linux/lib/scatterlist.c
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   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 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 * @free_fn:    Free function
 169 *
 170 *  Description:
 171 *    Free an sg table previously allocated and setup with
 172 *    __sg_alloc_table().  The @max_ents value must be identical to
 173 *    that previously used with __sg_alloc_table().
 174 *
 175 **/
 176void __sg_free_table(struct sg_table *table, unsigned int max_ents,
 177                     sg_free_fn *free_fn)
 178{
 179        struct scatterlist *sgl, *next;
 180
 181        if (unlikely(!table->sgl))
 182                return;
 183
 184        sgl = table->sgl;
 185        while (table->orig_nents) {
 186                unsigned int alloc_size = table->orig_nents;
 187                unsigned int sg_size;
 188
 189                /*
 190                 * If we have more than max_ents segments left,
 191                 * then assign 'next' to the sg table after the current one.
 192                 * sg_size is then one less than alloc size, since the last
 193                 * element is the chain pointer.
 194                 */
 195                if (alloc_size > max_ents) {
 196                        next = sg_chain_ptr(&sgl[max_ents - 1]);
 197                        alloc_size = max_ents;
 198                        sg_size = alloc_size - 1;
 199                } else {
 200                        sg_size = alloc_size;
 201                        next = NULL;
 202                }
 203
 204                table->orig_nents -= sg_size;
 205                free_fn(sgl, alloc_size);
 206                sgl = next;
 207        }
 208
 209        table->sgl = NULL;
 210}
 211EXPORT_SYMBOL(__sg_free_table);
 212
 213/**
 214 * sg_free_table - Free a previously allocated sg table
 215 * @table:      The mapped sg table header
 216 *
 217 **/
 218void sg_free_table(struct sg_table *table)
 219{
 220        __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
 221}
 222EXPORT_SYMBOL(sg_free_table);
 223
 224/**
 225 * __sg_alloc_table - Allocate and initialize an sg table with given allocator
 226 * @table:      The sg table header to use
 227 * @nents:      Number of entries in sg list
 228 * @max_ents:   The maximum number of entries the allocator returns per call
 229 * @gfp_mask:   GFP allocation mask
 230 * @alloc_fn:   Allocator to use
 231 *
 232 * Description:
 233 *   This function returns a @table @nents long. The allocator is
 234 *   defined to return scatterlist chunks of maximum size @max_ents.
 235 *   Thus if @nents is bigger than @max_ents, the scatterlists will be
 236 *   chained in units of @max_ents.
 237 *
 238 * Notes:
 239 *   If this function returns non-0 (eg failure), the caller must call
 240 *   __sg_free_table() to cleanup any leftover allocations.
 241 *
 242 **/
 243int __sg_alloc_table(struct sg_table *table, unsigned int nents,
 244                     unsigned int max_ents, gfp_t gfp_mask,
 245                     sg_alloc_fn *alloc_fn)
 246{
 247        struct scatterlist *sg, *prv;
 248        unsigned int left;
 249
 250        memset(table, 0, sizeof(*table));
 251
 252        if (nents == 0)
 253                return -EINVAL;
 254#ifndef ARCH_HAS_SG_CHAIN
 255        if (WARN_ON_ONCE(nents > max_ents))
 256                return -EINVAL;
 257#endif
 258
 259        left = nents;
 260        prv = NULL;
 261        do {
 262                unsigned int sg_size, alloc_size = left;
 263
 264                if (alloc_size > max_ents) {
 265                        alloc_size = max_ents;
 266                        sg_size = alloc_size - 1;
 267                } else
 268                        sg_size = alloc_size;
 269
 270                left -= sg_size;
 271
 272                sg = alloc_fn(alloc_size, gfp_mask);
 273                if (unlikely(!sg)) {
 274                        /*
 275                         * Adjust entry count to reflect that the last
 276                         * entry of the previous table won't be used for
 277                         * linkage.  Without this, sg_kfree() may get
 278                         * confused.
 279                         */
 280                        if (prv)
 281                                table->nents = ++table->orig_nents;
 282
 283                        return -ENOMEM;
 284                }
 285
 286                sg_init_table(sg, alloc_size);
 287                table->nents = table->orig_nents += sg_size;
 288
 289                /*
 290                 * If this is the first mapping, assign the sg table header.
 291                 * If this is not the first mapping, chain previous part.
