netdev - Re: [PATCH bpf-next v2 0/7] Add support for XDP

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Date:   Tue, 18 Dec 2018 15:04:00 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Björn Töpel <bjorn.topel@...el.com>
Cc:     Magnus Karlsson <magnus.karlsson@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>, ast@...nel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        William Tu <u9012063@...il.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>, andrew@...n.ch
Subject: Re: [PATCH bpf-next v2 0/7] Add support for XDP_ATTACH

On Mon, Dec 17, 2018 at 04:30:05PM +0100, Björn Töpel wrote:
> > 
> > Instead of introducing the XDP_ATTACH option to the bind call, can we
> > just make this association between rx queue id and xsk every single
> > time we bind? Then it is up to the user via the XDP program if he/she
> > wants to use this by calling xsk_redirect. No new option needed.
> > 
> 
> Nice! Then it would simply be a matter of adding the helper. Much better
> than extending the uapi. Thank you for pointing this out!

Magnus's by-default association approach sounds good to me.
I'm missing though why extra bpf helper is needed.
This soft-bind rx queue with xsk at the time
of normal bind() should work as-is and no program necessary.
No prog -> default assoc. Yet the prog has an ability to redirect
to specific xsk via existing bpf_redirect_map
or via faster (future) xsk_redirect.

Also I agree with Jesper that per-queue programs would be good to have
sooner than later, but I disagree that it's mandatory for this set.
It seems the patches will give us performance boost and simplification
of uapi while per-queue prog api is being discussed and implemented.

I like the other idea too (of having libbpf provide canned bpf progs
for different use cases). That's better than loading them
from the kernel.