1/* 2 * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com> 3 * 4 * Scatterlist handling helpers. 5 * 6 * This source code is licensed under the GNU General Public License, 7 * Version 2. See the file COPYING for more details. 8 */ 9#include <linux/export.h> 10#include <linux/slab.h> 11#include <linux/scatterlist.h> 12#include <linux/highmem.h> 13#include <linux/kmemleak.h> 14 15/** 16 * sg_next - return the next scatterlist entry in a list 17 * @sg: The current sg entry 18 * 19 * Description: 20 * Usually the next entry will be @sg@ + 1, but if this sg element is part 21 * of a chained scatterlist, it could jump to the start of a new 22 * scatterlist array. 23 * 24 **/ 25struct scatterlist *sg_next(struct scatterlist *sg) 26{ 27#ifdef CONFIG_DEBUG_SG 28 BUG_ON(sg->sg_magic != SG_MAGIC); 29#endif 30 if (sg_is_last(sg)) 31 return NULL; 32 33 sg++; 34 if (unlikely(sg_is_chain(sg))) 35 sg = sg_chain_ptr(sg); 36 37 return sg; 38} 39EXPORT_SYMBOL(sg_next); 40 41/** 42 * sg_nents - return total count of entries in scatterlist 43 * @sg: The scatterlist 44 * 45 * Description: 46 * Allows to know how many entries are in sg, taking into acount 47 * chaining as well 48 * 49 **/ 50int sg_nents(struct scatterlist *sg) 51{ 52 int nents; 53 for (nents = 0; sg; sg = sg_next(sg)) 54 nents++; 55 return nents; 56} 57EXPORT_SYMBOL(sg_nents); 58 59 60/** 61 * sg_last - return the last scatterlist entry in a list 62 * @sgl: First entry in the scatterlist 63 * @nents: Number of entries in the scatterlist 64 * 65 * Description: 66 * Should only be used casually, it (currently) scans the entire list 67 * to get the last entry. 68 * 69 * Note that the @sgl@ pointer passed in need not be the first one, 70 * the important bit is that @nents@ denotes the number of entries that 71 * exist from @sgl@. 72 * 73 **/ 74struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents) 75{ 76#ifndef CONFIG_ARCH_HAS_SG_CHAIN 77 struct scatterlist *ret = &sgl[nents - 1]; 78#else 79 struct scatterlist *sg, *ret = NULL; 80 unsigned int i; 81 82 for_each_sg(sgl, sg, nents, i) 83 ret = sg; 84 85#endif 86#ifdef CONFIG_DEBUG_SG 87 BUG_ON(sgl[0].sg_magic != SG_MAGIC); 88 BUG_ON(!sg_is_last(ret)); 89#endif 90 return ret; 91} 92EXPORT_SYMBOL(sg_last); 93 94/** 95 * sg_init_table - Initialize SG table 96 * @sgl: The SG table 97 * @nents: Number of entries in table 98 * 99 * Notes: 100 * If this is part of a chained sg table, sg_mark_end() should be 101 * used only on the last table part. 102 * 103 **/ 104void sg_init_table(struct scatterlist *sgl, unsigned int nents) 105{ 106 memset(sgl, 0, sizeof(*sgl) * nents); 107#ifdef CONFIG_DEBUG_SG 108 { 109 unsigned int i; 110 for (i = 0; i < nents; i++) 111 sgl[i].sg_magic = SG_MAGIC; 112 } 113#endif 114 sg_mark_end(&sgl[nents - 1]); 115} 116EXPORT_SYMBOL(sg_init_table); 117 118/** 119 * sg_init_one - Initialize a single entry sg list 120 * @sg: SG entry 121 * @buf: Virtual address for IO 122 * @buflen: IO length 123 * 124 **/ 125void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen) 126{ 127 sg_init_table(sg, 1); 128 sg_set_buf(sg, buf, buflen); 129} 130EXPORT_SYMBOL(sg_init_one); 131 132/* 133 * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree 134 * helpers. 