Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/lib/scatterlist.c

  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  **/
 25 struct 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 }
 39 EXPORT_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  **/
 50 int sg_nents(struct scatterlist *sg)
 51 {
 52         int nents;
 53         for (nents = 0; sg; sg = sg_next(sg))
 54                 nents++;
 55         return nents;
 56 }
 57 EXPORT_SYMBOL(sg_nents);
 58 
 59 /**
 60  * sg_nents_for_len - return total count of entries in scatterlist
 61  *                    needed to satisfy the supplied length
 62  * @sg:         The scatterlist
 63  * @len:        The total required length
 64  *
 65  * Description:
 66  * Determines the number of entries in sg that are required to meet
 67  * the supplied length, taking into acount chaining as well
 68  *
 69  * Returns:
 70  *   the number of sg entries needed, negative error on failure
 71  *
 72  **/
 73 int sg_nents_for_len(struct scatterlist *sg, u64 len)
 74 {
 75         int nents;
 76         u64 total;
 77 
 78         if (!len)
 79                 return 0;
 80 
 81         for (nents = 0, total = 0; sg; sg = sg_next(sg)) {
 82                 nents++;
 83                 total += sg->length;
 84                 if (total >= len)
 85                         return nents;
 86         }
 87 
 88         return -EINVAL;
 89 }
 90 EXPORT_SYMBOL(sg_nents_for_len);
 91 
 92 /**
 93  * sg_last - return the last scatterlist entry in a list
 94  * @sgl:        First entry in the scatterlist
 95  * @nents:      Number of entries in the scatterlist
 96  *
 97  * Description:
 98  *   Should only be used casually, it (currently) scans the entire list
 99  *   to get the last entry.
100  *
101  *   Note that the @sgl@ pointer passed in need not be the first one,
102  *   the important bit is that @nents@ denotes the number of entries that
103  *   exist from @sgl@.
104  *
105  **/
106 struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
107 {
108         struct scatterlist *sg, *ret = NULL;
109         unsigned int i;
110 
111         for_each_sg(sgl, sg, nents, i)
112                 ret = sg;
113 
114 #ifdef CONFIG_DEBUG_SG
115         BUG_ON(sgl[0].sg_magic != SG_MAGIC);
116         BUG_ON(!sg_is_last(ret));
117 #endif
118         return ret;
119 }
120 EXPORT_SYMBOL(sg_last);
121 
122 /**
123  * sg_init_table - Initialize SG table
124  * @sgl:           The SG table
125  * @nents:         Number of entries in table
126  *
127  * Notes:
128  *   If this is part of a chained sg table, sg_mark_end() should be
129  *   used only on the last table part.
130  *
131  **/
132 void sg_init_table(struct scatterlist *sgl, unsigned int nents)
133 {
134         memset(sgl, 0, sizeof(*sgl) * nents);
135 #ifdef CONFIG_DEBUG_SG
136         {
137                 unsigned int i;
138                 for (i = 0; i < nents; i++)
139                         sgl[i].sg_magic = SG_MAGIC;
140         }
141 #endif
142         sg_mark_end(&sgl[nents - 1]);
143 }
144 EXPORT_SYMBOL(sg_init_table);
145 
146 /**
147  * sg_init_one - Initialize a single entry sg list
148  * @sg:          SG entry
149  * @buf:         Virtual address for IO
150  * @buflen:      IO length
151  *
152  **/
153 void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
154 {
155         sg_init_table(sg, 1);
156         sg_set_buf(sg, buf, buflen);
157 }
158 EXPORT_SYMBOL(sg_init_one);
159 
160 /*
161  * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
162  * helpers.
163  */
164 static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
165 {
166         if (nents == SG_MAX_SINGLE_ALLOC) {
167                 /*
168                  * Kmemleak doesn't track page allocations as they are not
169                  * commonly used (in a raw form) for kernel data structures.
