Started implementing the backing system

src/backing.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include "utils.h"
+
+bool IsBackingIdentifierValid(const char* backing_identifier);
+int GetBackingIndex(const char* backing_identifier);
+
+Status GetBackingPoolPath(char** _backing_pool_path);
+Status GetBackingDiskPath(const char* backing_identifier, char** _backing_path);