Separate read function into blocking and async portions

src/kernel/block_device.h

@@ -0,0 +1,10 @@
+#pragma once
+/// \file block_device.h
+/// Interface definition for block devices
+
+/// Interface for block devices
+class block_device
+{
+public:
+	virtual size_t read(size_t offset, size_t length, void *buffer) = 0;
+};