netdev - Re: [PATCH bpf-next V1 3/6] bpf: add BPF-helper for reading MTU from net

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Message-ID: <a8b0dd01-bd6a-2a28-154e-c30a79ce3c83@gmail.com>
Date:   Wed, 7 Oct 2020 09:35:39 -0700
From:   David Ahern <dsahern@...il.com>
To:     Maciej Żenczykowski <maze@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        bpf <bpf@...r.kernel.org>, Linux NetDev <netdev@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Shaun Crampton <shaun@...era.io>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Marek Majkowski <marek@...udflare.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCH bpf-next V1 3/6] bpf: add BPF-helper for reading MTU from
 net_device via ifindex

On 10/6/20 6:24 PM, Maciej Żenczykowski wrote:
> 
> FYI: It would be nice to have a similar function to return a device's
> L2 header size (ie. 14 for ethernet) and/or hwtype.

Why does that need to be looked up via a helper? It's a static number
for a device and can plumbed to a program in a number of ways.