RFE: DRM_IOCTL_MODE_EXPOSE_LEASE

[Troll Berserker]

Goal: simplify multiseat support.

A new parameter was added to the Xorg server to make it use a passed file descriptor instead of /dev/dri/card*.
This enables  one to start the Xorg server with leased FD.
Although it is possible to organize multiseat using this approach, it does not integrate well with existing seat infrastructure (udev, logind).

It would be great to have a way to expose a DRM Lessee as /dev/dri/card* node and relevant /sys nodes etc., which would enable one to write an udev rule to create a new seat.
This new node should represent leased resources and *should support DRM_IOCTL_SET_MASTER/DRM_IOCTL_DROP_MASTER* as if it were a "real" device.

Interface: DRM_IOCTL_MODE_EXPOSE_LEASE ioctl request to DRM Lessor with lease FD as the ioctl parameter.