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