Add a skeleton framework for capabilities.

Use the first capability to spawn a child process.

zion/capability/capability.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "debug/debug.h"
+
+class Process;
+
+class Capability {
+ public:
+  enum Type {
+    UNDEFINED,
+    PROCESS,
+  };
+  Capability(void* obj, Type type, uint64_t id, uint64_t permissions)
+      : obj_(obj), type_(type), id_(id), permissions_(permissions) {}
+
+  template <typename T>
+  T& obj();
+
+  uint64_t id() { return id_; }
+
+  bool CheckType(Type type) { return type_ == type; }
+
+  uint64_t permissions() { return permissions_; }
+  bool HasPermissions(uint64_t requested) {
+    return (permissions_ & requested) == requested;
+  }
+
+ private:
+  // FIXME: This should somehow be a shared ptr to keep the object alive.
+  void* obj_;
+  Type type_;
+  uint64_t id_;
+  uint64_t permissions_;
+};
+
+template <class Process>
+Process& Capability::obj() {
+  if (type_ != PROCESS) {
+    panic("Accessing %u cap as object.", type_);
+  }
+  return *static_cast<Process*>(obj_);
+}