netdev - Re: [PATCH] filter: added BPF random opcode

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Message-ID: <1397572894.4222.98.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 15 Apr 2014 07:41:34 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Borkmann <dborkman@...hat.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 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.


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