netdev - Re: [PATCH bpf-next 1/3] libbpf: xsk: use bpf

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Date:   Wed, 17 Feb 2021 08:36:14 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Dan Siemon <dan@...erfire.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Ciara Loftus <ciara.loftus@...el.com>
Subject: Re: [PATCH bpf-next 1/3] libbpf: xsk: use bpf_link

On Wed, Feb 17, 2021 at 8:16 AM Magnus Karlsson
<magnus.karlsson@...il.com> wrote:
>
> On Wed, Feb 17, 2021 at 3:26 AM Dan Siemon <dan@...erfire.com> wrote:
> >
> > On Mon, 2021-02-15 at 22:38 +0100, Toke Høiland-Jørgensen wrote:
> > > The idea is to keep libbpf focused on bpf, and move the AF_XDP stuff
> > > to
> > > libxdp (so the socket stuff in xsk.h). We're adding the existing code
> > > wholesale, and keeping API compatibility during the move, so all
> > > that's
> > > needed is adding -lxdp when compiling. And obviously the existing
> > > libbpf
> > > code isn't going anywhere until such a time as there's a general
> > > backwards compatibility-breaking deprecation in libbpf (which I
> > > believe
> > > Andrii is planning to do in an upcoming and as-of-yet unannounced
> > > v1.0
> > > release).
> >
> > I maintain a Rust binding to the AF_XDP parts of libbpf [1][2]. On the
> > chance that more significant changes can be entertained in the switch
> > to libxdp... The fact that many required functions like the ring access
> > functions exist only in xsk.h makes building a binding more difficult
> > because we need to wrap it with an extra C function [3]. From that
> > perspective, it would be great if those could move to xsk.c.
>
> The only reason they were put in xsk.h is performance. But with LTO
> (link-time optimizations) being present in most C-compilers these
> days, it might not be a valid argument anymore. I will perform some
> experiments and let you know. As you say, it would be much nicer to
> hide away these functions in the library proper and make your life
> easier.

I would be very grateful for any more suggested changes that users out
there would like to see. Now, when we move to libxdp is the perfect
chance to fix those things. We might even decide to partially break
compatibility or change some behavior if the gain is large enough.

> > [1] - https://github.com/aterlo/afxdp-rs
> > [2] - https://github.com/alexforster/libbpf-sys
> > [3] - https://github.com/alexforster/libbpf-sys/blob/master/bindings.c
> >