[v2 PATCH] crypto: scatterwalk - Add memcpy_sglist

[Herbert Xu <herbert@gondor.apana.org.au>]

On Wed, Mar 05, 2025 at 07:13:59PM -0800, Eric Biggers wrote:
> 
> Local kmaps must be released in reverse order of the mapping, so
> scatterwalk_done_dst() must be done before scatterwalk_done_src() above.

Good catch.  Thanks for the review!

---8<---
Add memcpy_sglist which copies one SG list to another.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
---
 crypto/scatterwalk.c         | 27 +++++++++++++++++++++++++++
 include/crypto/scatterwalk.h |  3 +++
 2 files changed, 30 insertions(+)

diff --git a/crypto/scatterwalk.c b/crypto/scatterwalk.c
index 20a28c6d94da..e57ce08e0d8d 100644
--- a/crypto/scatterwalk.c
+++ b/crypto/scatterwalk.c
@@ -86,6 +86,33 @@ void memcpy_to_sglist(struct scatterlist *sg, unsigned int start,
 }
 EXPORT_SYMBOL_GPL(memcpy_to_sglist);
 
+void memcpy_sglist(struct scatterlist *dst, struct scatterlist *src,
+		   unsigned int nbytes)
+{
+	struct scatter_walk swalk;
+	struct scatter_walk dwalk;
+
+	if (unlikely(nbytes == 0)) /* in case sg == NULL */
+		return;
+
+	scatterwalk_start(&swalk, src);
+	scatterwalk_start(&dwalk, dst);
+
+	do {
+		unsigned int slen, dlen;
+		unsigned int len;
+
+		slen = scatterwalk_next(&swalk, nbytes);
+		dlen = scatterwalk_next(&dwalk, nbytes);
+		len = min(slen, dlen);
+		memcpy(dwalk.addr, swalk.addr, len);
+		scatterwalk_done_src(&swalk, len);
+		scatterwalk_done_dst(&dwalk, len);
+		nbytes -= len;
+	} while (nbytes);
+}
+EXPORT_SYMBOL_GPL(memcpy_sglist);
+
 struct scatterlist *scatterwalk_ffwd(struct scatterlist dst[2],
 				     struct scatterlist *src,
 				     unsigned int len)
diff --git a/include/crypto/scatterwalk.h b/include/crypto/scatterwalk.h
index 40c3c629e27f..1201543295f9 100644
--- a/include/crypto/scatterwalk.h
+++ b/include/crypto/scatterwalk.h
@@ -208,6 +208,9 @@ void memcpy_from_sglist(void *buf, struct scatterlist *sg,
 void memcpy_to_sglist(struct scatterlist *sg, unsigned int start,
 		      const void *buf, unsigned int nbytes);
 
+void memcpy_sglist(struct scatterlist *dst, struct scatterlist *src,
+		   unsigned int nbytes);
+
 /* In new code, please use memcpy_{from,to}_sglist() directly instead. */
 static inline void scatterwalk_map_and_copy(void *buf, struct scatterlist *sg,
 					    unsigned int start,
-- 
2.39.5

-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt