devfree releases devices from exclusive use. Exclusive use is requested with the command
devreserv.
When devfree is invoked with only the key argument, it releases all devices that have been reserved for that key. When called with key and device arguments, devfree releases the specified devices that have been reserved with that key.
The commands devreserv and devfree are used to manage the availability of devices on a system. These commands do not place any constraints on the access to the device. They serve only as a centralized bookkeeping point for those who wish to use them. Processes
that do not use devreserv may concurrently use a device with a process that has reserved that device.