make bluescreen demo more general for paging

c_os/user/demo/PagingDemo.cc

@@ -0,0 +1,51 @@
+#include "user/demo/PagingDemo.h"
+#include "kernel/Paging.h"
+
+void PagingDemo::writeprotect_page() {
+    kout << "Accessing a writeprotected page triggers bluescreen,\nif you can read this it didn't work" << endl;
+
+    // BlueScreen 1
+    // asm("int $3");
+
+    // BlueScreen 2
+    log.info() << "Allocating page" << endl;
+    unsigned int* page = pg_alloc_page();
+    *page = 42;
+    log.info() << "Writeprotecting page..." << endl;
+    pg_write_protect_page(page);
+
+    log.info() << "Accessing writeprotected page" << endl;
+    *page = 42; // We map logical to physical 1:1 so no need to do any lookup
+
+    // No free because bluescreen
+}
+
+void PagingDemo::notpresent_page() {
+    kout << "Produces pagefault, if you can read this it didn't work" << endl;
+
+    log.info() << "Allocating page" << endl;
+    unsigned int* page = pg_alloc_page();
+    *page = 42;
+
+    log.info() << "Marking page notpresent..." << endl;
+    pg_notpresent_page(page);
+
+    log.info() << "Accessing page" << endl;
+    kout << "Page not accessible: " << *page << endl;
+
+    // No free because bluescreen
+}
+
+void PagingDemo::run() {
+    kout << "Press w for writeprotect demo, n for notpresent demo" << endl;
+    switch(listener.waitForKeyEvent()) {
+    case 'w':
+        writeprotect_page();
+        break;
+    case 'n':
+        notpresent_page();
+        break;
+    }
+
+    scheduler.exit();
+}