2 * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
4 * Scatterlist handling helpers.
6 * This source code is licensed under the GNU General Public License,
7 * Version 2. See the file COPYING for more details.
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>
16 * sg_next - return the next scatterlist entry in a list
17 * @sg: The current sg entry
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
25 struct scatterlist
*sg_next(struct scatterlist
*sg
)
27 #ifdef CONFIG_DEBUG_SG
28 BUG_ON(sg
->sg_magic
!= SG_MAGIC
);
34 if (unlikely(sg_is_chain(sg
)))
35 sg
= sg_chain_ptr(sg
);
39 EXPORT_SYMBOL(sg_next
);
42 * sg_nents - return total count of entries in scatterlist
43 * @sg: The scatterlist
46 * Allows to know how many entries are in sg, taking into acount
50 int sg_nents(struct scatterlist
*sg
)
53 for (nents
= 0; sg
; sg
= sg_next(sg
))
57 EXPORT_SYMBOL(sg_nents
);
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
66 * Determines the number of entries in sg that are required to meet
67 * the supplied length, taking into acount chaining as well
70 * the number of sg entries needed, negative error on failure
73 int sg_nents_for_len(struct scatterlist
*sg
, u64 len
)
81 for (nents
= 0, total
= 0; sg
; sg
= sg_next(sg
)) {
90 EXPORT_SYMBOL(sg_nents_for_len
);
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
98 * Should only be used casually, it (currently) scans the entire list
99 * to get the last entry.
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
106 struct scatterlist
*sg_last(struct scatterlist
*sgl
, unsigned int nents
)
108 struct scatterlist
*sg
, *ret
= NULL
;
111 for_each_sg(sgl
, sg
, nents
, i
)
114 #ifdef CONFIG_DEBUG_SG
115 BUG_ON(sgl
[0].sg_magic
!= SG_MAGIC
);
116 BUG_ON(!sg_is_last(ret
));
120 EXPORT_SYMBOL(sg_last
);
123 * sg_init_table - Initialize SG table
125 * @nents: Number of entries in table
128 * If this is part of a chained sg table, sg_mark_end() should be
129 * used only on the last table part.
132 void sg_init_table(struct scatterlist
*sgl
, unsigned int nents
)
134 memset(sgl
, 0, sizeof(*sgl
) * nents
);
135 #ifdef CONFIG_DEBUG_SG
138 for (i
= 0; i
< nents
; i
++)
139 sgl
[i
].sg_magic
= SG_MAGIC
;
142 sg_mark_end(&sgl
[nents
- 1]);
144 EXPORT_SYMBOL(sg_init_table
);
147 * sg_init_one - Initialize a single entry sg list
149 * @buf: Virtual address for IO
153 void sg_init_one(struct scatterlist
*sg
, const void *buf
, unsigned int buflen
)
155 sg_init_table(sg
, 1);
156 sg_set_buf(sg
, buf
, buflen
);
158 EXPORT_SYMBOL(sg_init_one
);
161 * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
164 static struct scatterlist
*sg_kmalloc(unsigned int nents
, gfp_t gfp_mask
)
166 if (nents
== SG_MAX_SINGLE_ALLOC
) {
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.
176 void *ptr
= (void *) __get_free_page(gfp_mask
);
177 kmemleak_alloc(ptr
, PAGE_SIZE
, 1, gfp_mask
);
180 return kmalloc(nents
* sizeof(struct scatterlist
), gfp_mask
);
183 static void sg_kfree(struct scatterlist
*sg
, unsigned int nents
)
185 if (nents
== SG_MAX_SINGLE_ALLOC
) {
187 free_page((unsigned long) sg
);
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
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().
205 void __sg_free_table(struct sg_table
*table
, unsigned int max_ents
,
206 bool skip_first_chunk
, sg_free_fn
*free_fn
)
208 struct scatterlist
*sgl
, *next
;
210 if (unlikely(!table
->sgl
))
214 while (table
->orig_nents
) {
215 unsigned int alloc_size
= table
->orig_nents
;
216 unsigned int sg_size
;
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.
