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From:   KeithG <ys3al35l@gmail.com>
Date:   Fri, 25 Dec 2020 14:32:26 -0600
Message-ID: <CAG17S_Mq+fMy6gGU-dXaNpsNkbqP47YskYJV7SE7mNUtbz=CYg@mail.gmail.com>
Subject: Re: Request for help with btmgmt
To:     Barry Byford <31baz66@gmail.com>
Cc:     Bluez mailing list <linux-bluetooth@vger.kernel.org>
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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