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

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Message-ID: <df48ff0b-d96b-7231-1b3d-02509a574c9b@redhat.com>
Date:   Sat, 18 Feb 2023 15:01:54 +0100
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Martin KaFai Lau <martin.lau@...ux.dev>
Cc:     brouer@...hat.com, 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: [xdp-hints] Re: [PATCH bpf-next V2] xdp: bpf_xdp_metadata use
 NODEV for no device support



On 17/02/2023 21.49, Toke Høiland-Jørgensen wrote:
> Stanislav Fomichev <sdf@...gle.com> writes:
> 
>> On Fri, Feb 17, 2023 at 9:55 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>>>
>>> On 2/17/23 9:40 AM, Stanislav Fomichev wrote:
>>>> On Fri, Feb 17, 2023 at 9:39 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>>>>>
>>>>> 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?

Okay, lets go in this direction then.
I will update the drivers to not return EOPNOTSUPP.

What should drivers then return instead.
I will propose that driver return ENODATA instead?

--Jesper