linux-kernel - RE: [PATCH bpf-next 0/2] Clarify and Enhance XDP Rx Metadata Handling

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Message-ID: <IA3PR11MB9254F5CDD8812A6D56932407D84EA@IA3PR11MB9254.namprd11.prod.outlook.com>
Date: Tue, 8 Jul 2025 02:32:03 +0000
From: "Song, Yoong Siang" <yoong.siang.song@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: "David S . Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>, Jonathan Corbet <corbet@....net>, Alexei Starovoitov
	<ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, "Jesper Dangaard
 Brouer" <hawk@...nel.org>, 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>, "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 0/2] Clarify and Enhance XDP Rx Metadata Handling

On Tuesday, July 8, 2025 10:18 AM, Jakub Kicinski <kuba@...nel.org> wrote:
>On Tue, 8 Jul 2025 02:06:11 +0000 Song, Yoong Siang wrote:
>>> Why would the driver need to move it back?
>>> On XDP_PASS an skb is constructed, so the metadata should
>>> be transferred to the skb. There is no need to copy it back
>>> as a prepend.
>>
>> I said so because I thought need to put back the timestamp
>> as prepend and then point skb_shared_hwtstamps.netdev_data to it
>> to support the ndo_get_tstamp().
>
>No need, the timestamps are set in shared info directly.
>There are multiple drivers which use the metadata prepend
>method, so I'm pretty sure it should work.

Thanks for pointing me in the right direction.
I'll proceed with updating the IGC driver and conduct tests
to ensure everything works as expected.