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