Re: [PATCH V4 net-next 4/6] ethtool: extend ringparam setting uAPI with rx_buf_len

On 25.10.2021 10:45:05, Jakub Kicinski wrote:

On Mon, 25 Oct 2021 15:27:18 +0200 Marc Kleine-Budde wrote:

quoted

On 25.10.2021 15:11:49, Marc Kleine-Budde wrote:

quoted

On 14.10.2021 19:39:41, Guangbin Huang wrote:  

quoted

From: Hao Chen <redacted>

Add two new parameters ringparam_ext and extack for
.get_ringparam and .set_ringparam to extend more ring params
through netlink.

Signed-off-by: Hao Chen <redacted>
Signed-off-by: Guangbin Huang <redacted>  

While discussing a different ethtool ring param extension,  

Let me explain my requirements:

There is a not Ethernet based bus system, called CAN (mainly used in the
automotive and industrial world). It comes in 2 different generations or
modes (CAN-2.0 and CAN-FD) and the 3rd one CAN-XL has already been
specified.

Due to different frame sizes used in these CAN modes and HW limitations,
we need the possibility to set a RX/TX ring configuration for each of
these modes.

The approach Andrew suggested is two-fold. First introduce a "struct
ethtool_kringparam" that's only used inside the kernel, as "struct
ethtool_ringparam" is ABI. Then extend "struct ethtool_kringparam" as
needed.

Indeed, there are different ways to extend the API for drivers,
I think it comes down to personal taste. I find the "inheritance" 
models in C (kstruct usually contains the old struct as some "base")
awkward.

I don't think we have agreed-on best practice in the area.

The set/get_coalesce as just extended, using a 3rd parameter for the new
values:

| 	int	(*set_coalesce)(struct net_device *,
| 				struct ethtool_coalesce *,
| 				struct kernel_ethtool_coalesce *,
| 				struct netlink_ext_ack *);

https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=f3ccfda19319

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |