netdev - Re: [PATCH] net: implement IP_RECVHDRS option to get full headers through recvmsg cmsg.

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Message-Id: <20180402.104215.190691630693019156.davem@davemloft.net>
Date:   Mon, 02 Apr 2018 10:42:15 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     zenczykowski@...il.com
Cc:     maze@...gle.com, netdev@...r.kernel.org, lrizzo@...gle.com,
        edumazet@...gle.com
Subject: Re: [PATCH] net: implement IP_RECVHDRS option to get full headers
 through recvmsg cmsg.

From: Maciej Żenczykowski <zenczykowski@...il.com>
Date: Sat, 31 Mar 2018 22:43:14 -0700

> From: Luigi Rizzo <lrizzo@...gle.com>
> 
> We have all sorts of different ways to fetch pre-UDP payload metadata:
>   IP_RECVTOS
>   IP_RECVTTL
>   IP_RECVOPTS
>   IP_RETOPTS
> 
> But nothing generic which simply allows you to receive the entire packet header.
> 
> This is in similar vein to TCP_SAVE_SYN but for UDP and other datagram sockets.
> 
> This is envisioned as a way to get GUE extension metadata for encapsulated
> packets, but implemented in a way to be much more future proof.
> 
> (Implemented by Luigi, who asked me to send it upstream)
> 
> Cc: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Luigi Rizzo <lrizzo@...gle.com>
> Signed-off-by: Maciej Żenczykowski <maze@...gle.com>

This is an ipv4 level socket option, so why are you copying in the MAC
header(s)?

That part I don't like at all.

First of all, you have no idea what the link level protocol is for that
MAC header, therefore how could you even begin to interpret it's contents
correctly?

Second of all, MAC level details belong not in AF_INET socket interfaces.

Thank you.