How devices are described for registration with rtdm_dev_register() is
significantly modified, affecting both named and protocol device
drivers exactly the same way. Aside of fixing consistency issues, the
bulk of changes is aimed at narrowing the gap between the regular
Linux device driver model and RTDM.

RTDM now shares the Linux namespace for named devices, which are
backed by common character device objects from the regular Linux
device model. As a consequence of this, file descriptors obtained on
named RTDM devices are regular file descriptors on real chrdevs,
visible from the /proc/<pid>/fd interface.

The major change required for supporting this closer integration of
RTDM into the regular Linux driver model involved splitting the device
class properties from the device instance definitions, which used to
be combined in Xenomai 2.x into the rtdm_device descriptor.

A new rtdm_device_class descriptor is introduced, for describing the
general static properties of the devices exposed by a
driver. rtdm_device now represents an instance of such class.

rtdm_device objects link to the descriptor of the rtdm_device class
they belong to.

Hotplug support
---------------

RTDM first allocates and reserves a major and a range of device minors
when the first device of a named device class is registered via
rtdm_dev_register(). Up to class->device_count minors will be
reserved. Minor number are assigned to devices in order of
registration, starting from minor #0.

Device nodes for named RTDM devices are automatically visible from the
/dev/rtdm/ hierarchy with hotplug-enabled device fs (DEVTMPFS now
recommended).