as
2046  *    REQ_SPECIAL in to the corresponding request queue, and letting them be
2047  *    scheduled for actual execution by the request queue.
2048  *
2049  *    We have the option of inserting the head or the tail of the queue.
2050  *    Typically we use the tail for new ioctls and so forth.  We use the head
2051  *    of the queue for things like a QUEUE_FULL message from a device, or a
2052  *    host that is unable to accept a particular command.
2053  */
2054 void blk_insert_request(request_queue_t *q, struct request *rq,
2055                         int at_head, void *data)
2056 {
2057         int where = at_head ? ELEVATOR_INSERT_FRONT : ELEVATOR_INSERT_BACK;
2058         unsigned long flags;
2059
2060         /*
2061          * tell I/O scheduler that this isn't a regular read/write (ie it
2062          * must not attempt merges on this) and that it acts as a soft
2063          * barrier
2064          */
2065         rq->flags |= REQ_SPECIAL | REQ_SOFTBARRIER;
2066
2067         rq->special = data;
2068
2069         spin_lock_irqsave(q->queue_lock, flags);
2070
2071         /*
2072          * If command is tagged, release the tag
2073          */
2074         if (blk_rq_tagged(rq))
2075                 blk_queue_end_tag(q, rq);
2076
2077         drive_stat_acct(rq, rq->nr_sectors, 1);
2078         __elv_add_request(q, rq, where, 0);
2079
2080         if (blk_queue_plugged(q))
2081                 __generic_unplug_device(q);
2082         else
2083                 q->request_fn(q);
2084         spin_unlock_irqrestore(q->queue_lock, flags);
2085 }
2086
2087 EXPORT_SYMBOL(blk_insert_request);
2088
2089 /**
2090  * blk_rq_map_user - map user data to a request, for REQ_BLOCK_PC usage
2091  * @q:          request queue where request should be inserted
2092  * @rw:         READ or WRITE data
2093  * @ubuf:       the user buffer
2094  * @len:        length of user data
2095  *
2096  * Description:
2097  *    Data will be mapped directly for zero copy io, if possible. Otherwise
2098  *    a kernel bounce buffer is used.
2099  *
2100  *    A matching blk_rq_unmap_user() must be issued at the end of io, while
2101  *    still in process context.
2102  *
2103  *    Note: The mapped bio may need to be bounced through blk_queue_bounce()
2104  *    before being submitted to the device, as pages mapped may be out of
2105  *    reach. It's the callers responsibility to make sure this happens. The
2106  *    original bio must be passed back in to blk_rq_unmap_user() for proper
2107  *    unmapping.
2108  */
2109 struct request *blk_rq_map_user(request_queue_t *q, int rw, void __user *ubuf,
2110                                 unsigned int len)
2111 {
2112         unsigned long uaddr;
2113         struct request *rq;
2114         struct bio *bio;
2115
2116         if (len > (q->max_sectors << 9))
2117                 return ERR_PTR(-EINVAL);
2118         if ((!len && ubuf) || (len && !ubuf))
2119                 return ERR_PTR(-EINVAL);
2120
2121         rq = blk_get_request(q, rw, __GFP_WAIT);
2122         if (!rq)
2123                 return ERR_PTR(-ENOMEM);
2124
2125         /*
2126          * if alignment requirement is satisfied, map in user pages for
2127          * direct dma. else, set up kernel bounce buffers
2128          */
2129         uaddr = (unsigned long) ubuf;
2130         if (!(uaddr & queue_dma_alignment(q)) && !(len & queue_dma_alignment(q)))
2131                 bio = bio_map_user(q, NULL, uaddr, len, rw == READ);
2132         else
2133                 bio = bio_copy_user(q, uaddr, len, rw == READ);
2134
2135         if (!IS_ERR(bio)) {
2136                 rq->bio = rq->biotail = bio;
2137                 blk_rq_bio_prep(q, rq, bio);
2138
2139                 rq->buffer = rq->data = NULL;
2140                 rq->data_len = len;
2141                 return rq;
2142         }
2143
2144         /*
2145          * bio is the err-ptr
2146          */
2147         blk_put_request(rq);
2148         return (struct request *) bio;
2149 }
2150
2151 EXPORT_SYMBOL(blk_rq_map_user);
2152
2153 /**
2154  * blk_rq_unmap_user - unmap a request with user data
2155  * @rq:         request to be unmapped
2156  * @bio:        bio for the request
2157  * @ulen:       length of user buffer
2158  *
2159  * Description:
2160  *    Unmap a request previously mapped by blk_rq_map_user().
2161  */
2162 int blk_rq_unmap_user(struct request *rq, struct bio *bio, unsigned int ulen)
2163 {
2164         int ret = 0;
2165
2166         if (bio) {
2167                 if (bio_flagged(bio, BIO_USER_MAPPED))
2168                         bio_unmap_user(bio);
2169                 else
2170                         ret = bio_uncopy_user(bio);
2171         }
2172
2173         blk_put_request(rq);
2174         return ret;
2175 }
2176
2177 EXPORT_SYMBOL(blk_rq_unmap_user);
2178
2179 /**
2180  * blk_execute_rq - insert a request into queue for execution
2181  * @q:          queue to insert the request in
2182  * @bd_disk:    matching gendisk
2183  * @rq:         request to insert
2184  *
2185  * Description:
2186  *    Insert a fully prepared request at the back of the io scheduler queue
2187  *    for execution.
2188  */
2189 int blk_execute_rq(request_queue_t *q, struct gendisk *bd_disk,
2190                    struct request *rq)
2191 {
2192         DECLARE_COMPLETION(wait);
2193         char sense[SCSI_SENSE_BUFFERSIZE];
2194         int err = 0;
2195
2196         rq->rq_disk = bd_disk;
2197
2198         /*
2199          * we need an extra reference to the request, so we can look at
2200          * it after io completion
2201          */
2202         rq->ref_count++;
2203
2204         if (!rq->sense) {
2205                 memset(sense, 0, sizeof(sense));
2206                 rq->sense = sense;
2207                 rq->sense_len = 0;
2208         }
2209
2210         rq->flags |= REQ_NOMERGE;
2211         rq->waiting = &wait;
2212         rq->end_io = blk_end_sync_rq;
2213         elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
2214         generic_unplug_device(q);
2215         wait_for_completion(&wait);
2216         rq->waiting = NULL;
2217
2218         if (rq->errors)
2219                 err = -EIO;
2220
2221         return err;
2222 }
2223
2224 EXPORT_SYMBOL(blk_execute_rq);
2225
2226 /**
2227  * blkdev_issue_flush - queue a flush
2228  * @bdev:       blockdev to issue flush for
2229  * @error_sector:       error sector
2230  *
2231  * Description:
2232  *    Issue a flush for the block device in question. Caller can supply
2233  *    room for storing the error offset in case of a flush error, if they
2234  *    wish to.  Caller must run wait_for_completion() on its own.
