linux-kernel - Re: [RFC PATCH net-next v3 15/21] ethtool: provide link settings and link modes in GET

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Date:   Thu, 21 Feb 2019 11:14:25 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jiri Pirko <jiri@...nulli.us>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net-next v3 15/21] ethtool: provide link settings and
 link modes in GET_SETTINGS request

On Wed, Feb 20, 2019 at 07:14:50PM -0800, Florian Fainelli wrote:
> On 2/18/2019 10:22 AM, Michal Kubecek wrote:
> > +#define ETH_SETTINGS_IM_LINKINFO		0x01
> > +#define ETH_SETTINGS_IM_LINKMODES		0x02
> > +
> > +#define ETH_SETTINGS_IM_ALL			0x03
> 
> You could define ETH_SETTINGS_IM_ALL as:
> 
> #define ETH_SETTING_IM_ALL		\
> 		(ETH_SETTINGS_IM_LINKINFO |
> 		 ETH_SETTINGS_IM_LINMODES)
> 
> that would scale better IMHO, especially given that you have to keep
> bumping that mask with new bits in subsequent patches.

I'm considering going even further and using something similar to what
is used for NETIF_F_* constants so that the *_ALL value would be
calculated automatically. But I'm not sure if it's not too fancy for
a uapi header file.

> > +	if (tb[ETHA_SETTINGS_INFOMASK])
> > +		req_info->req_mask = nla_get_u32(tb[ETHA_SETTINGS_INFOMASK]);
> > +	if (tb[ETHA_SETTINGS_COMPACT])
> > +		req_info->compact = true;
> > +	if (req_info->req_mask == 0)
> > +		req_info->req_mask = ETH_SETTINGS_IM_ALL;
> 
> What if userland is newer than the kernel and specifies a req_mask with
> bits set that you don't support? Should not you always do an &
> ETH_SETTINGS_IM_ALL here?

In that case only known bits would be handled and the check at the end
of prepare_info() would add a warning to extack that part of the
information couldn't be provided (same as if some of the recognized
parts didn't have necessary ethtool_ops handlers or if they failed).

Michal