Re: [RFC PATCH net 1/2] net: introduce CAN specific pointer in the struct net_device

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:

quoted

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?

quoted

+#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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