kernel modules: add a quick scull port from LDD3

Also:

* fix fops.c on both kernels:
  * 5.9: the out of space error code was 1 not 8
  * 6.6: for whatever reason we can't read the user buffer as before on the
         diagnostic print, it leads to segfault and oops
* create memfile.c which is like fops.c but of unlimited size

linux-kernel-module-cheat.code-workspace

@@ -11,6 +11,13 @@
             "out.docker/**": true,
             "out/**": true,
             "submodules/**": true,
-        }
+        },
+        "search.exclude": {
+            "data/**": true,
+            ".git/**": true,
+            "out.docker/**": true,
+            "out/**": true,
+            "submodules/**": true,
+        },
     }
 }