netdev - Re: [PATCH bpf-next v3 2/6] net: tun: enable transfer of XDP metadata to skb

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Message-ID: <67be0b60a6b36_25ccfc294f5@willemb.c.googlers.com.notmuch>
Date: Tue, 25 Feb 2025 13:26:40 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Marcus Wichelmann <marcus.wichelmann@...zner-cloud.de>, 
 netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 bpf@...r.kernel.org, 
 linux-kselftest@...r.kernel.org
Cc: willemdebruijn.kernel@...il.com, 
 jasowang@...hat.com, 
 andrew+netdev@...n.ch, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 andrii@...nel.org, 
 eddyz87@...il.com, 
 mykolal@...com, 
 ast@...nel.org, 
 daniel@...earbox.net, 
 martin.lau@...ux.dev, 
 song@...nel.org, 
 yonghong.song@...ux.dev, 
 john.fastabend@...il.com, 
 kpsingh@...nel.org, 
 sdf@...ichev.me, 
 haoluo@...gle.com, 
 jolsa@...nel.org, 
 shuah@...nel.org, 
 hawk@...nel.org, 
 marcus.wichelmann@...zner-cloud.de
Subject: Re: [PATCH bpf-next v3 2/6] net: tun: enable transfer of XDP metadata
 to skb

Marcus Wichelmann wrote:
> When the XDP metadata area was used, it is expected that the same
> metadata can also be accessed from TC, as can be read in the description
> of the bpf_xdp_adjust_meta helper function. In the tun driver, this was
> not yet implemented.
> 
> To make this work, the skb that is being built on XDP_PASS should know
> of the current size of the metadata area. This is ensured by adding
> calls to skb_metadata_set. For the tun_xdp_one code path, an additional
> check is necessary to handle the case where the externally initialized
> xdp_buff has no metadata support (xdp->data_meta == xdp->data + 1).
> 
> More information about this feature can be found in the commit message
> of commit de8f3a83b0a0 ("bpf: add meta pointer for direct access").
> 
> Signed-off-by: Marcus Wichelmann <marcus.wichelmann@...zner-cloud.de>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>