 292                 */
 293                if (prv)
 294                        sg_chain(prv, max_ents, sg);
 295                else
 296                        table->sgl = sg;
 297
 298                /*
 299                 * If no more entries after this one, mark the end
 300                 */
 301                if (!left)
 302                        sg_mark_end(&sg[sg_size - 1]);
 303
 304                prv = sg;
 305        } while (left);
 306
 307        return 0;
 308}
 309EXPORT_SYMBOL(__sg_alloc_table);
 310
 311/**
 312 * sg_alloc_table - Allocate and initialize an sg table
 313 * @table:      The sg table header to use
 314 * @nents:      Number of entries in sg list
 315 * @gfp_mask:   GFP allocation mask
 316 *
 317 *  Description:
 318 *    Allocate and initialize an sg table. If @nents@ is larger than
 319 *    SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
 320 *
 321 **/
 322int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
 323{
 324        int ret;
 325
 326        ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
 327                               gfp_mask, sg_kmalloc);
 328        if (unlikely(ret))
 329                __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
 330
 331        return ret;
 332}
 333EXPORT_SYMBOL(sg_alloc_table);
 334
 335/**
 336 * sg_alloc_table_from_pages - Allocate and initialize an sg table from
 337 *                             an array of pages
 338 * @sgt:        The sg table header to use
 339 * @pages:      Pointer to an array of page pointers
 340 * @n_pages:    Number of pages in the pages array
 341 * @offset:     Offset from start of the first page to the start of a buffer
 342 * @size:       Number of valid bytes in the buffer (after offset)
 343 * @gfp_mask:   GFP allocation mask
 344 *
 345 *  Description:
 346 *    Allocate and initialize an sg table from a list of pages. Contiguous
 347 *    ranges of the pages are squashed into a single scatterlist node. A user
 348 *    may provide an offset at a start and a size of valid data in a buffer
 349 *    specified by the page array. The returned sg table is released by
 350 *    sg_free_table.
 351 *
 352 * Returns:
 353 *   0 on success, negative error on failure
 354 */
 355int sg_alloc_table_from_pages(struct sg_table *sgt,
 356        struct page **pages, unsigned int n_pages,
 357        unsigned long offset, unsigned long size,
 358        gfp_t gfp_mask)
 359{
 360        unsigned int chunks;
 361        unsigned int i;
 362        unsigned int cur_page;
 363        int ret;
 364        struct scatterlist *s;
 365
 366        /* compute number of contiguous chunks */
 367        chunks = 1;
 368        for (i = 1; i < n_pages; ++i)
 369                if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
 370                        ++chunks;
 371
 372        ret = sg_alloc_table(sgt, chunks, gfp_mask);
 373        if (unlikely(ret))
 374                return ret;
 375
 376        /* merging chunks and putting them into the scatterlist */
 377        cur_page = 0;
 378        for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
 379                unsigned long chunk_size;
 380                unsigned int j;
 381
 382                /* look for the end of the current chunk */
 383                for (j = cur_page + 1; j < n_pages; ++j)
 384                        if (page_to_pfn(pages[j]) !=
 385                            page_to_pfn(pages[j - 1]) + 1)
 386                                break;
 387
 388                chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
 389                sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
 390                size -= chunk_size;
 391                offset = 0;
 392                cur_page = j;
 393        }
 394
 395        return 0;
 396}
 397EXPORT_SYMBOL(sg_alloc_table_from_pages);
 398
 399void __sg_page_iter_start(struct sg_page_iter *piter,
 400                          struct scatterlist *sglist, unsigned int nents,
 401                          unsigned long pgoffset)
 402{
 403        piter->__pg_advance = 0;
 404        piter->__nents = nents;
 405
 406        piter->sg = sglist;
 407        piter->sg_pgoffset = pgoffset;
 408}
 409EXPORT_SYMBOL(__sg_page_iter_start);
 410
 411static int sg_page_count(struct scatterlist *sg)
 412{
 413        return PAGE_ALIGN(sg->offset + sg->length) >> PAGE_SHIFT;
 414}
 415
 416bool __sg_page_iter_next(struct sg_page_iter *piter)
 417{
 418        if (!piter->__nents || !piter->sg)
 419                return false;
 420
 421        piter->sg_pgoffset += piter->__pg_advance;
 422        piter->__pg_advance = 1;
 423
 424        while (piter->sg_pgoffset >= sg_page_count(piter->sg)) {
 425                piter->sg_pgoffset -= sg_page_count(piter->sg);
 426                piter->sg = sg_next(piter->sg);
 427                if (!--piter->__nents || !piter->sg)
 428                        return false;
 429        }
 430
 431        return true;
 432}
 433EXPORT_SYMBOL(__sg_page_iter_next);
 434
 435/**
 436 * sg_miter_start - start mapping iteration over a sg list
 437 * @miter: sg mapping iter to be started
 438 * @sgl: sg list to iterate over
 439 * @nents: number of sg entries
 440 *
 441 * Description:
 442 *   Starts mapping iterator @miter.
