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_last - return the last scatterlist entry in a list
43 * @sgl: First entry in the scatterlist
44 * @nents: Number of entries in the scatterlist
47 * Should only be used casually, it (currently) scans the entire list
48 * to get the last entry.
50 * Note that the @sgl@ pointer passed in need not be the first one,
51 * the important bit is that @nents@ denotes the number of entries that
55 struct scatterlist
*sg_last(struct scatterlist
*sgl
, unsigned int nents
)
57 #ifndef ARCH_HAS_SG_CHAIN
58 struct scatterlist
*ret
= &sgl
[nents
- 1];
60 struct scatterlist
*sg
, *ret
= NULL
;
63 for_each_sg(sgl
, sg
, nents
, i
)
67 #ifdef CONFIG_DEBUG_SG
68 BUG_ON(sgl
[0].sg_magic
!= SG_MAGIC
);
69 BUG_ON(!sg_is_last(ret
));
73 EXPORT_SYMBOL(sg_last
);
76 * sg_init_table - Initialize SG table
78 * @nents: Number of entries in table
81 * If this is part of a chained sg table, sg_mark_end() should be
82 * used only on the last table part.
85 void sg_init_table(struct scatterlist
*sgl
, unsigned int nents
)
87 memset(sgl
, 0, sizeof(*sgl
) * nents
);
88 #ifdef CONFIG_DEBUG_SG
91 for (i
= 0; i
< nents
; i
++)
92 sgl
[i
].sg_magic
= SG_MAGIC
;
95 sg_mark_end(&sgl
[nents
- 1]);
97 EXPORT_SYMBOL(sg_init_table
);
100 * sg_init_one - Initialize a single entry sg list
102 * @buf: Virtual address for IO
106 void sg_init_one(struct scatterlist
*sg
, const void *buf
, unsigned int buflen
)
108 sg_init_table(sg
, 1);
109 sg_set_buf(sg
, buf
, buflen
);
111 EXPORT_SYMBOL(sg_init_one
);
114 * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
117 static struct scatterlist
*sg_kmalloc(unsigned int nents
, gfp_t gfp_mask
)
119 if (nents
== SG_MAX_SINGLE_ALLOC
) {
121 * Kmemleak doesn't track page allocations as they are not
122 * commonly used (in a raw form) for kernel data structures.
123 * As we chain together a list of pages and then a normal
124 * kmalloc (tracked by kmemleak), in order to for that last
125 * allocation not to become decoupled (and thus a
126 * false-positive) we need to inform kmemleak of all the
127 * intermediate allocations.
129 void *ptr
= (void *) __get_free_page(gfp_mask
);
130 kmemleak_alloc(ptr
, PAGE_SIZE
, 1, gfp_mask
);
133 return kmalloc(nents
* sizeof(struct scatterlist
), gfp_mask
);
136 static void sg_kfree(struct scatterlist
*sg
, unsigned int nents
)
138 if (nents
== SG_MAX_SINGLE_ALLOC
) {
140 free_page((unsigned long) sg
);
146 * __sg_free_table - Free a previously mapped sg table
147 * @table: The sg table header to use
148 * @max_ents: The maximum number of entries per single scatterlist
149 * @free_fn: Free function
152 * Free an sg table previously allocated and setup with
153 * __sg_alloc_table(). The @max_ents value must be identical to
154 * that previously used with __sg_alloc_table().
157 void __sg_free_table(struct sg_table
*table
, unsigned int max_ents
,
160 struct scatterlist
*sgl
, *next
;
162 if (unlikely(!table
->sgl
))
166 while (table
->orig_nents
) {
167 unsigned int alloc_size
= table
->orig_nents
;
168 unsigned int sg_size
;
171 * If we have more than max_ents segments left,
172 * then assign 'next' to the sg table after the current one.
173 * sg_size is then one less than alloc size, since the last
174 * element is the chain pointer.
176 if (alloc_size
> max_ents
) {
177 next
= sg_chain_ptr(&sgl
[max_ents
- 1]);
178 alloc_size
= max_ents
;
179 sg_size
= alloc_size
- 1;
181 sg_size
= alloc_size
;
185 table
->orig_nents
-= sg_size
;
186 free_fn(sgl
, alloc_size
);
192 EXPORT_SYMBOL(__sg_free_table
);
195 * sg_free_table - Free a previously allocated sg table
196 * @table: The mapped sg table header
199 void sg_free_table(struct sg_table
*table
)
201 __sg_free_table(table
, SG_MAX_SINGLE_ALLOC
, sg_kfree
);
203 EXPORT_SYMBOL(sg_free_table
);
206 * __sg_alloc_table - Allocate and initialize an sg table with given allocator
207 * @table: The sg table header to use
208 * @nents: Number of entries in sg list
209 * @max_ents: The maximum number of entries the allocator returns per call
210 * @gfp_mask: GFP allocation mask
211 * @alloc_fn: Allocator to use
214 * This function returns a @table @nents long. The allocator is
215 * defined to return scatterlist chunks of maximum size @max_ents.
216 * Thus if @nents is bigger than @max_ents, the scatterlists will be
217 * chained in units of @max_ents.
