From: Greg KH <greg@kroah.com>
To: Jeffrey Walton <noloader@gmail.com>
Cc: kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: Re: How to make /dev/ttyACM0 (and friends) exclusive?
Date: Sat, 2 Mar 2019 08:50:07 +0100 [thread overview]
Message-ID: <20190302075007.GB16604@kroah.com> (raw)
In-Reply-To: <CAH8yC8kY5Dnxpxwy-CoRcAT-spuAz+eQ7haKY1ACR02tKqy7_w@mail.gmail.com>
On Fri, Mar 01, 2019 at 11:29:53PM -0500, Jeffrey Walton wrote:
> Hi Everyone,
>
> I'm trying to trackdown a problem using my dialup modem. I have a
> program that opens the modem and watches caller id's. It flashes the
> hook when a telemarketer calls. It works well until...
>
> When another program opens the modem then my program starts reading
> intermittent responses intended for the other program.
>
> I cannot seem to open the device in exclusive mode. The current open
> is (I also tried with O_EXCL):
>
> int modem = open(device_path, O_RDWR | O_NOCTTY | O_SYNC);
>
> I'm not sure if it because udev configures the device incorrectly or
> the kernel driver is configured incorrectly. Or maybe it is impossible
> to do.
This isn't a kernel thing, it is a userspace configuration issue. Just
change the permissions of the device node such that only your one
program can open it. Or, once you open it, change the permissions such
that no one else can open it.
Or better yet, uninstall modem manager, that's what is probably opening
up the device at random points in time :)
good luck!
greg k-h
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next prev parent reply other threads:[~2019-03-02 7:50 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-02 4:29 How to make /dev/ttyACM0 (and friends) exclusive? Jeffrey Walton
2019-03-02 7:50 ` Greg KH [this message]
2019-03-02 18:45 ` valdis.kletnieks
2019-03-02 19:36 ` Jeffrey Walton
2019-03-03 5:55 ` valdis.kletnieks
2019-03-03 8:55 ` Jeffrey Walton
2019-03-03 11:00 ` Greg KH
2019-03-04 13:04 ` Jeffrey Walton
2019-03-04 13:20 ` Greg KH
2019-03-04 15:38 ` Yann Droneaud
2019-03-04 22:01 ` valdis.kletnieks
2020-10-06 20:41 ` Daniel Santos
2020-10-11 14:52 ` linux lover
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