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Subject: Re: iwlist scanning: how to exclude old scan results from output?
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Bruno Dantas <wireless@dantas.airpost.net>,
        linux-wireless@vger.kernel.org
Date:   Thu, 28 May 2020 21:02:30 +0200
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On Thu, 2020-05-28 at 14:57 -0400, Bruno Dantas wrote:
> > Does it go away if you wait long enough for the "last seen" to go above
> > 30 seconds (30000ms)? You should use "iw wlan0 scan dump" (no need for
> > sudo, and don't scan again) to check.
> > 
> > Because if not, then there's a bug in the references, and the entry is
> > just being kept alive by ... something. Did you previously connect to
> > it? Does it also happen if you never connect? Then I guess we'll need to
> > know what the kernel version is too. :)
> 
> Yes, it goes way if I wait 30 seconds. Whether I had connected to the
> hotspot or not makes no difference. Kernel version is 5.4.3.

So at least it's not completely stuck.

> I thought discovering *currently-available* hotspots would be a common
> need. I'm a bit surprised that getting this information is tricky.

That's why 'flush' exists :)

> Like I said, reloading the wireless interface's kernel module does the
> trick.

Obviously. But still, now I'm wondering if there's a bug?

But then again, I think we use this a lot in the hwsim tests and rely on
it for a quick succession of tests to not find previous APs, and
"scan_for_auth" seems to be a fairly direct test for this as well?

Hmm. Not sure. What driver are you using?

johannes