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 void blk_recalc_rq_sectors(struct request *rq, int nsect) 13 { 14 if (blk_fs_request(rq) || blk_discard_rq(rq)) { 15 rq->hard_sector += nsect; 16 rq->hard_nr_sectors -= nsect; 17 18 /* 19 * Move the I/O submission pointers ahead if required. 20 */ 21 if ((rq->nr_sectors >= rq->hard_nr_sectors) && 22 (rq->sector <= rq->hard_sector)) { 23 rq->sector = rq->hard_sector; 24 rq->nr_sectors = rq->hard_nr_sectors; 25 rq->hard_cur_sectors = bio_cur_sectors(rq->bio); 26 rq->current_nr_sectors = rq->hard_cur_sectors; 27 rq->buffer = bio_data(rq->bio); 28 } 29 30 /* 31 * if total number of sectors is less than the first segment 32 * size, something has gone terribly wrong 33 */ 34 if (rq->nr_sectors < rq->current_nr_sectors) { 35 printk(KERN_ERR "blk: request botched\n"); 36 rq->nr_sectors = rq->current_nr_sectors; 37 } 38 } 39 } 40 41 void blk_recalc_rq_segments(struct request *rq) 42 { 43 int nr_phys_segs; 44 unsigned int phys_size; 45 struct bio_vec *bv, *bvprv = NULL; 46 int seg_size; 47 int cluster; 48 struct req_iterator iter; 49 int high, highprv = 1; 50 struct request_queue *q = rq->q; 51 52 if (!rq->bio) 53 return; 54 55 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); 56 seg_size = 0; 57 phys_size = nr_phys_segs = 0; 58 rq_for_each_segment(bv, rq, iter) { 59 /* 60 * the trick here is making sure that a high page is never 61 * considered part of another segment, since that might 62 * change with the bounce page. 63 */ 64 high = page_to_pfn(bv->bv_page) > q->bounce_pfn; 65 if (high || highprv) 66 goto new_segment; 67 if (cluster) { 68 if (seg_size + bv->bv_len > q->max_segment_size) 69 goto new_segment; 70 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv)) 71 goto new_segment; 72 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv)) 73 goto new_segment; 74 75 seg_size += bv->bv_len; 76 bvprv = bv; 77 continue; 78 } 79 new_segment: 80 if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size) 81 rq->bio->bi_seg_front_size = seg_size; 82 83 nr_phys_segs++; 84 bvprv = bv; 85 seg_size = bv->bv_len; 86 highprv = high; 87 } 88 89 if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size) 90 rq->bio->bi_seg_front_size = seg_size; 91 if (seg_size > rq->biotail->bi_seg_back_size) 92 rq->biotail->bi_seg_back_size = seg_size; 93 94 rq->nr_phys_segments = nr_phys_segs; 95 } 96 97 void blk_recount_segments(struct request_queue *q, struct bio *bio) 98 { 99 struct request rq; 100 struct bio *nxt = bio->bi_next; 101 rq.q = q; 102 rq.bio = rq.biotail = bio; 103 bio->bi_next = NULL; 104 blk_recalc_rq_segments(&rq); 105 bio->bi_next = nxt; 106 bio->bi_phys_segments = rq.nr_phys_segments; 107 bio->bi_flags |= (1 << BIO_SEG_VALID); 108 } 109 EXPORT_SYMBOL(blk_recount_segments); 110 111 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio, 112 struct bio *nxt) 113 { 114 if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags)) 115 return 0; 116 117 if (bio->bi_seg_back_size + nxt->bi_seg_front_size > 118 q->max_segment_size) 119 return 0; 120 121 if (!bio_has_data(bio)) 122 return 1; 123 124 if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt))) 125 return 0; 126 127 /* 128 * bio and nxt are contiguous in memory; check if the queue allows 129 * these two to be merged into one 130 */ 131 if (BIO_SEG_BOUNDARY(q, bio, nxt)) 132 return 1; 133 134 return 0; 135 } 136 137 /* 138 * map a request to scatterlist, return number of sg entries setup. Caller 139 * must make sure sg can hold rq->nr_phys_segments entries 140 */ 141 int blk_rq_map_sg(struct request_queue *q, struct request *rq, 142 struct scatterlist *sglist) 143 { 144 struct bio_vec *bvec, *bvprv; 145 struct req_iterator iter; 146 struct scatterlist *sg; 147 int nsegs, cluster; 148 149 nsegs = 0; 150 