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Date: Mon, 7 Jul 2025 13:55:07 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Song Yoong Siang <yoong.siang.song@intel.com>
Cc: "David S . Miller" <davem@davemloft.net>, Eric Dumazet
 <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>, Simon Horman
 <horms@kernel.org>, Jonathan Corbet <corbet@lwn.net>, Alexei Starovoitov
 <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, Jesper Dangaard
 Brouer <hawk@kernel.org>, John Fastabend <john.fastabend@gmail.com>,
 Stanislav Fomichev <sdf@fomichev.me>, Andrii Nakryiko <andrii@kernel.org>,
 Martin KaFai Lau <martin.lau@linux.dev>, Eduard Zingerman
 <eddyz87@gmail.com>, Song Liu <song@kernel.org>, Yonghong Song
 <yonghong.song@linux.dev>, KP Singh <kpsingh@kernel.org>, Hao Luo
 <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, Mykola Lysenko
 <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>, netdev@vger.kernel.org,
 linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
 bpf@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf-next 0/2] Clarify and Enhance XDP Rx Metadata
 Handling
Message-ID: <20250707135507.29cb55be@kernel.org>
In-Reply-To: <20250701042940.3272325-1-yoong.siang.song@intel.com>
References: <20250701042940.3272325-1-yoong.siang.song@intel.com>
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On Tue,  1 Jul 2025 12:29:38 +0800 Song Yoong Siang wrote:
>                         |<---sizeof(xdp_meta)--|
>                         |                      |
>                  struct xdp_meta               rx_desc->address
>                         ^                      ^
>                         |                      |
> +----------+----------------------+------------+------+
> | headroom |    custom metadata   |  reserved  | data |
> +----------+----------------------+------------+------+
>            ^                      ^            ^
>            |                      |            |
>     struct xdp_meta     xdp_buff->data_meta    xdp_buff->data
>            |                      |
>            |<---sizeof(xdp_meta)--|

Huh. Did AF_XDP maintainers explicitly sign off on this or it's just how
IGC implementation works and nobody noticed?

For normal XDP my understanding is that its the driver's responsibility
to move the "reserved" stuff out of place before presenting the frame to
program.