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