netdev - Re: [can-next 0/5] can: remove private skb headroom infrastructure

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Message-ID: <aWd5wdMhpEuN9NFB@pengutronix.de>
Date: Wed, 14 Jan 2026 12:10:57 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Oliver Hartkopp <socketcan@...tkopp.net>
Cc: linux-can@...r.kernel.org, Marc Kleine-Budde <mkl@...gutronix.de>,
	Jakub Kicinski <kuba@...nel.org>,
	Vincent Mailhol <mailhol@...nel.org>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>,
	Simon Horman <horms@...nel.org>, davem@...emloft.net
Subject: Re: [can-next 0/5] can: remove private skb headroom infrastructure

Hi Oliver,

On Mon, Jan 12, 2026 at 04:09:03PM +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. To store the data for CAN specific use-cases
> unused space in CAN skbs is used, namely the inner protocol space for
> ethernet/IP encapsulation.
>
> [1] https://lore.kernel.org/linux-can/20260104074222.29e660ac@kernel.org/
>
> Oliver Hartkopp (5):
>   can: use skb hash instead of private variable in headroom
>   can: move can_iif from private headroom to struct sk_buff
>   can: move frame length from private headroom to struct sk_buff
>   can: remove private skb headroom infrastructure
>   can: gw: use new can_gw_hops variable instead of re-using csum_start
>
>  drivers/net/can/dev/skb.c | 45 ++++++++++++++++-----------------------
>  include/linux/can/core.h  |  1 +
>  include/linux/can/skb.h   | 33 ----------------------------
>  include/linux/skbuff.h    | 27 +++++++++++++++++------
>  net/can/af_can.c          | 35 +++++++++++++++++++-----------
>  net/can/bcm.c             | 13 ++++-------
>  net/can/gw.c              | 25 ++++++----------------
>  net/can/isotp.c           | 18 ++++++----------
>  net/can/j1939/socket.c    |  7 ++----
>  net/can/j1939/transport.c | 13 ++++-------
>  net/can/raw.c             | 14 ++++++------
>  11 files changed, 92 insertions(+), 139 deletions(-)

J1939 related part seems to work without regressions.
For j1939:
Tested-by: Oleksij Rempel <o.rempel@...gutronix.de>
Acked-by: Oleksij Rempel <o.rempel@...gutronix.de>

Thank you!

Best Regards,
Oleksij