netdev - Re: [net-next 0/6] move CAN skb headroom content to skb extensions

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Message-ID: <67cb17f4-2f72-4847-aa04-3633f3d8df33@hartkopp.net>
Date: Wed, 28 Jan 2026 09:42:14 +0100
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: Jakub Kicinski <kuba@...nel.org>, Marc Kleine-Budde <mkl@...gutronix.de>
Cc: netdev@...r.kernel.org, linux-can@...r.kernel.org
Subject: Re: [net-next 0/6] move CAN skb headroom content to skb extensions

On 28.01.26 02:49, Jakub Kicinski wrote:
> On Sun, 25 Jan 2026 21:15:55 +0100 Oliver Hartkopp wrote:
>> CAN bus related skbuffs (ETH_P_CAN/ETH_P_CANFD/ETH_P_CANXL) simply contain
>> CAN frame structs for CAN CC/FD/XL of skb->len length at skb->data.
>> Those CAN skbs do not have network/mac/transport headers nor other such
>> references for encapsulated protocols like ethernet/IP protocols.
>>
>> To store data for CAN specific use-cases all CAN bus related skbuffs are
>> created with a 16 byte private skb headroom (struct can_skb_priv).
>> Using the skb headroom and accessing skb->head for this private data
>> led to several problems in the past likely due to "The struct can_skb_priv
>> business is highly unconventional for the networking stack." [1]
>>
>> This patch set aims to remove the unconventional skb headroom usage for
>> CAN bus related skbuffs and use the common skb extensions instead.
> 
> This is fine. Wish we could make md_dst work, since skb_ext still burns
> a bit in the skb (last extension bit in fact, next user will have to
> bump the filed size). And you very much do not route these frames,
> so dst would work perfectly fine. But whatever.
> 
> lore never received patch 6, tho, you'll need to repost.

Thanks for looking at it.

In fact patch 6 stuck in my providers mail system which responded this 
to (only) patch 6 ¯\_(ツ)_/¯

5.7.1 Refused by local policy. No SPAM please! (B-EX 
155302::1769588601-AC38E895-223F95BA/10/71040183929) see 
https://www.strato-hosting.co.uk/faq/product/why-are-my-emails-not-being-delivered 
[MSG0011]

As this could not been solved since Sunday I'll kindly ask Marc to send 
the attached v2 patchset (including your __u32 remark) to the mailing 
list, so that also the AI bot can take a look at it.

Many thanks!
Oliver
Download attachment "can_skb_ext.tar.gz" of type "application/gzip" (14024 bytes)