170                  * As we chain together a list of pages and then a normal
171                  * kmalloc (tracked by kmemleak), in order to for that last
172                  * allocation not to become decoupled (and thus a
173                  * false-positive) we need to inform kmemleak of all the
174                  * intermediate allocations.
175                  */
176                 void *ptr = (void *) __get_free_page(gfp_mask);
177                 kmemleak_alloc(ptr, PAGE_SIZE, 1, gfp_mask);
178                 return ptr;
179         } else
180                 return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
181 }
182 
183 static void sg_kfree(struct scatterlist *sg, unsigned int nents)
184 {
185         if (nents == SG_MAX_SINGLE_ALLOC) {
186                 kmemleak_free(sg);
187                 free_page((unsigned long) sg);
188         } else
189                 kfree(sg);
190 }
191 
192 /**
193  * __sg_free_table - Free a previously mapped sg table
194  * @table:      The sg table header to use
195  * @max_ents:   The maximum number of entries per single scatterlist
196  * @skip_first_chunk: don't free the (preallocated) first scatterlist chunk
197  * @free_fn:    Free function
198  *
199  *  Description:
200  *    Free an sg table previously allocated and setup with
201  *    __sg_alloc_table().  The @max_ents value must be identical to
202  *    that previously used with __sg_alloc_table().
203  *
204  **/
205 void __sg_free_table(struct sg_table *table, unsigned int max_ents,
206                      bool skip_first_chunk, sg_free_fn *free_fn)
207 {
208         struct scatterlist *sgl, *next;
209 
210         if (unlikely(!table->sgl))
211                 return;
212 
213         sgl = table->sgl;
214         while (table->orig_nents) {
215                 unsigned int alloc_size = table->orig_nents;
216                 unsigned int sg_size;
217 
218                 /*
219                  * If we have more than max_ents segments left,
220                  * then assign 'next' to the sg table after the current one.
221                  * sg_size is then one less than alloc size, since the last
222                  * element is the chain pointer.
223                  */
224                 if (alloc_size > max_ents) {
225                         next = sg_chain_ptr(&sgl[max_ents - 1]);
226                         alloc_size = max_ents;
227                         sg_size = alloc_size - 1;
228                 } else {
229                         sg_size = alloc_size;
230                         next = NULL;
231                 }
232 
233                 table->orig_nents -= sg_size;
234                 if (skip_first_chunk)
235                         skip_first_chunk = false;
236                 else
237                         free_fn(sgl, alloc_size);
238                 sgl = next;
239         }
240 
241         table->sgl = NULL;
242 }
243 EXPORT_SYMBOL(__sg_free_table);
244 
245 /**
246  * sg_free_table - Free a previously allocated sg table
247  * @table:      The mapped sg table header
248  *
249  **/
250 void sg_free_table(struct sg_table *table)
251 {
252         __sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
253 }
254 EXPORT_SYMBOL(sg_free_table);
255 
256 /**
257  * __sg_alloc_table - Allocate and initialize an sg table with given allocator
258  * @table:      The sg table header to use
259  * @nents:      Number of entries in sg list
260  * @max_ents:   The maximum number of entries the allocator returns per call
261  * @gfp_mask:   GFP allocation mask
262  * @alloc_fn:   Allocator to use
263  *
264  * Description:
265  *   This function returns a @table @nents long. The allocator is
266  *   defined to return scatterlist chunks of maximum size @max_ents.
267  *   Thus if @nents is bigger than @max_ents, the scatterlists will be
268  *   chained in units of @max_ents.
269  *
270  * Notes:
271  *   If this function returns non-0 (eg failure), the caller must call
272  *   __sg_free_table() to cleanup any leftover allocations.