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;
229 sg_size
= alloc_size
;
233 table
->orig_nents
-= sg_size
;
234 if (skip_first_chunk
)
235 skip_first_chunk
= false;
237 free_fn(sgl
, alloc_size
);
243 EXPORT_SYMBOL(__sg_free_table
);
246 * sg_free_table - Free a previously allocated sg table
247 * @table: The mapped sg table header
250 void sg_free_table(struct sg_table
*table
)
252 __sg_free_table(table
, SG_MAX_SINGLE_ALLOC
, false, sg_kfree
);
254 EXPORT_SYMBOL(sg_free_table
);
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
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.
271 * If this function returns non-0 (eg failure), the caller must call
272 * __sg_free_table() to cleanup any leftover allocations.
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
)
279 struct scatterlist
*sg
, *prv
;
282 memset(table
, 0, sizeof(*table
));
286 #ifndef CONFIG_ARCH_HAS_SG_CHAIN
287 if (WARN_ON_ONCE(nents
> max_ents
))
294 unsigned int sg_size
, alloc_size
= left
;
296 if (alloc_size
> max_ents
) {
297 alloc_size
= max_ents
;
298 sg_size
= alloc_size
- 1;
300 sg_size
= alloc_size
;
308 sg
= alloc_fn(alloc_size
, gfp_mask
);
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
318 table
->nents
= ++table
->orig_nents
;
323 sg_init_table(sg
, alloc_size
);
324 table
->nents
= table
->orig_nents
+= sg_size
;
327 * If this is the first mapping, assign the sg table header.
328 * If this is not the first mapping, chain previous part.
331 sg_chain(prv
, max_ents
, sg
);
336 * If no more entries after this one, mark the end
339 sg_mark_end(&sg
[sg_size
- 1]);
346 EXPORT_SYMBOL(__sg_alloc_table
);
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
355 * Allocate and initialize an sg table. If @nents@ is larger than
356 * SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
359 int sg_alloc_table(struct sg_table
*table
, unsigned int nents
, gfp_t gfp_mask
)
363 ret
= __sg_alloc_table(table
, nents
, SG_MAX_SINGLE_ALLOC
,
364 NULL
, gfp_mask
, sg_kmalloc
);
366 __sg_free_table(table
, SG_MAX_SINGLE_ALLOC
, false, sg_kfree
);
370 EXPORT_SYMBOL(sg_alloc_table
);
373 * __sg_alloc_table_from_pages - Allocate and initialize an sg table from
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 * @max_segment: Maximum size of a scatterlist node in bytes (page aligned)
381 * @gfp_mask: GFP allocation mask
384 * Allocate and initialize an sg table from a list of pages. Contiguous
385 * ranges of the pages are squashed into a single scatterlist node up to the
386 * maximum size specified in @max_segment. An user may provide an offset at a
387 * start and a size of valid data in a buffer specified by the page array.
388 * The returned sg table is released by sg_free_table.
