# Re: \[PATCH bpf-next v4 2/6\] net: tun: enable transfer of XDP metadata to skb

- From: Martin KaFai Lau \<martin.lau@linux.dev\>
- Date: 2025-03-03 19:28:54 
- List: netdev
- Page: https://ratatoskr.run/netdev/2025/03/2954129
- Thread: https://ratatoskr.run/netdev/2025/02/2948200/t.md

```text
On 3/3/25 8:13 AM, Marcus Wichelmann wrote:
> Am 28.02.25 um 20:49 schrieb Martin KaFai Lau:
>> On 2/27/25 6:23 AM, 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>
>>> Acked-by: Jason Wang <redacted>
>>> ---
>>>    drivers/net/tun.c | 25 ++++++++++++++++++++++---
>>>    1 file changed, 22 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>> index 4ec8fbd93c8d..70208b3a2e93 100644
>>> --- a/drivers/net/tun.c
>>> +++ b/drivers/net/tun.c
>>
>> The changes have conflicts with the commit 2506251e81d1 ("tun: Decouple vnet handling").
>>
>> It is better to rebase the works onto the bpf-next/net,
>> i.e. the "net" branch instead of the "master" branch.
>
> Alright, will do that. Should I send it as a v5 and still with "PATCH bpf-next"
> in the header or something else?

That should do. The bpf CI should pick up the bpf-next/net if it fails to apply to the bpf-next/master because of the conflict mentioned above.

For patch 3, it should help to avoid the future merge conflict if the open_tuntap() is added a few lines above in the network_helpers.h. For patch 6, the "test_ns_" naming is not in bpf-next/net yet. Other tests in the same file is doing netns_new. May be just do the same and cleanup all at once of this file later.

```