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Subject: Re: Temporary device removal during discovery
From:   Bastien Nocera <hadess@hadess.net>
To:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     Andrey Batyiev <batyiev@gmail.com>,
        linux-bluetooth <linux-bluetooth@vger.kernel.org>
Date:   Fri, 10 Jul 2020 21:00:35 +0200
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On Fri, 2020-07-10 at 11:06 -0700, Luiz Augusto von Dentz wrote:
> Hi Bastien,
> 
> On Thu, Jul 9, 2020 at 1:26 AM Bastien Nocera <hadess@hadess.net>
> wrote:
> > On Thu, 2020-07-09 at 01:57 +0300, Andrey Batyiev wrote:
> > > Hi Luiz,
> > > 
> > > On Thu, Jul 9, 2020 at 12:14 AM Luiz Augusto von Dentz
> > > <luiz.dentz@gmail.com> wrote:
> > > > The delta logic might be a nice addition as a separate patch,
> > > > it is
> > > > more for detecting devices disappearing then actually cleanup
> > > > during
> > > > power off.
> > > No-no, it's not about adapter powering off.
> > > 
> > > I meant that (external) devices never disappear from the bluez
> > > device
> > > list during the discovery,
> > > even if the (external) devices are turned off (i.e. they should
> > > be
> > > purged by bluez).
> > > 
> > > So:
> > > - bluez is central
> > > - bluez is discovering
> > > - peripheral appear for a moment, than disappear (i.e. peripheral
> > > would be turned off)
> > > - bluez would not remove device from the list (at least until
> > > discovery is stopped)
> > > 
> > > Use case:
> > > - bluez is monitoring environment (discovering literally forever)
> > > - peripherals are brought in and out of bluez visibility range
> > > - bluez list of visible devices grows infinitely and causes
> > > problems
> > > (hundreds of devices)
> > 
> > I'd also expect devices that are recently discovered to disappear
> > if
> > they haven't replied to a discovery in 30 seconds. It would stop
> > GNOME's Bluetooth Settings's Bluetooth list forever expanding.
> > 
> > Or we need to give the ability for front-ends to do that by
> > exporting
> > the "last seen" dates.
> 
> I am fine with that as well, 30 seconds doesn't sound too bad even
> for
> cleanup temporary devices as the current 3 minutes seems awful long
> sometimes, we could perhaps have a filter for configuring that though
> so if the application wants to have its own timeout, the only problem
> is if there are multiple application doing that on parallel we would
> need a strategy on how to handle that.

In which case it might be easier to export that last seen date,
otherwise that's just a lot of moving parts inside bluetoothd when we
could filter it trivially in the front-ends.