391 * 0 on success, negative error on failure
393 int __sg_alloc_table_from_pages(struct sg_table
*sgt
, struct page
**pages
,
394 unsigned int n_pages
, unsigned int offset
,
395 unsigned long size
, unsigned int max_segment
,
398 unsigned int chunks
, cur_page
, seg_len
, i
;
400 struct scatterlist
*s
;
402 if (WARN_ON(!max_segment
|| offset_in_page(max_segment
)))
405 /* compute number of contiguous chunks */
408 for (i
= 1; i
< n_pages
; i
++) {
409 seg_len
+= PAGE_SIZE
;
410 if (seg_len
>= max_segment
||
411 page_to_pfn(pages
[i
]) != page_to_pfn(pages
[i
- 1]) + 1) {
417 ret
= sg_alloc_table(sgt
, chunks
, gfp_mask
);
421 /* merging chunks and putting them into the scatterlist */
423 for_each_sg(sgt
->sgl
, s
, sgt
->orig_nents
, i
) {
424 unsigned int j
, chunk_size
;
426 /* look for the end of the current chunk */
428 for (j
= cur_page
+ 1; j
< n_pages
; j
++) {
429 seg_len
+= PAGE_SIZE
;
430 if (seg_len
>= max_segment
||
431 page_to_pfn(pages
[j
]) !=
432 page_to_pfn(pages
[j
- 1]) + 1)
436 chunk_size
= ((j
- cur_page
) << PAGE_SHIFT
) - offset
;
437 sg_set_page(s
, pages
[cur_page
],
438 min_t(unsigned long, size
, chunk_size
), offset
);
446 EXPORT_SYMBOL(__sg_alloc_table_from_pages
);
449 * sg_alloc_table_from_pages - Allocate and initialize an sg table from
451 * @sgt: The sg table header to use
452 * @pages: Pointer to an array of page pointers
453 * @n_pages: Number of pages in the pages array
454 * @offset: Offset from start of the first page to the start of a buffer
455 * @size: Number of valid bytes in the buffer (after offset)
456 * @gfp_mask: GFP allocation mask
459 * Allocate and initialize an sg table from a list of pages. Contiguous
460 * ranges of the pages are squashed into a single scatterlist node. A user
461 * may provide an offset at a start and a size of valid data in a buffer
462 * specified by the page array. The returned sg table is released by
466 * 0 on success, negative error on failure
468 int sg_alloc_table_from_pages(struct sg_table
*sgt
, struct page
**pages
,
469 unsigned int n_pages
, unsigned int offset
,
470 unsigned long size
, gfp_t gfp_mask
)
472 return __sg_alloc_table_from_pages(sgt
, pages
, n_pages
, offset
, size
,
473 SCATTERLIST_MAX_SEGMENT
, gfp_mask
);
475 EXPORT_SYMBOL(sg_alloc_table_from_pages
);
477 #ifdef CONFIG_SGL_ALLOC
480 * sgl_alloc_order - allocate a scatterlist and its pages
481 * @length: Length in bytes of the scatterlist. Must be at least one
482 * @order: Second argument for alloc_pages()
483 * @chainable: Whether or not to allocate an extra element in the scatterlist
484 * for scatterlist chaining purposes
485 * @gfp: Memory allocation flags
486 * @nent_p: [out] Number of entries in the scatterlist that have pages
488 * Returns: A pointer to an initialized scatterlist or %NULL upon failure.
490 struct scatterlist
*sgl_alloc_order(unsigned long long length
,
491 unsigned int order
, bool chainable
,
492 gfp_t gfp
, unsigned int *nent_p
)
494 struct scatterlist
*sgl
, *sg
;
496 unsigned int nent
, nalloc
;
499 nent
= round_up(length
, PAGE_SIZE
<< order
) >> (PAGE_SHIFT
+ order
);
500 /* Check for integer overflow */
501 if (length
> (nent
<< (PAGE_SHIFT
+ order
)))
505 /* Check for integer overflow */
506 if (nalloc
+ 1 < nalloc
)
510 sgl
= kmalloc_array(nalloc
, sizeof(struct scatterlist
),
511 (gfp
& ~GFP_DMA
) | __GFP_ZERO
);
515 sg_init_table(sgl
, nent
);
518 elem_len
= min_t(u64
, length
, PAGE_SIZE
<< order
);
519 page
= alloc_pages(gfp
, order
);
525 sg_set_page(sg
, page
, elem_len
, 0);
534 EXPORT_SYMBOL(sgl_alloc_order
);
537 * sgl_alloc - allocate a scatterlist and its pages
538 * @length: Length in bytes of the scatterlist
539 * @gfp: Memory allocation flags
540 * @nent_p: [out] Number of entries in the scatterlist
542 * Returns: A pointer to an initialized scatterlist or %NULL upon failure.
