netdev - RE: [PATCH 16/17] netfilter: nft_byteorder: provide 64bit le/be conversion

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Date:	Fri, 8 Jan 2016 14:26:31 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Pablo Neira Ayuso' <pablo@...filter.org>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 16/17] netfilter: nft_byteorder: provide 64bit le/be
 conversion

From: Pablo Neira Ayuso
> Sent: 08 January 2016 14:02
> From: Florian Westphal <fw@...len.de>
> 
> Needed to convert the (64bit) conntrack counters to BE ordering.
> 
...
>  	switch (priv->size) {
> +	case 8: {
> +		u64 src64;
> +
> +		switch (priv->op) {
> +		case NFT_BYTEORDER_NTOH:
> +			for (i = 0; i < priv->len / 8; i++) {
> +				src64 = get_unaligned_be64(&src[i]);
> +				src64 = be64_to_cpu((__force __be64)src64);
> +				put_unaligned_be64(src64, &dst[i]);
> +			}
> +			break;
> +		case NFT_BYTEORDER_HTON:
> +			for (i = 0; i < priv->len / 8; i++) {
> +				src64 = get_unaligned_be64(&src[i]);
> +				src64 = (__force u64)cpu_to_be64(src64);
> +				put_unaligned_be64(src64, &dst[i]);
> +			}
> +			break;
> +		}
> +		break;

That is horrid.
On a little-endian system you are byteswapping the data 3 times.
Image the code on a cpu that doesn't support misaligned transfers
and doesn't have a byteswap instruction.

	David