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crypto: scatterwalk - add new functions for skipping data

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Add scatterwalk_skip() to skip the given number of bytes in a
scatter_walk.  Previously support for skipping was provided through
scatterwalk_copychunks(..., 2) followed by scatterwalk_done(), which was
confusing and less efficient.

Also add scatterwalk_start_at_pos() which starts a scatter_walk at the
given position, equivalent to scatterwalk_start() + scatterwalk_skip().
This addresses another common need in a more streamlined way.

Later patches will convert various users to use these functions.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Eric Biggers 2025-02-19 10:23:24 -08:00 committed by Herbert Xu
parent 3bd4b2c603
commit e21d01a2a3
2 changed files with 33 additions and 0 deletions
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15
crypto/scatterwalk.c
View File

@ -15,6 +15,21 @@
#include <linux/module.h>
#include <linux/scatterlist.h>
void scatterwalk_skip(struct scatter_walk *walk, unsigned int nbytes)
{
struct scatterlist *sg = walk->sg;
nbytes += walk->offset - sg->offset;
while (nbytes > sg->length) {
nbytes -= sg->length;
sg = sg_next(sg);
}
walk->sg = sg;
walk->offset = sg->offset + nbytes;
}
EXPORT_SYMBOL_GPL(scatterwalk_skip);
static inline void memcpy_dir(void *buf, void *sgdata, size_t nbytes, int out)
{
void *src = out ? buf : sgdata;

18
include/crypto/scatterwalk.h
View File

@ -33,6 +33,22 @@ static inline void scatterwalk_start(struct scatter_walk *walk,
walk->offset = sg->offset;
}
/*
* This is equivalent to scatterwalk_start(walk, sg) followed by
* scatterwalk_skip(walk, pos).
*/
static inline void scatterwalk_start_at_pos(struct scatter_walk *walk,
struct scatterlist *sg,
unsigned int pos)
{
while (pos > sg->length) {
pos -= sg->length;
sg = sg_next(sg);
}
walk->sg = sg;
walk->offset = sg->offset + pos;
}
static inline unsigned int scatterwalk_pagelen(struct scatter_walk *walk)
{
unsigned int len = walk->sg->offset + walk->sg->length - walk->offset;
@ -92,6 +108,8 @@ static inline void scatterwalk_done(struct scatter_walk *walk, int out,
scatterwalk_pagedone(walk, out, more);
}
void scatterwalk_skip(struct scatter_walk *walk, unsigned int nbytes);
void scatterwalk_copychunks(void *buf, struct scatter_walk *walk,
size_t nbytes, int out);