544 struct scatterlist
*sgl_alloc(unsigned long long length
, gfp_t gfp
,
545 unsigned int *nent_p
)
547 return sgl_alloc_order(length
, 0, false, gfp
, nent_p
);
549 EXPORT_SYMBOL(sgl_alloc
);
552 * sgl_free_order - free a scatterlist and its pages
553 * @sgl: Scatterlist with one or more elements
554 * @order: Second argument for __free_pages()
556 void sgl_free_order(struct scatterlist
*sgl
, int order
)
558 struct scatterlist
*sg
;
561 for (sg
= sgl
; sg
; sg
= sg_next(sg
)) {
564 __free_pages(page
, order
);
568 EXPORT_SYMBOL(sgl_free_order
);
571 * sgl_free - free a scatterlist and its pages
572 * @sgl: Scatterlist with one or more elements
574 void sgl_free(struct scatterlist
*sgl
)
576 sgl_free_order(sgl
, 0);
578 EXPORT_SYMBOL(sgl_free
);
580 #endif /* CONFIG_SGL_ALLOC */
582 void __sg_page_iter_start(struct sg_page_iter
*piter
,
583 struct scatterlist
*sglist
, unsigned int nents
,
584 unsigned long pgoffset
)
586 piter
->__pg_advance
= 0;
587 piter
->__nents
= nents
;
590 piter
->sg_pgoffset
= pgoffset
;
592 EXPORT_SYMBOL(__sg_page_iter_start
);
594 static int sg_page_count(struct scatterlist
*sg
)
596 return PAGE_ALIGN(sg
->offset
+ sg
->length
) >> PAGE_SHIFT
;
599 bool __sg_page_iter_next(struct sg_page_iter
*piter
)
601 if (!piter
->__nents
|| !piter
->sg
)
604 piter
->sg_pgoffset
+= piter
->__pg_advance
;
605 piter
->__pg_advance
= 1;
607 while (piter
->sg_pgoffset
>= sg_page_count(piter
->sg
)) {
608 piter
->sg_pgoffset
-= sg_page_count(piter
->sg
);
609 piter
->sg
= sg_next(piter
->sg
);
610 if (!--piter
->__nents
|| !piter
->sg
)
616 EXPORT_SYMBOL(__sg_page_iter_next
);
619 * sg_miter_start - start mapping iteration over a sg list
620 * @miter: sg mapping iter to be started
621 * @sgl: sg list to iterate over
622 * @nents: number of sg entries
625 * Starts mapping iterator @miter.
630 void sg_miter_start(struct sg_mapping_iter
*miter
, struct scatterlist
*sgl
,
631 unsigned int nents
, unsigned int flags
)
633 memset(miter
, 0, sizeof(struct sg_mapping_iter
));
635 __sg_page_iter_start(&miter
->piter
, sgl
, nents
, 0);
636 WARN_ON(!(flags
& (SG_MITER_TO_SG
| SG_MITER_FROM_SG
)));
637 miter
->__flags
= flags
;
639 EXPORT_SYMBOL(sg_miter_start
);
641 static bool sg_miter_get_next_page(struct sg_mapping_iter
*miter
)
643 if (!miter
->__remaining
) {
644 struct scatterlist
*sg
;
646 if (!__sg_page_iter_next(&miter
->piter
))
649 sg
= miter
->piter
.sg
;
651 miter
->__offset
= miter
->piter
.sg_pgoffset
? 0 : sg
->offset
;
652 miter
->piter
.sg_pgoffset
+= miter
->__offset
>> PAGE_SHIFT
;
653 miter
->__offset
&= PAGE_SIZE
- 1;
654 miter
->__remaining
= sg
->offset
+ sg
->length
-
655 (miter
->piter
.sg_pgoffset
<< PAGE_SHIFT
) -
657 miter
->__remaining
= min_t(unsigned long, miter
->__remaining
,
658 PAGE_SIZE
- miter
->__offset
);
665 * sg_miter_skip - reposition mapping iterator
666 * @miter: sg mapping iter to be skipped
667 * @offset: number of bytes to plus the current location
670 * Sets the offset of @miter to its current location plus @offset bytes.
