Re: [PATCH net-next v2 1/1] net: selftests: add PHY-loopback test for bad TCP checksums

[Jakub Kicinski]

On Fri, 11 Jul 2025 09:24:49 +0200 Oleksij Rempel wrote:
> +			/* To avoid sparse warnings about operating on
> +			 * restricted __sum16/__be16 types, explicitly cast the
> +			 * checksum to a plain u16, perform the manipulation,
> +			 * and then cast the result back.
> +			 */
> +			csum = (__force u16)thdr->check;
> +
> +			/* Mangle the checksum by flipping the LSB. */
> +			csum ^= 1;
> +			/* If mangling resulted in 0, use the raw value for a
> +			 * mangled-zero checksum. We use the literal 0xffff
> +			 * because CSUM_MANGLED_0 has a restricted type.
> +			 */
> +			if (!csum)
> +				csum = 0xffff;
> +
> +			/* Cast the final integer value back to the restricted
> +			 * type
> +			 */
> +			thdr->check = (__force __sum16)csum;

Way to manny lines of code for something this simple.
Can csum_add() help you get rid of all these casts and comments?
-- 
pw-bot: cr