gcc-4.6: block: fix unused but set variables in blk-merge
[linux-2.6.git] / block / blk-merge.c
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         struct bio_vec *bv, *bvprv = NULL;
16         int cluster, i, high, highprv = 1;
17         unsigned int seg_size, nr_phys_segs;
18         struct bio *fbio, *bbio;
19
20         if (!bio)
21                 return 0;
22
23         fbio = bio;
24         cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
25         seg_size = 0;
26         nr_phys_segs = 0;
27         for_each_bio(bio) {
28                 bio_for_each_segment(bv, bio, i) {
29                         /*
30                          * the trick here is making sure that a high page is
31                          * never considered part of another segment, since that
32                          * might change with the bounce page.
33                          */
34                         high = page_to_pfn(bv->bv_page) > queue_bounce_pfn(q);
35                         if (high || highprv)
36                                 goto new_segment;
37                         if (cluster) {
38                                 if (seg_size + bv->bv_len
39                                     > queue_max_segment_size(q))
40                                         goto new_segment;
41                                 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
42                                         goto new_segment;
43                                 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
44                                         goto new_segment;
45
46                                 seg_size += bv->bv_len;
47                                 bvprv = bv;
48                                 continue;
49                         }
50 new_segment:
51                         if (nr_phys_segs == 1 && seg_size >
52                             fbio->bi_seg_front_size)
53                                 fbio->bi_seg_front_size = seg_size;
54
55                         nr_phys_segs++;
56                         bvprv = bv;
57                         seg_size = bv->bv_len;
58                         highprv = high;
59                 }
60                 bbio = bio;
61         }
62
63         if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
64                 fbio->bi_seg_front_size = seg_size;
65         if (seg_size > bbio->bi_seg_back_size)
66                 bbio->bi_seg_back_size = seg_size;
67
68         return nr_phys_segs;
69 }
70
71 void blk_recalc_rq_segments(struct request *rq)
72 {
73         rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
74 }
75
76 void blk_recount_segments(struct request_queue *q, struct bio *bio)
77 {
78         struct bio *nxt = bio->bi_next;
79
80         bio->bi_next = NULL;
81         bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
82         bio->bi_next = nxt;
83         bio->bi_flags |= (1 << BIO_SEG_VALID);
84 }
85 EXPORT_SYMBOL(blk_recount_segments);
86
87 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
88                                    struct bio *nxt)
89 {
90         if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
91                 return 0;
92
93         if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
94             queue_max_segment_size(q))
95                 return 0;
96
97         if (!bio_has_data(bio))
98                 return 1;
99
100         if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
101                 return 0;
102
103         /*
104          * bio and nxt are contiguous in memory; check if the queue allows
105          * these two to be merged into one
106          */
107         if (BIO_SEG_BOUNDARY(q, bio, nxt))
108                 return 1;
109
110         return 0;
111 }
112
113 /*
114  * map a request to scatterlist, return number of sg entries setup. Caller
115  * must make sure sg can hold rq->nr_phys_segments entries
116  */
117 int blk_rq_map_sg(struct request_queue *q, struct request *rq,
118                   struct scatterlist *sglist)
119 {
120         struct bio_vec *bvec, *bvprv;
121         struct req_iterator iter;
122         struct scatterlist *sg;
123         int nsegs, cluster;
124
125         nsegs = 0;
126         cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
127
128         /*
129          * for each bio in rq
130          */
131         bvprv = NULL;
132         sg = NULL;
133         rq_for_each_segment(bvec, rq, iter) {
134                 int nbytes = bvec->bv_len;
135
136                 if (bvprv && cluster) {
137                         if (sg->length + nbytes > queue_max_segment_size(q))
138                                 goto new_segment;
139
140                         if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
141                                 goto new_segment;
142                         if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
143                                 goto new_segment;
144
145                         sg->length += nbytes;
146                 } else {
147 new_segment:
148                         if (!sg)
149                                 sg = sglist;
150                         else {
151                                 /*
152                                  * If the driver previously mapped a shorter
153                                  * list, we could see a termination bit
154                                  * prematurely unless it fully inits the sg
155                                  * table on each mapping. We KNOW that there
156                                  * must be more entries here or the driver
157                                  * would be buggy, so force clear the
158                                  * termination bit to avoid doing a full
159                                  * sg_init_table() in drivers for each command.
160                                  */
161                                 sg->page_link &= ~0x02;
162                                 sg = sg_next(sg);
163                         }
164
165                         sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
166                         nsegs++;
167                 }
168                 bvprv = bvec;
169         } /* segments in rq */
170
171
172         if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
173             (blk_rq_bytes(rq) & q->dma_pad_mask)) {
174                 unsigned int pad_len =
175                         (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;
176
177                 sg->length += pad_len;
178                 rq->extra_len += pad_len;
179         }
180
181         if (q->dma_drain_size && q->dma_drain_needed(rq)) {
182                 if (rq->cmd_flags & REQ_WRITE)
183                         memset(q->dma_drain_buffer, 0, q->dma_drain_size);
184
185                 sg->page_link &= ~0x02;
186                 sg = sg_next(sg);
187                 sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
188                             q->dma_drain_size,
189                             ((unsigned long)q->dma_drain_buffer) &
190                             (PAGE_SIZE - 1));
191                 nsegs++;
192                 rq->extra_len += q->dma_drain_size;
193         }
194
195         if (sg)
196                 sg_mark_end(sg);
197
198         return nsegs;
199 }
200 EXPORT_SYMBOL(blk_rq_map_sg);
201
202 static inline int ll_new_hw_segment(struct request_queue *q,
203                                     struct request *req,
204                                     struct bio *bio)
205 {
206         int nr_phys_segs = bio_phys_segments(q, bio);
207
208         if (req->nr_phys_segments + nr_phys_segs > queue_max_segments(q)) {
209                 req->cmd_flags |= REQ_NOMERGE;
210                 if (req == q->last_merge)
211                         q->last_merge = NULL;
212                 return 0;
213         }
214
215         /*
216          * This will form the start of a new hw segment.  Bump both
217          * counters.
218          */
219         req->nr_phys_segments += nr_phys_segs;
220         return 1;
221 }
222
223 int ll_back_merge_fn(struct request_queue *q, struct request *req,
224                      struct bio *bio)
225 {
226         unsigned short max_sectors;
227
228         if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
229                 max_sectors = queue_max_hw_sectors(q);
230         else
231                 max_sectors = queue_max_sectors(q);
232
233         if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
234                 req->cmd_flags |= REQ_NOMERGE;
235                 if (req == q->last_merge)
236                         q->last_merge = NULL;
237                 return 0;
238         }
239         if (!bio_flagged(req->biotail, BIO_SEG_VALID))
240                 blk_recount_segments(q, req->biotail);
241         if (!bio_flagged(bio, BIO_SEG_VALID))
242                 blk_recount_segments(q, bio);
243
244         return ll_new_hw_segment(q, req, bio);
245 }
246
247 int ll_front_merge_fn(struct request_queue *q, struct request *req,
248                       struct bio *bio)
249 {
250         unsigned short max_sectors;
251
252         if (unlikely(req->cmd_type == REQ_TYPE_BLOCK_PC))
253                 max_sectors = queue_max_hw_sectors(q);
254         else
255                 max_sectors = queue_max_sectors(q);
256
257
258         if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
259                 req->cmd_flags |= REQ_NOMERGE;
260                 if (req == q->last_merge)
261                         q->last_merge = NULL;
262                 return 0;
263         }
264         if (!bio_flagged(bio, BIO_SEG_VALID))
265                 blk_recount_segments(q, bio);
266         if (!bio_flagged(req->bio, BIO_SEG_VALID))
267                 blk_recount_segments(q, req->bio);
268
269         return ll_new_hw_segment(q, req, bio);
270 }
271
272 static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
273                                 struct request *next)
274 {
275         int total_phys_segments;
276         unsigned int seg_size =
277                 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;
278
279         /*
280          * First check if the either of the requests are re-queued
281          * requests.  Can't merge them if they are.
282          */
283         if (req->special || next->special)
284                 return 0;
285
286         /*
287          * Will it become too large?
288          */
289         if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q))
290                 return 0;
291
292         total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
293         if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
294                 if (req->nr_phys_segments == 1)
295                         req->bio->bi_seg_front_size = seg_size;
296                 if (next->nr_phys_segments == 1)
297                         next->biotail->bi_seg_back_size = seg_size;
298                 total_phys_segments--;
299         }
300
301         if (total_phys_segments > queue_max_segments(q))
302                 return 0;
303
304         /* Merge is OK... */
305         req->nr_phys_segments = total_phys_segments;
306         return 1;
307 }
308
309 /**
310  * blk_rq_set_mixed_merge - mark a request as mixed merge
311  * @rq: request to mark as mixed merge
312  *
313  * Description:
314  *     @rq is about to be mixed merged.  Make sure the attributes
315  *     which can be mixed are set in each bio and mark @rq as mixed
316  *     merged.
