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1 /*
2  * Functions related to segment and merge handling
3  */
4 #include <linux/kernel.h>
5 #include <linux/module.h>
6 #include <linux/bio.h>
7 #include <linux/blkdev.h>
8 #include <linux/scatterlist.h>
9 
10 #include "blk.h"
11 
__blk_recalc_rq_segments(struct request_queue * q,struct bio * bio,bool no_sg_merge)12 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
13 					     struct bio *bio,
14 					     bool no_sg_merge)
15 {
16 	struct bio_vec bv, bvprv = { NULL };
17 	int cluster, high, highprv = 1;
18 	unsigned int seg_size, nr_phys_segs;
19 	struct bio *fbio, *bbio;
20 	struct bvec_iter iter;
21 
22 	if (!bio)
23 		return 0;
24 
25 	/*
26 	 * This should probably be returning 0, but blk_add_request_payload()
27 	 * (Christoph!!!!)
28 	 */
29 	if (bio->bi_rw & REQ_DISCARD)
30 		return 1;
31 
32 	if (bio->bi_rw & REQ_WRITE_SAME)
33 		return 1;
34 
35 	fbio = bio;
36 	cluster = blk_queue_cluster(q);
37 	seg_size = 0;
38 	nr_phys_segs = 0;
39 	high = 0;
40 	for_each_bio(bio) {
41 		bio_for_each_segment(bv, bio, iter) {
42 			/*
43 			 * If SG merging is disabled, each bio vector is
44 			 * a segment
45 			 */
46 			if (no_sg_merge)
47 				goto new_segment;
48 
49 			/*
50 			 * the trick here is making sure that a high page is
51 			 * never considered part of another segment, since
52 			 * that might change with the bounce page.
53 			 */
54 			high = page_to_pfn(bv.bv_page) > queue_bounce_pfn(q);
55 			if (!high && !highprv && cluster) {
56 				if (seg_size + bv.bv_len
57 				    > queue_max_segment_size(q))
58 					goto new_segment;
59 				if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
60 					goto new_segment;
61 				if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
62 					goto new_segment;
63 
64 				seg_size += bv.bv_len;
65 				bvprv = bv;
66 				continue;
67 			}
68 new_segment:
69 			if (nr_phys_segs == 1 && seg_size >
70 			    fbio->bi_seg_front_size)
71 				fbio->bi_seg_front_size = seg_size;
72 
73 			nr_phys_segs++;
74 			bvprv = bv;
75 			seg_size = bv.bv_len;
76 			highprv = high;
77 		}
78 		bbio = bio;
79 	}
80 
81 	if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
82 		fbio->bi_seg_front_size = seg_size;
83 	if (seg_size > bbio->bi_seg_back_size)
84 		bbio->bi_seg_back_size = seg_size;
85 
86 	return nr_phys_segs;
87 }
88 
blk_recalc_rq_segments(struct request * rq)89 void blk_recalc_rq_segments(struct request *rq)
90 {
91 	bool no_sg_merge = !!test_bit(QUEUE_FLAG_NO_SG_MERGE,
92 			&rq->q->queue_flags);
93 
94 	rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio,
95 			no_sg_merge);
96 }
97 
blk_recount_segments(struct request_queue * q,struct bio * bio)98 void blk_recount_segments(struct request_queue *q, struct bio *bio)
99 {
100 	unsigned short seg_cnt;
101 
102 	/* estimate segment number by bi_vcnt for non-cloned bio */
103 	if (bio_flagged(bio, BIO_CLONED))
104 		seg_cnt = bio_segments(bio);
105 	else
106 		seg_cnt = bio->bi_vcnt;
107 
108 	if (test_bit(QUEUE_FLAG_NO_SG_MERGE, &q->queue_flags) &&
109 			(seg_cnt < queue_max_segments(q)))
110 		bio->bi_phys_segments = seg_cnt;
111 	else {
112 		struct bio *nxt = bio->bi_next;
113 
114 		bio->bi_next = NULL;
115 		bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, false);
