linux-kernel - Re: [PATCH net-next v5 09/22] ethtool: implement EVENT notifications

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Date:   Wed, 27 Mar 2019 15:14:43 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        John Linville <linville@...driver.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v5 09/22] ethtool: implement EVENT notifications

On Wed, Mar 27, 2019 at 02:04:28PM +0100, Jiri Pirko wrote:
> Mon, Mar 25, 2019 at 06:08:21PM CET, mkubecek@...e.cz wrote:
> >Three types of netlink notifications are introduced:
> >
> >  - ETHA_EVENT_NEWDEV to notify about newly registered network devices
> >  - ETHA_EVENT_DELDEV to notify about unregistered network devices
> >  - ETHA_EVENT_RENAMEDEV to notify about renamed network device
> >
> >The notifications are triggered by NETDEV_REGISTER, NETDEV_UNREGISTER and
> >NETDEV_CHANGENAME notifiers.
> >
> >These notifications are intended for applications and daemons monitoring
> >ethtool events to allow updating the list of existing devices without
> >having to open another socket for rtnetlink.
> 
> Wait. You duplicate events that are already going out through RTNETLINK.
> App should open RTNETLINK in order to get those. Other apps are doing
> that too. I don't think that duplications like this are desirable :/

Is there a way to filter or at least recognize these events when using
rtnetlink? I couldn't find any. The only way seems to be getting every
RTM_NEWLINK message (there can be quite a lot of those), always perform
the lookup in my device list and recognize what happened - only to
almost always find that nothing interesting. It is possible, sure, but
I would really like to avoid it.

Michal