  This work presents a formal model that is part of our effort to construct a
verified file system for Flash memory. To modularize the verification we factor
out generic aspects into a common component that is inspired by the Linux
Virtual Filesystem Switch (VFS) and provides POSIX compatible operations. It
relies on an abstract specification of its internal interface to concrete file
system implementations (AFS). We proved that preconditions of AFS are respected
and that the state is kept consistent. The model can be made executable and
mounted into the Linux directory tree using FUSE.
