Re: [PATCH v4] net: fix checksum with unaligned buffer

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 23 Jun 2022 14:39:00 +0200
Morten Brørup <mb@smartsharesystems.com> wrote:

> +	/* if buffer is unaligned, keeping it byte order independent */
> +	if (unlikely(unaligned)) {
> +		uint16_t first = 0;
> +		if (unlikely(len == 0))
> +			return 0;

Why is length == 0 unique to unaligned case?

> +		((unsigned char *)&first)[1] = *(const unsigned char *)buf;

Use a proper union instead of casting to avoid aliasing warnings.

> +		bsum += first;
> +		buf = RTE_PTR_ADD(buf, 1);
> +		len--;
> +	}

Many CPU's (such as x86) won't care about alignment and therefore the extra
code to handle this is not worth doing.

Perhaps DPDK needs a macro (like Linux kernel) for efficient unaligned access.

In Linux kernel it is CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS