UNIVERSITY OF HOUSTON
                 Department of Computer Science
                                
                  COSC 6360--Operating Systems
                     QUALIFYING EXAMINATION
                          Graduate Part
                       FINAL  EXAMINATION
                             Part I
                           May 5, 1997
                                
   This exam is closed book.  You can have two sheets (i.e., four
   pages) of notes.

1.   A New Spritely Distributed File system:

     The  Sprite file system was designed in the mid  80’s  at  a
     time where most workstations did not have a local disk.  How
     would  you redesign a new version of Sprite if you  had  the
     chance?  Your design should remain faithful to the major
     Sprite tenets such as implementing the UNIX semantics of
     sharing and using a stateful server while being tailored  to
     workstations that have a local disk.  You are free to borrow
     as much as you want from other DFS designs among which AFS,
     Coda and xFS (not discussed in class).  (20 points)

2.   Lazy Receiver Processing

     Most operating systems use an interrupt driven network
     subsystem architecture that gives the highest priority to
     the processing of network packets.  We consider here the
     applicability of this approach to network servers such as
     file servers, firewall gateway and WWW servers.

     a)   This approach greatly increases the vulnerability of the
          servers to some attacks.  Which ones? (8 points)

    b)   What would be the other advantage of scheduling incoming
         network traffic at the same priority as the  application
         process that receives the traffic? (4 points)

    c)   Are recent changes in CPU and network technology making
         this approach more or less attractive and why? (8 points)


                             Part II
                           May 8, 1996
                                
     This exam is closed book.  You can have two sheets (i.e., four
     pages) of notes.

                                
1.   What is the problem of false sharing in distributed shared
     memory? (5 points)  What did the designers of Munin do to
     alleviate this problem?  (5 points)  How is their technique
     implemented? (10 points)

2.   A system of clocks is said to be strongly consistent if for two
     events e1 and e2,

     Ci(e1) < Cj(e2)

     always implies that e1 happened before e2.
     Show that the system of logical clocks proposed by Lampson
     is not strongly consistent.  (10 points)
 
3.   How does Grapevine handle the problem of merging different
     copies of the same registry after they have been modified ?  (10
     points)

4.   What is the motivation for callbacks in AFS?  (5 points)  How
     does AFS handle the problem of lost callbacks? ( 5 points)
  
5.   What does Amoeba to reduce the overhead of remote procedure
     calls (or remote operations as they are known in Amoeba
     parlance)?  (5 points)
 
6.   What is the major advantage of allowing Coda clients to
     operate in disconnected mode? (5 points)