netdev - Re: [RFC PATCH net-next v2 06/17] ethtool: support for netlink notifications

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Date:   Mon, 30 Jul 2018 19:01:21 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Miller <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Jakub Kicinski <kubakici@...pl>,
        "John W. Linville" <linville@...driver.com>
Subject: Re: [RFC PATCH net-next v2 06/17] ethtool: support for netlink
 notifications

On Mon, Jul 30, 2018 at 03:16:55PM +0200, Jiri Pirko wrote:
> Mon, Jul 30, 2018 at 02:53:12PM CEST, mkubecek@...e.cz wrote:
> 
> [...]
> 
> >diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> >index c1295c7a452e..c4b0c575d57e 100644
> >--- a/include/linux/netdevice.h
> >+++ b/include/linux/netdevice.h
> >@@ -2444,6 +2444,7 @@ enum netdev_cmd {
> > 	NETDEV_CVLAN_FILTER_DROP_INFO,
> > 	NETDEV_SVLAN_FILTER_PUSH_INFO,
> > 	NETDEV_SVLAN_FILTER_DROP_INFO,
> >+	NETDEV_ETHTOOL,
> 
> I don't understand why this goes through netdev notifier. What's the
> reason?

To allow triggering a notification from other code (ethtool ioctl or
e.g. netdev_features_change()) when netlink interface is built as a
module. If it's a (performance?) problem, an alternative could be having
a global pointer which would be either null or point to ethtool_notify()
depending on whether the module is loaded (and ready).

(Which made me realize I forgot to handle a race between module
unloading and processing a notification.)

Another question is if we really need the option to build the netlink
interface as a module. I must admit my main motivation to have it as
a module is that it makes testing and debugging easier.

Michal