[RFC libevdev] Enable event logging for debugging

[Peter Hutterer]

On Thu, Apr 03, 2014 at 04:51:26PM +0200, David Herrmann wrote:
> Hi
> 
> On Thu, Apr 3, 2014 at 4:30 PM, Benjamin Tissoires
> <benjamin.tissoires at gmail.com> wrote:
> > So I am definitively in favour of being able to filter the device node
> > from libevdev directly.
> 
> What I was saying is I rather prefer a log-message that says
> "libevdev: eventXY: <some_message>" than to require me to set
> event-masks via env-vars. Because I usually prefer having as much
> information as possible and filter afterwards, than having to redo
> some testing because I didn't get enough information. Especially for
> libevdev which is quite low-traffic debug messaging (or do we log each
> received message?).

I see a couple of issues here: one is that libevdev has _no_ connection to
systemd at all. it doesn't even use udev and I like to keep it simple that
way. which is why the minor number is currently required instead of the
device node. so that makes filtering on the device node hard to begin with
(we could guess the node with a loop through /dev/input though)

In regards to:
> (or do we log each received message?).
that is exactly the point of this patch. logging every event from every
device at all times is a large amount of data, especially with touchpads,
touchscreens or graphics tablets. And in 99% of the use-cases that data is
just wasting space and isn't used.

The real use of this is to be able to get sequences for _bugs_ without
having to tell users to apply a patch from here and then another patch from
there. Hence the environment variable, it's easy to set, no recompilation is
needed but the data still goes to the same log as before.

Cheers,
  Peter