Re: [PATCH RFC net-next] net: Use fixed slots for skb extensions

[Oliver Hartkopp <socketcan@hartkopp.net>]

On 27.08.26 09:42, Paolo Abeni wrote:
> On 8/26/26 11:02 PM, Florian Westphal wrote:
>> Jakub Sitnicki <jakub@cloudflare.com> wrote:

> Still WRT optimizing skb_ext size, I think that it should be feasible to
> optimize the layout proposed by Florian by taking in account that some
> exts are 'mutually exclusive' i.e. on top of my head mptcp and bridge
> should never be attached to the same skb, and I *guess* can_skb_ext is
> mutually exclusive with most of the others.

I would say with *all* of the others. CAN skbs only interact with 
ARPHDR_CAN netdevs containing a special ml_priv reference. And 
routing/forwarding is done by a CAN specific net/can/gw.c code.

The only code outside net/can that looks into CAN skbs is:
em_canid.c  Ematch rule to match CAN frames according to their CAN IDs

But I think this is not even relevant for CONFIG_NET_TC_SKB_EXT.

> The layout could be adapted to such constraints, and there could be
> run-time checks (under DEBUG_NET) to verify such constrains at skb_add
> time leveraging `present_extensions` and a static matrix describing the
> mutual exclusive status for all extensions.

+1

Best regards,
Oliver