220 * If this function returns non-0 (eg failure), the caller must call
221 * __sg_free_table() to cleanup any leftover allocations.
224 int __sg_alloc_table(struct sg_table
*table
, unsigned int nents
,
225 unsigned int max_ents
, gfp_t gfp_mask
,
226 sg_alloc_fn
*alloc_fn
)
228 struct scatterlist
*sg
, *prv
;
231 #ifndef ARCH_HAS_SG_CHAIN
232 BUG_ON(nents
> max_ents
);
235 memset(table
, 0, sizeof(*table
));
240 unsigned int sg_size
, alloc_size
= left
;
242 if (alloc_size
> max_ents
) {
243 alloc_size
= max_ents
;
244 sg_size
= alloc_size
- 1;
246 sg_size
= alloc_size
;
250 sg
= alloc_fn(alloc_size
, gfp_mask
);
253 * Adjust entry count to reflect that the last
254 * entry of the previous table won't be used for
255 * linkage. Without this, sg_kfree() may get
259 table
->nents
= ++table
->orig_nents
;
264 sg_init_table(sg
, alloc_size
);
265 table
->nents
= table
->orig_nents
+= sg_size
;
268 * If this is the first mapping, assign the sg table header.
269 * If this is not the first mapping, chain previous part.
272 sg_chain(prv
, max_ents
, sg
);
277 * If no more entries after this one, mark the end
280 sg_mark_end(&sg
[sg_size
- 1]);
283 * only really needed for mempool backed sg allocations (like
284 * SCSI), a possible improvement here would be to pass the
285 * table pointer into the allocator and let that clear these
288 gfp_mask
&= ~__GFP_WAIT
;
289 gfp_mask
|= __GFP_HIGH
;
295 EXPORT_SYMBOL(__sg_alloc_table
);
298 * sg_alloc_table - Allocate and initialize an sg table
299 * @table: The sg table header to use
300 * @nents: Number of entries in sg list
301 * @gfp_mask: GFP allocation mask
304 * Allocate and initialize an sg table. If @nents@ is larger than
305 * SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
308 int sg_alloc_table(struct sg_table
*table
, unsigned int nents
, gfp_t gfp_mask
)
312 ret
= __sg_alloc_table(table
, nents
, SG_MAX_SINGLE_ALLOC
,
313 gfp_mask
, sg_kmalloc
);
315 __sg_free_table(table
, SG_MAX_SINGLE_ALLOC
, sg_kfree
);
319 EXPORT_SYMBOL(sg_alloc_table
);
322 * sg_alloc_table_from_pages - Allocate and initialize an sg table from
324 * @sgt: The sg table header to use
325 * @pages: Pointer to an array of page pointers
326 * @n_pages: Number of pages in the pages array
327 * @offset: Offset from start of the first page to the start of a buffer
328 * @size: Number of valid bytes in the buffer (after offset)
329 * @gfp_mask: GFP allocation mask
332 * Allocate and initialize an sg table from a list of pages. Contiguous
333 * ranges of the pages are squashed into a single scatterlist node. A user
334 * may provide an offset at a start and a size of valid data in a buffer
335 * specified by the page array. The returned sg table is released by
339 * 0 on success, negative error on failure
341 int sg_alloc_table_from_pages(struct sg_table
*sgt
,
342 struct page
**pages
, unsigned int n_pages
,
343 unsigned long offset
, unsigned long size
,
348 unsigned int cur_page
;
350 struct scatterlist
*s
;
352 /* compute number of contiguous chunks */
354 for (i
= 1; i
< n_pages
; ++i
)
355 if (page_to_pfn(pages
[i
]) != page_to_pfn(pages
[i
- 1]) + 1)
358 ret
= sg_alloc_table(sgt
, chunks
, gfp_mask
);
362 /* merging chunks and putting them into the scatterlist */
364 for_each_sg(sgt
->sgl
, s
, sgt
->orig_nents
, i
) {
365 unsigned long chunk_size
;
368 /* look for the end of the current chunk */
369 for (j
= cur_page
+ 1; j
< n_pages
; ++j
)
370 if (page_to_pfn(pages
[j
]) !=
371 page_to_pfn(pages
[j
- 1]) + 1)
374 chunk_size
= ((j
- cur_page
) << PAGE_SHIFT
) - offset
;
375 sg_set_page(s
, pages
[cur_page
], min(size
, chunk_size
), offset
);
383 EXPORT_SYMBOL(sg_alloc_table_from_pages
);
386 * sg_miter_start - start mapping iteration over a sg list
387 * @miter: sg mapping iter to be started
388 * @sgl: sg list to iterate over
389 * @nents: number of sg entries
392 * Starts mapping iterator @miter.
