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From: Jeffrey Walton <noloader@gmail.com>
To: Greg KH <greg@kroah.com>
Cc: kernelnewbies <kernelnewbies@kernelnewbies.org>
Subject: Re: How to make /dev/ttyACM0 (and friends) exclusive?
Date: Mon, 4 Mar 2019 08:04:23 -0500	[thread overview]
Message-ID: <CAH8yC8mDG-fzaM3LGMw-C=sPs04Xmfs_CW2mGDCu0W+8hDG=fQ@mail.gmail.com> (raw)
In-Reply-To: <20190303110011.GA10485@kroah.com>

On Sun, Mar 3, 2019 at 6:00 AM Greg KH <greg@kroah.com> wrote:
>
> On Sun, Mar 03, 2019 at 03:55:44AM -0500, Jeffrey Walton wrote:
> > ...
>
> Again, go delete modem manager off of your system, it is the thing that
> keeps opening the port up to see if you have made a valid connection on
> the device or not.  If you write your own program to talk to the device,
> modem manager is not needed at all, and is known to cause this problem.

Thanks Greg. I deleted modem manager, then ran two instances of my
program. Both opened the device with O_EXCL, and both opens succeeded.
They proceeded to much with one another's state.

I don't think modem manager is the problem here.

The first problem is the way this device is setup. An exclusive
resource is being treated as a shared resource. The second problem is
open silently ignores flags. Epic fail.

Thanks again for the help.

Jeff

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  reply	other threads:[~2019-03-04 13:06 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
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 [this message]
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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