2235  */
2236 int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
2237 {
2238         request_queue_t *q;
2239
2240         if (bdev->bd_disk == NULL)
2241                 return -ENXIO;
2242
2243         q = bdev_get_queue(bdev);
2244         if (!q)
2245                 return -ENXIO;
2246         if (!q->issue_flush_fn)
2247                 return -EOPNOTSUPP;
2248
2249         return q->issue_flush_fn(q, bdev->bd_disk, error_sector);
2250 }
2251
2252 EXPORT_SYMBOL(blkdev_issue_flush);
2253
2254 static void drive_stat_acct(struct request *rq, int nr_sectors, int new_io)
2255 {
2256         int rw = rq_data_dir(rq);
2257
2258         if (!blk_fs_request(rq) || !rq->rq_disk)
2259                 return;
2260
2261         if (rw == READ) {
2262                 __disk_stat_add(rq->rq_disk, read_sectors, nr_sectors);
2263                 if (!new_io)
2264                         __disk_stat_inc(rq->rq_disk, read_merges);
2265         } else if (rw == WRITE) {
2266                 __disk_stat_add(rq->rq_disk, write_sectors, nr_sectors);
2267                 if (!new_io)
2268                         __disk_stat_inc(rq->rq_disk, write_merges);
2269         }
2270         if (new_io) {
2271                 disk_round_stats(rq->rq_disk);
2272                 rq->rq_disk->in_flight++;
2273         }
2274 }
2275
2276 /*
2277  * add-request adds a request to the linked list.
2278  * queue lock is held and interrupts disabled, as we muck with the
2279  * request queue list.
2280  */
2281 static inline void add_request(request_queue_t * q, struct request * req)
2282 {
2283         drive_stat_acct(req, req->nr_sectors, 1);
2284
2285         if (q->activity_fn)
2286                 q->activity_fn(q->activity_data, rq_data_dir(req));
2287
2288         /*
2289          * elevator indicated where it wants this request to be
2290          * inserted at elevator_merge time
2291          */
2292         __elv_add_request(q, req, ELEVATOR_INSERT_SORT, 0);
2293 }
2294  
2295 /*
2296  * disk_round_stats()   - Round off the performance stats on a struct
2297  * disk_stats.
2298  *
2299  * The average IO queue length and utilisation statistics are maintained
2300  * by observing the current state of the queue length and the amount of
2301  * time it has been in this state for.
2302  *
2303  * Normally, that accounting is done on IO completion, but that can result
2304  * in more than a second's worth of IO being accounted for within any one
2305  * second, leading to >100% utilisation.  To deal with that, we call this
2306  * function to do a round-off before returning the results when reading
2307  * /proc/diskstats.  This accounts immediately for all queue usage up to
2308  * the current jiffies and restarts the counters again.
2309  */
2310 void disk_round_stats(struct gendisk *disk)
2311 {
2312         unsigned long now = jiffies;
2313
2314         __disk_stat_add(disk, time_in_queue,
2315                         disk->in_flight * (now - disk->stamp));
2316         disk->stamp = now;
2317
2318         if (disk->in_flight)
2319                 __disk_stat_add(disk, io_ticks, (now - disk->stamp_idle));
2320         disk->stamp_idle = now;
2321 }
2322
2323 /*
2324  * queue lock must be held
2325  */
2326 static void __blk_put_request(request_queue_t *q, struct request *req)
2327 {
2328         struct request_list *rl = req->rl;
2329
2330         if (unlikely(!q))
2331                 return;
2332         if (unlikely(--req->ref_count))
2333                 return;
2334
2335         req->rq_status = RQ_INACTIVE;
2336         req->q = NULL;
2337         req->rl = NULL;
2338
2339         /*
2340          * Request may not have originated from ll_rw_blk. if not,
2341          * it didn't come out of our reserved rq pools
2342          */
2343         if (rl) {
2344                 int rw = rq_data_dir(req);
2345
2346                 elv_completed_request(q, req);
2347
2348                 BUG_ON(!list_empty(&req->queuelist));
2349
2350                 blk_free_request(q, req);
2351                 freed_request(q, rw);
2352         }
2353 }
2354
2355 void blk_put_request(struct request *req)
2356 {
2357         /*
2358          * if req->rl isn't set, this request didnt originate from the
2359          * block layer, so it's safe to just disregard it
2360          */
2361         if (req->rl) {
2362                 unsigned long flags;
2363                 request_queue_t *q = req->q;
2364
2365                 spin_lock_irqsave(q->queue_lock, flags);
2366                 __blk_put_request(q, req);
2367                 spin_unlock_irqrestore(q->queue_lock, flags);
2368         }
2369 }
2370
2371 EXPORT_SYMBOL(blk_put_request);
2372
2373 /**
2374  * blk_end_sync_rq - executes a completion event on a request
2375  * @rq: request to complete
2376  */
2377 void blk_end_sync_rq(struct request *rq)
2378 {
2379         struct completion *waiting = rq->waiting;
2380
2381         rq->waiting = NULL;
2382         __blk_put_request(rq->q, rq);
2383
2384         /*
2385          * complete last, if this is a stack request the process (and thus
2386          * the rq pointer) could be invalid right after this complete()
2387          */
2388         complete(waiting);
2389 }
2390 EXPORT_SYMBOL(blk_end_sync_rq);
2391
2392 /**
2393  * blk_congestion_wait - wait for a queue to become uncongested
2394  * @rw: READ or WRITE
2395  * @timeout: timeout in jiffies
2396  *
2397  * Waits for up to @timeout jiffies for a queue (any queue) to exit congestion.
2398  * If no queues are congested then just wait for the next request to be
2399  * returned.
