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

From: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Lorenzo Bianconi <lorenzo@kernel.org>,
	bpf@vger.kernel.org, netdev@vger.kernel.org, ast@kernel.org,
	daniel@iogearbox.net, andrii@kernel.org, davem@davemloft.net,
	hawk@kernel.org, pabeni@redhat.com, edumazet@google.com,
	toke@redhat.com, memxor@gmail.com, alardam@gmail.com,
	saeedm@nvidia.com, anthony.l.nguyen@intel.com,
	gospo@broadcom.com, vladimir.oltean@nxp.com, nbd@nbd.name,
	john@phrozen.org, leon@kernel.org, simon.horman@corigine.com,
	aelior@marvell.com, christophe.jaillet@wanadoo.fr,
	ecree.xilinx@gmail.com, grygorii.strashko@ti.com, mst@redhat.com,
	bjorn@kernel.org, magnus.karlsson@intel.com,
	maciej.fijalkowski@intel.com, intel-wired-lan@lists.osuosl.org
Subject: Re: [RFC bpf-next 2/8] net: introduce XDP features flag
Date: Tue, 20 Dec 2022 10:20:32 +0100	[thread overview]
Message-ID: <Y6F+YJSkI19m/kMv@lore-desk> (raw)
In-Reply-To: <20221219171321.7a67002b@kernel.org>

[-- Attachment #1: Type: text/plain, Size: 2832 bytes --]

> 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.
> 

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]