linux-kernel - Re: [PATCH] af_packet: Handle outgoing VLAN packets without hardware offloading

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Message-ID: <3acef339-cdeb-407c-b643-0481bfbe3c80@orange.com>
Date: Sat, 25 May 2024 22:55:59 +0200
From: alexandre.ferrieux@...nge.com
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, Chengen Du
	<chengen.du@...onical.com>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] af_packet: Handle outgoing VLAN packets without hardware
 offloading

On 25/05/2024 17:51, Willem de Bruijn wrote:
> 
> First, we need to even understand better why anything is using
> SOCK_DGRAM when access to L2.5 headers is important, and whether the
> process can convert to using SOCK_RAW instead.

For libpcap, it seems to be linked to the fact that the "any" device can 
aggregate links with varied L2 header sizes, which in turn complicates filtering 
(see Guy Harris' comment on this [1]).

Given that 99% of useful traffic is Ethernet, such considerations look awkward 
now. I for one would love to see an "any2" based on SOCK_RAW. And while you're 
at it, please let the new variant of SLL contain the full Ethernet header at the 
end, so that a simple offset gives access to the whole linear wire image...

-Alex

[1] https://github.com/the-tcpdump-group/libpcap/issues/1105#issuecomment-1092221785
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