First cut at file system checker project

filesystems-checker/CONTEST.md

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+## Contest: A Better Checker
+
+For this project, there is a contest, which will compare checkers that can
+handle these more challenging condition checks:
+
+- Each `..` entry in directory refers to the proper parent inode, and parent inode
+points back to it. If not, print `ERROR: parent directory mismatch.`
+
+- Every directory traces back to the root directory. (i.e. no loops in the
+directory tree). If not, print `ERROR: inaccessible directory exists.`
+
+This better checker will also have to do something new: actually repair the
+image, in one specific case. Specifically, your task will be to repair the
+"inode marked use but not found in a directory" error. 
+
+We will provide you with an xv6 image that has a number of in-use inodes that
+are not linked by any directory. Your job is to collect these nodes and put
+them into the `lost_found` directory (which is already in the provided image
+under the root directory). Real checkers do this in order to preserve files
+that may be useful but for some reason are not linked into a directory.
+
+To do so, you will need to obtain write access to the file system image in
+order to modify it. This repair operation of your checker program should only
+be performed when `-r` flag is specified:
+
+```
+prompt> xcheck -r image_to_be_repaired
+```
+
+In this repair mode, your program should **not** exit when an error is
+encountered, but rather continue processing. For simplicity, you can also
+assume there is no other types of error in the provided image. It should exit
+only after it has created an entry under the `lost_found` directory for every
+lost inode. 
+
+The contest will be judged based on whether all extra tests are passed. If
+they are, the winner will be given to the most readable implementation.
+
+
+
+
+