             +-------------------------+
             |         CS 140          |
             | PROJECT 4: FILE SYSTEMS |
             |     DESIGN DOCUMENT     |
             +-------------------------+

---- GROUP ----

>> Fill in the names and email addresses of your group members.

FirstName LastName <email@domain.example>
FirstName LastName <email@domain.example>
FirstName LastName <email@domain.example>

---- PRELIMINARIES ----

>> If you have any preliminary comments on your submission, notes for the
>> TAs, or extra credit, please give them here.

>> Please cite any offline or online sources you consulted while
>> preparing your submission, other than the Pintos documentation, course
>> text, lecture notes, and course staff.

             INDEXED AND EXTENSIBLE FILES
             ============================

---- DATA STRUCTURES ----

>> A1: Copy here the declaration of each new or changed `struct' or
>> `struct' member, global or static variable, `typedef', or
>> enumeration.  Identify the purpose of each in 25 words or less.

>> A2: What is the maximum size of a file supported by your inode
>> structure?  Show your work.

---- SYNCHRONIZATION ----

>> A3: Explain how your code avoids a race if two processes attempt to
>> extend a file at the same time.

>> A4: Suppose processes A and B both have file F open, both
>> positioned at end-of-file.  If A reads and B writes F at the same
>> time, A may read all, part, or none of what B writes.  However, A
>> may not read data other than what B writes, e.g. if B writes
>> nonzero data, A is not allowed to see all zeros.  Explain how your
>> code avoids this race.

>> A5: Explain how your synchronization design provides "fairness".
>> File access is "fair" if readers cannot indefinitely block writers
>> or vice versa.  That is, many processes reading from a file cannot
>> prevent forever another process from writing the file, and many
>> processes writing to a file cannot prevent another process forever
>> from reading the file.

---- RATIONALE ----

>> A6: Is your inode structure a multilevel index?  If so, why did you
>> choose this particular combination of direct, indirect, and doubly
>> indirect blocks?  If not, why did you choose an alternative inode
>> structure, and what advantages and disadvantages does your
>> structure have, compared to a multilevel index?

                SUBDIRECTORIES
                ==============

---- DATA STRUCTURES ----

>> B1: Copy here the declaration of each new or changed `struct' or
>> `struct' member, global or static variable, `typedef', or
>> enumeration.  Identify the purpose of each in 25 words or less.

---- ALGORITHMS ----

>> B2: Describe your code for traversing a user-specified path.  How
>> do traversals of absolute and relative paths differ?

---- SYNCHRONIZATION ----

>> B4: How do you prevent races on directory entries?  For example,
>> only one of two simultaneous attempts to remove a single file
>> should succeed, as should only one of two simultaneous attempts to
>> create a file with the same name, and so on.

>> B5: Does your implementation allow a directory to be removed if it
>> is open by a process or if it is in use as a process's current
>> working directory?  If so, what happens to that process's future
>> file system operations?  If not, how do you prevent it?

---- RATIONALE ----

>> B6: Explain why you chose to represent the current directory of a
>> process the way you did.

                 BUFFER CACHE
                 ============

---- DATA STRUCTURES ----

>> C1: Copy here the declaration of each new or changed `struct' or
>> `struct' member, global or static variable, `typedef', or
>> enumeration.  Identify the purpose of each in 25 words or less.

---- ALGORITHMS ----

>> C2: Describe how your cache replacement algorithm chooses a cache
>> block to evict.

>> C3: Describe your implementation of write-behind.

>> C4: Describe your implementation of read-ahead.

---- SYNCHRONIZATION ----

>> C5: When one process is actively reading or writing data in a
>> buffer cache block, how are other processes prevented from evicting
>> that block?

>> C6: During the eviction of a block from the cache, how are other
>> processes prevented from attempting to access the block?

---- RATIONALE ----

>> C7: Describe a file workload likely to benefit from buffer caching,
>> and workloads likely to benefit from read-ahead and write-behind.

               SURVEY QUESTIONS
               ================

Answering these questions is optional, but it will help us improve the
course in future quarters.  Feel free to tell us anything you
want--these questions are just to spur your thoughts.  You may also
choose to respond anonymously in the course evaluations at the end of
the quarter.

>> In your opinion, was this assignment, or any one of the three problems
>> in it, too easy or too hard?  Did it take too long or too little time?

>> Did you find that working on a particular part of the assignment gave
>> you greater insight into some aspect of OS design?

>> Is there some particular fact or hint we should give students in
>> future quarters to help them solve the problems?  Conversely, did you
>> find any of our guidance to be misleading?

>> Do you have any suggestions for the TAs to more effectively assist
>> students in future quarters?

>> Any other comments?
