On Sat, Sep 05, 2015 at 01:49:14PM +0200, shraptor wrote:
> On arch linux xf86-input-evdev is reported to have a dependency on systemd.
>
> I thought the dependency is on udev and that is usually reported on arch
> like
> systemd(udev).
>
> I downloaded xf86-input-evdev for recompilation but could not find any
> switches
> to compile without systemd though some evidence pointing at a udev
> dependency was there.
>
> Does anyone know?

Long explanation here.

xf86-input-evdev, as shipped by upstream, is intended to be loaded by Xorg's
hotplug support, which depends on libudev (or an API-compatible replacement
such as libudev-compat or libeudev...); at least in theory, you can also
use it as a pre-configured device driver.
The hotplug path will load evdev for *all* input devices that are
hotplugged--power buttons included.

So, evdev needs to check if a device is "virtual".
This is a simple matter of checking that the canonical path in sysfs
contains the string "LNXSYSTM".
Getting that canonical path is the hard part, since you receive a device
path instead of anything pointing into sysfs.

This can be done more-or-less by getting the device major and minor
via stat(), checking that it's a char device, then identifying the
corresponding link in /sys/dev/ - this would be the string returned by:
sprintf(buf, "/sys/dev/char/%hu:%hu", major, minor)
and then use readlink() to check where it points; the result is the
canonical path.

However, most people prefer to avoid depending on the sysfs layout even
where its behavior is documented; libudev provides a thin veneer to hide
it.
So in src/evdev.c, function EvdevDeviceIsVirtual, they use libudev to do
this.
There is no dependency on udev being running.

I've redone that function without udev but using my own library libsysdev,
which I mentioned earlier this summer.
Repositories that you'd need to build that:

-https://github.com/idunham/libsysdev
-https://github.com/idunham/xf86-input-evdev (branch sysdev)

But that does require something that has no Debian packaging yet.

There are also two other options:
- comment out that function and disable device hotplug in Xorg.conf or
xorg.conf.d
- replace the function with one that does all the work itself.

HTH,
Isaac Dunham