Re: [PATCH] crypto: scatterwalk - Add memcpy_sglist

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Mar 06, 2025 at 11:03:22AM +0800, Herbert Xu wrote:
> +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);

Local kmaps must be released in reverse order of the mapping, so
scatterwalk_done_dst() must be done before scatterwalk_done_src() above.

- Eric