Objective
=========

A high-performance FUSE API that minimizes pitfalls with writing
correct filesystems.

Decisions
=========

   * Nodes contain references to their children. This is useful
     because most filesystems will need to construct tree-like
     structures.

   * Nodes contain references to their parents. As a result, we can
     derive the path for each Inode, and there is no need for a
     separate PathFS.

   * Nodes can be "persistent", meaning their lifetime is not under
     control of the kernel. This is useful for constructing FS trees
     in advance, rather than driven by LOOKUP.

   * The NodeID for FS tree node must be defined on creation and are
     immutable. By contrast, reusing NodeIds (eg. rsc/bazil FUSE, as
     well as old go-fuse/fuse/nodefs) needs extra synchronization to
     avoid races with notify and FORGET, and makes handling the inode
     Generation more complicated.
     
   * The mode of an Inode is defined on creation.  Files cannot change
     type during their lifetime. This also prevents the common error
     of forgetting to return the filetype in Lookup/GetAttr.
     
   * The NodeID (used for communicating with kernel) is equal to
     Attr.Ino (value shown in Stat and Lstat return values.). 

   * No global treelock, to ensure scalability.

   * Support for hard links. libfuse doesn't support this in the
     high-level API.  Extra care for race conditions is needed when
     looking up the same file through different paths.

   * do not issue Notify{Entry,Delete} as part of
     AddChild/RmChild/MvChild: because NodeIDs are unique and
     immutable, there is no confusion about which nodes are
     invalidated, and the notification doesn't have to happen under
     lock.

   * Directory reading uses the DirStream. Semantics for rewinding
     directory reads, and adding files after opening (but before
     reading) are handled automatically. No support for directory
     seeks.

   * Method names are based on syscall names. Where there is no
     syscall (eg. "open directory"), we bias towards writing
     everything together (Opendir)

To do/To decide
=========

   * Symlink []byte vs string.