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From:   Steve deRosier <derosier@gmail.com>
Date:   Tue, 3 Mar 2020 13:59:11 -0800
Message-ID: <CALLGbRKPCSZW8PFQXat+_=+iD_ED81j16vNtTbF=KW-B-tTWPQ@mail.gmail.com>
Subject: Re: [PATCH 1/3] nl80211: add monitor mode scan feature
To:     Johannes Berg <johannes@sipsolutions.net>,
        Markus Theil <markus.theil@tu-ilmenau.de>
Cc:     linux-wireless <linux-wireless@vger.kernel.org>, nbd@nbd.name,
        lorenzo@kernel.org
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On Tue, Mar 3, 2020 at 1:28 PM Johannes Berg <johannes@sipsolutions.net> wrote:
>
> On Tue, 2020-03-03 at 12:50 +0100, Markus Theil wrote:
> > Back in 2007 "mac80211: don't allow scanning in monitor mode"
> > (f27b62d3e7ec) disabled scanning in monitor mode, because hw
> > controlled by the zd1211rw driver got confused during this operation.
> >
> > Nevertheless, it can be useful to scan in monitor mode, e.g.
> > when building a tool which processes scans, channel surveys and
> > monitors the channel passively in monitor mode.
>
> Hmm. I'm not really sure that this makes sense.
>
> You're in monitor mode, so you won't get any scan processing as such
> (you will not be able to use nl80211 to retrieve the results!), and
> there will be a lot of confusion over sending probe requests (the code
> now looks like it would in fact attempt to do so ... but how?).
>

Additionally, I don't see what this solves for sure.  At least on an
ath10k device I've been using, I can have two interfaces on one phy
(phy0), wlan0 and mon0, and I can issue a `iw wlan0 scan` and it works
famously and then capture fine on mon0. Granted, I haven't tried doing
a scan while at the same time am actively capturing, but I wonder of
the meaning of that anyway as the capturing radio would have to then
go off channel and issue probe requests etc., sort of screwing up my
capture for that time period.  But anyway, can you not do this on your
radio?

- Steve