273  *
274  **/
275 int __sg_alloc_table(struct sg_table *table, unsigned int nents,
276                      unsigned int max_ents, struct scatterlist *first_chunk,
277                      gfp_t gfp_mask, sg_alloc_fn *alloc_fn)
278 {
279         struct scatterlist *sg, *prv;
280         unsigned int left;
281 
282         memset(table, 0, sizeof(*table));
283 
284         if (nents == 0)
285                 return -EINVAL;
286 #ifndef CONFIG_ARCH_HAS_SG_CHAIN
287         if (WARN_ON_ONCE(nents > max_ents))
288                 return -EINVAL;
289 #endif
290 
291         left = nents;
292         prv = NULL;
293         do {
294                 unsigned int sg_size, alloc_size = left;
295 
296                 if (alloc_size > max_ents) {
297                         alloc_size = max_ents;
298                         sg_size = alloc_size - 1;
299                 } else
300                         sg_size = alloc_size;
301 
302                 left -= sg_size;
303 
304                 if (first_chunk) {
305                         sg = first_chunk;
306                         first_chunk = NULL;
307                 } else {
308                         sg = alloc_fn(alloc_size, gfp_mask);
309                 }
310                 if (unlikely(!sg)) {
311                         /*
312                          * Adjust entry count to reflect that the last
313                          * entry of the previous table won't be used for
314                          * linkage.  Without this, sg_kfree() may get
315                          * confused.
316                          */
317                         if (prv)
318                                 table->nents = ++table->orig_nents;
319 
320                         return -ENOMEM;
321                 }
322 
323                 sg_init_table(sg, alloc_size);
324                 table->nents = table->orig_nents += sg_size;
325 
326                 /*
327                  * If this is the first mapping, assign the sg table header.
328                  * If this is not the first mapping, chain previous part.
329                  */
330                 if (prv)
331                         sg_chain(prv, max_ents, sg);
332                 else
333                         table->sgl = sg;
334 
335                 /*
336                  * If no more entries after this one, mark the end
337                  */
338                 if (!left)
339                         sg_mark_end(&sg[sg_size - 1]);
340 
341                 prv = sg;
342         } while (left);
343 
344         return 0;
345 }
346 EXPORT_SYMBOL(__sg_alloc_table);
347 
348 /**
349  * sg_alloc_table - Allocate and initialize an sg table
350  * @table:      The sg table header to use
351  * @nents:      Number of entries in sg list
352  * @gfp_mask:   GFP allocation mask
353  *
354  *  Description:
355  *    Allocate and initialize an sg table. If @nents@ is larger than
356  *    SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
357  *
358  **/
359 int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
360 {
361         int ret;
362 
363         ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
364                                NULL, gfp_mask, sg_kmalloc);
365         if (unlikely(ret))
366                 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
367 
368         return ret;
369 }
370 EXPORT_SYMBOL(sg_alloc_table);
371 
372 /**
373  * sg_alloc_table_from_pages - Allocate and initialize an sg table from
374  *                             an array of pages
375  * @sgt:        The sg table header to use
376  * @pages:      Pointer to an array of page pointers
377  * @n_pages:    Number of pages in the pages array
378  * @offset:     Offset from start of the first page to the start of a buffer
379  * @size:       Number of valid bytes in the buffer (after offset)
380  * @gfp_mask:   GFP allocation mask
381  *
382  *  Description:
383  *    Allocate and initialize an sg table from a list of pages. Contiguous
384  *    ranges of the pages are squashed into a single scatterlist node. A user
385  *    may provide an offset at a start and a size of valid data in a buffer
386  *    specified by the page array. The returned sg table is released by
387  *    sg_free_table.