135 */ 136static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask) 137{ 138 if (nents == SG_MAX_SINGLE_ALLOC) { 139 /* 140 * Kmemleak doesn't track page allocations as they are not 141 * commonly used (in a raw form) for kernel data structures. 142 * As we chain together a list of pages and then a normal 143 * kmalloc (tracked by kmemleak), in order to for that last 144 * allocation not to become decoupled (and thus a 145 * false-positive) we need to inform kmemleak of all the 146 * intermediate allocations. 147 */ 148 void *ptr = (void *) __get_free_page(gfp_mask); 149 kmemleak_alloc(ptr, PAGE_SIZE, 1, gfp_mask); 150 return ptr; 151 } else 152 return kmalloc(nents * sizeof(struct scatterlist), gfp_mask); 153} 154 155static void sg_kfree(struct scatterlist *sg, unsigned int nents) 156{ 157 if (nents == SG_MAX_SINGLE_ALLOC) { 158 kmemleak_free(sg); 159 free_page((unsigned long) sg); 160 } else 161 kfree(sg); 162} 163 164/** 165 * __sg_free_table - Free a previously mapped sg table 166 * @table: The sg table header to use 167 * @max_ents: The maximum number of entries per single scatterlist 168 * @skip_first_chunk: don't free the (preallocated) first scatterlist chunk 169 * @free_fn: Free function 170 * 171 * Description: 172 * Free an sg table previously allocated and setup with 173 * __sg_alloc_table(). The @max_ents value must be identical to 174 * that previously used with __sg_alloc_table(). 175 * 176 **/ 177void __sg_free_table(struct sg_table *table, unsigned int max_ents, 178 bool skip_first_chunk, sg_free_fn *free_fn) 179{ 180 struct scatterlist *sgl, *next; 181 182 if (unlikely(!table->sgl)) 183 return; 184 185 sgl = table->sgl; 186 while (table->orig_nents) { 187 unsigned int alloc_size = table->orig_nents; 188 unsigned int sg_size; 189 190 /* 191 * If we have more than max_ents segments left, 192 * then assign 'next' to the sg table after the current one. 193 * sg_size is then one less than alloc size, since the last 194 * element is the chain pointer. 195 */ 196 if (alloc_size > max_ents) { 197 next = sg_chain_ptr(&sgl[max_ents - 1]); 198 alloc_size = max_ents; 199 sg_size = alloc_size - 1; 200 } else { 201 sg_size = alloc_size; 202 next = NULL; 203 } 204 205 table->orig_nents -= sg_size; 206 if (skip_first_chunk) 207 skip_first_chunk = false; 208 else 209 free_fn(sgl, alloc_size); 210 sgl = next; 211 } 212 213 table->sgl = NULL; 214} 215EXPORT_SYMBOL(__sg_free_table); 216 217/** 218 * sg_free_table - Free a previously allocated sg table 219 * @table: The mapped sg table header 220 * 221 **/ 222void sg_free_table(struct sg_table *table) 223{ 224 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree); 225} 226EXPORT_SYMBOL(sg_free_table); 227 228/** 229 * __sg_alloc_table - Allocate and initialize an sg table with given allocator 230 * @table: The sg table header to use 231 * @nents: Number of entries in sg list 232 * @max_ents: The maximum number of entries the allocator returns per call 233 * @gfp_mask: GFP allocation mask 234 * @alloc_fn: Allocator to use 235 * 236 * Description: 237 * This function returns a @table @nents long. The allocator is 238 * defined to return scatterlist chunks of maximum size @max_ents. 239 * Thus if @nents is bigger than @max_ents, the scatterlists will be 240 * chained in units of @max_ents. 241 * 242 * Notes: 243 * If this function returns non-0 (eg failure), the caller must call 244 * __sg_free_table() to cleanup any leftover allocations. 