linux-kernel - Re: [PATCH bpf-next] bpf/xdp: Can't detach BPF XDP prog if not exist

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Date:   Wed, 04 May 2022 13:19:49 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Zhengchao Shao <shaozhengchao@...wei.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com
Cc:     ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
        john.fastabend@...il.com, andrii@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, kpsingh@...nel.org,
        bigeasy@...utronix.de, imagedong@...cent.com, petrm@...dia.com,
        memxor@...il.com, arnd@...db.de, weiyongjun1@...wei.com,
        shaozhengchao@...wei.com, yuehaibing@...wei.com
Subject: Re: [PATCH bpf-next] bpf/xdp: Can't detach BPF XDP prog if not exist

Zhengchao Shao <shaozhengchao@...wei.com> writes:

> if user sets nonexistent xdp_flags to detach xdp prog, kernel should
> return err and tell user that detach failed with detail info.
>
> Signed-off-by: Zhengchao Shao <shaozhengchao@...wei.com>

I kinda see your point, but this will change user-visible behaviour that
applications might be relying on, so I don't think we can make this
change at this stage. Why can't your application just query the link for
whether a program is attached?

-Toke