2400  */
2401 long blk_congestion_wait(int rw, long timeout)
2402 {
2403         long ret;
2404         DEFINE_WAIT(wait);
2405         wait_queue_head_t *wqh = &congestion_wqh[rw];
2406
2407         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
2408         ret = io_schedule_timeout(timeout);
2409         finish_wait(wqh, &wait);
2410         return ret;
2411 }
2412
2413 EXPORT_SYMBOL(blk_congestion_wait);
2414
2415 /*
2416  * Has to be called with the request spinlock acquired
2417  */
2418 static int attempt_merge(request_queue_t *q, struct request *req,
2419                           struct request *next)
2420 {
2421         if (!rq_mergeable(req) || !rq_mergeable(next))
2422                 return 0;
2423
2424         /*
2425          * not contigious
2426          */
2427         if (req->sector + req->nr_sectors != next->sector)
2428                 return 0;
2429
2430         if (rq_data_dir(req) != rq_data_dir(next)
2431             || req->rq_disk != next->rq_disk
2432             || next->waiting || next->special)
2433                 return 0;
2434
2435         /*
2436          * If we are allowed to merge, then append bio list
2437          * from next to rq and release next. merge_requests_fn
2438          * will have updated segment counts, update sector
2439          * counts here.
2440          */
2441         if (!q->merge_requests_fn(q, req, next))
2442                 return 0;
2443
2444         /*
2445          * At this point we have either done a back merge
2446          * or front merge. We need the smaller start_time of
2447          * the merged requests to be the current request
2448          * for accounting purposes.
2449          */
2450         if (time_after(req->start_time, next->start_time))
2451                 req->start_time = next->start_time;
2452
2453         req->biotail->bi_next = next->bio;
2454         req->biotail = next->biotail;
2455
2456         req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;
2457
2458         elv_merge_requests(q, req, next);
2459
2460         if (req->rq_disk) {
2461                 disk_round_stats(req->rq_disk);
2462                 req->rq_disk->in_flight--;
2463         }
2464
2465         __blk_put_request(q, next);
2466         return 1;
2467 }
2468
2469 static inline int attempt_back_merge(request_queue_t *q, struct request *rq)
2470 {
2471         struct request *next = elv_latter_request(q, rq);
2472
2473         if (next)
2474                 return attempt_merge(q, rq, next);
2475
2476         return 0;
2477 }
2478
2479 static inline int attempt_front_merge(request_queue_t *q, struct request *rq)
2480 {
2481         struct request *prev = elv_former_request(q, rq);
2482
2483         if (prev)
2484                 return attempt_merge(q, prev, rq);
2485
2486         return 0;
2487 }
2488
2489 /**
2490  * blk_attempt_remerge  - attempt to remerge active head with next request
2491  * @q:    The &request_queue_t belonging to the device
2492  * @rq:   The head request (usually)
2493  *
2494  * Description:
2495  *    For head-active devices, the queue can easily be unplugged so quickly
2496  *    that proper merging is not done on the front request. This may hurt
2497  *    performance greatly for some devices. The block layer cannot safely
2498  *    do merging on that first request for these queues, but the driver can
2499  *    call this function and make it happen any way. Only the driver knows
2500  *    when it is safe to do so.
2501  **/
2502 void blk_attempt_remerge(request_queue_t *q, struct request *rq)
2503 {
2504         unsigned long flags;
2505
2506         spin_lock_irqsave(q->queue_lock, flags);
2507         attempt_back_merge(q, rq);
2508         spin_unlock_irqrestore(q->queue_lock, flags);
2509 }
2510
2511 EXPORT_SYMBOL(blk_attempt_remerge);
2512
2513 static int __make_request(request_queue_t *q, struct bio *bio)
2514 {
2515         struct request *req, *freereq = NULL;
2516         int el_ret, rw, nr_sectors, cur_nr_sectors, barrier, err, sync;
2517         sector_t sector;
2518
2519         sector = bio->bi_sector;
2520         nr_sectors = bio_sectors(bio);
2521         cur_nr_sectors = bio_cur_sectors(bio);
2522
2523         rw = bio_data_dir(bio);
2524         sync = bio_sync(bio);
2525
2526         /*
2527          * low level driver can indicate that it wants pages above a
2528          * certain limit bounced to low memory (ie for highmem, or even
2529          * ISA dma in theory)
2530          */
2531         blk_queue_bounce(q, &bio);
2532
2533         spin_lock_prefetch(q->queue_lock);
2534
2535         barrier = bio_barrier(bio);
2536         if (unlikely(barrier) && (q->ordered == QUEUE_ORDERED_NONE)) {
2537                 err = -EOPNOTSUPP;
2538                 goto end_io;
2539         }
2540
2541 again:
2542         spin_lock_irq(q->queue_lock);
2543
2544         if (elv_queue_empty(q)) {
2545                 blk_plug_device(q);
2546                 goto get_rq;
2547         }
2548         if (barrier)
2549                 goto get_rq;
2550
2551         el_ret = elv_merge(q, &req, bio);
2552         switch (el_ret) {
2553                 case ELEVATOR_BACK_MERGE:
2554                         BUG_ON(!rq_mergeable(req));
2555
2556                         if (!q->back_merge_fn(q, req, bio))
2557                                 break;
2558
2559                         req->biotail->bi_next = bio;
2560                         req->biotail = bio;
2561                         req->nr_sectors = req->hard_nr_sectors += nr_sectors;
2562                         drive_stat_acct(req, nr_sectors, 0);
2563                         if (!attempt_back_merge(q, req))
2564                                 elv_merged_request(q, req);
2565                         goto out;
2566
2567                 case ELEVATOR_FRONT_MERGE:
2568                         BUG_ON(!rq_mergeable(req));
2569
2570                         if (!q->front_merge_fn(q, req, bio))
2571                                 break;
2572
2573                         bio->bi_next = req->bio;
2574                         req->bio = bio;
2575
2576                         /*
2577                          * may not be valid. if the low level driver said
2578                          * it didn't need a bounce buffer then it better
2579                          * not touch req->buffer either...
2580                          */
2581                         req->buffer = bio_data(bio);
2582                         req->current_nr_sectors = cur_nr_sectors;
2583                         req->hard_cur_sectors = cur_nr_sectors;
2584                         req->sector = req->hard_sector = sector;
2585                         req->nr_sectors = req->hard_nr_sectors += nr_sectors;
2586                         drive_stat_acct(req, nr_sectors, 0);
2587                         if (!attempt_front_merge(q, req))
2588                                 elv_merged_request(q, req);
2589                         goto out;
2590
2591                 /*
2592                  * elevator says don't/can't merge. get new request
2593                  */
2594                 case ELEVATOR_NO_MERGE:
2595                         break;
2596
2597                 default:
2598                         printk("elevator returned crap (%d)\n", el_ret);
2599                         BUG();
2600         }
2601
2602         /*
2603          * Grab a free request from the freelist - if that is empty, check
2604          * if we are doing read ahead and abort instead of blocking for
2605          * a free slot.
2606          */
2607 get_rq:
2608         if (freereq) {
2609                 req = freereq;
2610                 freereq = NULL;
2611         } else {
2612                 spin_unlock_irq(q->queue_lock);
2613                 if ((freereq = get_request(q, rw, GFP_ATOMIC)) == NULL) {
2614                         /*
2615                          * READA bit set
2616                          */
2617                         err = -EWOULDBLOCK;
2618                         if (bio_rw_ahead(bio))
2619                                 goto end_io;
2620         
2621                         freereq = get_request_wait(q, rw);
2622                 }
2623                 goto again;
2624         }
2625
2626         req->flags |= REQ_CMD;
2627
2628         /*
2629          * inherit FAILFAST from bio (for read-ahead, and explicit FAILFAST)
2630          */
2631         if (bio_rw_ahead(bio) || bio_failfast(bio))
2632                 req->flags |= REQ_FAILFAST;
2633
2634         /*
2635          * REQ_BARRIER implies no merging, but lets make it explicit
2636          */
2637         if (unlikely(barrier))
2638                 req->flags |= (REQ_HARDBARRIER | REQ_NOMERGE);
2639
2640         req->errors = 0;
2641         req->hard_sector = req->sector = sector;
2642         req->hard_nr_sectors = req->nr_sectors = nr_sectors;
2643         req->current_nr_sectors = req->hard_cur_sectors = cur_nr_sectors;
2644         req->nr_phys_segments = bio_phys_segments(q, bio);
2645         req->nr_hw_segments = bio_hw_segments(q, bio);
2646         req->buffer = bio_data(bio);    /* see ->buffer comment above */
2647         req->waiting = NULL;
2648         req->bio = req->biotail = bio;
2649         req->rq_disk = bio->bi_bdev->bd_disk;
2650         req->start_time = jiffies;
2651
2652         add_request(q, req);
2653 out:
2654         if (freereq)
2655                 __blk_put_request(q, freereq);
2656         if (sync)
2657                 __generic_unplug_device(q);
2658
2659         spin_unlock_irq(q->queue_lock);
2660         return 0;
2661
2662 end_io:
2663         bio_endio(bio, nr_sectors << 9, err);
2664         return 0;
2665 }
2666
2667 /*
2668  * If bio->bi_dev is a partition, remap the location
2669  */
2670 static inline void blk_partition_remap(struct bio *bio)
2671 {
2672         struct block_device *bdev = bio->bi_bdev;
2673
2674         if (bdev != bdev->bd_contains) {
2675                 struct hd_struct *p = bdev->bd_part;
2676
2677                 switch (bio->bi_rw) {
2678                 case READ:
2679                         p->read_sectors += bio_sectors(bio);
2680                         p->reads++;
2681                         break;
2682                 case WRITE:
2683                         p->write_sectors += bio_sectors(bio);
2684                         p->writes++;
2685                         break;
2686                 }
2687                 bio->bi_sector += p->start_sect;
2688                 bio->bi_bdev = bdev->bd_contains;
2689         }
2690 }
2691
2692 void blk_finish_queue_drain(request_queue_t *q)
2693 {
2694         struct request_list *rl = &q->rq;
2695         struct request *rq;
2696
2697         spin_lock_irq(q->queue_lock);
2698         clear_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
2699
2700         while (!list_empty(&q->drain_list)) {
2701                 rq = list_entry_rq(q->drain_list.next);
2702
2703                 list_del_init(&rq->queuelist);
2704                 __elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
2705         }
2706
2707         spin_unlock_irq(q->queue_lock);
2708
2709         wake_up(&rl->wait[0]);
2710         wake_up(&rl->wait[1]);
2711         wake_up(&rl->drain);
2712 }
2713
2714 static int wait_drain(request_queue_t *q, struct request_list *rl, int dispatch)
2715 {
2716         int wait = rl->count[READ] + rl->count[WRITE];
2717
2718         if (dispatch)
2719                 wait += !list_empty(&q->queue_head);
2720
2721         return wait;
2722 }
2723
2724 /*
2725  * We rely on the fact that only requests allocated through blk_alloc_request()
2726  * have io scheduler private data structures associated with them. Any other
2727  * type of request (allocated on stack or through kmalloc()) should not go
2728  * to the io scheduler core, but be attached to the queue head instead.
2729  */
2730 void blk_wait_queue_drained(request_queue_t *q, int wait_dispatch)
2731 {
2732         struct request_list *rl = &q->rq;
2733         DEFINE_WAIT(wait);
2734
2735         spin_lock_irq(q->queue_lock);
2736         set_bit(QUEUE_FLAG_DRAIN, &q->queue_flags);
2737
2738         while (wait_drain(q, rl, wait_dispatch)) {
2739                 prepare_to_wait(&rl->drain, &wait, TASK_UNINTERRUPTIBLE);
2740
2741                 if (wait_drain(q, rl, wait_dispatch)) {
2742                         __generic_unplug_device(q);
2743                         spin_unlock_irq(q->queue_lock);
2744                         io_schedule();
2745                         spin_lock_irq(q->queue_lock);
2746                 }
2747
2748                 finish_wait(&rl->drain, &wait);
2749         }
2750
2751         spin_unlock_irq(q->queue_lock);
2752 }
2753
2754 /*
2755  * block waiting for the io scheduler being started again.
