@menu
* Project 4 Background::
+* Project 4 Suggested Order of Implementation::
* Project 4 Requirements::
* Project 4 FAQ::
@end menu
@menu
* File System New Code::
+* Testing File System Persistence::
@end menu
@node File System New Code
While most of your work will be in @file{filesys}, you should be
prepared for interactions with all previous parts.
+@node Testing File System Persistence
+@subsection Testing File System Persistence
+
+By now, you should be familiar with the basic process of running the
+Pintos tests. @xref{Testing}, for review, if necessary.
+
+Until now, each test invoked Pintos just once. However, an important
+purpose of a file system is to ensure that data remains accessible from
+one boot to another. Thus, the tests that are part of the file system
+project invoke Pintos a second time. The second run combines all the
+files and directories in the file system into a single file, then copies
+that file out of the Pintos file system into the host (Unix) file
+system.
+
+The grading scripts check the file system's correctness based on the
+contents of the file copied out in the second run. This means that your
+project will not pass any of the extended file system tests until the
+file system is implemented well enough to support @command{tar}, the
+Pintos user program that produces the file that is copied out. The
+@command{tar} program is fairly demanding (it requires both extensible
+file and subdirectory support), so this will take some work. Until
+then, you can ignore errors from @command{make check} regarding the
+extracted file system.
+
+Incidentally, as you may have surmised, the file format used for copying
+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
You must also support special file names @file{.} and @file{..}, which
have the same meanings as they do in Unix.
-Update the @code{remove} system call so that it can delete empty
-directories in addition to regular files. Directories may only be
-deleted if they do not contain any files or subdirectories (other than
-@file{.} and @file{..}).
-
Update the @code{open} system call so that it can also open directories.
Of the existing system calls, only @code{close} needs to accept a file
descriptor for a directory.
+Update the @code{remove} system call so that it can delete empty
+directories (other than the root) in addition to regular files.
+Directories may only be deleted if they do not contain any files or
+subdirectories (other than @file{.} and @file{..}). You may decide
+whether to allow deletion of a directory that is open by a process or in
+use as a process's current working directory. If it is allowed, then
+attempts to open files (including @file{.} and @file{..}) or create new
+files in a deleted directory must be disallowed.
+
Implement the following new system calls:
@deftypefn {System Call} bool chdir (const char *@var{dir})
@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
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.
@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
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
projects / pintos-anon / blobdiff