RedirFS

This is an attempt to resurrect and extend the discontinued redirfs project from https://github.com/fhrbata/redirfs

What's new:

• the redirfs.ko module was made compilable up to 4.14 kernel
• some fixies to vfsmount usage
• complete set of file_operations
• address_space_operations support
• shared object for hooked operations instead of a per-object structure
• new object model to manage reference counting
• character devices operations (requires adding /dev path as redirfs_add_path doesn't cross mount points)
• debug build without optimization (make modules_debug)