netdev - RE: [PATCH bpf-next,v3 2/2] selftests/bpf: Enhance XDP Rx metadata handling

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Message-ID: <IA3PR11MB92546301B67FB3A9FDCD716DD842A@IA3PR11MB9254.namprd11.prod.outlook.com>
Date: Fri, 4 Jul 2025 01:17:06 +0000
From: "Song, Yoong Siang" <yoong.siang.song@...el.com>
To: Jesper Dangaard Brouer <hawk@...nel.org>, "David S . Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>, Jonathan Corbet <corbet@....net>, Alexei Starovoitov
	<ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, John Fastabend
	<john.fastabend@...il.com>, Stanislav Fomichev <sdf@...ichev.me>, "Andrii
 Nakryiko" <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, "Yonghong
 Song" <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, Hao Luo
	<haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko
	<mykolal@...com>, Shuah Khan <shuah@...nel.org>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: RE: [PATCH bpf-next,v3 2/2] selftests/bpf: Enhance XDP Rx metadata
 handling

On Friday, July 4, 2025 1:05 AM, Jesper Dangaard Brouer <hawk@...nel.org> wrote:
>On 02/07/2025 18.57, Song Yoong Siang wrote:
>> Introduce the XDP_METADATA_SIZE macro as a conservative measure to
>> accommodate any metadata areas reserved by Ethernet devices.
>>
>
>This seems like a sloppy workaround :-(
>
>To me, the problem arise because AF_XDP is lacking the ability to
>communicate the size of the data_meta area.  If we had this capability,
>then we could allow the IGC driver to take some of the space, have the
>BPF-prog expand it futher (bpf_xdp_adjust_meta) and then userspace
>AF_XDP would simply be able to see the size of the data_meta area, and
>apply the struct xdp_meta at right offset.
>
Thanks for your input.

I agree with you that the implementation will be simple if user application
able to get the size of data_meta area. The intention of this patch set is to let
developer aware of such limitations before we have a perfect solution.

Btw, do you got any suggestion on how to expose the metadata length?
I not sure whether xdp_desc.options is a simple and good idea or not?