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From:   KeithG <ys3al35l@gmail.com>
Date:   Sat, 26 Dec 2020 10:28:24 -0600
Message-ID: <CAG17S_MJCuMaqX7uczZBLXn9N-QiDhL-0ASAhMNN-aubbHE8Jw@mail.gmail.com>
Subject: Re: Request for help with btmgmt
Cc:     Bluez mailing list <linux-bluetooth@vger.kernel.org>
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In further reading, it may be that 'bluetoothctl info' should show all
the information about the BT bus but does not? Is that possible?
If I connect a keyboard, 'bluetoothctl info' shows that keyboard. If I
then connect a phone, 'btmgmt con' shows both connected, but
'bluetoothctl info' only shows the keyboard. This is why I was using
btmgmt. I have looked through the code for BlueZ and it is very
complicated. I was trying to figure out why btmgmt does not report
when run 'non interactively' and have given up. I will start
researching dbus to see if I can work with it that way.

Keith


On Fri, Dec 25, 2020 at 2:32 PM KeithG <ys3al35l@gmail.com> wrote:
>
> Barry,
>
> Thanks for the help. I will look into it. I fear it may be a bit 'up
> hill' for me.
>
> Can you shed any light as to why:
> 1) bluetoothctl does not have a command to list the currently connected devices?
> 2) why btmgmt cannot be run except from the command line? Not even
> 'btmgmt info' can be run from a script. If it runs, I cannot tell as
> no output is ever generated and no error is ever listed in the
> journal.
>
> Keith
>
> On Wed, Dec 23, 2020 at 1:53 AM Barry Byford <31baz66@gmail.com> wrote:
> >
> > Hello Keith,
> >
> > On Wed, 23 Dec 2020 at 00:34, KeithG <ys3al35l@gmail.com> wrote:
> > >
> > > I am developing a RPi based audio player. We are trying to add
> > > bluetooth capability to this player. We use alsa and not pulse-audio,
> > > so we need a bit more granular info to get it to run. I have written a
> > > script which is designed to be triggered by udev when a BT device is
> > > added or removed. This script will then use bluetoothctl to get the
> > > capabilities of the device and also add or remove it from a dynamic
> > > database list of MACs in redis. I have a simple script working as I
> > > want from the cli. The key command I am using is 'btmgmt con' which is
> > > the only command I have found that tells me what MACs are currently
> > > connected. I can run this command from the command line as root. I can
> > > set the setuid bit of btmgmt and also get it to run as a user (http in
> > > this case). I cannot, ever, get this command to run when triggered
> > > from udev. I get no response and no error.
> > >
> > > 1) Why is this particular command (query attached BT MACs) not part of
> > > bluetoothctl?  Is there a security issue?
> > > 2) Why can I not run 'btmgmt con' in a script (bash or php) triggered
> > > by udev when the device is added or removed?
> > > 3) is there a 'better way' for me to know what device MAC addresses
> > > are attached? I have not found another simple way to get this info.
> > >
> > > What I am doing in the script is: if an audio source is attached, I
> > > want to run a bluealsa-aplay service. When an audio sink is attached,
> > > I want to re-set my audio output to the bluealsa device. If it is not
> > > an audio device, I do not care, but do keep track of what is attached
> > > in my database so that the next time the script runs that it is not
> > > queried and is 'known'.
> > >
> > > Thanks for the help.
> > >
> > > Keith
> >
> > I would suggest that the D-Bus API would be a more appropriate way to
> > get the information you want.
> >
> > The "get managed objects" functionality is a good way to iterate
> > through all the devices that BlueZ knows about.
> > There are examples at:
> > https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/test/bluezutils.py
> > https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/test/list-devices
> >
> > The D-Bus API also allows your code to execute callbacks when a device
> > is added or its connection state changes.
> > This is done with the InterfacesAdded and PropertiesChanged signals.
> >
> > If you are going to use Python I would suggest the
> > https://pypi.org/project/pydbus/ library is a more "Pythonic" set of
> > D-Bus bindings.
> >
> > The API is documented at:
> > https://git.kernel.org/pub/scm/bluetooth/bluez.git/tree/doc
> >
> > Regards,
> > Barry