388  *
389  * Returns:
390  *   0 on success, negative error on failure
391  */
392 int sg_alloc_table_from_pages(struct sg_table *sgt,
393         struct page **pages, unsigned int n_pages,
394         unsigned long offset, unsigned long size,
395         gfp_t gfp_mask)
396 {
397         unsigned int chunks;
398         unsigned int i;
399         unsigned int cur_page;
400         int ret;
401         struct scatterlist *s;
402 
403         /* compute number of contiguous chunks */
404         chunks = 1;
405         for (i = 1; i < n_pages; ++i)
406                 if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
407                         ++chunks;
408 
409         ret = sg_alloc_table(sgt, chunks, gfp_mask);
410         if (unlikely(ret))
411                 return ret;
412 
413         /* merging chunks and putting them into the scatterlist */
414         cur_page = 0;
415         for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
416                 unsigned long chunk_size;
417                 unsigned int j;
418 
419                 /* look for the end of the current chunk */
420                 for (j = cur_page + 1; j < n_pages; ++j)
421                         if (page_to_pfn(pages[j]) !=
422                             page_to_pfn(pages[j - 1]) + 1)
423                                 break;
424 
425                 chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
426                 sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
427                 size -= chunk_size;
428                 offset = 0;
429                 cur_page = j;
430         }
431 
432         return 0;
433 }
434 EXPORT_SYMBOL(sg_alloc_table_from_pages);
435 
436 void __sg_page_iter_start(struct sg_page_iter *piter,
437                           struct scatterlist *sglist, unsigned int nents,
438                           unsigned long pgoffset)
439 {
440         piter->__pg_advance = 0;
441         piter->__nents = nents;
442 
443         piter->sg = sglist;
444         piter->sg_pgoffset = pgoffset;
445 }
446 EXPORT_SYMBOL(__sg_page_iter_start);
447 
448 static int sg_page_count(struct scatterlist *sg)
449 {
450         return PAGE_ALIGN(sg->offset + sg->length) >> PAGE_SHIFT;
451 }
452 
453 bool __sg_page_iter_next(struct sg_page_iter *piter)
454 {
455         if (!piter->__nents || !piter->sg)
456                 return false;
457 
458         piter->sg_pgoffset += piter->__pg_advance;
459         piter->__pg_advance = 1;
460 
461         while (piter->sg_pgoffset >= sg_page_count(piter->sg)) {
462                 piter->sg_pgoffset -= sg_page_count(piter->sg);
463                 piter->sg = sg_next(piter->sg);
464                 if (!--piter->__nents || !piter->sg)
465                         return false;
466         }
467 
468         return true;
469 }
470 EXPORT_SYMBOL(__sg_page_iter_next);
471 
472 /**
473  * sg_miter_start - start mapping iteration over a sg list
474  * @miter: sg mapping iter to be started
475  * @sgl: sg list to iterate over
476  * @nents: number of sg entries
477  *
478  * Description:
479  *   Starts mapping iterator @miter.
480  *
481  * Context:
482  *   Don't care.
483  */
484 void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
485                     unsigned int nents, unsigned int flags)
486 {
487         memset(miter, 0, sizeof(struct sg_mapping_iter));
488 
489         __sg_page_iter_start(&miter->piter, sgl, nents, 0);
490         WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
491         miter->__flags = flags;
492 }
493 EXPORT_SYMBOL(sg_miter_start);
494 
495 static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
496 {
497         if (!miter->__remaining) {
498                 struct scatterlist *sg;
499                 unsigned long pgoffset;
500 
501                 if (!__sg_page_iter_next(&miter->piter))
502                         return false;
503 
504                 sg = miter->piter.sg;
505                 pgoffset = miter->piter.sg_pgoffset;
506 
507                 miter->__offset = pgoffset ? 0 : sg->offset;
508                 miter->__remaining = sg->offset + sg->length -
509                                 (pgoffset << PAGE_SHIFT) - miter->__offset;
510                 miter->__remaining = min_t(unsigned long, miter->__remaining,
511                                            PAGE_SIZE - miter->__offset);
512         }
513 
514         return true;
515 }
516 
517 /**
518  * sg_miter_skip - reposition mapping iterator
519  * @miter: sg mapping iter to be skipped
520  * @offset: number of bytes to plus the current location
521  *
522  * Description:
523  *   Sets the offset of @miter to its current location plus @offset bytes.
524  *   If mapping iterator @miter has been proceeded by sg_miter_next(), this
525  *   stops @miter.