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); 151 152 /* 153 * for each bio in rq 154 */ 155 bvprv = NULL; 156 sg = NULL; 157 rq_for_each_segment(bvec, rq, iter) { 158 int nbytes = bvec->bv_len; 159 160 if (bvprv && cluster) { 161 if (sg->length + nbytes > q->max_segment_size) 162 goto new_segment; 163 164 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec)) 165 goto new_segment; 166 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec)) 167 goto new_segment; 168 169 sg->length += nbytes; 170 } else { 171 new_segment: 172 if (!sg) 173 sg = sglist; 174 else { 175 /* 176 * If the driver previously mapped a shorter 177 * list, we could see a termination bit 178 * prematurely unless it fully inits the sg 179 * table on each mapping. We KNOW that there 180 * must be more entries here or the driver 181 * would be buggy, so force clear the 182 * termination bit to avoid doing a full 183 * sg_init_table() in drivers for each command. 184 */ 185 sg->page_link &= ~0x02; 186 sg = sg_next(sg); 187 } 188 189 sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset); 190 nsegs++; 191 } 192 bvprv = bvec; 193 } /* segments in rq */ 194 195 196 if (unlikely(rq->cmd_flags & REQ_COPY_USER) && 197 (rq->data_len & q->dma_pad_mask)) { 198 unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1; 199 200 sg->length += pad_len; 201 rq->extra_len += pad_len; 202 } 203 204 if (q->dma_drain_size && q->dma_drain_needed(rq)) { 205 if (rq->cmd_flags & REQ_RW) 206 memset(q->dma_drain_buffer, 0, q->dma_drain_size); 207 208 sg->page_link &= ~0x02; 209 sg = sg_next(sg); 210 sg_set_page(sg, virt_to_page(q->dma_drain_buffer), 211 q->dma_drain_size, 212 ((unsigned long)q->dma_drain_buffer) & 213 (PAGE_SIZE - 1)); 214 nsegs++; 215 rq->extra_len += q->dma_drain_size; 216 } 217 218 if (sg) 219 sg_mark_end(sg); 220 221 return nsegs; 222 } 223 EXPORT_SYMBOL(blk_rq_map_sg); 224 225 static inline int ll_new_mergeable(struct request_queue *q, 226 struct request *req, 227 struct bio *bio) 228 { 229 int nr_phys_segs = bio_phys_segments(q, bio); 230 231 if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) { 232 req->cmd_flags |= REQ_NOMERGE; 233 if (req == q->last_merge) 234 q->last_merge = NULL; 235 return 0; 236 } 237 238 /* 239 * A hw segment is just getting larger, bump just the phys 240 * counter. 241 */ 242 req->nr_phys_segments += nr_phys_segs; 243 return 1; 244 } 245 246 static inline int ll_new_hw_segment(struct request_queue *q, 247 struct request *req, 248 struct bio *bio) 249 { 250 int nr_phys_segs = bio_phys_segments(q, bio); 251 252 if (req->nr_phys_segments + nr_phys_segs > q->max_hw_segments 253 || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) { 254 req->cmd_flags |= REQ_NOMERGE; 255 if (req == q->last_merge) 256 q->last_merge = NULL; 257 return 0; 258 } 259 260 /* 261 * This will form the start of a new hw segment. Bump both 262 * counters. 263 */ 264 req->nr_phys_segments += nr_phys_segs; 265 return 1; 266 } 267 268 int ll_back_merge_fn(struct request_queue *q, struct request *req, 269 struct bio *bio) 270 { 271 unsigned short max_sectors; 272 273 if (unlikely(blk_pc_request(req))) 274 max_sectors = q->max_hw_sectors; 275 else 276 max_sectors = q->max_sectors; 277 278 if (req->nr_sectors + bio_sectors(bio) > max_sectors) { 279 req->cmd_flags |= REQ_NOMERGE; 280 if (req == q->last_merge) 281 q->last_merge = NULL; 282 return 0; 283 } 284 if (!bio_flagged(req->biotail, BIO_SEG_VALID)) 285 blk_recount_segments(q, req->biotail); 286 if (!bio_flagged(bio, BIO_SEG_VALID)) 287 blk_recount_segments(q, bio); 288 289 return ll_new_hw_segment(q, req, bio); 290 } 291 292 int ll_front_merge_fn(struct request_queue *q, struct request *req, 293 struct bio *bio) 294 { 295 unsigned short max_sectors; 296 297 if (unlikely(blk_pc_request(req))) 