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 return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
169 static void sg_kfree(struct scatterlist *sg, unsigned int nents)
175 * __sg_free_table - Free a previously mapped sg table
176 * @table: The sg table header to use
177 * @max_ents: The maximum number of entries per single scatterlist
178 * @skip_first_chunk: don't free the (preallocated) first scatterlist chunk
179 * @free_fn: Free function
182 * Free an sg table previously allocated and setup with
183 * __sg_alloc_table(). The @max_ents value must be identical to
184 * that previously used with __sg_alloc_table().
187 void __sg_free_table(struct sg_table *table, unsigned int max_ents,
188 bool skip_first_chunk, sg_free_fn *free_fn)
190 struct scatterlist *sgl, *next;
192 if (unlikely(!table->sgl))
196 while (table->orig_nents) {
197 unsigned int alloc_size = table->orig_nents;
198 unsigned int sg_size;
201 * If we have more than max_ents segments left,
202 * then assign 'next' to the sg table after the current one.
203 * sg_size is then one less than alloc size, since the last
204 * element is the chain pointer.
206 if (alloc_size > max_ents) {
207 next = sg_chain_ptr(&sgl[max_ents - 1]);
208 alloc_size = max_ents;
209 sg_size = alloc_size - 1;
211 sg_size = alloc_size;
215 table->orig_nents -= sg_size;
216 if (skip_first_chunk)
217 skip_first_chunk = false;
219 free_fn(sgl, alloc_size);
225 EXPORT_SYMBOL(__sg_free_table);
228 * sg_free_table - Free a previously allocated sg table
229 * @table: The mapped sg table header
232 void sg_free_table(struct sg_table *table)
234 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
236 EXPORT_SYMBOL(sg_free_table);
239 * __sg_alloc_table - Allocate and initialize an sg table with given allocator
240 * @table: The sg table header to use
241 * @nents: Number of entries in sg list
242 * @max_ents: The maximum number of entries the allocator returns per call
243 * @gfp_mask: GFP allocation mask
244 * @alloc_fn: Allocator to use
247 * This function returns a @table @nents long. The allocator is
248 * defined to return scatterlist chunks of maximum size @max_ents.
249 * Thus if @nents is bigger than @max_ents, the scatterlists will be
250 * chained in units of @max_ents.
253 * If this function returns non-0 (eg failure), the caller must call
254 * __sg_free_table() to cleanup any leftover allocations.
257 int __sg_alloc_table(struct sg_table *table, unsigned int nents,
258 unsigned int max_ents, struct scatterlist *first_chunk,
259 gfp_t gfp_mask, sg_alloc_fn *alloc_fn)
261 struct scatterlist *sg, *prv;
264 memset(table, 0, sizeof(*table));
268 #ifndef CONFIG_ARCH_HAS_SG_CHAIN
269 if (WARN_ON_ONCE(nents > max_ents))
276 unsigned int sg_size, alloc_size = left;
278 if (alloc_size > max_ents) {
279 alloc_size = max_ents;
280 sg_size = alloc_size - 1;
282 sg_size = alloc_size;
290 sg = alloc_fn(alloc_size, gfp_mask);
294 * Adjust entry count to reflect that the last
295 * entry of the previous table won't be used for
296 * linkage. Without this, sg_kfree() may get
300 table->nents = ++table->orig_nents;
305 sg_init_table(sg, alloc_size);
306 table->nents = table->orig_nents += sg_size;
309 * If this is the first mapping, assign the sg table header.
310 * If this is not the first mapping, chain previous part.
