netdev - Re: [PATCH bpf-next v2 1/2] net: xdp: refactor XDP_QUERY_PROG{,

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Date:   Tue, 4 Jun 2019 07:18:48 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Saeed Mahameed <saeedm@...lanox.com>
Cc:     "jakub.kicinski@...ronome.com" <jakub.kicinski@...ronome.com>,
        "toke@...hat.com" <toke@...hat.com>,
        "magnus.karlsson@...el.com" <magnus.karlsson@...el.com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "ast@...nel.org" <ast@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "bjorn.topel@...el.com" <bjorn.topel@...el.com>
Subject: Re: [PATCH bpf-next v2 1/2] net: xdp: refactor XDP_QUERY_PROG{,_HW}
 to netdev

On Mon, 3 Jun 2019 at 23:20, Saeed Mahameed <saeedm@...lanox.com> wrote:
>
> On Mon, 2019-06-03 at 11:04 +0200, Björn Töpel wrote:
> > On Sat, 1 Jun 2019 at 21:42, Jakub Kicinski
> > <jakub.kicinski@...ronome.com> wrote:
> > > On Fri, 31 May 2019 19:18:17 +0000, Saeed Mahameed wrote:
> > > > On Fri, 2019-05-31 at 11:42 +0200, Björn Töpel wrote:
> > > > > From: Björn Töpel <bjorn.topel@...el.com>
> > > > >
> > > > > All XDP capable drivers need to implement the
> > > > > XDP_QUERY_PROG{,_HW}
> > > > > command of ndo_bpf. The query code is fairly generic. This
> > > > > commit
> > > > > refactors the query code up from the drivers to the netdev
> > > > > level.
> > > > >
> > > > > The struct net_device has gained two new members: xdp_prog_hw
> > > > > and
> > > > > xdp_flags. The former is the offloaded XDP program, if any, and
> > > > > the
> > > > > latter tracks the flags that the supplied when attaching the
> > > > > XDP
> > > > > program. The flags only apply to SKB_MODE or DRV_MODE, not
> > > > > HW_MODE.
> > > > >
> > > > > The xdp_prog member, previously only used for SKB_MODE, is
> > > > > shared
> > > > > with
> > > > > DRV_MODE. This is OK, due to the fact that SKB_MODE and
> > > > > DRV_MODE are
> > > > > mutually exclusive. To differentiate between the two modes, a
> > > > > new
> > > > > internal flag is introduced as well.
> > > >
> > > > Just thinking out loud, why can't we allow any combination of
> > > > HW/DRV/SKB modes? they are totally different attach points in a
> > > > totally
> > > > different checkpoints in a frame life cycle.
> > >
> > > FWIW see Message-ID: <20190201080236.446d84d4@...hat.com>
> > >
> >
> > I've always seen the SKB-mode as something that will eventually be
> > removed.
> >
>
> I don't think so, we are too deep into SKB-mode.
>

You might be right. :-(

Are you envisioning sk_buff specfic XDP_SKB functions, that only apply
for XDP_SKB? Ick.

> > Clickable link:
> > https://lore.kernel.org/netdev/20190201080236.446d84d4@redhat.com/ :-
> > P
> >
>
> So we are all hanging on Jesper's refactoring ideas that are not
> getting any priority for now :).
>
>
> > > > Down the road i think we will utilize this fact and start
> > > > introducing
> > > > SKB helpers for SKB mode and driver helpers for DRV mode..
> > >
> > > Any reason why we would want the extra complexity?  There is
> > > cls_bpf
> > > if someone wants skb features after all..
>
> Donno, SKB mode is earlier in the stack maybe ..
>
>