vm: implement private and shared address space mappings

whether a mapping is private or shared determines how the mapping is handled
when a task is duplicated.

include/kernel/address-space.h

@@ -22,6 +22,8 @@ struct vm_area {
 	struct address_space *vma_space;
 	/* used to link to vm_object->vo_mappings */
 	struct queue_entry vma_object_entry;
+	/* the memory control flags applied to this area */
+	vm_flags_t vma_flags;
 	/* the memory protection flags applied to this area */
 	vm_prot_t vma_prot;
 	/* offset in bytes to the start of the object data that was mapped */
@@ -83,6 +85,7 @@ extern kern_status_t address_space_map(
 	struct vm_object *object,
 	off_t object_offset,
 	size_t length,
+	vm_flags_t flags,
 	vm_prot_t prot,
 	virt_addr_t *out);
 extern kern_status_t address_space_unmap(