2756  */
2757 static inline void block_wait_queue_running(request_queue_t *q)
2758 {
2759         DEFINE_WAIT(wait);
2760
2761         while (unlikely(test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))) {
2762                 struct request_list *rl = &q->rq;
2763
2764                 prepare_to_wait_exclusive(&rl->drain, &wait,
2765                                 TASK_UNINTERRUPTIBLE);
2766
2767                 /*
2768                  * re-check the condition. avoids using prepare_to_wait()
2769                  * in the fast path (queue is running)
2770                  */
2771                 if (test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags))
2772                         io_schedule();
2773
2774                 finish_wait(&rl->drain, &wait);
2775         }
2776 }
2777
2778 static void handle_bad_sector(struct bio *bio)
2779 {
2780         char b[BDEVNAME_SIZE];
2781
2782         printk(KERN_INFO "attempt to access beyond end of device\n");
2783         printk(KERN_INFO "%s: rw=%ld, want=%Lu, limit=%Lu\n",
2784                         bdevname(bio->bi_bdev, b),
2785                         bio->bi_rw,
2786                         (unsigned long long)bio->bi_sector + bio_sectors(bio),
2787                         (long long)(bio->bi_bdev->bd_inode->i_size >> 9));
2788
2789         set_bit(BIO_EOF, &bio->bi_flags);
2790 }
2791
2792 /**
2793  * generic_make_request: hand a buffer to its device driver for I/O
2794  * @bio:  The bio describing the location in memory and on the device.
2795  *
2796  * generic_make_request() is used to make I/O requests of block
2797  * devices. It is passed a &struct bio, which describes the I/O that needs
2798  * to be done.
2799  *
2800  * generic_make_request() does not return any status.  The
2801  * success/failure status of the request, along with notification of
2802  * completion, is delivered asynchronously through the bio->bi_end_io
2803  * function described (one day) else where.
2804  *
2805  * The caller of generic_make_request must make sure that bi_io_vec
2806  * are set to describe the memory buffer, and that bi_dev and bi_sector are
2807  * set to describe the device address, and the
2808  * bi_end_io and optionally bi_private are set to describe how
2809  * completion notification should be signaled.
2810  *
2811  * generic_make_request and the drivers it calls may use bi_next if this
2812  * bio happens to be merged with someone else, and may change bi_dev and
2813  * bi_sector for remaps as it sees fit.  So the values of these fields
2814  * should NOT be depended on after the call to generic_make_request.
2815  */
2816 void generic_make_request(struct bio *bio)
2817 {
2818         request_queue_t *q;
2819         sector_t maxsector;
2820         int ret, nr_sectors = bio_sectors(bio);
2821
2822         might_sleep();
2823         /* Test device or partition size, when known. */
2824         maxsector = bio->bi_bdev->bd_inode->i_size >> 9;
2825         if (maxsector) {
2826                 sector_t sector = bio->bi_sector;
2827
2828                 if (maxsector < nr_sectors || maxsector - nr_sectors < sector) {
2829                         /*
2830                          * This may well happen - the kernel calls bread()
2831                          * without checking the size of the device, e.g., when
2832                          * mounting a device.
2833                          */
2834                         handle_bad_sector(bio);
2835                         goto end_io;
2836                 }
2837         }
2838
2839         /*
2840          * Resolve the mapping until finished. (drivers are
2841          * still free to implement/resolve their own stacking
2842          * by explicitly returning 0)
2843          *
2844          * NOTE: we don't repeat the blk_size check for each new device.
2845          * Stacking drivers are expected to know what they are doing.
2846          */
2847         do {
2848                 char b[BDEVNAME_SIZE];
2849
2850                 q = bdev_get_queue(bio->bi_bdev);
2851                 if (!q) {
2852                         printk(KERN_ERR
2853                                "generic_make_request: Trying to access "
2854                                 "nonexistent block-device %s (%Lu)\n",
2855                                 bdevname(bio->bi_bdev, b),
2856                                 (long long) bio->bi_sector);
2857 end_io:
2858                         bio_endio(bio, bio->bi_size, -EIO);
2859                         break;
2860                 }
2861
2862                 if (unlikely(bio_sectors(bio) > q->max_hw_sectors)) {
2863                         printk("bio too big device %s (%u > %u)\n", 
2864                                 bdevname(bio->bi_bdev, b),
2865                                 bio_sectors(bio),
2866                                 q->max_hw_sectors);
2867                         goto end_io;
2868                 }
2869
2870                 if (unlikely(test_bit(QUEUE_FLAG_DEAD, &q->queue_flags)))
2871                         goto end_io;
2872
2873                 block_wait_queue_running(q);
2874
2875                 /*
2876                  * If this device has partitions, remap block n
2877                  * of partition p to block n+start(p) of the disk.
2878                  */
2879                 blk_partition_remap(bio);
2880
2881                 ret = q->make_request_fn(q, bio);
2882         } while (ret);
2883 }
2884
2885 EXPORT_SYMBOL(generic_make_request);
2886
2887 /**
2888  * submit_bio: submit a bio to the block device layer for I/O
2889  * @rw: whether to %READ or %WRITE, or maybe to %READA (read ahead)
2890  * @bio: The &struct bio which describes the I/O
2891  *
2892  * submit_bio() is very similar in purpose to generic_make_request(), and
2893  * uses that function to do most of the work. Both are fairly rough
2894  * interfaces, @bio must be presetup and ready for I/O.
2895  *
2896  */
2897 void submit_bio(int rw, struct bio *bio)
2898 {
2899         int count = bio_sectors(bio);
2900
2901         BIO_BUG_ON(!bio->bi_size);
2902         BIO_BUG_ON(!bio->bi_io_vec);
2903         bio->bi_rw = rw;
2904         if (rw & WRITE)
2905                 mod_page_state(pgpgout, count);
2906         else
2907                 mod_page_state(pgpgin, count);
2908
2909         if (unlikely(block_dump)) {
2910                 char b[BDEVNAME_SIZE];
2911                 printk(KERN_DEBUG "%s(%d): %s block %Lu on %s\n",
2912                         current->comm, current->pid,
2913                         (rw & WRITE) ? "WRITE" : "READ",
2914                         (unsigned long long)bio->bi_sector,
2915                         bdevname(bio->bi_bdev,b));
2916         }
2917
2918         generic_make_request(bio);
2919 }
2920
2921 EXPORT_SYMBOL(submit_bio);
2922
2923 static void blk_recalc_rq_segments(struct request *rq)
2924 {
2925         struct bio *bio, *prevbio = NULL;
2926         int nr_phys_segs, nr_hw_segs;
2927         unsigned int phys_size, hw_size;
2928         request_queue_t *q = rq->q;
2929
2930         if (!rq->bio)
2931                 return;
2932
2933         phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
2934         rq_for_each_bio(bio, rq) {
2935                 /* Force bio hw/phys segs to be recalculated. */
2936                 bio->bi_flags &= ~(1 << BIO_SEG_VALID);
2937
2938                 nr_phys_segs += bio_phys_segments(q, bio);
2939                 nr_hw_segs += bio_hw_segments(q, bio);
2940                 if (prevbio) {
2941                         int pseg = phys_size + prevbio->bi_size + bio->bi_size;
2942                         int hseg = hw_size + prevbio->bi_size + bio->bi_size;
2943
2944                         if (blk_phys_contig_segment(q, prevbio, bio) &&
2945                             pseg <= q->max_segment_size) {
2946                                 nr_phys_segs--;
2947                                 phys_size += prevbio->bi_size + bio->bi_size;
2948                         } else
2949                                 phys_size = 0;
2950
2951                         if (blk_hw_contig_segment(q, prevbio, bio) &&
2952                             hseg <= q->max_segment_size) {
2953                                 nr_hw_segs--;
2954                                 hw_size += prevbio->bi_size + bio->bi_size;
2955                         } else
2956                                 hw_size = 0;
2957                 }
2958                 prevbio = bio;
2959         }
2960
2961         rq->nr_phys_segments = nr_phys_segs;
2962         rq->nr_hw_segments = nr_hw_segs;
2963 }
2964
2965 static void blk_recalc_rq_sectors(struct request *rq, int nsect)
2966 {
2967         if (blk_fs_request(rq)) {
2968                 rq->hard_sector += nsect;
2969                 rq->hard_nr_sectors -= nsect;
2970
2971                 /*
2972                  * Move the I/O submission pointers ahead if required.
