Re: [PATCH nf-next] netfilter: meta: add PRANDOM support

[Daniel Borkmann <daniel@iogearbox.net>]

Hi Florian,

On 02/16/2016 01:09 PM, Florian Westphal wrote:
> Can be used to randomly match a packet, e.g. for statistical traffic
> sampling.
>
> See commit 3ad0040573b0c00f8848
> ("bpf: split state from prandom_u32() and consolidate {c, e}BPF prngs")
> for more info why this doesn't use prandom_u32 directly.
>
> Unlike bpf nft_meta can be built as a module, so add an EXPORT_SYMBOL
> for prandom_seed_full_state too.
>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Signed-off-by: Florian Westphal <fw@strlen.de>
[...]
> @@ -241,6 +248,7 @@ int nft_meta_get_init(const struct nft_ctx *ctx,
>   {
>   	struct nft_meta *priv = nft_expr_priv(expr);
>   	unsigned int len;
> +	static bool prand_inited __read_mostly;
>
>   	priv->key = ntohl(nla_get_be32(tb[NFTA_META_KEY]));
>   	switch (priv->key) {
> @@ -277,6 +285,13 @@ int nft_meta_get_init(const struct nft_ctx *ctx,
>   	case NFT_META_OIFNAME:
>   		len = IFNAMSIZ;
>   		break;
> +	case NFT_META_PRANDOM:
> +		if (!prand_inited) {
> +			prandom_seed_full_state(&nft_prandom_state);
> +			prand_inited = true;
> +		}

Should this be: prandom_init_once() ?

> +		len = sizeof(u32);
> +		break;
>   	default:
>   		return -EOPNOTSUPP;
>   	}
>

Thanks,
Daniel