526  *
527  * Context:
528  *   Don't care if @miter is stopped, or not proceeded yet.
529  *   Otherwise, preemption disabled if the SG_MITER_ATOMIC is set.
530  *
531  * Returns:
532  *   true if @miter contains the valid mapping.  false if end of sg
533  *   list is reached.
534  */
535 bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset)
536 {
537         sg_miter_stop(miter);
538 
539         while (offset) {
540                 off_t consumed;
541 
542                 if (!sg_miter_get_next_page(miter))
543                         return false;
544 
545                 consumed = min_t(off_t, offset, miter->__remaining);
546                 miter->__offset += consumed;
547                 miter->__remaining -= consumed;
548                 offset -= consumed;
549         }
550 
551         return true;
552 }
553 EXPORT_SYMBOL(sg_miter_skip);
554 
555 /**
556  * sg_miter_next - proceed mapping iterator to the next mapping
557  * @miter: sg mapping iter to proceed
558  *
559  * Description:
560  *   Proceeds @miter to the next mapping.  @miter should have been started
561  *   using sg_miter_start().  On successful return, @miter->page,
562  *   @miter->addr and @miter->length point to the current mapping.
563  *
564  * Context:
565  *   Preemption disabled if SG_MITER_ATOMIC.  Preemption must stay disabled
566  *   till @miter is stopped.  May sleep if !SG_MITER_ATOMIC.
567  *
568  * Returns:
569  *   true if @miter contains the next mapping.  false if end of sg
570  *   list is reached.
571  */
572 bool sg_miter_next(struct sg_mapping_iter *miter)
573 {
574         sg_miter_stop(miter);
575 
576         /*
577          * Get to the next page if necessary.
578          * __remaining, __offset is adjusted by sg_miter_stop
579          */
580         if (!sg_miter_get_next_page(miter))
581                 return false;
582 
583         miter->page = sg_page_iter_page(&miter->piter);
584         miter->consumed = miter->length = miter->__remaining;
585 
586         if (miter->__flags & SG_MITER_ATOMIC)
587                 miter->addr = kmap_atomic(miter->page) + miter->__offset;
588         else
589                 miter->addr = kmap(miter->page) + miter->__offset;
590 
591         return true;
592 }
593 EXPORT_SYMBOL(sg_miter_next);
594 
595 /**
596  * sg_miter_stop - stop mapping iteration
597  * @miter: sg mapping iter to be stopped
598  *
599  * Description:
600  *   Stops mapping iterator @miter.  @miter should have been started
601  *   using sg_miter_start().  A stopped iteration can be resumed by
602  *   calling sg_miter_next() on it.  This is useful when resources (kmap)
603  *   need to be released during iteration.
604  *
605  * Context:
606  *   Preemption disabled if the SG_MITER_ATOMIC is set.  Don't care
607  *   otherwise.
608  */
609 void sg_miter_stop(struct sg_mapping_iter *miter)
610 {
611         WARN_ON(miter->consumed > miter->length);
612 
613         /* drop resources from the last iteration */
614         if (miter->addr) {
615                 miter->__offset += miter->consumed;
616                 miter->__remaining -= miter->consumed;
617 
618                 if ((miter->__flags & SG_MITER_TO_SG) &&
619                     !PageSlab(miter->page))
620                         flush_kernel_dcache_page(miter->page);
621 
622                 if (miter->__flags & SG_MITER_ATOMIC) {
623                         WARN_ON_ONCE(preemptible());
624                         kunmap_atomic(miter->addr);
625                 } else
626                         kunmap(miter->page);
627 
628                 miter->page = NULL;
629                 miter->addr = NULL;
630                 miter->length = 0;
631                 miter->consumed = 0;
632         }
633 }
634 EXPORT_SYMBOL(sg_miter_stop);
635 
636 /**
637  * sg_copy_buffer - Copy data between a linear buffer and an SG list
638  * @sgl:                 The SG list
639  * @nents:               Number of SG entries
640  * @buf:                 Where to copy from
641  * @buflen:              The number of bytes to copy
642  * @skip:                Number of bytes to skip before copying
643  * @to_buffer:           transfer direction (true == from an sg list to a
644  *                       buffer, false == from a buffer to an sg list
645  *
646  * Returns the number of copied bytes.
