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

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Date:   Thu, 28 Mar 2019 07:41:43 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Jiri Pirko <jiri@...nulli.us>, David Miller <davem@...emloft.net>,
        netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Andrew Lunn <andrew@...n.ch>,
        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 07:14:43PM -0700, Florian Fainelli wrote:
> 
> 
> On 3/27/2019 7:14 AM, Michal Kubecek wrote:
> > 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.
> 
> I am afraid you are right about this, would adding a filtering
> capability specifically for this in rtnetlink be a better route?

Maybe we could add new IFLA_EVENT_* values and use IFLA_EVENT to mark
RTM_NEWLINK messages announcing "new device" and "device rename". That
way, monitoring application would still need to parse all RTM_NEWLINK
messages but it would be able to recognize which announce a change in
device list without a lookup in its structures.

Michal