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

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Message-ID: <20221219171321.7a67002b@kernel.org>
Date:   Mon, 19 Dec 2022 17:13:21 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     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, alardam@...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, lorenzo.bianconi@...hat.com
Subject: Re: [RFC bpf-next 2/8] net: introduce XDP features flag

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.

> +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?

> +*  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?

> +*  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?

> +*  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.

> +*  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.