671 * If mapping iterator @miter has been proceeded by sg_miter_next(), this
675 * Don't care if @miter is stopped, or not proceeded yet.
676 * Otherwise, preemption disabled if the SG_MITER_ATOMIC is set.
679 * true if @miter contains the valid mapping. false if end of sg
682 bool sg_miter_skip(struct sg_mapping_iter
*miter
, off_t offset
)
684 sg_miter_stop(miter
);
689 if (!sg_miter_get_next_page(miter
))
692 consumed
= min_t(off_t
, offset
, miter
->__remaining
);
693 miter
->__offset
+= consumed
;
694 miter
->__remaining
-= consumed
;
700 EXPORT_SYMBOL(sg_miter_skip
);
703 * sg_miter_next - proceed mapping iterator to the next mapping
704 * @miter: sg mapping iter to proceed
707 * Proceeds @miter to the next mapping. @miter should have been started
708 * using sg_miter_start(). On successful return, @miter->page,
709 * @miter->addr and @miter->length point to the current mapping.
712 * Preemption disabled if SG_MITER_ATOMIC. Preemption must stay disabled
713 * till @miter is stopped. May sleep if !SG_MITER_ATOMIC.
716 * true if @miter contains the next mapping. false if end of sg
719 bool sg_miter_next(struct sg_mapping_iter
*miter
)
721 sg_miter_stop(miter
);
724 * Get to the next page if necessary.
725 * __remaining, __offset is adjusted by sg_miter_stop
727 if (!sg_miter_get_next_page(miter
))
730 miter
->page
= sg_page_iter_page(&miter
->piter
);
731 miter
->consumed
= miter
->length
= miter
->__remaining
;
733 if (miter
->__flags
& SG_MITER_ATOMIC
)
734 miter
->addr
= kmap_atomic(miter
->page
) + miter
->__offset
;
736 miter
->addr
= kmap(miter
->page
) + miter
->__offset
;
740 EXPORT_SYMBOL(sg_miter_next
);
743 * sg_miter_stop - stop mapping iteration
744 * @miter: sg mapping iter to be stopped
747 * Stops mapping iterator @miter. @miter should have been started
748 * using sg_miter_start(). A stopped iteration can be resumed by
749 * calling sg_miter_next() on it. This is useful when resources (kmap)
750 * need to be released during iteration.
753 * Preemption disabled if the SG_MITER_ATOMIC is set. Don't care
756 void sg_miter_stop(struct sg_mapping_iter
*miter
)
758 WARN_ON(miter
->consumed
> miter
->length
);
760 /* drop resources from the last iteration */
762 miter
->__offset
+= miter
->consumed
;
763 miter
->__remaining
-= miter
->consumed
;
765 if ((miter
->__flags
& SG_MITER_TO_SG
) &&
766 !PageSlab(miter
->page
))
767 flush_kernel_dcache_page(miter
->page
);
769 if (miter
->__flags
& SG_MITER_ATOMIC
) {
770 WARN_ON_ONCE(preemptible());
771 kunmap_atomic(miter
->addr
);
781 EXPORT_SYMBOL(sg_miter_stop
);
784 * sg_copy_buffer - Copy data between a linear buffer and an SG list
786 * @nents: Number of SG entries
787 * @buf: Where to copy from
788 * @buflen: The number of bytes to copy
789 * @skip: Number of bytes to skip before copying
790 * @to_buffer: transfer direction (true == from an sg list to a
791 * buffer, false == from a buffer to an sg list
793 * Returns the number of copied bytes.