116 		bio->bi_next = nxt;
117 	}
118 
119 	bio->bi_flags |= (1 << BIO_SEG_VALID);
120 }
121 EXPORT_SYMBOL(blk_recount_segments);
122 
blk_phys_contig_segment(struct request_queue * q,struct bio * bio,struct bio * nxt)123 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
124 				   struct bio *nxt)
125 {
126 	struct bio_vec end_bv = { NULL }, nxt_bv;
127 	struct bvec_iter iter;
128 
129 	if (!blk_queue_cluster(q))
130 		return 0;
131 
132 	if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
133 	    queue_max_segment_size(q))
134 		return 0;
135 
136 	if (!bio_has_data(bio))
137 		return 1;
138 
139 	bio_for_each_segment(end_bv, bio, iter)
140 		if (end_bv.bv_len == iter.bi_size)
141 			break;
142 
143 	nxt_bv = bio_iovec(nxt);
144 
145 	if (!BIOVEC_PHYS_MERGEABLE(&end_bv, &nxt_bv))
146 		return 0;
147 
148 	/*
149 	 * bio and nxt are contiguous in memory; check if the queue allows
150 	 * these two to be merged into one
151 	 */
152 	if (BIOVEC_SEG_BOUNDARY(q, &end_bv, &nxt_bv))
153 		return 1;
154 
155 	return 0;
156 }
157 
158 static inline void
__blk_segment_map_sg(struct request_queue * q,struct bio_vec * bvec,struct scatterlist * sglist,struct bio_vec * bvprv,struct scatterlist ** sg,int * nsegs,int * cluster)159 __blk_segment_map_sg(struct request_queue *q, struct bio_vec *bvec,
160 		     struct scatterlist *sglist, struct bio_vec *bvprv,
161 		     struct scatterlist **sg, int *nsegs, int *cluster)
162 {
163 
164 	int nbytes = bvec->bv_len;
165 
166 	if (*sg && *cluster) {
167 		if ((*sg)->length + nbytes > queue_max_segment_size(q))
168 			goto new_segment;
169 
170 		if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
171 			goto new_segment;
172 		if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
173 			goto new_segment;
174 
175 		(*sg)->length += nbytes;
176 	} else {
177 new_segment:
178 		if (!*sg)
179 			*sg = sglist;
180 		else {
181 			/*
182 			 * If the driver previously mapped a shorter
183 			 * list, we could see a termination bit
184 			 * prematurely unless it fully inits the sg
185 			 * table on each mapping. We KNOW that there
186 			 * must be more entries here or the driver
187 			 * would be buggy, so force clear the
188 			 * termination bit to avoid doing a full
189 			 * sg_init_table() in drivers for each command.
190 			 */
191 			sg_unmark_end(*sg);
192 			*sg = sg_next(*sg);
193 		}
194 
195 		sg_set_page(*sg, bvec->bv_page, nbytes, bvec->bv_offset);
196 		(*nsegs)++;
197 	}
198 	*bvprv = *bvec;
199 }
200 
__blk_bios_map_sg(struct request_queue * q,struct bio * bio,struct scatterlist * sglist,struct scatterlist ** sg)201 static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
202 			     struct scatterlist *sglist,
203 			     struct scatterlist **sg)
204 {
205 	struct bio_vec bvec, bvprv = { NULL };
206 	struct bvec_iter iter;
207 	int nsegs, cluster;
208 
209 	nsegs = 0;
210 	cluster = blk_queue_cluster(q);
211 
212 	if (bio->bi_rw & REQ_DISCARD) {
213 		/*
214 		 * This is a hack - drivers should be neither modifying the
215 		 * biovec, nor relying on bi_vcnt - but because of
216 		 * blk_add_request_payload(), a discard bio may or may not have
217 		 * a payload we need to set up here (thank you Christoph) and
218 		 * bi_vcnt is really the only way of telling if we need to.