2973                  */
2974                 if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
2975                     (rq->sector <= rq->hard_sector)) {
2976                         rq->sector = rq->hard_sector;
2977                         rq->nr_sectors = rq->hard_nr_sectors;
2978                         rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
2979                         rq->current_nr_sectors = rq->hard_cur_sectors;
2980                         rq->buffer = bio_data(rq->bio);
2981                 }
2982
2983                 /*
2984                  * if total number of sectors is less than the first segment
2985                  * size, something has gone terribly wrong
2986                  */
2987                 if (rq->nr_sectors < rq->current_nr_sectors) {
2988                         printk("blk: request botched\n");
2989                         rq->nr_sectors = rq->current_nr_sectors;
2990                 }
2991         }
2992 }
2993
2994 static int __end_that_request_first(struct request *req, int uptodate,
2995                                     int nr_bytes)
2996 {
2997         int total_bytes, bio_nbytes, error, next_idx = 0;
2998         struct bio *bio;
2999
3000         /*
3001          * extend uptodate bool to allow < 0 value to be direct io error
3002          */
3003         error = 0;
3004         if (end_io_error(uptodate))
3005                 error = !uptodate ? -EIO : uptodate;
3006
3007         /*
3008          * for a REQ_BLOCK_PC request, we want to carry any eventual
3009          * sense key with us all the way through
3010          */
3011         if (!blk_pc_request(req))
3012                 req->errors = 0;
3013
3014         if (!uptodate) {
3015                 if (blk_fs_request(req) && !(req->flags & REQ_QUIET))
3016                         printk("end_request: I/O error, dev %s, sector %llu\n",
3017                                 req->rq_disk ? req->rq_disk->disk_name : "?",
3018                                 (unsigned long long)req->sector);
3019         }
3020
3021         total_bytes = bio_nbytes = 0;
3022         while ((bio = req->bio) != NULL) {
3023                 int nbytes;
3024
3025                 if (nr_bytes >= bio->bi_size) {
3026                         req->bio = bio->bi_next;
3027                         nbytes = bio->bi_size;
3028                         bio_endio(bio, nbytes, error);
3029                         next_idx = 0;
3030                         bio_nbytes = 0;
3031                 } else {
3032                         int idx = bio->bi_idx + next_idx;
3033
3034                         if (unlikely(bio->bi_idx >= bio->bi_vcnt)) {
3035                                 blk_dump_rq_flags(req, "__end_that");
3036                                 printk("%s: bio idx %d >= vcnt %d\n",
3037                                                 __FUNCTION__,
3038                                                 bio->bi_idx, bio->bi_vcnt);
3039                                 break;
3040                         }
3041
3042                         nbytes = bio_iovec_idx(bio, idx)->bv_len;
3043                         BIO_BUG_ON(nbytes > bio->bi_size);
3044
3045                         /*
3046                          * not a complete bvec done
3047                          */
3048                         if (unlikely(nbytes > nr_bytes)) {
3049                                 bio_nbytes += nr_bytes;
3050                                 total_bytes += nr_bytes;
3051                                 break;
3052                         }
3053
3054                         /*
3055                          * advance to the next vector
3056                          */
3057                         next_idx++;
3058                         bio_nbytes += nbytes;
3059                 }
3060
3061                 total_bytes += nbytes;
3062                 nr_bytes -= nbytes;
3063
3064                 if ((bio = req->bio)) {
3065                         /*
3066                          * end more in this run, or just return 'not-done'
3067                          */
3068                         if (unlikely(nr_bytes <= 0))
3069                                 break;
3070                 }
3071         }
3072
3073         /*
3074          * completely done
3075          */
3076         if (!req->bio)
3077                 return 0;
3078
3079         /*
3080          * if the request wasn't completed, update state
3081          */
3082         if (bio_nbytes) {
3083                 bio_endio(bio, bio_nbytes, error);
3084                 bio->bi_idx += next_idx;
3085                 bio_iovec(bio)->bv_offset += nr_bytes;
3086                 bio_iovec(bio)->bv_len -= nr_bytes;
3087         }
3088
3089         blk_recalc_rq_sectors(req, total_bytes >> 9);
3090         blk_recalc_rq_segments(req);
3091         return 1;
3092 }
3093
3094 /**
3095  * end_that_request_first - end I/O on a request
3096  * @req:      the request being processed
3097  * @uptodate: 1 for success, 0 for I/O error, < 0 for specific error
3098  * @nr_sectors: number of sectors to end I/O on
3099  *
3100  * Description:
3101  *     Ends I/O on a number of sectors attached to @req, and sets it up
3102  *     for the next range of segments (if any) in the cluster.
