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

- From: Willem de Bruijn \<willemdebruijn.kernel@gmail.com\>
- Date: 2025-02-25 18:26:42 
- List: netdev
- Page: https://ratatoskr.run/netdev/2025/02/2943951
- Thread: https://ratatoskr.run/netdev/2025/02/2941285/t.md

```text
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 <redacted>

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