 443 *
 444 * Context:
 445 *   Don't care.
 446 */
 447void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
 448                    unsigned int nents, unsigned int flags)
 449{
 450        memset(miter, 0, sizeof(struct sg_mapping_iter));
 451
 452        __sg_page_iter_start(&miter->piter, sgl, nents, 0);
 453        WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
 454        miter->__flags = flags;
 455}
 456EXPORT_SYMBOL(sg_miter_start);
 457
 458static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
 459{
 460        if (!miter->__remaining) {
 461                struct scatterlist *sg;
 462                unsigned long pgoffset;
 463
 464                if (!__sg_page_iter_next(&miter->piter))
 465                        return false;
 466
 467                sg = miter->piter.sg;
 468                pgoffset = miter->piter.sg_pgoffset;
 469
 470                miter->__offset = pgoffset ? 0 : sg->offset;
 471                miter->__remaining = sg->offset + sg->length -
 472                                (pgoffset << PAGE_SHIFT) - miter->__offset;
 473                miter->__remaining = min_t(unsigned long, miter->__remaining,
 474                                           PAGE_SIZE - miter->__offset);
 475        }
 476
 477        return true;
 478}
 479
 480/**
 481 * sg_miter_skip - reposition mapping iterator
 482 * @miter: sg mapping iter to be skipped
 483 * @offset: number of bytes to plus the current location
 484 *
 485 * Description:
 486 *   Sets the offset of @miter to its current location plus @offset bytes.
 487 *   If mapping iterator @miter has been proceeded by sg_miter_next(), this
 488 *   stops @miter.
 489 *
 490 * Context:
 491 *   Don't care if @miter is stopped, or not proceeded yet.
 492 *   Otherwise, preemption disabled if the SG_MITER_ATOMIC is set.
 493 *
 494 * Returns:
 495 *   true if @miter contains the valid mapping.  false if end of sg
 496 *   list is reached.
 497 */
 498static bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset)
 499{
 500        sg_miter_stop(miter);
 501
 502        while (offset) {
 503                off_t consumed;
 504
 505                if (!sg_miter_get_next_page(miter))
 506                        return false;
 507
 508                consumed = min_t(off_t, offset, miter->__remaining);
 509                miter->__offset += consumed;
 510                miter->__remaining -= consumed;
 511                offset -= consumed;
 512        }
 513
 514        return true;
 515}
 516
 517/**
 518 * sg_miter_next - proceed mapping iterator to the next mapping
 519 * @miter: sg mapping iter to proceed
 520 *
 521 * Description:
 522 *   Proceeds @miter to the next mapping.  @miter should have been started
 523 *   using sg_miter_start().  On successful return, @miter->page,
 524 *   @miter->addr and @miter->length point to the current mapping.
 525 *
 526 * Context:
 527 *   Preemption disabled if SG_MITER_ATOMIC.  Preemption must stay disabled
 528 *   till @miter is stopped.  May sleep if !SG_MITER_ATOMIC.
 529 *
 530 * Returns:
 531 *   true if @miter contains the next mapping.  false if end of sg
 532 *   list is reached.
 533 */
 534bool sg_miter_next(struct sg_mapping_iter *miter)
 535{
 536        sg_miter_stop(miter);
 537
 538        /*
 539         * Get to the next page if necessary.
 540         * __remaining, __offset is adjusted by sg_miter_stop
 541         */
 542        if (!sg_miter_get_next_page(miter))
 543                return false;
 544
 545        miter->page = sg_page_iter_page(&miter->piter);
 546        miter->consumed = miter->length = miter->__remaining;
 547
 548        if (miter->__flags & SG_MITER_ATOMIC)
 549                miter->addr = kmap_atomic(miter->page) + miter->__offset;
 550        else
 551                miter->addr = kmap(miter->page) + miter->__offset;
 552
 553        return true;
 554}
 555EXPORT_SYMBOL(sg_miter_next);
 556
 557/**
 558 * sg_miter_stop - stop mapping iteration
 559 * @miter: sg mapping iter to be stopped
 560 *
 561 * Description:
 562 *   Stops mapping iterator @miter.  @miter should have been started
 563 *   started using sg_miter_start().  A stopped iteration can be
 564 *   resumed by calling sg_miter_next() on it.  This is useful when
 565 *   resources (kmap) need to be released during iteration.
 566 *
 567 * Context:
 568 *   Preemption disabled if the SG_MITER_ATOMIC is set.  Don't care
 569 *   otherwise.