3103  *
3104  * Return:
3105  *     0 - we are done with this request, call end_that_request_last()
3106  *     1 - still buffers pending for this request
3107  **/
3108 int end_that_request_first(struct request *req, int uptodate, int nr_sectors)
3109 {
3110         return __end_that_request_first(req, uptodate, nr_sectors << 9);
3111 }
3112
3113 EXPORT_SYMBOL(end_that_request_first);
3114
3115 /**
3116  * end_that_request_chunk - end I/O on a request
3117  * @req:      the request being processed
3118  * @uptodate: 1 for success, 0 for I/O error, < 0 for specific error
3119  * @nr_bytes: number of bytes to complete
3120  *
3121  * Description:
3122  *     Ends I/O on a number of bytes attached to @req, and sets it up
3123  *     for the next range of segments (if any). Like end_that_request_first(),
3124  *     but deals with bytes instead of sectors.
3125  *
3126  * Return:
3127  *     0 - we are done with this request, call end_that_request_last()
3128  *     1 - still buffers pending for this request
3129  **/
3130 int end_that_request_chunk(struct request *req, int uptodate, int nr_bytes)
3131 {
3132         return __end_that_request_first(req, uptodate, nr_bytes);
3133 }
3134
3135 EXPORT_SYMBOL(end_that_request_chunk);
3136
3137 /*
3138  * queue lock must be held
3139  */
3140 void end_that_request_last(struct request *req)
3141 {
3142         struct gendisk *disk = req->rq_disk;
3143
3144         if (unlikely(laptop_mode) && blk_fs_request(req))
3145                 laptop_io_completion();
3146
3147         if (disk && blk_fs_request(req)) {
3148                 unsigned long duration = jiffies - req->start_time;
3149                 switch (rq_data_dir(req)) {
3150                     case WRITE:
3151                         __disk_stat_inc(disk, writes);
3152                         __disk_stat_add(disk, write_ticks, duration);
3153                         break;
3154                     case READ:
3155                         __disk_stat_inc(disk, reads);
3156                         __disk_stat_add(disk, read_ticks, duration);
3157                         break;
3158                 }
3159                 disk_round_stats(disk);
3160                 disk->in_flight--;
3161         }
3162         if (req->end_io)
3163                 req->end_io(req);
3164         else
3165                 __blk_put_request(req->q, req);
3166 }
3167
3168 EXPORT_SYMBOL(end_that_request_last);
3169
3170 void end_request(struct request *req, int uptodate)
3171 {
3172         if (!end_that_request_first(req, uptodate, req->hard_cur_sectors)) {
3173                 add_disk_randomness(req->rq_disk);
3174                 blkdev_dequeue_request(req);
3175                 end_that_request_last(req);
3176         }
3177 }
3178
3179 EXPORT_SYMBOL(end_request);
3180
3181 void blk_rq_bio_prep(request_queue_t *q, struct request *rq, struct bio *bio)
3182 {
3183         /* first three bits are identical in rq->flags and bio->bi_rw */
3184         rq->flags |= (bio->bi_rw & 7);
3185
3186         rq->nr_phys_segments = bio_phys_segments(q, bio);
3187         rq->nr_hw_segments = bio_hw_segments(q, bio);
3188         rq->current_nr_sectors = bio_cur_sectors(bio);
3189         rq->hard_cur_sectors = rq->current_nr_sectors;
3190         rq->hard_nr_sectors = rq->nr_sectors = bio_sectors(bio);
3191         rq->buffer = bio_data(bio);
3192
3193         rq->bio = rq->biotail = bio;
3194 }
3195
3196 EXPORT_SYMBOL(blk_rq_bio_prep);
3197
3198 int kblockd_schedule_work(struct work_struct *work)
3199 {
3200         return queue_work(kblockd_workqueue, work);
3201 }
3202
3203 EXPORT_SYMBOL(kblockd_schedule_work);
3204
3205 void kblockd_flush(void)
3206 {
3207         flush_workqueue(kblockd_workqueue);
3208 }
3209 EXPORT_SYMBOL(kblockd_flush);
3210
3211 int __init blk_dev_init(void)
3212 {
3213         kblockd_workqueue = create_workqueue("kblockd");
3214         if (!kblockd_workqueue)
3215                 panic("Failed to create kblockd\n");
3216
3217         request_cachep = kmem_cache_create("blkdev_requests",
3218                         sizeof(struct request), 0, SLAB_PANIC, NULL, NULL);
3219
3220         requestq_cachep = kmem_cache_create("blkdev_queue",
3221                         sizeof(request_queue_t), 0, SLAB_PANIC, NULL, NULL);
3222
3223         iocontext_cachep = kmem_cache_create("blkdev_ioc",
3224                         sizeof(struct io_context), 0, SLAB_PANIC, NULL, NULL);
3225
3226         blk_max_low_pfn = max_low_pfn;
3227         blk_max_pfn = max_pfn;
3228
3229         return 0;
3230 }
3231
3232 /*
3233  * IO Context helper functions
3234  */
3235 void put_io_context(struct io_context *ioc)
3236 {
3237         if (ioc == NULL)
3238                 return;
3239
3240         BUG_ON(atomic_read(&ioc->refcount) == 0);
3241
3242         if (atomic_dec_and_test(&ioc->refcount)) {
3243                 if (ioc->aic && ioc->aic->dtor)
3244                         ioc->aic->dtor(ioc->aic);
3245                 if (ioc->cic && ioc->cic->dtor)
3246                         ioc->cic->dtor(ioc->cic);
3247
3248                 kmem_cache_free(iocontext_cachep, ioc);
3249         }
3250 }
3251 EXPORT_SYMBOL(put_io_context);
3252
3253 /* Called by the exitting task */
3254 void exit_io_context(void)
3255 {
3256         unsigned long flags;
3257         struct io_context *ioc;
3258
3259         local_irq_save(flags);
3260         ioc = current->io_context;
3261         current->io_context = NULL;
3262         local_irq_restore(flags);
3263
3264         if (ioc->aic && ioc->aic->exit)
3265                 ioc->aic->exit(ioc->aic);
3266         if (ioc->cic && ioc->cic->exit)
3267                 ioc->cic->exit(ioc->cic);
3268
3269         put_io_context(ioc);
3270 }
3271
3272 /*
3273  * If the current task has no IO context then create one and initialise it.
3274  * If it does have a context, take a ref on it.
3275  *
3276  * This is always called in the context of the task which submitted the I/O.
3277  * But weird things happen, so we disable local interrupts to ensure exclusive
3278  * access to *current.
