On Fri, Jan 15, 2021 at 04:07:23PM -0800, Jakub Kicinski wrote:
> On Fri, 15 Jan 2021 15:30:35 +0100 Oleksij Rempel wrote:
> > Since 20dd3850bcf8 ("can: Speed up CAN frame receiption by using
> > ml_priv") the CAN framework uses per device specific data in the AF_CAN
> > protocol. For this purpose the struct net_device->ml_priv is used. Later
> > the ml_priv usage in CAN was extended for other users, one of them being
> > CAN_J1939.
> > 
> > Later in the kernel ml_priv was converted to an union, used by other
> > drivers. E.g. the tun driver started storing it's stats pointer.
> > 
> > Since tun devices can claim to be a CAN device, CAN specific protocols
> > will wrongly interpret this pointer, which will cause system crashes.
> > Mostly this issue is visible in the CAN_J1939 stack.
> > 
> > To fix this issue, we request a dedicated CAN pointer within the
> > net_device struct.
> 
> No strong objection, others already added their pointers, but 
> I wonder if we can't save those couple of bytes by adding a
> ml_priv_type, to check instead of dev->type? And leave it 0
> for drivers using stats?

Sounds good.

If we want to save even more bytes, it might be possible, to move the
wireless and wpan pointers to ml_priv.

	struct wireless_dev	*ieee80211_ptr;
	struct wpan_dev		*ieee802154_ptr;

> That way other device types which are limited by all being 
> ARPHDR_ETHER can start using ml_priv as well?
> 
> > +#if IS_ENABLED(CONFIG_CAN)
> > +	struct can_ml_priv	*can;
> > +#endif
> 
> Perhaps put it next to all the _ptr fields?

Makes sense. Oleksij will resping the series.

regards,
Marc

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