245 * 246 **/ 247int __sg_alloc_table(struct sg_table *table, unsigned int nents, 248 unsigned int max_ents, struct scatterlist *first_chunk, 249 gfp_t gfp_mask, sg_alloc_fn *alloc_fn) 250{ 251 struct scatterlist *sg, *prv; 252 unsigned int left; 253 254 memset(table, 0, sizeof(*table)); 255 256 if (nents == 0) 257 return -EINVAL; 258#ifndef CONFIG_ARCH_HAS_SG_CHAIN 259 if (WARN_ON_ONCE(nents > max_ents)) 260 return -EINVAL; 261#endif 262 263 left = nents; 264 prv = NULL; 265 do { 266 unsigned int sg_size, alloc_size = left; 267 268 if (alloc_size > max_ents) { 269 alloc_size = max_ents; 270 sg_size = alloc_size - 1; 271 } else 272 sg_size = alloc_size; 273 274 left -= sg_size; 275 276 if (first_chunk) { 277 sg = first_chunk; 278 first_chunk = NULL; 279 } else { 280 sg = alloc_fn(alloc_size, gfp_mask); 281 } 282 if (unlikely(!sg)) { 283 /* 284 * Adjust entry count to reflect that the last 285 * entry of the previous table won't be used for 286 * linkage. Without this, sg_kfree() may get 287 * confused. 288 */ 289 if (prv) 290 table->nents = ++table->orig_nents; 291 292 return -ENOMEM; 293 } 294 295 sg_init_table(sg, alloc_size); 296 table->nents = table->orig_nents += sg_size; 297 298 /* 299 * If this is the first mapping, assign the sg table header. 300 * If this is not the first mapping, chain previous part. 301 */ 302 if (prv) 303 sg_chain(prv, max_ents, sg); 304 else 305 table->sgl = sg; 306 307 /* 308 * If no more entries after this one, mark the end 309 */ 310 if (!left) 311 sg_mark_end(&sg[sg_size - 1]); 312 313 prv = sg; 314 } while (left); 315 316 return 0; 317} 318EXPORT_SYMBOL(__sg_alloc_table); 319 320/** 321 * sg_alloc_table - Allocate and initialize an sg table 322 * @table: The sg table header to use 323 * @nents: Number of entries in sg list 324 * @gfp_mask: GFP allocation mask 325 * 326 * Description: 327 * Allocate and initialize an sg table. If @nents@ is larger than 328 * SG_MAX_SINGLE_ALLOC a chained sg table will be setup. 329 * 330 **/ 331int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask) 332{ 333 int ret; 334 335 ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC, 336 NULL, gfp_mask, sg_kmalloc); 337 if (unlikely(ret)) 338 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree); 339 340 return ret; 341} 342EXPORT_SYMBOL(sg_alloc_table); 343 344/** 345 * sg_alloc_table_from_pages - Allocate and initialize an sg table from 346 * an array of pages 347 * @sgt: The sg table header to use 348 * @pages: Pointer to an array of page pointers 349 * @n_pages: Number of pages in the pages array 350 * @offset: Offset from start of the first page to the start of a buffer 351 * @size: Number of valid bytes in the buffer (after offset) 352 * @gfp_mask: GFP allocation mask 353 * 354 * Description: 355 * Allocate and initialize an sg table from a list of pages. Contiguous 356 * ranges of the pages are squashed into a single scatterlist node. A user 357 * may provide an offset at a start and a size of valid data in a buffer 358 * specified by the page array. The returned sg table is released by 359 * sg_free_table. 