[RFC] Add MatchDMI support in InputClass sections

[Daniel Martin]

Hi,

this series adds support to match on DMI identifiers in InputClass
sections. Its main purpose is to be able to workaround the shortcomings
of synaptics touch- and clickpads.

In their latest (Haswell) laptop models Lenovo decided to remove the HW
buttons below the trackpoint and therefor marks to top area of the
clickpad as (soft) buttons, see [1]. But, this clickpad can't be
distinguished from any other clickpad being build in other models (i.e.
the Lenovo X1 Carbon, which still had the HW buttons) as the product id
and revision is the same on _all_ synaptics touch- and clickpads (i.e.
in an old T400). It's possible to distinguish between touch- and clipads
via device flags. Though, this doesn't gives a hint if it's necessary to
configure the top area as a `softarea` in xf86-input-synaptics (as the
firmware of the foopad has no clue what the vendor of the laptop painted
on it).

To be able to distinguish between those clickpads and to apply a special
configuration if necessary an additional matching on DMI identifiers is
requried. And this series makes it possible to add 'MatchDMI' tokens in
InputClass sections for this purpose.
One has to add a 'MatchDMI "key|value"' line into the InputClass section
to make use of it. 'key' is a DMI identifier and 'value' the desired
value. All supported/valid keys are listed in the man-page.

An example would be (values out of the had don't have the laptop at
hand atm.):
    MatchDMI "SystemVendor|LENOVO"
    MatchDMI "ProductName|ThinkPad T440s"

This series implements MatchDMI support for Linux only, requiring a
decent old kernel providing the DMI informations via sysfs at
    /sys/devices/virtual/dmi/id.
Though, the generic stubs are there and for any other OS it's sufficient
to implement the initialization.


Sure, this matching is not necessary for installations where someone
can modify the configuration as wanted. It's more usefull for
distributions and live systems willing to provide some "works out of the
box" experience.


I hope you'll find it as usefull as I do,
    Daniel Martin

[1] http://www.lenovo.com/images/gallery/1060x596/lenovo-laptop-thinkpad-t440s-overhead-keyboard-2.jpg