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The Linux user-space NFS server is relatively easy to implement. It
only uses the user-space RPC calls. It has several features:
- The directory hierarchy exported by the user-space NFS server
mount points within an exported filesystem transparently; thus
the client sees the same directory hierarchy as is seen from
the server.
- Since the server is running in the user space, it is easy to
do uid and gid mapping as well as access DNS, NIS, NIS+,
etc.
However the user-space NFS server has some drawbacks:
- Since it is running in the user space, it has to do extra
memory copy between user and kernel spaces. Also there is an
overhead for context switch. They can be very expensive.
- There are no supports for NLM nor NSM. File and record locks
are not available.
- The current implementation is not multithreaded which impacts
its performance.
- Since the export control is initialized at the startup time,
the server process has to be restarted when /etc/exports is
changed.
H.J. Lu
1999-08-15