796 size_t sg_copy_buffer(struct scatterlist
*sgl
, unsigned int nents
, void *buf
,
797 size_t buflen
, off_t skip
, bool to_buffer
)
799 unsigned int offset
= 0;
800 struct sg_mapping_iter miter
;
801 unsigned int sg_flags
= SG_MITER_ATOMIC
;
804 sg_flags
|= SG_MITER_FROM_SG
;
806 sg_flags
|= SG_MITER_TO_SG
;
808 sg_miter_start(&miter
, sgl
, nents
, sg_flags
);
810 if (!sg_miter_skip(&miter
, skip
))
813 while ((offset
< buflen
) && sg_miter_next(&miter
)) {
816 len
= min(miter
.length
, buflen
- offset
);
819 memcpy(buf
+ offset
, miter
.addr
, len
);
821 memcpy(miter
.addr
, buf
+ offset
, len
);
826 sg_miter_stop(&miter
);
830 EXPORT_SYMBOL(sg_copy_buffer
);
833 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
835 * @nents: Number of SG entries
836 * @buf: Where to copy from
837 * @buflen: The number of bytes to copy
839 * Returns the number of copied bytes.
842 size_t sg_copy_from_buffer(struct scatterlist
*sgl
, unsigned int nents
,
843 const void *buf
, size_t buflen
)
845 return sg_copy_buffer(sgl
, nents
, (void *)buf
, buflen
, 0, false);
847 EXPORT_SYMBOL(sg_copy_from_buffer
);
850 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
852 * @nents: Number of SG entries
853 * @buf: Where to copy to
854 * @buflen: The number of bytes to copy
856 * Returns the number of copied bytes.
859 size_t sg_copy_to_buffer(struct scatterlist
*sgl
, unsigned int nents
,
860 void *buf
, size_t buflen
)
862 return sg_copy_buffer(sgl
, nents
, buf
, buflen
, 0, true);
864 EXPORT_SYMBOL(sg_copy_to_buffer
);
867 * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
869 * @nents: Number of SG entries
870 * @buf: Where to copy from
871 * @buflen: The number of bytes to copy
872 * @skip: Number of bytes to skip before copying
874 * Returns the number of copied bytes.
877 size_t sg_pcopy_from_buffer(struct scatterlist
*sgl
, unsigned int nents
,
878 const void *buf
, size_t buflen
, off_t skip
)
880 return sg_copy_buffer(sgl
, nents
, (void *)buf
, buflen
, skip
, false);
882 EXPORT_SYMBOL(sg_pcopy_from_buffer
);
885 * sg_pcopy_to_buffer - Copy from an SG list to a linear buffer
887 * @nents: Number of SG entries
888 * @buf: Where to copy to
889 * @buflen: The number of bytes to copy
890 * @skip: Number of bytes to skip before copying
892 * Returns the number of copied bytes.
895 size_t sg_pcopy_to_buffer(struct scatterlist
*sgl
, unsigned int nents
,
896 void *buf
, size_t buflen
, off_t skip
)
898 return sg_copy_buffer(sgl
, nents
, buf
, buflen
, skip
, true);
900 EXPORT_SYMBOL(sg_pcopy_to_buffer
);
903 * sg_zero_buffer - Zero-out a part of a SG list
905 * @nents: Number of SG entries
906 * @buflen: The number of bytes to zero out
907 * @skip: Number of bytes to skip before zeroing
909 * Returns the number of bytes zeroed.
911 size_t sg_zero_buffer(struct scatterlist
*sgl
, unsigned int nents
,
912 size_t buflen
, off_t skip
)
914 unsigned int offset
= 0;
915 struct sg_mapping_iter miter
;
916 unsigned int sg_flags
= SG_MITER_ATOMIC
| SG_MITER_TO_SG
;
918 sg_miter_start(&miter
, sgl
, nents
, sg_flags
);
920 if (!sg_miter_skip(&miter
, skip
))
923 while (offset
< buflen
&& sg_miter_next(&miter
)) {
926 len
= min(miter
.length
, buflen
- offset
);
927 memset(miter
.addr
, 0, len
);
932 sg_miter_stop(&miter
);
935 EXPORT_SYMBOL(sg_zero_buffer
);