360 * 361 * Returns: 362 * 0 on success, negative error on failure 363 */ 364int sg_alloc_table_from_pages(struct sg_table *sgt, 365 struct page **pages, unsigned int n_pages, 366 unsigned long offset, unsigned long size, 367 gfp_t gfp_mask) 368{ 369 unsigned int chunks; 370 unsigned int i; 371 unsigned int cur_page; 372 int ret; 373 struct scatterlist *s; 374 375 /* compute number of contiguous chunks */ 376 chunks = 1; 377 for (i = 1; i < n_pages; ++i) 378 if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) 379 ++chunks; 380 381 ret = sg_alloc_table(sgt, chunks, gfp_mask); 382 if (unlikely(ret)) 383 return ret; 384 385 /* merging chunks and putting them into the scatterlist */ 386 cur_page = 0; 387 for_each_sg(sgt->sgl, s, sgt->orig_nents, i) { 388 unsigned long chunk_size; 389 unsigned int j; 390 391 /* look for the end of the current chunk */ 392 for (j = cur_page + 1; j < n_pages; ++j) 393 if (page_to_pfn(pages[j]) != 394 page_to_pfn(pages[j - 1]) + 1) 395 break; 396 397 chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset; 398 sg_set_page(s, pages[cur_page], min(size, chunk_size), offset); 399 size -= chunk_size; 400 offset = 0; 401 cur_page = j; 402 } 403 404 return 0; 405} 406EXPORT_SYMBOL(sg_alloc_table_from_pages); 407 408void __sg_page_iter_start(struct sg_page_iter *piter, 409 struct scatterlist *sglist, unsigned int nents, 410 unsigned long pgoffset) 411{ 412 piter->__pg_advance = 0; 413 piter->__nents = nents; 414 415 piter->sg = sglist; 416 piter->sg_pgoffset = pgoffset; 417} 418EXPORT_SYMBOL(__sg_page_iter_start); 419 420static int sg_page_count(struct scatterlist *sg) 421{ 422 return PAGE_ALIGN(sg->offset + sg->length) >> PAGE_SHIFT; 423} 424 425bool __sg_page_iter_next(struct sg_page_iter *piter) 426{ 427 if (!piter->__nents || !piter->sg) 428 return false; 429 430 piter->sg_pgoffset += piter->__pg_advance; 431 piter->__pg_advance = 1; 432 433 while (piter->sg_pgoffset >= sg_page_count(piter->sg)) { 434 piter->sg_pgoffset -= sg_page_count(piter->sg); 435 piter->sg = sg_next(piter->sg); 436 if (!--piter->__nents || !piter->sg) 437 return false; 438 } 439 440 return true; 441} 442EXPORT_SYMBOL(__sg_page_iter_next); 443 444/** 445 * sg_miter_start - start mapping iteration over a sg list 446 * @miter: sg mapping iter to be started 447 * @sgl: sg list to iterate over 448 * @nents: number of sg entries 449 * 450 * Description: 451 * Starts mapping iterator @miter. 452 * 453 * Context: 454 * Don't care. 455 */ 456void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl, 457 unsigned int nents, unsigned int flags) 458{ 459 memset(miter, 0, sizeof(struct sg_mapping_iter)); 460 461 __sg_page_iter_start(&miter->piter, sgl, nents, 0); 462 WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG))); 463 miter->__flags = flags; 464} 465EXPORT_SYMBOL(sg_miter_start); 466 467static bool sg_miter_get_next_page(struct sg_mapping_iter *miter) 468{ 469 if (!miter->__remaining) { 470 struct scatterlist *sg; 471 unsigned long pgoffset; 472 473 if (!__sg_page_iter_next(&miter->piter)) 474 return false; 475 476 sg = miter->piter.sg; 477 pgoffset = miter->piter.sg_pgoffset; 478 479 miter->__offset = pgoffset ? 0 : sg->offset; 480 miter->__remaining = sg->offset + sg->length - 481 (pgoffset << PAGE_SHIFT) - miter->__offset; 482 miter->__remaining = min_t(unsigned long, miter->__remaining, 483 PAGE_SIZE - miter->__offset); 484 } 485 486 return true; 487} 488 489/** 490 * sg_miter_skip - reposition mapping iterator 491 * @miter: sg mapping iter to be skipped 492 * @offset: number of bytes to plus the current location 493 * 494 * Description: 495 * Sets the offset of @miter to its current location plus @offset bytes. 