/* * uvm_map_submap: punch down part of a map into a submap * * => only the kernel_map is allowed to be submapped * => the purpose of submapping is to break up the locking granularity * of a larger map * => the range specified must have been mapped previously with a uvm_map() * call [with uobj==NULL] to create a blank map entry in the main map. * [And it had better still be blank!] * => maps which contain submaps should never be copied or forked. * => to remove a submap, use uvm_unmap() on the main map * and then uvm_map_deallocate() the submap. * => main map must be unlocked. * => submap must have been init'd and have a zero reference count. * [need not be locked as we don't actually reference it] */