netdev - Re: [RFC PATCH 2/2] bpf: let bpf_warn_invalid_xdp

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Date:   Mon, 15 Nov 2021 18:09:28 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, bpf@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] bpf: let bpf_warn_invalid_xdp_action() report
 more info

Paolo Abeni <pabeni@...hat.com> writes:

>> > -	pr_warn_once("%s XDP return value %u, expect packet loss!\n",
>> > +	pr_warn_once("%s XDP return value %u on prog %d dev %s attach type %d, expect packet loss!\n",
>> >  		     act > act_max ? "Illegal" : "Driver unsupported",
>> > -		     act);
>> > +		     act, prog->aux->id, dev->name, prog->expected_attach_type);
>> 
>> This will only ever trigger once per reboot even if the message differs,
>> right? Which makes it less useful as a debugging aid; so I'm not sure if
>> it's really worth it with this intrusive change unless we also do
>> something to add a proper debugging aid (like a tracepoint)...
>
> Yes, the idea would be to add a tracepoint there, if there is general
> agreement about this change.
>
> I think this patch is needed because the WARN_ONCE splat gives
> implicitly information about the related driver and attach type.
> Replacing with a simple printk we lose them.

Ah, right, good point. Pointing that out in the commit message might be
a good idea; otherwise people may miss that ;)

-Toke