496 * If mapping iterator @miter has been proceeded by sg_miter_next(), this 497 * stops @miter. 498 * 499 * Context: 500 * Don't care if @miter is stopped, or not proceeded yet. 501 * Otherwise, preemption disabled if the SG_MITER_ATOMIC is set. 502 * 503 * Returns: 504 * true if @miter contains the valid mapping. false if end of sg 505 * list is reached. 506 */ 507bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset) 508{ 509 sg_miter_stop(miter); 510 511 while (offset) { 512 off_t consumed; 513 514 if (!sg_miter_get_next_page(miter)) 515 return false; 516 517 consumed = min_t(off_t, offset, miter->__remaining); 518 miter->__offset += consumed; 519 miter->__remaining -= consumed; 520 offset -= consumed; 521 } 522 523 return true; 524} 525EXPORT_SYMBOL(sg_miter_skip); 526 527/** 528 * sg_miter_next - proceed mapping iterator to the next mapping 529 * @miter: sg mapping iter to proceed 530 * 531 * Description: 532 * Proceeds @miter to the next mapping. @miter should have been started 533 * using sg_miter_start(). On successful return, @miter->page, 534 * @miter->addr and @miter->length point to the current mapping. 535 * 536 * Context: 537 * Preemption disabled if SG_MITER_ATOMIC. Preemption must stay disabled 538 * till @miter is stopped. May sleep if !SG_MITER_ATOMIC. 539 * 540 * Returns: 541 * true if @miter contains the next mapping. false if end of sg 542 * list is reached. 543 */ 544bool sg_miter_next(struct sg_mapping_iter *miter) 545{ 546 sg_miter_stop(miter); 547 548 /* 549 * Get to the next page if necessary. 550 * __remaining, __offset is adjusted by sg_miter_stop 551 */ 552 if (!sg_miter_get_next_page(miter)) 553 return false; 554 555 miter->page = sg_page_iter_page(&miter->piter); 556 miter->consumed = miter->length = miter->__remaining; 557 558 if (miter->__flags & SG_MITER_ATOMIC) 559 miter->addr = kmap_atomic(miter->page) + miter->__offset; 560 else 561 miter->addr = kmap(miter->page) + miter->__offset; 562 563 return true; 564} 565EXPORT_SYMBOL(sg_miter_next); 566 567/** 568 * sg_miter_stop - stop mapping iteration 569 * @miter: sg mapping iter to be stopped 570 * 571 * Description: 572 * Stops mapping iterator @miter. @miter should have been started 573 * started using sg_miter_start(). A stopped iteration can be 574 * resumed by calling sg_miter_next() on it. This is useful when 575 * resources (kmap) need to be released during iteration. 576 * 577 * Context: 578 * Preemption disabled if the SG_MITER_ATOMIC is set. Don't care 579 * otherwise. 580 */ 581void sg_miter_stop(struct sg_mapping_iter *miter) 582{ 583 WARN_ON(miter->consumed > miter->length); 584 585 /* drop resources from the last iteration */ 586 if (miter->addr) { 587 miter->__offset += miter->consumed; 588 miter->__remaining -= miter->consumed; 589 590 if ((miter->__flags & SG_MITER_TO_SG) && 591 !PageSlab(miter->page)) 592 flush_kernel_dcache_page(miter->page); 593 594 if (miter->__flags & SG_MITER_ATOMIC) { 595 WARN_ON_ONCE(preemptible()); 596 kunmap_atomic(miter->addr); 597 } else 598 kunmap(miter->page); 599 600 miter->page = NULL; 601 miter->addr = NULL; 602 miter->length = 0; 603 miter->consumed = 0; 604 } 605} 606EXPORT_SYMBOL(sg_miter_stop); 607 608/** 609 * sg_copy_buffer - Copy data between a linear buffer and an SG list 610 * @sgl: The SG list 611 * @nents: Number of SG entries 612 * @buf: Where to copy from 613 * @buflen: The number of bytes to copy 614 * @skip: Number of bytes to skip before copying 615 * @to_buffer: transfer direction (true == from an sg list to a 616 * buffer, false == from a buffer to an sg list 617 * 618 * Returns the number of copied bytes. 