netdev - Re: [PATCH v21 bpf-next 18/23] libbpf: Add SEC name for xdp

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Date:   Fri, 14 Jan 2022 17:35:48 +0100
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Jesper Dangaard Brouer <jbrouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        Zvi Effron <zeffron@...tgames.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Shay Agroskin <shayagr@...zon.com>,
        john fastabend <john.fastabend@...il.com>,
        David Ahern <dsahern@...nel.org>,
        Eelco Chaudron <echaudro@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Saeed Mahameed <saeed@...nel.org>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        tirthendu.sarkar@...el.com
Subject: Re: [PATCH v21 bpf-next 18/23] libbpf: Add SEC name for xdp_mb
 programs

> On Thu, Jan 13, 2022 at 2:22 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> > > > >
> > > > > I would prefer to keep the "_mb" postfix, but naming is hard and I am
> > > > > polarized :)
> > > >
> > > > I would lean towards keeping _mb as well, but if it does have to be
> > > > changed why not _mbuf? At least that's not quite as verbose :)
> > >
> > > I dislike the "mb" abbreviation as I forget it stands for multi-buffer.
> > > I like the "mbuf" suggestion, even-though it conflicts with (Free)BSD mbufs
> > > (which is their SKB).
> >
> > If we all agree, I can go over the series and substitute mb postfix with mbuf.
> > Any objections?
> 
> mbuf has too much bsd taste.
> 
> How about ".frags" instead?
> Then xdp_buff_is_mb() will be xdp_buff_has_frags().
> 
> I agree that it's not obvious what "mb" suffix stands for,
> but I don't buy at all that it can be confused with "megabyte".
> It's the context that matters.
> In "100mb" it's obvious that "mb" is likely "megabyte",
> but in "xdp.mb" it's certainly not "xdp megabyte".
> Such a sentence has no meaning.
> Imagine we used that suffix for "tc"...
> it would be "tc.mb"... "Traffic Control Megabyte" ??
> 
> Anyway "xdp.frags" ?
> 
> Btw "xdp_cpumap" should be cleaned up.
> xdp_cpumap is an attach type. It's not prog type.
> Probably it should be "xdp/cpumap" to align with "cgroup/bind[46]" ?

If we change xdp_devmap/ in xdp/devmap (and xdp_cpumap/ in xdp/cpumap),
are we going to break backward compatibility?
Maybe there are programs already deployed using it.
This is not a xdp multi-buff problem since we are not breaking backward
compatibility there, we can just use:

xdp.frags/devmap
xdp.frags/cpumap

Moreover in samples/bpf we have something like:

SEC("xdp_devmap/egress")

It seems to me the egress postfix is not really used, right? Can we just drop
it?

Regards,
Lorenzo

> 
> In patch 22 there is a comment:
> /* try to attach BPF_XDP_DEVMAP multi-buff program"
> 
> It creates further confusion. There is no XDP_DEVMAP program type.
> It should probably read
> "Attach BPF_XDP program with frags to devmap"
> 
> Patch 21 still has "CHECK". Pls replace it with ASSERT.

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