linux-kernel - Re: [PATCH net-next v8 0/6] move CAN skb headroom content to skb extensions

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Message-ID: <7d544645-8699-409f-89c0-6fc606113627@redhat.com>
Date: Tue, 3 Feb 2026 15:40:03 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: socketcan@...tkopp.net, Marc Kleine-Budde <mkl@...gutronix.de>,
 Vincent Mailhol <mailhol@...nel.org>,
 Robin van der Gracht <robin@...tonic.nl>,
 Oleksij Rempel <o.rempel@...gutronix.de>, kernel@...gutronix.de,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>
Cc: linux-can@...r.kernel.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH net-next v8 0/6] move CAN skb headroom content to skb
 extensions

On 2/1/26 3:33 PM, Oliver Hartkopp via B4 Relay 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.
> 
> [1] https://lore.kernel.org/linux-can/20260104074222.29e660ac@kernel.org/

Could you please share how skb_ext size change with this series?
(possibly breaking down the actual size to each separate extension).

Ideally/hopefully the  skbuff_ext_cache size is not going to change, and
that would ensure that this change will not cause any indirect regressions.

/P