3279  */
3280 struct io_context *get_io_context(int gfp_flags)
3281 {
3282         struct task_struct *tsk = current;
3283         unsigned long flags;
3284         struct io_context *ret;
3285
3286         local_irq_save(flags);
3287         ret = tsk->io_context;
3288         if (ret)
3289                 goto out;
3290
3291         local_irq_restore(flags);
3292
3293         ret = kmem_cache_alloc(iocontext_cachep, gfp_flags);
3294         if (ret) {
3295                 atomic_set(&ret->refcount, 1);
3296                 ret->pid = tsk->pid;
3297                 ret->last_waited = jiffies; /* doesn't matter... */
3298                 ret->nr_batch_requests = 0; /* because this is 0 */
3299                 ret->aic = NULL;
3300                 ret->cic = NULL;
3301                 spin_lock_init(&ret->lock);
3302
3303                 local_irq_save(flags);
3304
3305                 /*
3306                  * very unlikely, someone raced with us in setting up the task
3307                  * io context. free new context and just grab a reference.
3308                  */
3309                 if (!tsk->io_context)
3310                         tsk->io_context = ret;
3311                 else {
3312                         kmem_cache_free(iocontext_cachep, ret);
3313                         ret = tsk->io_context;
3314                 }
3315
3316 out:
3317                 atomic_inc(&ret->refcount);
3318                 local_irq_restore(flags);
3319         }
3320
3321         return ret;
3322 }
3323 EXPORT_SYMBOL(get_io_context);
3324
3325 void copy_io_context(struct io_context **pdst, struct io_context **psrc)
3326 {
3327         struct io_context *src = *psrc;
3328         struct io_context *dst = *pdst;
3329
3330         if (src) {
3331                 BUG_ON(atomic_read(&src->refcount) == 0);
3332                 atomic_inc(&src->refcount);
3333                 put_io_context(dst);
3334                 *pdst = src;
3335         }
3336 }
3337 EXPORT_SYMBOL(copy_io_context);
3338
3339 void swap_io_context(struct io_context **ioc1, struct io_context **ioc2)
3340 {
3341         struct io_context *temp;
3342         temp = *ioc1;
3343         *ioc1 = *ioc2;
3344         *ioc2 = temp;
3345 }
3346 EXPORT_SYMBOL(swap_io_context);
3347
3348 /*
3349  * sysfs parts below
3350  */
3351 struct queue_sysfs_entry {
3352         struct attribute attr;
3353         ssize_t (*show)(struct request_queue *, char *);
3354         ssize_t (*store)(struct request_queue *, const char *, size_t);
3355 };
3356
3357 static ssize_t
3358 queue_var_show(unsigned int var, char *page)
3359 {
3360         return sprintf(page, "%d\n", var);
3361 }
3362
3363 static ssize_t
3364 queue_var_store(unsigned long *var, const char *page, size_t count)
3365 {
3366         char *p = (char *) page;
3367
3368         *var = simple_strtoul(p, &p, 10);
3369         return count;
3370 }
3371
3372 static ssize_t queue_requests_show(struct request_queue *q, char *page)
3373 {
3374         return queue_var_show(q->nr_requests, (page));
3375 }
3376
3377 static ssize_t
3378 queue_requests_store(struct request_queue *q, const char *page, size_t count)
3379 {
3380         struct request_list *rl = &q->rq;
3381
3382         int ret = queue_var_store(&q->nr_requests, page, count);
3383         if (q->nr_requests < BLKDEV_MIN_RQ)
3384                 q->nr_requests = BLKDEV_MIN_RQ;
3385         blk_queue_congestion_threshold(q);
3386
3387         if (rl->count[READ] >= queue_congestion_on_threshold(q))
3388                 set_queue_congested(q, READ);
3389         else if (rl->count[READ] < queue_congestion_off_threshold(q))
3390                 clear_queue_congested(q, READ);
3391
3392         if (rl->count[WRITE] >= queue_congestion_on_threshold(q))
3393                 set_queue_congested(q, WRITE);
3394         else if (rl->count[WRITE] < queue_congestion_off_threshold(q))
3395                 clear_queue_congested(q, WRITE);
3396
3397         if (rl->count[READ] >= q->nr_requests) {
3398                 blk_set_queue_full(q, READ);
3399         } else if (rl->count[READ]+1 <= q->nr_requests) {
3400                 blk_clear_queue_full(q, READ);
3401                 wake_up(&rl->wait[READ]);
3402         }
3403
3404         if (rl->count[WRITE] >= q->nr_requests) {
3405                 blk_set_queue_full(q, WRITE);
3406         } else if (rl->count[WRITE]+1 <= q->nr_requests) {
3407                 blk_clear_queue_full(q, WRITE);
3408                 wake_up(&rl->wait[WRITE]);
3409         }
3410         return ret;
3411 }
3412
3413 static ssize_t queue_ra_show(struct request_queue *q, char *page)
3414 {
3415         int ra_kb = q->backing_dev_info.ra_pages << (PAGE_CACHE_SHIFT - 10);
3416
3417         return queue_var_show(ra_kb, (page));
3418 }
3419
3420 static ssize_t
3421 queue_ra_store(struct request_queue *q, const char *page, size_t count)
3422 {
3423         unsigned long ra_kb;
3424         ssize_t ret = queue_var_store(&ra_kb, page, count);
3425
3426         spin_lock_irq(q->queue_lock);
3427         if (ra_kb > (q->max_sectors >> 1))
3428                 ra_kb = (q->max_sectors >> 1);
3429
3430         q->backing_dev_info.ra_pages = ra_kb >> (PAGE_CACHE_SHIFT - 10);
3431         spin_unlock_irq(q->queue_lock);
3432
3433         return ret;
3434 }
3435
3436 static ssize_t queue_max_sectors_show(struct request_queue *q, char *page)
3437 {
3438         int max_sectors_kb = q->max_sectors >> 1;
3439
3440         return queue_var_show(max_sectors_kb, (page));
3441 }
3442
3443 static ssize_t
3444 queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
3445 {
3446         unsigned long max_sectors_kb,
3447                         max_hw_sectors_kb = q->max_hw_sectors >> 1,
3448                         page_kb = 1 << (PAGE_CACHE_SHIFT - 10);
3449         ssize_t ret = queue_var_store(&max_sectors_kb, page, count);
3450         int ra_kb;
3451
3452         if (max_sectors_kb > max_hw_sectors_kb || max_sectors_kb < page_kb)
3453                 return -EINVAL;
3454         /*
3455          * Take the queue lock to update the readahead and