298 max_sectors = q->max_hw_sectors; 299 else 300 max_sectors = q->max_sectors; 301 302 303 if (req->nr_sectors + bio_sectors(bio) > max_sectors) { 304 req->cmd_flags |= REQ_NOMERGE; 305 if (req == q->last_merge) 306 q->last_merge = NULL; 307 return 0; 308 } 309 if (!bio_flagged(bio, BIO_SEG_VALID)) 310 blk_recount_segments(q, bio); 311 if (!bio_flagged(req->bio, BIO_SEG_VALID)) 312 blk_recount_segments(q, req->bio); 313 314 return ll_new_hw_segment(q, req, bio); 315 } 316 317 static int ll_merge_requests_fn(struct request_queue *q, struct request *req, 318 struct request *next) 319 { 320 int total_phys_segments; 321 unsigned int seg_size = 322 req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size; 323 324 /* 325 * First check if the either of the requests are re-queued 326 * requests. Can't merge them if they are. 327 */ 328 if (req->special || next->special) 329 return 0; 330 331 /* 332 * Will it become too large? 333 */ 334 if ((req->nr_sectors + next->nr_sectors) > q->max_sectors) 335 return 0; 336 337 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; 338 if (blk_phys_contig_segment(q, req->biotail, next->bio)) { 339 if (req->nr_phys_segments == 1) 340 req->bio->bi_seg_front_size = seg_size; 341 if (next->nr_phys_segments == 1) 342 next->biotail->bi_seg_back_size = seg_size; 343 total_phys_segments--; 344 } 345 346 if (total_phys_segments > q->max_phys_segments) 347 return 0; 348 349 if (total_phys_segments > q->max_hw_segments) 350 return 0; 351 352 /* Merge is OK... */ 353 req->nr_phys_segments = total_phys_segments; 354 return 1; 355 } 356 357 /* 358 * Has to be called with the request spinlock acquired 359 */ 360 static int attempt_merge(struct request_queue *q, struct request *req, 361 struct request *next) 362 { 363 if (!rq_mergeable(req) || !rq_mergeable(next)) 364 return 0; 365 366 /* 367 * not contiguous 368 */ 369 if (req->sector + req->nr_sectors != next->sector) 370 return 0; 371 372 if (rq_data_dir(req) != rq_data_dir(next) 373 || req->rq_disk != next->rq_disk 374 || next->special) 375 return 0; 376 377 if (blk_integrity_rq(req) != blk_integrity_rq(next)) 378 return 0; 379 380 /* 381 * If we are allowed to merge, then append bio list 382 * from next to rq and release next. merge_requests_fn 383 * will have updated segment counts, update sector 384 * counts here. 385 */ 386 if (!ll_merge_requests_fn(q, req, next)) 387 return 0; 388 389 /* 390 * At this point we have either done a back merge 391 * or front merge. We need the smaller start_time of 392 * the merged requests to be the current request 393 * for accounting purposes. 394 */ 395 if (time_after(req->start_time, next->start_time)) 396 req->start_time = next->start_time; 397 398 req->biotail->bi_next = next->bio; 399 req->biotail = next->biotail; 400 401 req->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors; 402 403 elv_merge_requests(q, req, next); 404 405 if (req->rq_disk) { 406 struct hd_struct *part; 407 int cpu; 408 409 cpu = part_stat_lock(); 410 part = disk_map_sector_rcu(req->rq_disk, req->sector); 411 412 part_round_stats(cpu, part); 413 part_dec_in_flight(part); 414 415 part_stat_unlock(); 416 } 417 418 req->ioprio = ioprio_best(req->ioprio, next->ioprio); 419 if (blk_rq_cpu_valid(next)) 420 req->cpu = next->cpu; 421 422 __blk_put_request(q, next); 423 return 1; 424 } 425 426 int attempt_back_merge(struct request_queue *q, struct request *rq) 427 { 428 struct request *next = elv_latter_request(q, rq); 429 430 if (next) 431 return attempt_merge(q, rq, next); 432 433 return 0; 434 } 435 436 int attempt_front_merge(struct request_queue *q, struct request *rq) 437 { 438 struct request *prev = elv_former_request(q, rq); 439 440 if (prev) 441 return attempt_merge(q, prev, rq); 442 443 return 0; 444 } 445