Root/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 **/
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            !PageSlab(miter->page))
582            flush_kernel_dcache_page(miter->page);
583
584        if (miter->__flags & SG_MITER_ATOMIC) {
585            WARN_ON_ONCE(preemptible());
586            kunmap_atomic(miter->addr);
587        } else
588            kunmap(miter->page);
589
590        miter->page = NULL;
591        miter->addr = NULL;
592        miter->length = 0;
593        miter->consumed = 0;
594    }
595}
596EXPORT_SYMBOL(sg_miter_stop);
597
598/**
599 * sg_copy_buffer - Copy data between a linear buffer and an SG list
600 * @sgl: The SG list
601 * @nents: Number of SG entries
602 * @buf: Where to copy from
603 * @buflen: The number of bytes to copy
604 * @skip: Number of bytes to skip before copying
605 * @to_buffer: transfer direction (true == from an sg list to a
606 * buffer, false == from a buffer to an sg list
607 *
608 * Returns the number of copied bytes.
609 *
610 **/
611static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
612                 void *buf, size_t buflen, off_t skip,
613                 bool to_buffer)
614{
615    unsigned int offset = 0;
616    struct sg_mapping_iter miter;
617    unsigned long flags;
618    unsigned int sg_flags = SG_MITER_ATOMIC;
619
620    if (to_buffer)
621        sg_flags |= SG_MITER_FROM_SG;
622    else
623        sg_flags |= SG_MITER_TO_SG;
624
625    sg_miter_start(&miter, sgl, nents, sg_flags);
626
627    if (!sg_miter_skip(&miter, skip))
628        return false;
629
630    local_irq_save(flags);
631
632    while (sg_miter_next(&miter) && offset < buflen) {
633        unsigned int len;
634
635        len = min(miter.length, buflen - offset);
636
637        if (to_buffer)
638            memcpy(buf + offset, miter.addr, len);
639        else
640            memcpy(miter.addr, buf + offset, len);
641
642        offset += len;
643    }
644
645    sg_miter_stop(&miter);
646
647    local_irq_restore(flags);
648    return offset;
649}
650
651/**
652 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
653 * @sgl: The SG list
654 * @nents: Number of SG entries
655 * @buf: Where to copy from
656 * @buflen: The number of bytes to copy
657 *
658 * Returns the number of copied bytes.
659 *
660 **/
661size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
662               void *buf, size_t buflen)
663{
664    return sg_copy_buffer(sgl, nents, buf, buflen, 0, false);
665}
666EXPORT_SYMBOL(sg_copy_from_buffer);
667
668/**
669 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
670 * @sgl: The SG list
671 * @nents: Number of SG entries
672 * @buf: Where to copy to
673 * @buflen: The number of bytes to copy
674 *
675 * Returns the number of copied bytes.
676 *
677 **/
678size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
679             void *buf, size_t buflen)
680{
681    return sg_copy_buffer(sgl, nents, buf, buflen, 0, true);
682}
683EXPORT_SYMBOL(sg_copy_to_buffer);
684
685/**
686 * sg_pcopy_from_buffer - Copy from a linear buffer to an SG list
687 * @sgl: The SG list
688 * @nents: Number of SG entries
689 * @buf: Where to copy from
690 * @skip: Number of bytes to skip before copying
691 * @buflen: The number of bytes to copy
692 *
693 * Returns the number of copied bytes.
694 *
695 **/
696size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents,
697                void *buf, size_t buflen, off_t skip)
698{
699    return sg_copy_buffer(sgl, nents, buf, buflen, skip, false);
700}
701EXPORT_SYMBOL(sg_pcopy_from_buffer);
702
703/**
704 * sg_pcopy_to_buffer - Copy from an SG list to a linear buffer
705 * @sgl: The SG list
706 * @nents: Number of SG entries
707 * @buf: Where to copy to
708 * @skip: Number of bytes to skip before copying
709 * @buflen: The number of bytes to copy
710 *
711 * Returns the number of copied bytes.
712 *
713 **/
714size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,
715              void *buf, size_t buflen, off_t skip)
716{
717    return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
718}
719EXPORT_SYMBOL(sg_pcopy_to_buffer);
720

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