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Date: Thu, 10 Jul 2025 10:28:25 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: "Song, Yoong Siang" <yoong.siang.song@intel.com>
Cc: Stanislav Fomichev <stfomichev@gmail.com>, Daniel Borkmann
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Subject: Re: [PATCH bpf-next,v3 2/2] selftests/bpf: Enhance XDP Rx metadata
 handling
Message-ID: <20250710102825.744f2653@kernel.org>
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On Thu, 10 Jul 2025 15:35:32 +0000 Song, Yoong Siang wrote:
> Would it be advisable to update the documentation to indicate that
> drivers are expected to copy any device-reserved metadata from the
> metadata area? This would ensure that xdp_buff->data_meta is equal
> to xdp_buff->data before a BPF program is executed. This approach
> would allow BPF programs to freely manipulate the metadata area
> in XDP_REDIRECT scenarios.

Documenting sounds good.

> Additionally, I am uncertain about the need to overriding metadata in
> XDP_PASS scenarios. Should BPF programs refrain from overriding the
> metadata in this case?

IIRC XDP_PASS was the initial use case for the metadata area.
The driver needs to evacuate any HW metadata before handing over
to the XDP program.