     Flexible and Safe Resolution of File Conflicts

           Puneet Kumar and M. Satyanarayanan
               Carnegie Mellon University

                        Abstract

  In  this paper  we  describe the  support provided  by
the  Coda  File System  for  transparent  resolution  of
conflicts  arising from  concurrent  updates to  a  file
in  different  network  partitions.     Such  partitions
often occur  in  mobile computing  environments.    Coda
provides a framework  for invoking customized pieces  of
code called  application-specific resolvers (asrs)  that
encapsulate the  knowledge needed  for file  resolution.
If  resolution  succeeds,   the  user  notices   nothing
more  than  a  slight  performance  delay.      Only  if
resolution fails does the user have to  resort to manual
repair.   Our design combines  a rule-based approach  to
asr selection  with transactional  encapsulation of  asr
execution.  This paper shows how such  an approach leads
to flexible and  efficient file resolution without  loss
of security or robustness.

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