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
12 static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
13 struct bio *bio)
14 {
15 unsigned int phys_size;
16 struct bio_vec *bv, *bvprv = NULL;
17 int cluster, i, high, highprv = 1;
18 unsigned int seg_size, nr_phys_segs;
19 struct bio *fbio, *bbio;
20
21 if (!bio)
22 return 0;
23
24 fbio = bio;
25 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
26 seg_size = 0;
27 phys_size = nr_phys_segs = 0;
28 for_each_bio(bio) {
29 bio_for_each_segment(bv, bio, i) {
30 /*
31 * the trick here is making sure that a high page is
32 * never considered part of another segment, since that
33 * might change with the bounce page.
34 */
35 high = page_to_pfn(bv->bv_page) > queue_bounce_pfn(q);
36 if (high || highprv)
37 goto new_segment;
38 if (cluster) {
39 if (seg_size + bv->bv_len
40 > queue_max_segment_size(q))
41 goto new_segment;
42 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
43 goto new_segment;
44 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
45 goto new_segment;
46
47 seg_size += bv->bv_len;
48 bvprv = bv;
49 continue;
50 }
51 new_segment:
52 if (nr_phys_segs == 1 && seg_size >
53 fbio->bi_seg_front_size)
54 fbio->bi_seg_front_size = seg_size;
55
56 nr_phys_segs++;
57 bvprv = bv;
58 seg_size = bv->bv_len;
59 highprv = high;
60 }
61 bbio = bio;
62 }
63
64 if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
65 fbio->bi_seg_front_size = seg_size;
66 if (seg_size > bbio->bi_seg_back_size)
67 bbio->bi_seg_back_size = seg_size;
68
69 return nr_phys_segs;
70 }
71
72 void blk_recalc_rq_segments(struct request *rq)
73 {
74 rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
75 }
76
77 void blk_recount_segments(struct request_queue *q, struct bio *bio)
78 {
79 struct bio *nxt = bio->bi_next;
80
81 bio->bi_next = NULL;
82 bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
83 bio->bi_next = nxt;
84 bio->bi_flags |= (1 << BIO_SEG_VALID);
85 }
86 EXPORT_SYMBOL(blk_recount_segments);
87
88 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
89 struct bio *nxt)
90 {
91 if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
92 return 0;
93
94 if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
95 queue_max_segment_size(q))
96 return 0;
97
98 if (!bio_has_data(bio))
99 return 1;
100
101 if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
102 return 0;
103
104 /*
105 * bio and nxt are contiguous in memory; check if the queue allows
106 * these two to be merged into one
107 */
108 if (BIO_SEG_BOUNDARY(q, bio, nxt))
109 return 1;
110
111 return 0;
112 }
113
114 /*
115 * map a request to scatterlist, return number of sg entries setup. Caller
116 * must make sure sg can hold rq->nr_phys_segments entries
117 */
118 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
119 struct scatterlist *sglist)
120 {
121 struct bio_vec *bvec, *bvprv;
122 struct req_iterator iter;
123 struct scatterlist *sg;
124 int nsegs, cluster;
125
126 nsegs = 0;
127 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
128
129 /*
130 * for each bio in rq
131 */
132 bvprv = NULL;
133 sg = NULL;
134 rq_for_each_segment(bvec, rq, iter) {
135 int nbytes = bvec->bv_len;
136
137 if (bvprv && cluster) {
138 if (sg->length + nbytes > queue_max_segment_size(q))
139 goto new_segment;
140
141 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
142 goto new_segment;
143 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
144 goto new_segment;
145
146 sg->length += nbytes;
147 } else {
148 new_segment:
149 if (!sg)
150 sg = sglist;
151 else {
152 /*
153 * If the driver previously mapped a shorter
154 * list, we could see a termination bit
155 * prematurely unless it fully inits the sg
156 * table on each mapping. We KNOW that there
157 * must be more entries here or the driver
158 * would be buggy, so force clear the
159 * termination bit to avoid doing a full
160 * sg_init_table() in drivers for each command.
161 */
162 sg->page_link &= ~0x02;
163 sg = sg_next(sg);
164 }
165
166 sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
167 nsegs++;
168 }
169 bvprv = bvec;
170 } /* segments in rq */
171
172
173 if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
174 (blk_rq_bytes(rq) & q->dma_pad_mask)) {
175 unsigned int pad_len =
176 (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
177
178 sg->length += pad_len;
179 rq->extra_len += pad_len;
180 }
181
182 if (q->dma_drain_size && q->dma_drain_needed(rq)) {
183 if (rq->cmd_flags & REQ_RW)
184 memset(q->dma_drain_buffer, 0, q->dma_drain_size);
185
186 sg->page_link &= ~0x02;
187 sg = sg_next(sg);
188 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
189 q->dma_drain_size,
190 ((unsigned long)q->dma_drain_buffer) &
191 (PAGE_SIZE - 1));
192 nsegs++;
193 rq->extra_len += q->dma_drain_size;
194 }
195
196 if (sg)
197 sg_mark_end(sg);
198
199 return nsegs;
200 }
201 EXPORT_SYMBOL(blk_rq_map_sg);
202
203 static inline int ll_new_hw_segment(struct request_queue *q,
204 struct request *req,
205 struct bio *bio)
206 {
207 int nr_phys_segs = bio_phys_segments(q, bio);
208
209 if (req->nr_phys_segments + nr_phys_segs > queue_max_hw_segments(q) ||
210 req->nr_phys_segments + nr_phys_segs > queue_max_phys_segments(q)) {
211 req->cmd_flags |= REQ_NOMERGE;
212 if (req == q->last_merge)
213 q->last_merge = NULL;
214 return 0;
215 }
216
217 /*
218 * This will form the start of a new hw segment. Bump both
219 * counters.