219 		 */
220 
221 		if (bio->bi_vcnt)
222 			goto single_segment;
223 
224 		return 0;
225 	}
226 
227 	if (bio->bi_rw & REQ_WRITE_SAME) {
228 single_segment:
229 		*sg = sglist;
230 		bvec = bio_iovec(bio);
231 		sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
232 		return 1;
233 	}
234 
235 	for_each_bio(bio)
236 		bio_for_each_segment(bvec, bio, iter)
237 			__blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
238 					     &nsegs, &cluster);
239 
240 	return nsegs;
241 }
242 
243 /*
244  * map a request to scatterlist, return number of sg entries setup. Caller
245  * must make sure sg can hold rq->nr_phys_segments entries
246  */
blk_rq_map_sg(struct request_queue * q,struct request * rq,struct scatterlist * sglist)247 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
248 		  struct scatterlist *sglist)
249 {
250 	struct scatterlist *sg = NULL;
251 	int nsegs = 0;
252 
253 	if (rq->bio)
254 		nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
255 
256 	if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
257 	    (blk_rq_bytes(rq) & q->dma_pad_mask)) {
258 		unsigned int pad_len =
259 			(q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
260 
261 		sg->length += pad_len;
262 		rq->extra_len += pad_len;
263 	}
264 
265 	if (q->dma_drain_size && q->dma_drain_needed(rq)) {
266 		if (rq->cmd_flags & REQ_WRITE)
267 			memset(q->dma_drain_buffer, 0, q->dma_drain_size);
268 
269 		sg->page_link &= ~0x02;
270 		sg = sg_next(sg);
271 		sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
272 			    q->dma_drain_size,
273 			    ((unsigned long)q->dma_drain_buffer) &
274 			    (PAGE_SIZE - 1));
275 		nsegs++;
276 		rq->extra_len += q->dma_drain_size;
277 	}
278 
279 	if (sg)
280 		sg_mark_end(sg);
281 
282 	return nsegs;
283 }
284 EXPORT_SYMBOL(blk_rq_map_sg);
285 
286 /**
287  * blk_bio_map_sg - map a bio to a scatterlist
288  * @q: request_queue in question
289  * @bio: bio being mapped
290  * @sglist: scatterlist being mapped
291  *
292  * Note:
293  *    Caller must make sure sg can hold bio->bi_phys_segments entries
294  *
295  * Will return the number of sg entries setup
296  */
blk_bio_map_sg(struct request_queue * q,struct bio * bio,struct scatterlist * sglist)297 int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
298 		   struct scatterlist *sglist)
299 {
300 	struct scatterlist *sg = NULL;
301 	int nsegs;
302 	struct bio *next = bio->bi_next;
303 	bio->bi_next = NULL;
304 
305 	nsegs = __blk_bios_map_sg(q, bio, sglist, &sg);
306 	bio->bi_next = next;
307 	if (sg)
308 		sg_mark_end(sg);
309 
310 	BUG_ON(bio->bi_phys_segments && nsegs > bio->bi_phys_segments);
311 	return nsegs;
312 }
313 EXPORT_SYMBOL(blk_bio_map_sg);
314 
ll_new_hw_segment(struct request_queue * q,struct request * req,struct bio * bio)315 static inline int ll_new_hw_segment(struct request_queue *q,
316 				    struct request *req,
317 				    struct bio *bio)
318 {
319 	int nr_phys_segs = bio_phys_segments(q, bio);
320 
321 	if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q))
322 		goto no_merge;
323 
324 	if (blk_integrity_merge_bio(q, req, bio) == false)
325 		goto no_merge;
326 
327 	/*
328 	 * This will form the start of a new hw segment.  Bump both
329 	 * counters.
330 	 */
331 	req->nr_phys_segments += nr_phys_segs;
332 	return 1;
333 
334 no_merge:
335 	req->cmd_flags |= REQ_NOMERGE;
336 	if (req == q->last_merge)
337 		q->last_merge = NULL;
338 	return 0;
339 }
340 
ll_back_merge_fn(struct request_queue * q,struct request * req,struct bio * bio)341 int ll_back_merge_fn(struct request_queue *q, struct request *req,
342 		     struct bio *bio)
343 {
344 	if (blk_rq_sectors(req) + bio_sectors(bio) >
345 	    blk_rq_get_max_sectors(req)) {
346 		req->cmd_flags |= REQ_NOMERGE;
347 		if (req == q->last_merge)
348 			q->last_merge = NULL;
349 		return 0;
350 	}
351 	if (!bio_flagged(req->biotail, BIO_SEG_VALID))
352 		blk_recount_segments(q, req->biotail);
353 	if (!bio_flagged(bio, BIO_SEG_VALID))
354 		blk_recount_segments(q, bio);
355 
356 	return ll_new_hw_segment(q, req, bio);
357 }
358 
ll_front_merge_fn(struct request_queue * q,struct request * req,struct bio * bio)359 int ll_front_merge_fn(struct request_queue *q, struct request *req,
360 		      struct bio *bio)
361 {
362 	if (blk_rq_sectors(req) + bio_sectors(bio) >
363 	    blk_rq_get_max_sectors(req)) {
364 		req->cmd_flags |= REQ_NOMERGE;
365 		if (req == q->last_merge)
366 			q->last_merge = NULL;
367 		return 0;
368 	}
369 	if (!bio_flagged(bio, BIO_SEG_VALID))
370 		blk_recount_segments(q, bio);
371 	if (!bio_flagged(req->bio, BIO_SEG_VALID))
372 		blk_recount_segments(q, req->bio);
373 
374 	return ll_new_hw_segment(q, req, bio);
375 }
376 
377 /*
378  * blk-mq uses req->special to carry normal driver per-request payload, it
379  * does not indicate a prepared command that we cannot merge with.
