Simulator

This exercise introduces fsck.py, a simple file system simulator. Some familiarity with the vsfs.py simulator (described in an earlier chapter on file system implementation would be useful, but is not necessary.

The file system tool changes the on-disk state of the file system, and then leaves it to you, the user, to detect the problem, much like a file system consistency checker would do (e.g., fsck). The file system itself is based on a simplified VSFS, the very simple file system described in an earlier chapter. The tool first generates an on-disk file system; then, either randomly or through more specific controls, the tool changes the on-disk state of one aspect of the file system.

The challenge for you, the user, is to figure out which part of the file system’s on-disk state was changed and hence has become inconsistent. In many cases, the problem should be readily detected; in others, perhaps less so.

Let’s get into the details. Here is an example run of the tool:

prompt> ./fsck.py -S 1
...
Final state of file system:

inode bitmap 1100100010000010
inodes       [d a:0 r:4] [f a:-1 r:1] [] [] [d a:8 r:2] [] [] []