Issues with rfcomm: rfcomm_bind: Address already in use (98)

Issues with rfcomm: rfcomm_bind: Address already in use (98)

[Sergio Callegari]

Hi,

writing with reference to an issue with bluez 5 and rfcomm found in recent linux 
distributions (seen on ubuntu 18.04, 18.10 and fedora >= 27).

Libreoffice uses rfcomm to let a mobile phone using a dedicated application work 
as a remote and as a pointer for presentations.

This has worked fine until slightly more than 1 year ago, then it has broken.

Starting libreoffice impress shuld activate an rfcomm listener for incoming 
bluetooth connections from the app running on the mobile phone.  However, it 
does not succeed and an entry is created in the system logs (visible with 
journalctl). For instance

bluetoothd[1470]: RFCOMM server failed for LibreOffice Impress Remote: 
rfcomm_bind: Address already in use (98).

- libreoffice started supporting bluez 5 a few years ago, and I have 
successfully used the remote with bluez 5 (e.g. i ubuntu 17.x)

- libreoffice developers indicate that nothing has changed on their side and I 
have confirmed that older versions of Libreoffice have the same issue on recent 
distributions.  For this reason, the libreoffice developers are reluctant to 
looking into the bug, and tend to think that the problem may be in a regression 
or a change of behavior in bluez or in the way in which recent distributions 
deploy bluez breaking their application.

- distributions appear similarly inactive on the bug until one can actually 
point at something proving that the issue is on their side.

Unfortunately, the message on the system logs is not detailed enough for me to 
try to understand where the issue may lay.

I am thus asking for advice on how to try identifying whether the problem is in 
a the bluetooth kernel code, in the bluetoothd daemon code, in the bluez dbus 
api, in libreoffice or in the way distributions package and configure bluez, so 
that I can address a bug report to the appropriate developers.

Thanks,

Sergio