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    routine file_getfh (
    	file: file_t;
    	RPT
    	out filehandle: data_t, dealloc);

Return a file handle for this file.  This can be used by NFS and such.  It is
not guaranteed that this call will work;  if it doesn't, then this filesystem
cannot be NFS mounted.

Currently file handles are only used by `nfsd` with the purpose of
having some stable representation of nodes (TODO: Add references).
The only translator library that implements `file_getfh` and the
complementary [[`fsys_getfile`|fsys_getfile]] is `libdiskfs`, so if
you are linking against a different library you should expect that the
filesystem exported by your translator will not be supported by `nfsd`
by default.

If you would like your non-`libdiskfs` translator to be supported by
`nfsd`, you should implement these two RPCs on your own.  The idea is
that to each node exported by your translator you should put in
correspondence a unique file handle.  A file handle is a 28-byte
value.  The first 4 bytes are not used.  Then comes a 4-byte number
which should identify your node somehow (`libdiskfs` uses the index
into the internally maintained node cache).  After it there comes a
4-byte number which should bear a similar function to the `st_gen`
field of a `stat` structure.  Following this specification, you should
be able to implement `file_getfh` and `fsys_getfile` in a proper way
to get `nfsd` support.