netdev - Re: [RFC bpf-next 2/8] net: introduce XDP features flag

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Date:   Tue, 20 Dec 2022 23:51:31 +0100
From:   Marek Majtyka <alardam@...il.com>
To:     Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, davem@...emloft.net, hawk@...nel.org,
        pabeni@...hat.com, edumazet@...gle.com, toke@...hat.com,
        memxor@...il.com, saeedm@...dia.com, anthony.l.nguyen@...el.com,
        gospo@...adcom.com, vladimir.oltean@....com, nbd@....name,
        john@...ozen.org, leon@...nel.org, simon.horman@...igine.com,
        aelior@...vell.com, christophe.jaillet@...adoo.fr,
        ecree.xilinx@...il.com, grygorii.strashko@...com, mst@...hat.com,
        bjorn@...nel.org, magnus.karlsson@...el.com,
        maciej.fijalkowski@...el.com, intel-wired-lan@...ts.osuosl.org
Subject: Re: [RFC bpf-next 2/8] net: introduce XDP features flag

On Tue, Dec 20, 2022 at 10:20 AM Lorenzo Bianconi
<lorenzo.bianconi@...hat.com> wrote:
>
> > On Mon, 19 Dec 2022 16:41:31 +0100 Lorenzo Bianconi wrote:
> > > +=====================
> > > +Netdev XDP features
> > > +=====================
> > > +
> > > + * XDP FEATURES FLAGS
> > > +
> > > +Following netdev xdp features flags can be retrieved over route netlink
> > > +interface (compact form) - the same way as netdev feature flags.
> >
> > How likely is it that I'll be able to convince you that cramming more
> > stuff in rtnl is a bad idea? I can convert this for you to a YAML-
> > -compatible genetlink family for you in a jiffy, just say yes :S
> >
> > rtnl is hard to parse, and already overloaded with random stuff.
> > And the messages are enormous.
>
> Hi Jakub,
>
> I am fine to use YAML for this, but I will let Marek comment since he is the
> original author of this patch.
>
> >
> > > +These features flags are read only and cannot be change at runtime.
> > > +
> > > +*  XDP_ABORTED
> > > +
> > > +This feature informs if netdev supports xdp aborted action.
> > > +
> > > +*  XDP_DROP
> > > +
> > > +This feature informs if netdev supports xdp drop action.
> > > +
> > > +*  XDP_PASS
> > > +
> > > +This feature informs if netdev supports xdp pass action.
> > > +
> > > +*  XDP_TX
> > > +
> > > +This feature informs if netdev supports xdp tx action.
> > > +
> > > +*  XDP_REDIRECT
> > > +
> > > +This feature informs if netdev supports xdp redirect action.
> > > +It assumes the all beforehand mentioned flags are enabled.
> > > +
> > > +*  XDP_SOCK_ZEROCOPY
> > > +
> > > +This feature informs if netdev driver supports xdp zero copy.
> > > +It assumes the all beforehand mentioned flags are enabled.
> >
> > Why is this "assumption" worth documenting?
>
> I guess we can remove it.
> @Marek: any comment?
>
> >
> > > +*  XDP_HW_OFFLOAD
> > > +
> > > +This feature informs if netdev driver supports xdp hw oflloading.
> > > +
> > > +*  XDP_TX_LOCK
> > > +
> > > +This feature informs if netdev ndo_xdp_xmit function requires locking.
> >
> > Why is it relevant to the user?
>
> Probably not, I kept it since it was in Marek's original patch.
> @Marek: any comment?
>
> >
> > > +*  XDP_REDIRECT_TARGET
> > > +
> > > +This feature informs if netdev implements ndo_xdp_xmit callback.
> >
> > Does it make sense to rename XDP_REDIRECT -> XDP_REDIRECT_SOURCE then?
>
> yes, naming is always hard :)
>
> >
> > > +*  XDP_FRAG_RX
> > > +
> > > +This feature informs if netdev implements non-linear xdp buff support in
> > > +the driver napi callback.
> >
> > Who's the target audience? Maybe FRAG is not the best name?
> > Scatter-gather or multi-buf may be more widely understood.
>
> ack, fine. I will rename it in the formal series.
>
> Regards,
> Lorenzo
>
> >
> > > +*  XDP_FRAG_TARGET
> > > +
> > > +This feature informs if netdev implements non-linear xdp buff support in
> > > +ndo_xdp_xmit callback. XDP_FRAG_TARGET requires XDP_REDIRECT_TARGET is properly
> > > +supported.
> >
Everybody is allowed to make a good use of it. Every improvement is
highly appreciated. Thanks Lorenzo for taking this over.
Regards
Marek