netdev - Re: [PATCH net-next 1/6] ethtool: Add ability to control transceiver modules' power mode

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Date:   Tue, 5 Oct 2021 07:15:04 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, andrew@...n.ch,
        mkubecek@...e.cz, pali@...nel.org, jacob.e.keller@...el.com,
        jiri@...dia.com, vadimp@...dia.com, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next 1/6] ethtool: Add ability to control
 transceiver modules' power mode

On Tue, 5 Oct 2021 09:57:20 +0300 Ido Schimmel wrote:
> > > +static int module_set_power_mode(struct net_device *dev, struct nlattr **tb,
> > > +				 bool *p_mod, struct netlink_ext_ack *extack)
> > > +{
> > > +	struct ethtool_module_power_mode_params power = {};
> > > +	struct ethtool_module_power_mode_params power_new;
> > > +	const struct ethtool_ops *ops = dev->ethtool_ops;
> > > +	int ret;
> > > +
> > > +	if (!tb[ETHTOOL_A_MODULE_POWER_MODE_POLICY])
> > > +		return 0;  
> > 
> > Feels a little old school to allow set with no attrs, now that we 
> > do strict validation on attrs across netlink.  What's the reason?  
> 
> The power mode policy is the first parameter that can be set via
> MODULE_SET, but in the future there can be more and it is valid for user
> space to only want to change a subset. In which case, we will skip over
> attributes that were not specified.

Ack, I guess catching the "no parameter specified" case may be more
effort than it's worth. Nothing is going to break if we don't do it.

> > > +	if (!ops->get_module_power_mode || !ops->set_module_power_mode) {
> > > +		NL_SET_ERR_MSG_ATTR(extack,
> > > +				    tb[ETHTOOL_A_MODULE_POWER_MODE_POLICY],
> > > +				    "Setting power mode policy is not supported by this device");
> > > +		return -EOPNOTSUPP;
> > > +	}
> > > +
> > > +	power_new.policy = nla_get_u8(tb[ETHTOOL_A_MODULE_POWER_MODE_POLICY]);
> > > +	ret = ops->get_module_power_mode(dev, &power, extack);
> > > +	if (ret < 0)
> > > +		return ret;
> > > +	*p_mod = power_new.policy != power.policy;
> > > +
> > > +	return ops->set_module_power_mode(dev, &power_new, extack);  
> > 
> > Why still call set if *p_mod == false?  
> 
> Good question...
> 
> Thinking about this again, this seems better:
> 
> diff --git a/net/ethtool/module.c b/net/ethtool/module.c
> index 254ac84f9728..a6eefae906eb 100644
> --- a/net/ethtool/module.c
> +++ b/net/ethtool/module.c
> @@ -141,7 +141,10 @@ static int module_set_power_mode(struct net_device *dev, struct nlattr **tb,
>         ret = ops->get_module_power_mode(dev, &power, extack);
>         if (ret < 0)
>                 return ret;
> -       *p_mod = power_new.policy != power.policy;
> +
> +       if (power_new.policy == power.policy)
> +               return 0;
> +       *p_mod = true;
>  
>         return ops->set_module_power_mode(dev, &power_new, extack);
>  }
> 
> That way we avoid setting 'mod' to 'false' if it was already 'true'
> because of other parameters that were changed in ethnl_set_module(). We
> don't have any other parameters right now, but this can change.
> 
> Thanks for looking into this

👍