313 sg_chain(prv, max_ents, sg);
318 * If no more entries after this one, mark the end
321 sg_mark_end(&sg[sg_size - 1]);
328 EXPORT_SYMBOL(__sg_alloc_table);
331 * sg_alloc_table - Allocate and initialize an sg table
332 * @table: The sg table header to use
333 * @nents: Number of entries in sg list
334 * @gfp_mask: GFP allocation mask
337 * Allocate and initialize an sg table. If @nents@ is larger than
338 * SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
341 int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
345 ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
346 NULL, gfp_mask, sg_kmalloc);
348 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, false, sg_kfree);
352 EXPORT_SYMBOL(sg_alloc_table);
355 * sg_alloc_table_from_pages - Allocate and initialize an sg table from
357 * @sgt: The sg table header to use
358 * @pages: Pointer to an array of page pointers
359 * @n_pages: Number of pages in the pages array
360 * @offset: Offset from start of the first page to the start of a buffer
361 * @size: Number of valid bytes in the buffer (after offset)
362 * @gfp_mask: GFP allocation mask
365 * Allocate and initialize an sg table from a list of pages. Contiguous
366 * ranges of the pages are squashed into a single scatterlist node. A user
367 * may provide an offset at a start and a size of valid data in a buffer
368 * specified by the page array. The returned sg table is released by
372 * 0 on success, negative error on failure
374 int sg_alloc_table_from_pages(struct sg_table *sgt,
375 struct page **pages, unsigned int n_pages,
376 unsigned long offset, unsigned long size,
381 unsigned int cur_page;
383 struct scatterlist *s;
385 /* compute number of contiguous chunks */
387 for (i = 1; i < n_pages; ++i)
388 if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
391 ret = sg_alloc_table(sgt, chunks, gfp_mask);
395 /* merging chunks and putting them into the scatterlist */
397 for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
398 unsigned long chunk_size;
401 /* look for the end of the current chunk */
402 for (j = cur_page + 1; j < n_pages; ++j)
403 if (page_to_pfn(pages[j]) !=
404 page_to_pfn(pages[j - 1]) + 1)
407 chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
408 sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
416 EXPORT_SYMBOL(sg_alloc_table_from_pages);
418 void __sg_page_iter_start(struct sg_page_iter *piter,
419 struct scatterlist *sglist, unsigned int nents,
420 unsigned long pgoffset)
422 piter->__pg_advance = 0;
423 piter->__nents = nents;
426 piter->sg_pgoffset = pgoffset;
428 EXPORT_SYMBOL(__sg_page_iter_start);
430 static int sg_page_count(struct scatterlist *sg)
432 return PAGE_ALIGN(sg->offset + sg->length) >> PAGE_SHIFT;
435 bool __sg_page_iter_next(struct sg_page_iter *piter)
437 if (!piter->__nents || !piter->sg)
440 piter->sg_pgoffset += piter->__pg_advance;
441 piter->__pg_advance = 1;
443 while (piter->sg_pgoffset >= sg_page_count(piter->sg)) {
444 piter->sg_pgoffset -= sg_page_count(piter->sg);
445 piter->sg = sg_next(piter->sg);
446 if (!--piter->__nents || !piter->sg)
452 EXPORT_SYMBOL(__sg_page_iter_next);
455 * sg_miter_start - start mapping iteration over a sg list
456 * @miter: sg mapping iter to be started
457 * @sgl: sg list to iterate over
458 * @nents: number of sg entries
461 * Starts mapping iterator @miter.
466 void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
467 unsigned int nents, unsigned int flags)
469 memset(miter, 0, sizeof(struct sg_mapping_iter));
471 __sg_page_iter_start(&miter->piter, sgl, nents, 0);
472 WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
473 miter->__flags = flags;
475 EXPORT_SYMBOL(sg_miter_start);
477 static bool sg_miter_get_next_page(struct sg_mapping_iter *miter)
479 if (!miter->__remaining) {
480 struct scatterlist *sg;
482 if (!__sg_page_iter_next(&miter->piter))
485 sg = miter->piter.sg;
487 miter->__offset = miter->piter.sg_pgoffset ? 0 : sg->offset;
488 miter->piter.sg_pgoffset += miter->__offset >> PAGE_SHIFT;
489 miter->__offset &= PAGE_SIZE - 1;
490 miter->__remaining = sg->offset + sg->length -
491 (miter->piter.sg_pgoffset << PAGE_SHIFT) -
493 miter->__remaining = min_t(unsigned long, miter->__remaining,
494 PAGE_SIZE - miter->__offset);
501 * sg_miter_skip - reposition mapping iterator
502 * @miter: sg mapping iter to be skipped
503 * @offset: number of bytes to plus the current location
506 * Sets the offset of @miter to its current location plus @offset bytes.
507 * If mapping iterator @miter has been proceeded by sg_miter_next(), this
511 * Don't care if @miter is stopped, or not proceeded yet.
512 * Otherwise, preemption disabled if the SG_MITER_ATOMIC is set.
515 * true if @miter contains the valid mapping. false if end of sg
518 bool sg_miter_skip(struct sg_mapping_iter *miter, off_t offset)
520 sg_miter_stop(miter);
525 if (!sg_miter_get_next_page(miter))
528 consumed = min_t(off_t, offset, miter->__remaining);
529 miter->__offset += consumed;
530 miter->__remaining -= consumed;
536 EXPORT_SYMBOL(sg_miter_skip);
539 * sg_miter_next - proceed mapping iterator to the next mapping
540 * @miter: sg mapping iter to proceed
543 * Proceeds @miter to the next mapping. @miter should have been started
544 * using sg_miter_start(). On successful return, @miter->page,
545 * @miter->addr and @miter->length point to the current mapping.
548 * Preemption disabled if SG_MITER_ATOMIC. Preemption must stay disabled
549 * till @miter is stopped. May sleep if !SG_MITER_ATOMIC.
