Re: [RFC] network devices generating uevents?

[Stephen Hemminger <shemminger@vyatta.com>]

On Sun, 23 Nov 2008 03:13:29 +0100
Marcel Holtmann <marcel@holtmann.org> wrote:

> Hi Kay,
> 
> >> Perhaps the following would make it easier for applications to
> >> track network device events without having to use netlink.
> >
> > Sure, that might be useful.
> >
> > These events can not happen at a high frequency, at any time, right?
> > We are sure that things like UP/DOWN/CHANGE can not happen at a high
> > frequency, maybe in some failure situation?
> >
> > Uevents are pretty expensive, every single of them may fork a
> > /sbin/hotplug process, or a udev event process, regardless if anybody
> > is listening to these events or not.
> >
> > We can do that only if we can be sure, that there are never things
> > like "storms of events", which would cause a pretty high system load,
> > and can even crash non-udev systems with out-of-memory, caused by the
> > stateless non-managed (disabled by udev) /sbin/hotplug scripts.
> 
> I was looking into the same thing the other day. And just getting the  
> interface up/down events via uevent is pretty useful. I am also  
> interested in getting the carrier signal of Ethernet cards via a  
> CHANGE event.
> 
> If you look at the RTNL messages, it doesn't happen that often, but  
> the NEWLINK messages are maybe a little bit too much and we should  
> restrict it to event that really matter. So up/down are user triggered  
> event normally. So that should be safe. I would be a little bit  
> worried about the CHANGE event. Here we might wanna restrict it to a  
> subset of possible changes inside the network device.
> 
> Regards
> 
> Marcel
> 

The events are carrier events are sampled by the linkwatch mechanism already, to eliminate
too active bouncing. The other events only happen when administrator does
something like add new device or take it on/off line.