linux-kernel - Re: [PATCH bpf-next v5 1/2] bpf, xdp: Add tracepoint to xdp attaching failure

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Message-ID: <1483f6db-35a8-849b-9bda-00ad5aa81eff@gmail.com>
Date:   Wed, 2 Aug 2023 14:51:35 +0800
From:   Leon Hwang <hffilwlqm@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        john.fastabend@...il.com, andrii@...nel.org, martin.lau@...ux.dev,
        song@...nel.org, yonghong.song@...ux.dev, kpsingh@...nel.org,
        sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
        davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
        hawk@...nel.org, rostedt@...dmis.org, mhiramat@...nel.org,
        mykolal@...com, shuah@...nel.org, tangyeechou@...il.com,
        kernel-patches-bot@...com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 1/2] bpf, xdp: Add tracepoint to xdp attaching
 failure



On 2/8/23 06:08, Jakub Kicinski wrote:
> On Tue,  1 Aug 2023 22:26:20 +0800 Leon Hwang wrote:
>> When error happens in dev_xdp_attach(), it should have a way to tell
>> users the error message like the netlink approach.
>>
>> To avoid breaking uapi, adding a tracepoint in bpf_xdp_link_attach() is
>> an appropriate way to notify users the error message.
>>
>> Hence, bpf libraries are able to retrieve the error message by this
>> tracepoint, and then report the error message to users.
> 
> Whatevered-by: Jakub Kicinski <kuba@...nel.org> ?

Oh, it's not responsible for libraries to retrieve the error message. It
should be users' responsibility.

Sorry for the misguiding text.

In the previous patch[0], which changes uapi, it's able to back-propagate
the error message from dev_xdp_attach() to userspace through BPF syscall.
Then, tracepoint idea is suggested to avoid changing uapi. I do agree to
implement a tracepoint to avoid changing uapi.

[0] bpf: Introduce user log
https://lore.kernel.org/bpf/20230708040750.72570-1-hffilwlqm@gmail.com/

Thanks,
Leon