netdev - Re: [PATCH 4/4] ipv6: symbol_get to access a sit symbol

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Message-Id: <20200516.135548.2079608042651975047.davem@davemloft.net>
Date:   Sat, 16 May 2020 13:55:48 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     hch@....de
Cc:     kuba@...nel.org, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] ipv6: symbol_get to access a sit symbol

From: Christoph Hellwig <hch@....de>
Date: Fri, 15 May 2020 08:33:24 +0200

> My initial plan was to add a ->tunnel_ctl method to the net_device_ops,
> and lift the copy_{to,from}_user for SIOCADDTUNNEL, SIOCCHGTUNNEL,
> SIOCDELTUNNEL and maybe SIOCGETTUNNEL to net/socket.c.  But that turned
> out to have two problems:
> 
>  - first these ioctls names use SIOCDEVPRIVATE range, that can also
>    be implemented by other drivers
>  - the ip_tunnel_parm struture is only used by the ipv4 tunneling
>    drivers (including sit), the "real" ipv6 tunnels use a
>    ip6_tnl_parm or ip6_tnl_parm structure instead

Yes, this is the core of the problem, the user provided data's type
is unknown until we are very deep in the call chains.

I wonder if there is some clever way to propagate this size value
"up"?