647  *
648  **/
649 size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf,
650                       size_t buflen, off_t skip, bool to_buffer)
651 {
652         unsigned int offset = 0;
653         struct sg_mapping_iter miter;
654         unsigned long flags;
655         unsigned int sg_flags = SG_MITER_ATOMIC;
656 
657         if (to_buffer)
658                 sg_flags |= SG_MITER_FROM_SG;
659         else
660                 sg_flags |= SG_MITER_TO_SG;
661 
662         sg_miter_start(&miter, sgl, nents, sg_flags);
663 
664         if (!sg_miter_skip(&miter, skip))
665                 return false;
666 
667         local_irq_save(flags);
668 
669         while (sg_miter_next(&miter) && offset < buflen) {
670                 unsigned int len;
671 
672                 len = min(miter.length, buflen - offset);
673 
674                 if (to_buffer)
675                         memcpy(buf + offset, miter.addr, len);
676                 else
677                         memcpy(miter.addr, buf + offset, len);
678 
679                 offset += len;
680         }
681 
682         sg_miter_stop(&miter);
683 
684         local_irq_restore(flags);
685         return offset;
686 }
687 EXPORT_SYMBOL(sg_copy_buffer);
688 
689 /**
690  * sg_copy_from_buffer - Copy from a linear buffer to an SG list
691  * @sgl:                 The SG list
692  * @nents:               Number of SG entries
693  * @buf:                 Where to copy from
694  * @buflen:              The number of bytes to copy
695  *
696  * Returns the number of copied bytes.
697  *
698  **/
699 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
700                            const void *buf, size_t buflen)
701 {
702         return sg_copy_buffer(sgl, nents, (void *)buf, buflen, 0, false);
703 }
704 EXPORT_SYMBOL(sg_copy_from_buffer);
705 
706 /**
707  * sg_copy_to_buffer - Copy from an SG list to a linear buffer
708  * @sgl:                 The SG list
709  * @nents:               Number of SG entries
710  * @buf:                 Where to copy to
711  * @buflen:              The number of bytes to copy
712  *
713  * Returns the number of copied bytes.
714  *
715  **/
716 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
717                          void *buf, size_t buflen)
718 {
719         return sg_copy_buffer(sgl, nents, buf, buflen, 0, true);
720 }
721 EXPORT_SYMBOL(sg_copy_to_buffer);
722 
723 /**
724  * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
725  * @sgl:                 The SG list
726  * @nents:               Number of SG entries
727  * @buf:                 Where to copy from
728  * @buflen:              The number of bytes to copy
729  * @skip:                Number of bytes to skip before copying
730  *
731  * Returns the number of copied bytes.
732  *
733  **/
734 size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
735                             const void *buf, size_t buflen, off_t skip)
736 {
737         return sg_copy_buffer(sgl, nents, (void *)buf, buflen, skip, false);
738 }
739 EXPORT_SYMBOL(sg_pcopy_from_buffer);
740 
741 /**
742  * sg_pcopy_to_buffer - Copy from an SG list to a linear buffer
743  * @sgl:                 The SG list
744  * @nents:               Number of SG entries
745  * @buf:                 Where to copy to
746  * @buflen:              The number of bytes to copy
747  * @skip:                Number of bytes to skip before copying
748  *
749  * Returns the number of copied bytes.
750  *
751  **/
752 size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
753                           void *buf, size_t buflen, off_t skip)
754 {
755         return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
756 }
757 EXPORT_SYMBOL(sg_pcopy_to_buffer);
758 

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