Re: Flush scan list on resume

[Tony Espy <espy canonical com>]

Dan Williams wrote:
> On Wed, 2009-02-04 at 12:45 -0500, Dan Williams wrote:
> > On Tue, 2009-02-03 at 22:38 -0800, Howard Chu wrote:
> > > I haven't gone looking for this in the code yet, does NM get a DBUS event on 
> > > standby/suspend and/or resume? It would be nice if it would flush its AP list 
> > > at (one of) these points. I frequently set my laptop to sleep before going 
> > > elsewhere; when I wake up its scan list shows all the APs in the new location 
> > > but it also still shows the AP I was last associated with (even though it's 
> > > not in the present location) and tries (fruitlessly) to reassociate with it. 
> > > It should just forget the old info and only use the new scan results.
> > It does flush the scan list [1].  I looked into this a long time ago
> > (should probably do so again), and the actual problem wasn't in NM, but
> > in the supplicant or the driver, which had results left over from before
> > the suspend.  NM got those results when requesting the latest results
> > from the supplicant.  That's not to say that we can't do something fun
> > with "last_beacon" IE of the results, if we can get that from the
> > supplicant.
>
> So here's why old access points show up after resume...
>
> Executive summary: exclusively a *driver* problem
>
>
> Detailed explanation:
>
> Most kernel drivers use 'jiffies' as the timestamp for each scan result.
> jiffies is a kernel counter that counts *while the kernel is alive*, and
> thus does not reflect time spent in suspend and hibernate.
>
> When the supplicant requests scan results from the driver on resume, the
> supplicant (and NM) gets back a list of scan results with recent-looking
> timestamps that do not reflect the time the machine was suspended.
>
> The solutions are to move drivers to using the actual machine clock (the
> kernel equivalent of time(2)) for last_beacon, or to be more agressive
> about expiring entries on resume with something like (10 - time spent in
> sleep).

How 'bout getting drivers to add code to their resume functions that 
just clears the scan results queue?

For reference see:

http://madwifi-project.org/ticket/740

Ciao,
/tony