Note that struct file, struct dir are per-thread.

[pintos-anon] / doc / filesys.texi

diff --git a/doc/filesys.texi b/doc/filesys.texi
index 83900ce2fbf4f9e708aeff6fdca49cb9c997a2e8..f245daa48ea1e6d592a86146ddddf9947ca9cffe 100644 (file)
--- a/doc/filesys.texi
+++ b/doc/filesys.texi
@@ -16,6 +16,7 @@ to 5% extra credit if you do enable VM.
 
 @menu
 * Project 4 Background::        
+* Project 4 Suggested Order of Implementation::  
 * Project 4 Requirements::      
 * Project 4 FAQ::               
 @end menu
@@ -108,6 +109,33 @@ out the file system contents is the standard Unix ``tar'' format.  You
 can use the Unix @command{tar} program to examine them.  The tar file
 for test @var{t} is named @file{@var{t}.tar}.
 
+@node Project 4 Suggested Order of Implementation
+@section Suggested Order of Implementation
+
+We suggest implementing the parts of this project in the following
+order to make your job easier:
+
+@enumerate
+@item
+Buffer cache (@pxref{Buffer Cache}).  Implement the buffer cache and
+integrate it into the existing file system.  At this point all the
+tests from project 2 (and project 3, if you're building on it) should
+still pass.
+
+@item
+Extensible files (@pxref{Indexed and Extensible Files}).  After this
+step, your project should pass the file growth tests.
+
+@item
+Subdirectories (@pxref{Subdirectories}).  Afterward, your project
+should pass the directory tests.
+
+@item
+Remaining miscellaneous items.
+@end enumerate
+
+You should think about synchronization throughout.
+
 @node Project 4 Requirements
 @section Requirements
 
@@ -259,8 +287,8 @@ false if it represents an ordinary file.
 @end deftypefn
 
 @deftypefn {System Call} int inumber (int @var{fd})
-Returns the @dfn{inode number} of the inode associated with @var{fd}.
-Applicable to file descriptors for both files and directories.
+Returns the @dfn{inode number} of the inode associated with @var{fd},
+which may represent an ordinary file or a directory.
 
 An inode number persistently identifies a file or directory.  It is
 unique during the file's existence.  In Pintos, the sector number of the
@@ -287,11 +315,12 @@ disk.  Otherwise, fetch the block from disk into cache, evicting an
 older entry if necessary.  You are limited to a cache no greater than 64
 sectors in size.
 
-Be sure to choose an intelligent cache replacement algorithm.
-Experiment to see what combination of accessed, dirty, and other
-information results in the best performance, as measured by the number
-of disk accesses.  For example, metadata is generally more valuable to
-cache than data.
+You must implement a cache replacement algorithm that is at least as
+good as the ``clock'' algorithm.  Your algorithm must also account for
+the generally greater value of metadata compared to data.  Experiment
+to see what combination of accessed, dirty, and other information
+results in the best performance, as measured by the number of disk
+accesses.
 
 You can keep a cached copy of the free map permanently in memory if you
 like.  It doesn't have to count against the cache size.
@@ -311,11 +340,8 @@ blocks back to disk.  The cache should also be written back to disk in
 @func{filesys_done}, so that halting Pintos flushes the cache.
 
 If you have @func{timer_sleep} from the first project working, write-behind is
-an excellent application.  If you're still using the base
-implementation of @func{timer_sleep}, be aware that it busy-waits, which
-is not acceptable here (or elsewhere).  If @func{timer_sleep}'s delays seem too
-short or too long, reread the explanation of the @option{-r} option to
-@command{pintos} (@pxref{Debugging versus Testing}).
+an excellent application.  Otherwise, you may implement a less general
+facility, but make sure that it does not exhibit busy-waiting.
 
 You should also implement @dfn{read-ahead}, that is,
 automatically fetch the next block of a file
@@ -368,6 +394,10 @@ if B's data is all nonzero bytes, A is not allowed to see any zeros.
 Operations on different directories should take place concurrently.
 Operations on the same directory may wait for one another.
 
+Keep in mind that only data shared by multiple threads needs to be
+synchronized.  In the base file system, @struct{file} and @struct{dir}
+are accessed only by a single thread.
+
 @node Project 4 FAQ
 @section FAQ