netdev - Re: [PATCH bpf-next v2 2/6] net: tun: enable transfer of XDP metadata to skb

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Message-ID: <fea35f08-3f29-4f7e-8be5-c77d4cee8be1@hetzner-cloud.de>
Date: Wed, 19 Feb 2025 16:15:17 +0100
From: Marcus Wichelmann <marcus.wichelmann@...zner-cloud.de>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Cc: jasowang@...hat.com, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, ast@...nel.org,
 daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev,
 eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, mykolal@...com, shuah@...nel.org,
 hawk@...nel.org
Subject: Re: [PATCH bpf-next v2 2/6] net: tun: enable transfer of XDP metadata
 to skb

Am 19.02.25 um 16:06 schrieb Willem de Bruijn:
> Marcus Wichelmann wrote:
>> Am 18.02.25 um 02:47 schrieb Willem de Bruijn:
>>> [...]
>>> This is pointer comparison, which is tricky wrt type. It likely is
>>> ptrdiff_t and thus signed. But may want to use max_t(long int, ..) to
>>> make this explicit.
>>
>> Ah, I see, good point.
>>
>> So like that?
>>
>> 	metasize = max_t(long int, xdp->data - xdp->data_meta, 0);
>> 	if (metasize)
>> 		skb_metadata_set(skb, metasize);
> 
> Or just this? Also ensures the test uses signed int.
> 
>      int metasize;
> 
>      ...
> 
> 
>      metasize = xdp->data - xdp->data_meta;
>      if (metasize > 0)
>              skb_metadata_set(skb, metasize);
> 

Well, yeah, just keep it simple I guess. ;) Will do that.

I'll send a V3 patch series with the change.

Thanks!

Marcus