619 * 620 **/ 621static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, 622 void *buf, size_t buflen, off_t skip, 623 bool to_buffer) 624{ 625 unsigned int offset = 0; 626 struct sg_mapping_iter miter; 627 unsigned long flags; 628 unsigned int sg_flags = SG_MITER_ATOMIC; 629 630 if (to_buffer) 631 sg_flags |= SG_MITER_FROM_SG; 632 else 633 sg_flags |= SG_MITER_TO_SG; 634 635 sg_miter_start(&miter, sgl, nents, sg_flags); 636 637 if (!sg_miter_skip(&miter, skip)) 638 return false; 639 640 local_irq_save(flags); 641 642 while (sg_miter_next(&miter) && offset < buflen) { 643 unsigned int len; 644 645 len = min(miter.length, buflen - offset); 646 647 if (to_buffer) 648 memcpy(buf + offset, miter.addr, len); 649 else 650 memcpy(miter.addr, buf + offset, len); 651 652 offset += len; 653 } 654 655 sg_miter_stop(&miter); 656 657 local_irq_restore(flags); 658 return offset; 659} 660 661/** 662 * sg_copy_from_buffer - Copy from a linear buffer to an SG list 663 * @sgl: The SG list 664 * @nents: Number of SG entries 665 * @buf: Where to copy from 666 * @buflen: The number of bytes to copy 667 * 668 * Returns the number of copied bytes. 669 * 670 **/ 671size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents, 672 void *buf, size_t buflen) 673{ 674 return sg_copy_buffer(sgl, nents, buf, buflen, 0, false); 675} 676EXPORT_SYMBOL(sg_copy_from_buffer); 677 678/** 679 * sg_copy_to_buffer - Copy from an SG list to a linear buffer 680 * @sgl: The SG list 681 * @nents: Number of SG entries 682 * @buf: Where to copy to 683 * @buflen: The number of bytes to copy 684 * 685 * Returns the number of copied bytes. 686 * 687 **/ 688size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents, 689 void *buf, size_t buflen) 690{ 691 return sg_copy_buffer(sgl, nents, buf, buflen, 0, true); 692} 693EXPORT_SYMBOL(sg_copy_to_buffer); 694 695/** 696 * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list 697 * @sgl: The SG list 698 * @nents: Number of SG entries 699 * @buf: Where to copy from 700 * @skip: Number of bytes to skip before copying 701 * @buflen: The number of bytes to copy 702 * 703 * Returns the number of copied bytes. 704 * 705 **/ 706size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents, 707 void *buf, size_t buflen, off_t skip) 708{ 709 return sg_copy_buffer(sgl, nents, buf, buflen, skip, false); 710} 711EXPORT_SYMBOL(sg_pcopy_from_buffer); 712 713/** 714 * sg_pcopy_to_buffer - Copy from an SG list to a linear buffer 715 * @sgl: The SG list 716 * @nents: Number of SG entries 717 * @buf: Where to copy to 718 * @skip: Number of bytes to skip before copying 719 * @buflen: The number of bytes to copy 720 * 721 * Returns the number of copied bytes. 722 * 723 **/ 724size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents, 725 void *buf, size_t buflen, off_t skip) 726{ 727 return sg_copy_buffer(sgl, nents, buf, buflen, skip, true); 728} 729EXPORT_SYMBOL(sg_pcopy_to_buffer); 730