[systemd-devel] udev rules for MCS7715 USB-attached parallel port

[Lennart Poettering]

On Tue, 23.02.16 17:12, Alex Henrie (alexhenrie24 at gmail.com) wrote:

> 2016-02-22 7:15 GMT-07:00 Lennart Poettering <lennart at poettering.net>:
> > On Sun, 21.02.16 15:26, Alex Henrie (alexhenrie24 at gmail.com) wrote:
> >
> >> Hi,
> >>
> >> I recently bought an MCS7715 USB-attached parallel port,[1] but there
> >> seem to be a couple of problems using it with Linux:
> >>
> >> 1. The lp, parport, and parport_pc kernel modules are not loaded when
> >> the device is plugged in.
> >
> > AFAIK parport_pc is the driver for old built-in parallel ports, it
> > it not used f you have a USB paralell port adapter.
> 
> OK. Still, at minimum lp needs to be loaded when the USB parallel port
> adapter is plugged in.
> 
> >> 2. After manually loading the kernel modules, /dev/lp0 is not deleted
> >> when the device is unplugged.
> >
> > /dev/lp0 is also the old built-in parallel port. USB printers and
> > parallel ports show up as /dev/usb/lp0 or so..
> 
> When I plug in the device, /dev/lp0 appears; /dev/usb/lp0 does not.
> Furthermore, when I unplug and plug it back in, /dev/lp1 appears
> alongside /dev/lp0. A third time and I have /dev/lp0, /dev/lp1, and
> /dev/lp2.
> 
> Are you sure that this is not a udev rules bug? If it isn't, where
> should I report it?

Well, parallel ports are somewhat legacy, it'll be hard to find
somebody to fix this for you...

Generally, the lp hookup in udev rules is pretty minimal, the primary
work has to be done in the kernel modules to expose in the modalias
metadata when they want to be loaded, and via the kernel driver model
which device nodes they want.

Lennart

-- 
Lennart Poettering, Red Hat