397 void sg_miter_start(struct sg_mapping_iter
*miter
, struct scatterlist
*sgl
,
398 unsigned int nents
, unsigned int flags
)
400 memset(miter
, 0, sizeof(struct sg_mapping_iter
));
403 miter
->__nents
= nents
;
405 WARN_ON(!(flags
& (SG_MITER_TO_SG
| SG_MITER_FROM_SG
)));
406 miter
->__flags
= flags
;
408 EXPORT_SYMBOL(sg_miter_start
);
411 * sg_miter_next - proceed mapping iterator to the next mapping
412 * @miter: sg mapping iter to proceed
415 * Proceeds @miter@ to the next mapping. @miter@ should have been
416 * started using sg_miter_start(). On successful return,
417 * @miter@->page, @miter@->addr and @miter@->length point to the
421 * IRQ disabled if SG_MITER_ATOMIC. IRQ must stay disabled till
422 * @miter@ is stopped. May sleep if !SG_MITER_ATOMIC.
425 * true if @miter contains the next mapping. false if end of sg
428 bool sg_miter_next(struct sg_mapping_iter
*miter
)
430 unsigned int off
, len
;
432 /* check for end and drop resources from the last iteration */
436 sg_miter_stop(miter
);
438 /* get to the next sg if necessary. __offset is adjusted by stop */
439 while (miter
->__offset
== miter
->__sg
->length
) {
440 if (--miter
->__nents
) {
441 miter
->__sg
= sg_next(miter
->__sg
);
447 /* map the next page */
448 off
= miter
->__sg
->offset
+ miter
->__offset
;
449 len
= miter
->__sg
->length
- miter
->__offset
;
451 miter
->page
= nth_page(sg_page(miter
->__sg
), off
>> PAGE_SHIFT
);
453 miter
->length
= min_t(unsigned int, len
, PAGE_SIZE
- off
);
454 miter
->consumed
= miter
->length
;
456 if (miter
->__flags
& SG_MITER_ATOMIC
)
457 miter
->addr
= kmap_atomic(miter
->page
) + off
;
459 miter
->addr
= kmap(miter
->page
) + off
;
463 EXPORT_SYMBOL(sg_miter_next
);
466 * sg_miter_stop - stop mapping iteration
467 * @miter: sg mapping iter to be stopped
470 * Stops mapping iterator @miter. @miter should have been started
471 * started using sg_miter_start(). A stopped iteration can be
472 * resumed by calling sg_miter_next() on it. This is useful when
473 * resources (kmap) need to be released during iteration.
476 * IRQ disabled if the SG_MITER_ATOMIC is set. Don't care otherwise.
478 void sg_miter_stop(struct sg_mapping_iter
*miter
)
480 WARN_ON(miter
->consumed
> miter
->length
);
482 /* drop resources from the last iteration */
484 miter
->__offset
+= miter
->consumed
;
486 if (miter
->__flags
& SG_MITER_TO_SG
)
487 flush_kernel_dcache_page(miter
->page
);
489 if (miter
->__flags
& SG_MITER_ATOMIC
) {
490 WARN_ON(!irqs_disabled());
491 kunmap_atomic(miter
->addr
);
501 EXPORT_SYMBOL(sg_miter_stop
);
504 * sg_copy_buffer - Copy data between a linear buffer and an SG list
506 * @nents: Number of SG entries
507 * @buf: Where to copy from
508 * @buflen: The number of bytes to copy
509 * @to_buffer: transfer direction (non zero == from an sg list to a
510 * buffer, 0 == from a buffer to an sg list
512 * Returns the number of copied bytes.
515 static size_t sg_copy_buffer(struct scatterlist
*sgl
, unsigned int nents
,
516 void *buf
, size_t buflen
, int to_buffer
)
518 unsigned int offset
= 0;
519 struct sg_mapping_iter miter
;
521 unsigned int sg_flags
= SG_MITER_ATOMIC
;
524 sg_flags
|= SG_MITER_FROM_SG
;
526 sg_flags
|= SG_MITER_TO_SG
;
528 sg_miter_start(&miter
, sgl
, nents
, sg_flags
);
530 local_irq_save(flags
);
532 while (sg_miter_next(&miter
) && offset
< buflen
) {
535 len
= min(miter
.length
, buflen
- offset
);
538 memcpy(buf
+ offset
, miter
.addr
, len
);
540 memcpy(miter
.addr
, buf
+ offset
, len
);
545 sg_miter_stop(&miter
);
547 local_irq_restore(flags
);
552 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
554 * @nents: Number of SG entries
555 * @buf: Where to copy from
556 * @buflen: The number of bytes to copy
558 * Returns the number of copied bytes.
561 size_t sg_copy_from_buffer(struct scatterlist
*sgl
, unsigned int nents
,
562 void *buf
, size_t buflen
)
564 return sg_copy_buffer(sgl
, nents
, buf
, buflen
, 0);
566 EXPORT_SYMBOL(sg_copy_from_buffer
);
569 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
571 * @nents: Number of SG entries
572 * @buf: Where to copy to
573 * @buflen: The number of bytes to copy
575 * Returns the number of copied bytes.
578 size_t sg_copy_to_buffer(struct scatterlist
*sgl
, unsigned int nents
,
579 void *buf
, size_t buflen
)
581 return sg_copy_buffer(sgl
, nents
, buf
, buflen
, 1);
583 EXPORT_SYMBOL(sg_copy_to_buffer
);