File management

The file management subsystem controls all interactions involving files. Users can create, access, edit, and delete files, as well as cause processes to interact with files. The allocation of space to new files and to existing files as they grow in size is handled automatically by the file management subsystem, which also manages free space.

For the enforcement of security, the most important things that the file management subsystem does are

• controlling access to files

• guaranteeing the integrity of files

The file management subsystem identifies each file by its inode. The inode of a file on a general purpose filesystem contains the following information:

• file owner

• file type

• access permissions

• Access Control List (ACL) information - see ``Discretionary access control (DAC)''

• pointer to additional ACL information that does not fit in the inode

• addresses of the data in the file

• file size

• other bookkeeping information

The file management subsystem enforces security by keeping files separate and by guaranteeing that any subject that tries to access a file has the proper authorization.