552 * true if @miter contains the next mapping. false if end of sg
555 bool sg_miter_next(struct sg_mapping_iter *miter)
557 sg_miter_stop(miter);
560 * Get to the next page if necessary.
561 * __remaining, __offset is adjusted by sg_miter_stop
563 if (!sg_miter_get_next_page(miter))
566 miter->page = sg_page_iter_page(&miter->piter);
567 miter->consumed = miter->length = miter->__remaining;
569 if (miter->__flags & SG_MITER_ATOMIC)
570 miter->addr = kmap_atomic(miter->page) + miter->__offset;
572 miter->addr = kmap(miter->page) + miter->__offset;
576 EXPORT_SYMBOL(sg_miter_next);
579 * sg_miter_stop - stop mapping iteration
580 * @miter: sg mapping iter to be stopped
583 * Stops mapping iterator @miter. @miter should have been started
584 * started using sg_miter_start(). A stopped iteration can be
585 * resumed by calling sg_miter_next() on it. This is useful when
586 * resources (kmap) need to be released during iteration.
589 * Preemption disabled if the SG_MITER_ATOMIC is set. Don't care
592 void sg_miter_stop(struct sg_mapping_iter *miter)
594 WARN_ON(miter->consumed > miter->length);
596 /* drop resources from the last iteration */
598 miter->__offset += miter->consumed;
599 miter->__remaining -= miter->consumed;
601 if ((miter->__flags & SG_MITER_TO_SG) &&
602 !PageSlab(miter->page))
603 flush_kernel_dcache_page(miter->page);
605 if (miter->__flags & SG_MITER_ATOMIC) {
606 WARN_ON_ONCE(preemptible());
607 kunmap_atomic(miter->addr);
617 EXPORT_SYMBOL(sg_miter_stop);
620 * sg_copy_buffer - Copy data between a linear buffer and an SG list
622 * @nents: Number of SG entries
623 * @buf: Where to copy from
624 * @buflen: The number of bytes to copy
625 * @skip: Number of bytes to skip before copying
626 * @to_buffer: transfer direction (true == from an sg list to a
627 * buffer, false == from a buffer to an sg list
629 * Returns the number of copied bytes.
632 size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf,
633 size_t buflen, off_t skip, bool to_buffer)
635 unsigned int offset = 0;
636 struct sg_mapping_iter miter;
638 unsigned int sg_flags = SG_MITER_ATOMIC;
641 sg_flags |= SG_MITER_FROM_SG;
643 sg_flags |= SG_MITER_TO_SG;
645 sg_miter_start(&miter, sgl, nents, sg_flags);
647 if (!sg_miter_skip(&miter, skip))
650 local_irq_save(flags);
652 while (sg_miter_next(&miter) && offset < buflen) {
655 len = min(miter.length, buflen - offset);
658 memcpy(buf + offset, miter.addr, len);
660 memcpy(miter.addr, buf + offset, len);
665 sg_miter_stop(&miter);
667 local_irq_restore(flags);
670 EXPORT_SYMBOL(sg_copy_buffer);
673 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
675 * @nents: Number of SG entries
676 * @buf: Where to copy from
677 * @buflen: The number of bytes to copy
679 * Returns the number of copied bytes.
682 size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
683 const void *buf, size_t buflen)
685 return sg_copy_buffer(sgl, nents, (void *)buf, buflen, 0, false);
687 EXPORT_SYMBOL(sg_copy_from_buffer);
690 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
692 * @nents: Number of SG entries
693 * @buf: Where to copy to
694 * @buflen: The number of bytes to copy
696 * Returns the number of copied bytes.
699 size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
700 void *buf, size_t buflen)
702 return sg_copy_buffer(sgl, nents, buf, buflen, 0, true);
704 EXPORT_SYMBOL(sg_copy_to_buffer);
707 * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
709 * @nents: Number of SG entries
710 * @buf: Where to copy from
711 * @buflen: The number of bytes to copy
712 * @skip: Number of bytes to skip before copying
714 * Returns the number of copied bytes.
717 size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
718 const void *buf, size_t buflen, off_t skip)
720 return sg_copy_buffer(sgl, nents, (void *)buf, buflen, skip, false);
722 EXPORT_SYMBOL(sg_pcopy_from_buffer);
725 * sg_pcopy_to_buffer - Copy from an SG list to a linear buffer
727 * @nents: Number of SG entries
728 * @buf: Where to copy to
729 * @buflen: The number of bytes to copy
730 * @skip: Number of bytes to skip before copying
732 * Returns the number of copied bytes.
735 size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
736 void *buf, size_t buflen, off_t skip)
738 return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
740 EXPORT_SYMBOL(sg_pcopy_to_buffer);