On Mon, Mar 04, 2019 at 08:04:23AM -0500, Jeffrey Walton wrote: > On Sun, Mar 3, 2019 at 6:00 AM Greg KH <greg@xxxxxxxxx> 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. Yes, don't do that :) > I don't think modem manager is the problem here. The problem is your userspace is trying to open a device node twice without being _very_ careful about it :) > 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. character device nodes do not support O_EXCL, only block device nodes do in kernels newer than 2.6. Again, the kernel is working just fine the only "failure" is a lack of reading the man page for open(2) fully :) greg k-h _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
