linux-kernel - Is it ok if ModemManager process is killed AFTER network-interface is brought up and IP-Address assigned?

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Message-ID: <CAHP4M8XfO=tX1qJiu_fbQ9OaTbqwtRyA0jj6JpGmroVN-B3LZg@mail.gmail.com>
Date:	Tue, 9 Aug 2016 12:48:12 +0530
From:	Ajay Garg <ajaygargnsit@...il.com>
To:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Is it ok if ModemManager process is killed AFTER network-interface is
 brought up and IP-Address assigned?

Hi All.

We are using Sierra's USB-to-WWAN driver on Ubuntu-14 for Sierra's
MC8090 modem, and we have a requirement wherein we need to have access
to the modem-serial-port (from our user-application that is).

Right now, we see that /usr/sbin/ModemManager is always connected to
/dev/ttyUSB3 (which means we cannot connect to the port from our
application at the same time, or even if we can, received-data will be
at best inconsistent).

We are thinking of the following ::

* Initially, let nmcli and ModemManager do their work, and let them
bring the WWAN interface up.

* Once this happens, we permanently-down the ModemManager from our
application-binary, thereby freeing up /dev/ttyUSB3.

* Thereafter, we are free to connect to /dev/ttyUSB3 from our
application, thereby using features like SMS-notification (+CMTI),
signal-strength (+CSQ), etc.

Does our approach make sense?
We will be grateful to any help.

Thanks and Regards,
Ajay