A file system checker for the xv6 operating system.
This file system checker will check/validate an operating system to make sure itsatisfies the following conditions:
- Each inode is either unallocated or one of the valid types (T_FILE, T_DIR, T_DEV).ERROR:bad inode
- For in-use inodes, each address that is used by inode is valid (points to a valid datablock address within the image). Note: must check indirect blocks too, when they are in use.
ERROR:bad address in inode - Root directory exists, and it is inode number 1.
ERROR:root directory does not exist - Each directory contains . and .. entries.
ERROR:directory not properly formatted - Each .. entry in directory refers to the proper parent inode, and parent inode points back to it.
ERROR:parent directory mismatch - For in-use inodes, each address in use is also marked in use in the bitmap.
ERROR:address used by inode but marked free in bitmap - For blocks marked in-use in bitmap, actually is in-use in an inode or indirect block somewhere.
ERROR:bitmap marks block in use but it is not in use - For in-use inodes, any address in use is only used once.
ERROR:address used more than once - For inodes marked used in inode table, must be referred to in at least one directory.
ERROR:inode marked use but not found in a directory - For inode numbers referred to in a valid directory, actually marked in use in inode table.
ERROR:inode referred to in directory but marked free - Reference counts (number of links) for regular files match the number of times file is referred to in directories (i.e., hard links work correctly).
ERROR:bad reference count for file
First, run this on an uncorrupted file system:
make qemu-nox //run xv6 mkdir xyz //create some files and/or directories exit xv6 (ctrl+a followed by x) run chkfs on fs.img
Then, try it out on a corrupted filesystem:
cp fs.img corrupted.img ./corruptfs corrupted.img TYPE chkfs corrupted.img
TYPE is respective to the errors lsited above e.g. bad inode would be type 1
The corruptfs program randomly chooses which directory, inode, etc. to corrupt. To make the random selection deterministic, include a random seed (i.e., a positive integer) as an additional command line argument to corruptfs. Also, because of the random nature of corruptfs, it will occasionally make a random choice such that it is impossible to introduce the specified type of corruption. If this occurs, corruptfs will indicate that it failed to corrupt the image; simply run corruptfs again (with a different random seed) so it makes a different random choice.