Bug#877024: modemmanager should ask before messing with serial ports

[Aleksander Morgado <aleksander@aleksander.es>]

> Many such modems present as USB serial devices, eg ttyACM or ttyUSB.
> Consequently, modemmanager has the ability to open serial ports and
> probe them to see if they respond to Hayes-style AT commands.  That
> functionality is currently triggered automatically by default, even
> for USB serial ports whose USB device IDs are unknown to modemmanager,
> or whose device IDs correspond to generic USB-to-serial adapters.
> 
> I.e., if one is running a normal Debian installation and plugs in a
> usb-to-serial converter, modemmanager will open the device and send AT
> commands to it, to see if it is a modem.
> 
> This behaviour is IMO unaccaptable, as a default.
> 

A clarification here, ModemManager doesn't automatically probe usb-to-serial converters, those are "greylisted" so that they're only probed on "manual scans". Of course, the vid:pid needs to be known to MM and in the greylist, for this to happen.

ModemManager also doesn't automatically probe platform TTYs, like physical RS232 ports in the host.

-- 
Aleksander