Re: ModemManager serial port lock-files

[Dan Williams <dcbw redhat com>]

On Fri, 2013-06-07 at 17:43 +0400, Dmitry Ivanyushin wrote:
> I am working with git version of MM and Ubuntu 12.04.
>
> I have three different physical serial (RS232) ports and they are not
> USB-to-serial. Now MM probes all of them. I want MM to automatically detect
> the port the modem is connected to but there're another devices controlled
> by another daemon.
>
> If there were lock files, my daemon wouldn't probe the ports which are
> locked by MM and vice-versa.

ModemManager does not use lockfiles as there are various well-understood
problems with them.  It does, however use TIOCEXCL which any other
program using doing serial stuff should probably be doing too.  Doing it
through the ioctl means there are no stale lock files left if something
crashes and no need to write stuff out to random places.

Dan

> 2013/6/7 Aleksander Morgado <aleksander lanedo com>
>
> > > I have several serial ports in my system but also I have a daemon that
> > > is responsible for communication with several devices connected to those
> > > serial ports. This daemon runs as root. However when MM starts it tries
> > > to find modem via writing to all serial ports registered in the system.
> > > That operation break protocols of these devices.
> > >
> > > I am thinking of adding support of lock-files to MM. Is it good to add
> > > such support in mm-manager.c to test locks, in mm-serial-port to acquire
> > > and release those locks?
> >
> > What MM version is this? MM shouldn't be probing platform serial (RS232)
> > ports by default, unless they are explicitly white-listed. For USB
> > devices exposing ttys which aren't modems, we can blacklist them in our
> > udev rules. Would that help?
> >
> > --
> > Aleksander
>
>
>
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