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Date: Tue, 15 Apr 2014 17:04:18 +0200 From: Daniel Borkmann <dborkman@...hat.com> To: Eric Dumazet <eric.dumazet@...il.com> CC: Chema Gonzalez <chema@...gle.com>, David Miller <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org, ast@...mgrid.com Subject: Re: [PATCH] filter: added BPF random opcode On 04/15/2014 04:41 PM, Eric Dumazet wrote: > On Tue, 2014-04-15 at 09:24 +0200, Daniel Borkmann wrote: > >>> @@ -773,6 +779,7 @@ static bool convert_bpf_extensions(struct sock_filter *fp, >>> case SKF_AD_OFF + SKF_AD_NLATTR: >>> case SKF_AD_OFF + SKF_AD_NLATTR_NEST: >>> case SKF_AD_OFF + SKF_AD_CPU: >>> + case SKF_AD_OFF + SKF_AD_RANDOM: >> >> I think instead of a function call, this sould rather be modelled >> directly into the internal insn set and thus converted differently, >> so we can spare us the call. > > Hmmm... this would need percpu storage, thus preempt disable/enable > calls, and prandom_u32_state() is about 40 instructions. > > This is really not worth the pain. Absolutely, that was not what I meant actually. Calling to prandom_u32_state() is fine, no need to have another prng just for that. I was just wondering if it makes sense to model that directly as an instruction into a jump-table target that calls prandom_u32() from there instead 'indirectly'. Need to think about this a bit more ... -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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