220 */
221 req->nr_phys_segments += nr_phys_segs;
222 return 1;
223 }
224
225 int ll_back_merge_fn(struct request_queue *q, struct request *req,
226 struct bio *bio)
227 {
228 unsigned short max_sectors;
229
230 if (unlikely(blk_pc_request(req)))
231 max_sectors = queue_max_hw_sectors(q);
232 else
233 max_sectors = queue_max_sectors(q);
234
235 if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
236 req->cmd_flags |= REQ_NOMERGE;
237 if (req == q->last_merge)
238 q->last_merge = NULL;
239 return 0;
240 }
241 if (!bio_flagged(req->biotail, BIO_SEG_VALID))
242 blk_recount_segments(q, req->biotail);
243 if (!bio_flagged(bio, BIO_SEG_VALID))
244 blk_recount_segments(q, bio);
245
246 return ll_new_hw_segment(q, req, bio);
247 }
248
249 int ll_front_merge_fn(struct request_queue *q, struct request *req,
250 struct bio *bio)
251 {
252 unsigned short max_sectors;
253
254 if (unlikely(blk_pc_request(req)))
255 max_sectors = queue_max_hw_sectors(q);
256 else
257 max_sectors = queue_max_sectors(q);
258
259
260 if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
261 req->cmd_flags |= REQ_NOMERGE;
262 if (req == q->last_merge)
263 q->last_merge = NULL;
264 return 0;
265 }
266 if (!bio_flagged(bio, BIO_SEG_VALID))
267 blk_recount_segments(q, bio);
268 if (!bio_flagged(req->bio, BIO_SEG_VALID))
269 blk_recount_segments(q, req->bio);
270
271 return ll_new_hw_segment(q, req, bio);
272 }
273
274 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
275 struct request *next)
276 {
277 int total_phys_segments;
278 unsigned int seg_size =
279 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
280
281 /*
282 * First check if the either of the requests are re-queued
283 * requests. Can't merge them if they are.
284 */
285 if (req->special || next->special)
286 return 0;
287
288 /*
289 * Will it become too large?
290 */
291 if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q))
292 return 0;
293
294 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
295 if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
296 if (req->nr_phys_segments == 1)
297 req->bio->bi_seg_front_size = seg_size;
298 if (next->nr_phys_segments == 1)
299 next->biotail->bi_seg_back_size = seg_size;
300 total_phys_segments--;
301 }
302
303 if (total_phys_segments > queue_max_phys_segments(q))
304 return 0;
305
306 if (total_phys_segments > queue_max_hw_segments(q))
307 return 0;
308
309 /* Merge is OK... */
310 req->nr_phys_segments = total_phys_segments;
311 return 1;
312 }
313
314 static void blk_account_io_merge(struct request *req)
315 {
316 if (blk_do_io_stat(req)) {
317 struct hd_struct *part;
318 int cpu;
319
320 cpu = part_stat_lock();
321 part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req));
322
323 part_round_stats(cpu, part);
324 part_dec_in_flight(part);
325
326 part_stat_unlock();
327 }
328 }
329
330 /*
331 * Has to be called with the request spinlock acquired
332 */
333 static int attempt_merge(struct request_queue *q, struct request *req,
334 struct request *next)
335 {
336 if (!rq_mergeable(req) || !rq_mergeable(next))
337 return 0;
338
339 /*
340 * not contiguous
341 */
342 if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
343 return 0;
344
345 if (rq_data_dir(req) != rq_data_dir(next)
346 || req->rq_disk != next->rq_disk
347 || next->special)
348 return 0;
349
350 if (blk_integrity_rq(req) != blk_integrity_rq(next))
351 return 0;
352
353 /* don't merge requests of different failfast settings */
354 if (blk_failfast_dev(req) != blk_failfast_dev(next) ||
355 blk_failfast_transport(req) != blk_failfast_transport(next) ||
356 blk_failfast_driver(req) != blk_failfast_driver(next))
357 return 0;
358
359 /*
360 * If we are allowed to merge, then append bio list
361 * from next to rq and release next. merge_requests_fn
362 * will have updated segment counts, update sector
363 * counts here.
364 */
365 if (!ll_merge_requests_fn(q, req, next))
366 return 0;
367
368 /*
369 * At this point we have either done a back merge
370 * or front merge. We need the smaller start_time of
371 * the merged requests to be the current request
372 * for accounting purposes.
373 */
374 if (time_after(req->start_time, next->start_time))
375 req->start_time = next->start_time;
376
377 req->biotail->bi_next = next->bio;
378 req->biotail = next->biotail;
379
380 req->__data_len += blk_rq_bytes(next);
381
382 elv_merge_requests(q, req, next);
383
384 /*
385 * 'next' is going away, so update stats accordingly
386 */
387 blk_account_io_merge(next);
388
389 req->ioprio = ioprio_best(req->ioprio, next->ioprio);
390 if (blk_rq_cpu_valid(next))
391 req->cpu = next->cpu;
392
393 /* owner-ship of bio passed from next to req */
394 next->bio = NULL;
395 __blk_put_request(q, next);
396 return 1;
397 }
398
399 int attempt_back_merge(struct request_queue *q, struct request *rq)
400 {
401 struct request *next = elv_latter_request(q, rq);
402
403 if (next)
404 return attempt_merge(q, rq, next);
405
406 return 0;
407 }
408
409 int attempt_front_merge(struct request_queue *q, struct request *rq)
410 {
411 struct request *prev = elv_former_request(q, rq);
412
413 if (prev)
414 return attempt_merge(q, prev, rq);
415
416 return 0;
417 }
418
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