317  */
318 void blk_rq_set_mixed_merge(struct request *rq)
319 {
320         unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
321         struct bio *bio;
322
323         if (rq->cmd_flags & REQ_MIXED_MERGE)
324                 return;
325
326         /*
327          * @rq will no longer represent mixable attributes for all the
328          * contained bios.  It will just track those of the first one.
329          * Distributes the attributs to each bio.
330          */
331         for (bio = rq->bio; bio; bio = bio->bi_next) {
332                 WARN_ON_ONCE((bio->bi_rw & REQ_FAILFAST_MASK) &&
333                              (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
334                 bio->bi_rw |= ff;
335         }
336         rq->cmd_flags |= REQ_MIXED_MERGE;
337 }
338
339 static void blk_account_io_merge(struct request *req)
340 {
341         if (blk_do_io_stat(req)) {
342                 struct hd_struct *part;
343                 int cpu;
344
345                 cpu = part_stat_lock();
346                 part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req));
347
348                 part_round_stats(cpu, part);
349                 part_dec_in_flight(part, rq_data_dir(req));
350
351                 part_stat_unlock();
352         }
353 }
354
355 /*
356  * Has to be called with the request spinlock acquired
357  */
358 static int attempt_merge(struct request_queue *q, struct request *req,
359                           struct request *next)
360 {
361         if (!rq_mergeable(req) || !rq_mergeable(next))
362                 return 0;
363
364         /*
365          * not contiguous
366          */
367         if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
368                 return 0;
369
370         if (rq_data_dir(req) != rq_data_dir(next)
371             || req->rq_disk != next->rq_disk
372             || next->special)
373                 return 0;
374
375         if (blk_integrity_rq(req) != blk_integrity_rq(next))
376                 return 0;
377
378         /*
379          * If we are allowed to merge, then append bio list
380          * from next to rq and release next. merge_requests_fn
381          * will have updated segment counts, update sector
382          * counts here.
383          */
384         if (!ll_merge_requests_fn(q, req, next))
385                 return 0;
386
387         /*
388          * If failfast settings disagree or any of the two is already
389          * a mixed merge, mark both as mixed before proceeding.  This
390          * makes sure that all involved bios have mixable attributes
391          * set properly.
392          */
393         if ((req->cmd_flags | next->cmd_flags) & REQ_MIXED_MERGE ||
394             (req->cmd_flags & REQ_FAILFAST_MASK) !=
395             (next->cmd_flags & REQ_FAILFAST_MASK)) {
396                 blk_rq_set_mixed_merge(req);
397                 blk_rq_set_mixed_merge(next);
398         }
399
400         /*
401          * At this point we have either done a back merge
402          * or front merge. We need the smaller start_time of
403          * the merged requests to be the current request
404          * for accounting purposes.
405          */
406         if (time_after(req->start_time, next->start_time))
407                 req->start_time = next->start_time;
408
409         req->biotail->bi_next = next->bio;
410         req->biotail = next->biotail;
411
412         req->__data_len += blk_rq_bytes(next);
413
414         elv_merge_requests(q, req, next);
415
416         /*
417          * 'next' is going away, so update stats accordingly
418          */
419         blk_account_io_merge(next);
420
421         req->ioprio = ioprio_best(req->ioprio, next->ioprio);
422         if (blk_rq_cpu_valid(next))
423                 req->cpu = next->cpu;
424
425         /* owner-ship of bio passed from next to req */
426         next->bio = NULL;
427         __blk_put_request(q, next);
428         return 1;
429 }
430
431 int attempt_back_merge(struct request_queue *q, struct request *rq)
432 {
433         struct request *next = elv_latter_request(q, rq);
434
435         if (next)
436                 return attempt_merge(q, rq, next);
437
438         return 0;
439 }
440
441 int attempt_front_merge(struct request_queue *q, struct request *rq)
442 {
443         struct request *prev = elv_former_request(q, rq);
444
445         if (prev)
446                 return attempt_merge(q, prev, rq);
447
448         return 0;
449 }