 570 */
 571void sg_miter_stop(struct sg_mapping_iter *miter)
 572{
 573        WARN_ON(miter->consumed > miter->length);
 574
 575        /* drop resources from the last iteration */
 576        if (miter->addr) {
 577                miter->__offset += miter->consumed;
 578                miter->__remaining -= miter->consumed;
 579
 580                if (miter->__flags & SG_MITER_TO_SG)
 581                        flush_kernel_dcache_page(miter->page);
 582
 583                if (miter->__flags & SG_MITER_ATOMIC) {
 584                        WARN_ON_ONCE(preemptible());
 585                        kunmap_atomic(miter->addr);
 586                } else
 587                        kunmap(miter->page);
 588
 589                miter->page = NULL;
 590                miter->addr = NULL;
 591                miter->length = 0;
 592                miter->consumed = 0;
 593        }
 594}
 595EXPORT_SYMBOL(sg_miter_stop);
 596
 597/**
 598 * sg_copy_buffer - Copy data between a linear buffer and an SG list
 599 * @sgl:                 The SG list
 600 * @nents:               Number of SG entries
 601 * @buf:                 Where to copy from
 602 * @buflen:              The number of bytes to copy
 603 * @skip:                Number of bytes to skip before copying
 604 * @to_buffer:           transfer direction (true == from an sg list to a
 605 *                       buffer, false == from a buffer to an sg list
 606 *
 607 * Returns the number of copied bytes.
 608 *
 609 **/
 610static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
 611                             void *buf, size_t buflen, off_t skip,
 612                             bool to_buffer)
 613{
 614        unsigned int offset = 0;
 615        struct sg_mapping_iter miter;
 616        unsigned long flags;
 617        unsigned int sg_flags = SG_MITER_ATOMIC;
 618
 619        if (to_buffer)
 620                sg_flags |= SG_MITER_FROM_SG;
 621        else
 622                sg_flags |= SG_MITER_TO_SG;
 623
 624        sg_miter_start(&miter, sgl, nents, sg_flags);
 625
 626        if (!sg_miter_skip(&miter, skip))
 627                return false;
 628
 629        local_irq_save(flags);
 630
 631        while (sg_miter_next(&miter) && offset < buflen) {
 632                unsigned int len;
 633
 634                len = min(miter.length, buflen - offset);
 635
 636                if (to_buffer)
 637                        memcpy(buf + offset, miter.addr, len);
 638                else
 639                        memcpy(miter.addr, buf + offset, len);
 640
 641                offset += len;
 642        }
 643
 644        sg_miter_stop(&miter);
 645
 646        local_irq_restore(flags);
 647        return offset;
 648}
 649
 650/**
 651 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
 652 * @sgl:                 The SG list
 653 * @nents:               Number of SG entries
 654 * @buf:                 Where to copy from
 655 * @buflen:              The number of bytes to copy
 656 *
 657 * Returns the number of copied bytes.
 658 *
 659 **/
 660size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 661                           void *buf, size_t buflen)
 662{
 663        return sg_copy_buffer(sgl, nents, buf, buflen, 0, false);
 664}
 665EXPORT_SYMBOL(sg_copy_from_buffer);
 666
 667/**
 668 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
 669 * @sgl:                 The SG list
 670 * @nents:               Number of SG entries
 671 * @buf:                 Where to copy to
 672 * @buflen:              The number of bytes to copy
 673 *
 674 * Returns the number of copied bytes.
 675 *
 676 **/
 677size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 678                         void *buf, size_t buflen)
 679{
 680        return sg_copy_buffer(sgl, nents, buf, buflen, 0, true);
 681}
 682EXPORT_SYMBOL(sg_copy_to_buffer);
 683
 684/**
 685 * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
 686 * @sgl:                 The SG list
 687 * @nents:               Number of SG entries
 688 * @buf:                 Where to copy from
 689 * @skip:                Number of bytes to skip before copying
 690 * @buflen:              The number of bytes to copy
 691 *
 692 * Returns the number of copied bytes.
 693 *
 694 **/
 695size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
 696                            void *buf, size_t buflen, off_t skip)
 697{
 698        return sg_copy_buffer(sgl, nents, buf, buflen, skip, false);
 699}
 700EXPORT_SYMBOL(sg_pcopy_from_buffer);
 701
 702/**
 703 * sg_pcopy_to_buffer - Copy from an SG list to a linear buffer
 704 * @sgl:                 The SG list
 705 * @nents:               Number of SG entries
 706 * @buf:                 Where to copy to
 707 * @skip:                Number of bytes to skip before copying
 708 * @buflen:              The number of bytes to copy
 709 *
 710 * Returns the number of copied bytes.
 711 *
 712 **/
 713size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
 714                          void *buf, size_t buflen, off_t skip)
 715{
 716        return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
 717}
 718EXPORT_SYMBOL(sg_pcopy_to_buffer);
 719
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