From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next 0/8] Add complementary BPF conditional jump
 instructions
Date: Mon, 31 Dec 2012 19:29:02 -0800
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	 <20121231.143715.1238174487756359071.davem@davemloft.net>
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To: David Miller <davem@davemloft.net>
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On Mon, 2012-12-31 at 14:37 -0800, David Miller wrote:

> Whilst I agree that adding NE jumps adds great value and closes a
> serious gap, the rest can be synthesized by simply swapping the
> arguments and using a comparison that does already exist.
> 
> Why isn't that sufficient?

I am afraid none of these patches is needed at all.

Swapping the jt/jf is plainly enough for the user land compiler.

libcap seems to do it already

# tcpdump -i lo 'len!=0 && ip6' -d
(000) ld       #pktlen
(001) jeq      #0x0             jt 5	jf 2
(002) ldh      [12]
(003) jeq      #0x86dd          jt 4	jf 5
(004) ret      #96
(005) ret      #0
# tcpdump -i lo 'len==0 && ip6' -d
(000) ld       #pktlen
(001) jeq      #0x0             jt 2	jf 5
(002) ldh      [12]
(003) jeq      #0x86dd          jt 4	jf 5
(004) ret      #96
(005) ret      #0