netdev - Re: [RFC Patch net-next] net_sched: introduce eBPF based Qdisc

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Message-ID: <20210917041903.yuepvbvajtheuvct@kafai-mbp.dhcp.thefacebook.com>
Date:   Thu, 16 Sep 2021 21:19:03 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     Toke Høiland-Jørgensen <toke@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Cong Wang <cong.wang@...edance.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [RFC Patch net-next] net_sched: introduce eBPF based Qdisc

On Fri, Sep 03, 2021 at 06:09:46PM -0700, Cong Wang wrote:
> On Wed, Sep 1, 2021 at 10:45 AM Martin KaFai Lau <kafai@...com> wrote:
> > _if_ it is using as a qdisc object/interface,
> > the patch "looks" easier because it obscures some of the ops/interface
> > from the bpf user.  The user will eventually ask for more flexibility
> > and then an on-par interface as the kernel's qdisc.  If there are some
> > common 'ops', the common bpf code can be shared as a library in userspace
> > or there is also kfunc call to call into the kernel implementation.
> > For existing kernel qdisc author,  it will be easier to use the same
> > interface also.
> 
> Thanks for showing the advantages of a kernel module. And no, we
> are not writing kernel modules in eBPF.
The line is very blurry between a bpf_prog and kernel module,
especially with the advancement of bpf, btf, and CO-RE.

Both bpf_prog.o (struct_ops or not) and some_native_kern_mod.ko are attaching
to some kernel hooks to be called.  If writing bpf and attaching it to a hook
does not work for you, bpf does not fit your case.

> And kfunc call really sucks, it does not even guarantee a stable ABI, it
> is a serious mistake you made for eBPF.
Not ture.  It depends on what is allowed to be called by bpf.
Needless to say I cannot agree with the "sucks" description.

This kind of dismissive discussion is worse than unproductive
and not the best way to use the mailing list time.