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 nr_phys_segs++; 81 bvprv = bv; 82 seg_size = bv->bv_len; 83 highprv = high; 84 } 85 86 rq->nr_phys_segments = nr_phys_segs; 87 } 88 89 void blk_recount_segments(struct request_queue *q, struct bio *bio) 90 { 91 struct request rq; 92 struct bio *nxt = bio->bi_next; 93 rq.q = q; 94 rq.bio = rq.biotail = bio; 95 bio->bi_next = NULL; 96 blk_recalc_rq_segments(&rq); 97 bio->bi_next = nxt; 98 bio->bi_phys_segments = rq.nr_phys_segments; 99 bio->bi_flags |= (1 << BIO_SEG_VALID); 100 } 101 EXPORT_SYMBOL(blk_recount_segments); 102 103 static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio, 104 struct bio *nxt) 105 { 106 if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags)) 107 return 0; 108 109 if (bio->bi_size + nxt->bi_size > q->max_segment_size) 110 return 0; 111 112 if (!bio_has_data(bio)) 113 return 1; 114 115 if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt))) 116 return 0; 117 118 /* 119 * bio and nxt are contiguous in memory; check if the queue allows 120 * these two to be merged into one 121 */ 122 if (BIO_SEG_BOUNDARY(q, bio, nxt)) 123 return 1; 124 125 return 0; 126 } 127 128 /* 129 * map a request to scatterlist, return number of sg entries setup. Caller 130 * must make sure sg can hold rq->nr_phys_segments entries 131 */ 132 int blk_rq_map_sg(struct request_queue *q, struct request *rq, 133 struct scatterlist *sglist) 134 { 135 struct bio_vec *bvec, *bvprv; 136 struct req_iterator iter; 137 struct scatterlist *sg; 138 int nsegs, cluster; 139 140 nsegs = 0; 141 cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags); 142 143 /* 144 * for each bio in rq 145 */ 146 bvprv = NULL; 147 sg = NULL; 148 rq_for_each_segment(bvec, rq, iter) { 149 int nbytes = bvec->bv_len; 150 151 if (bvprv && cluster) { 152 if (sg->length + nbytes > q->max_segment_size) 153 goto new_segment; 154 155 if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec)) 156 goto new_segment; 157 if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec)) 158 goto new_segment; 159 160 sg->length += nbytes; 161 } else { 162 new_segment: 163 if (!sg) 164 sg = sglist; 165 else { 166 /* 167 * If the driver previously mapped a shorter 168 * list, we could see a termination bit 169 * prematurely unless it fully inits the sg 170 * table on each mapping. We KNOW that there 171 * must be more entries here or the driver 172 * would be buggy, so force clear the 173 * termination bit to avoid doing a full 174 * sg_init_table() in drivers for each command. 175 */ 176 sg->page_link &= ~0x02; 177 sg = sg_next(sg); 178 } 179 180 sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset); 181 nsegs++; 182 } 183 bvprv = bvec; 184 } /* segments in rq */ 185 186 187 if (unlikely(rq->cmd_flags & REQ_COPY_USER) && 188 (rq->data_len & q->dma_pad_mask)) { 189 unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 1; 190 191 sg->length += pad_len; 192 rq->extra_len += pad_len; 193 } 194 195 if (q->dma_drain_size && q->dma_drain_needed(rq)) { 196 if (rq->cmd_flags & REQ_RW) 197 memset(q->dma_drain_buffer, 0, q->dma_drain_size); 198 199 sg->page_link &= ~0x02; 200 sg = sg_next(sg); 201 sg_set_page(sg, virt_to_page(q->dma_drain_buffer), 202 q->dma_drain_size, 203 ((unsigned long)q->dma_drain_buffer) & 204 (PAGE_SIZE - 1)); 205 nsegs++; 206 rq->extra_len += q->dma_drain_size; 207 } 208 209 if (sg) 210 sg_mark_end(sg); 211 212 return nsegs; 213 } 214 EXPORT_SYMBOL(blk_rq_map_sg); 215 216 static inline int ll_new_mergeable(struct request_queue *q, 217 struct request *req, 218 struct bio *bio) 219 { 220 int nr_phys_segs = bio_phys_segments(q, bio); 221 222 if (req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) { 223 req->cmd_flags |= REQ_NOMERGE; 224 if (req == q->last_merge) 225 q->last_merge = NULL; 226 return 0; 227 } 228 229 /* 230 * A hw segment is just getting larger, bump just the phys 231 * counter. 232 */ 233 req->nr_phys_segments += nr_phys_segs; 234 return 1; 235 } 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; 312 313 /* 314 * First check if the either of the requests are re-queued 315 * requests. Can't merge them if they are. 316 */ 317 if (req->special || next->special) 318 return 0; 319 320 /* 321 * Will it become too large? 322 */ 323 if ((req->nr_sectors + next->nr_sectors) > q->max_sectors) 324 return 0; 325 326 total_phys_segments = req->nr_phys_segments + next->nr_phys_segments; 327 if (blk_phys_contig_segment(q, req->biotail, next->bio)) 328 total_phys_segments--; 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); 403 404 __blk_put_request(q, next); 405 return 1; 406 } 407 408 int attempt_back_merge(struct request_queue *q, struct request *rq) 409 { 410 struct request *next = elv_latter_request(q, rq); 411 412 if (next) 413 return attempt_merge(q, rq, next); 414 415 return 0; 416 } 417 418 int attempt_front_merge(struct request_queue *q, struct request *rq) 419 { 420 struct request *prev = elv_former_request(q, rq); 421 422 if (prev) 423 return attempt_merge(q, prev, rq); 424 425 return 0; 426 } 427