netdev - Re: [PATCH bpf-next V2] xdp: bpf_xdp_metadata use NODEV for no device support

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Date:   Fri, 17 Feb 2023 09:38:54 -0800
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     Stanislav Fomichev <sdf@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, martin.lau@...nel.org,
        ast@...nel.org, daniel@...earbox.net, alexandr.lobakin@...el.com,
        larysa.zaremba@...el.com, xdp-hints@...-project.net
Subject: Re: [PATCH bpf-next V2] xdp: bpf_xdp_metadata use NODEV for no device
 support

On 2/17/23 9:32 AM, Stanislav Fomichev wrote:
> On 02/17, Jesper Dangaard Brouer wrote:
>> With our XDP-hints kfunc approach, where individual drivers overload the
>> default implementation, it can be hard for API users to determine
>> whether or not the current device driver have this kfunc available.
> 
>> Change the default implementations to use an errno (ENODEV), that
>> drivers shouldn't return, to make it possible for BPF runtime to
>> determine if bpf kfunc for xdp metadata isn't implemented by driver.
> 
>> This is intended to ease supporting and troubleshooting setups. E.g.
>> when users on mailing list report -19 (ENODEV) as an error, then we can
>> immediately tell them their device driver is too old.
> 
> I agree with the v1 comments that I'm not sure how it helps.
> Why can't we update the doc in the same fashion and say that
> the drivers shouldn't return EOPNOTSUPP?
> 
> I'm fine with the change if you think it makes your/users life
> easier. Although I don't really understand how. We can, as Toke
> mentioned, ask the users to provide jited program dump if it's
> mostly about user reports.

and there is xdp-features also.