380  */
req_no_special_merge(struct request * req)381 static bool req_no_special_merge(struct request *req)
382 {
383 	struct request_queue *q = req->q;
384 
385 	return !q->mq_ops && req->special;
386 }
387 
ll_merge_requests_fn(struct request_queue * q,struct request * req,struct request * next)388 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
389 				struct request *next)
390 {
391 	int total_phys_segments;
392 	unsigned int seg_size =
393 		req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
394 
395 	/*
396 	 * First check if the either of the requests are re-queued
397 	 * requests.  Can't merge them if they are.
398 	 */
399 	if (req_no_special_merge(req) || req_no_special_merge(next))
400 		return 0;
401 
402 	/*
403 	 * Will it become too large?
404 	 */
405 	if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
406 	    blk_rq_get_max_sectors(req))
407 		return 0;
408 
409 	total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
410 	if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
411 		if (req->nr_phys_segments == 1)
412 			req->bio->bi_seg_front_size = seg_size;
413 		if (next->nr_phys_segments == 1)
414 			next->biotail->bi_seg_back_size = seg_size;
415 		total_phys_segments--;
416 	}
417 
418 	if (total_phys_segments > queue_max_segments(q))
419 		return 0;
420 
421 	if (blk_integrity_merge_rq(q, req, next) == false)
422 		return 0;
423 
424 	/* Merge is OK... */
425 	req->nr_phys_segments = total_phys_segments;
426 	return 1;
427 }
428 
429 /**
430  * blk_rq_set_mixed_merge - mark a request as mixed merge
431  * @rq: request to mark as mixed merge
432  *
433  * Description:
434  *     @rq is about to be mixed merged.  Make sure the attributes
435  *     which can be mixed are set in each bio and mark @rq as mixed
436  *     merged.
437  */
blk_rq_set_mixed_merge(struct request * rq)438 void blk_rq_set_mixed_merge(struct request *rq)
439 {
440 	unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
441 	struct bio *bio;
442 
443 	if (rq->cmd_flags & REQ_MIXED_MERGE)
444 		return;
445 
446 	/*
447 	 * @rq will no longer represent mixable attributes for all the
448 	 * contained bios.  It will just track those of the first one.
449 	 * Distributes the attributs to each bio.
450 	 */
451 	for (bio = rq->bio; bio; bio = bio->bi_next) {
452 		WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
453 			     (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
454 		bio->bi_rw |= ff;
455 	}
456 	rq->cmd_flags |= REQ_MIXED_MERGE;
457 }
458 
blk_account_io_merge(struct request * req)459 static void blk_account_io_merge(struct request *req)
460 {
461 	if (blk_do_io_stat(req)) {
462 		struct hd_struct *part;
463 		int cpu;
464 
465 		cpu = part_stat_lock();
466 		part = req->part;
467 
468 		part_round_stats(cpu, part);
469 		part_dec_in_flight(part, rq_data_dir(req));
470 
471 		hd_struct_put(part);
472 		part_stat_unlock();
473 	}
474 }
475 
476 /*
477  * Has to be called with the request spinlock acquired
478  */
attempt_merge(struct request_queue * q,struct request * req,struct request * next)479 static int attempt_merge(struct request_queue *q, struct request *req,
480 			  struct request *next)
481 {
482 	if (!rq_mergeable(req) || !rq_mergeable(next))
483 		return 0;
484 
485 	if (!blk_check_merge_flags(req->cmd_flags, next->cmd_flags))
486 		return 0;
487 
488 	/*
489 	 * not contiguous
490 	 */
491 	if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
492 		return 0;
493 
494 	if (rq_data_dir(req) != rq_data_dir(next)
495 	    || req->rq_disk != next->rq_disk
496 	    || req_no_special_merge(next))
497 		return 0;
498 
499 	if (req->cmd_flags & REQ_WRITE_SAME &&
500 	    !blk_write_same_mergeable(req->bio, next->bio))
501 		return 0;
502 
503 	/*
504 	 * If we are allowed to merge, then append bio list
505 	 * from next to rq and release next. merge_requests_fn
506 	 * will have updated segment counts, update sector
507 	 * counts here.
508 	 */
509 	if (!ll_merge_requests_fn(q, req, next))
510 		return 0;
511 
512 	/*
513 	 * If failfast settings disagree or any of the two is already
514 	 * a mixed merge, mark both as mixed before proceeding.  This
515 	 * makes sure that all involved bios have mixable attributes
516 	 * set properly.
517 	 */
518 	if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
519 	    (req->cmd_flags & REQ_FAILFAST_MASK) !=
520 	    (next->cmd_flags & REQ_FAILFAST_MASK)) {
521 		blk_rq_set_mixed_merge(req);
522 		blk_rq_set_mixed_merge(next);
523 	}
524 
525 	/*
526 	 * At this point we have either done a back merge
527 	 * or front merge. We need the smaller start_time of
528 	 * the merged requests to be the current request
529 	 * for accounting purposes.
530 	 */
531 	if (time_after(req->start_time, next->start_time))
532 		req->start_time = next->start_time;
533 
534 	req->biotail->bi_next = next->bio;
535 	req->biotail = next->biotail;
536 
537 	req->__data_len += blk_rq_bytes(next);
538 
539 	elv_merge_requests(q, req, next);
540 
541 	/*
542 	 * 'next' is going away, so update stats accordingly
543 	 */
544 	blk_account_io_merge(next);
545 
546 	req->ioprio = ioprio_best(req->ioprio, next->ioprio);
547 	if (blk_rq_cpu_valid(next))
548 		req->cpu = next->cpu;
549 
550 	/* owner-ship of bio passed from next to req */
551 	next->bio = NULL;
552 	__blk_put_request(q, next);
553 	return 1;
554 }
555 
attempt_back_merge(struct request_queue * q,struct request * rq)556 int attempt_back_merge(struct request_queue *q, struct request *rq)
557 {
558 	struct request *next = elv_latter_request(q, rq);
559 
560 	if (next)
561 		return attempt_merge(q, rq, next);
562 
563 	return 0;
564 }
565 
attempt_front_merge(struct request_queue * q,struct request * rq)566 int attempt_front_merge(struct request_queue *q, struct request *rq)
567 {
568 	struct request *prev = elv_former_request(q, rq);
569 
570 	if (prev)
571 		return attempt_merge(q, prev, rq);
572 
573 	return 0;
574 }
575 
blk_attempt_req_merge(struct request_queue * q,struct request * rq,struct request * next)576 int blk_attempt_req_merge(struct request_queue *q, struct request *rq,
577 			  struct request *next)
578 {
579 	return attempt_merge(q, rq, next);
580 }
581 
blk_rq_merge_ok(struct request * rq,struct bio * bio)582 bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
583 {
584 	struct request_queue *q = rq->q;
585 
586 	if (!rq_mergeable(rq) || !bio_mergeable(bio))
587 		return false;
588 
589 	if (!blk_check_merge_flags(rq->cmd_flags, bio->bi_rw))
590 		return false;
591 
592 	/* different data direction or already started, don't merge */
593 	if (bio_data_dir(bio) != rq_data_dir(rq))
594 		return false;
595 
596 	/* must be same device and not a special request */
597 	if (rq->rq_disk != bio->bi_bdev->bd_disk || req_no_special_merge(rq))
598 		return false;
599 
600 	/* only merge integrity protected bio into ditto rq */
601 	if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
602 		return false;
603 
604 	/* must be using the same buffer */
605 	if (rq->cmd_flags & REQ_WRITE_SAME &&
606 	    !blk_write_same_mergeable(rq->bio, bio))
607 		return false;
608 
609 	if (q->queue_flags & (1 << QUEUE_FLAG_SG_GAPS)) {
610 		struct bio_vec *bprev;
611 
612 		bprev = &rq->biotail->bi_io_vec[rq->biotail->bi_vcnt - 1];
613 		if (bvec_gap_to_prev(bprev, bio->bi_io_vec[0].bv_offset))
614 			return false;
615 	}
616 
617 	return true;
618 }
619 
blk_try_merge(struct request * rq,struct bio * bio)620 int blk_try_merge(struct request *rq, struct bio *bio)
621 {
622 	if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
623 		return ELEVATOR_BACK_MERGE;
624 	else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
625 		return ELEVATOR_FRONT_MERGE;
626 	return ELEVATOR_NO_MERGE;
627 }
628