Operating System Concepts Essentials – 8th Edition. Chapter 9: File-System Interface. ▫. File Concept. ▫. Access Methods. ▫. Disk and Directory Structure. ▫. Jump to File system as an abstract user interface - In some cases, a file system may not make use of a storage device but can be used to organize. File System Interface Amir H. Payberah [email protected] Amirkabir University of Technology (Tehran Polytechnic) Amir H. Payberah (Tehran.


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A master file directory is used to keep track of each users directory, and must be maintained when users are added to or removed from the system.

A separate directory is generally needed for system executable files. Systems may or may not allow users to access other directories besides their own If access to other directories is allowed, then file system interface must be made to file system interface the directory being accessed.

If access is denied, then special consideration must be made for users to run programs located in system directories. A search path is the list of directories in which to search for executable programs, and can be set uniquely for each user.

Directories are stored the same as any other file in the system, except there is a bit that identifies them as directories, and they have some special file system interface that the OS understands. One question for consideration is whether or not to allow the removal of directories that are not empty - Windows requires that directories be emptied first, and UNIX provides an option for deleting entire sub-trees.

Note the directed arcs from parent to child. UNIX provides two types of links for implementing the acyclic-graph structure.

File System Interface

See "man ln" for more details. A hard link usually just called a link involves multiple directory entries that both refer to the same file. Hard links are only valid for ordinary file system interface in the same filesystem.

  • Operating Systems: File-System Interface
  • File System Interface (The GNU C Library)
  • 14 File System Interface

A symbolic link, that involves a special file, containing information about where to find the linked file. Windows only supports file system interface links, termed shortcuts. Hard links require a reference count, or link count for each file, keeping track of how many directory entries are currently referring to this file.

Whenever one of the references is removed file system interface link count is reduced, file system interface when it reaches zero, the disk space can be reclaimed. For symbolic links there is some question as to what to do with the symbolic links when the original file is moved or deleted: One option is to find all the symbolic links and adjust them also.

Another is to leave the symbolic links dangling, and discover that they are no longer valid the next time they are used.

File system

What if the original file is removed, and replaced with another file having the same name before the symbolic file system interface is next used? Search algorithms can go into infinite loops.


One solution is to not follow links in search algorithms. Or not to follow symbolic links, and to only allow symbolic file system interface to refer to directories.

Sub-trees can become disconnected from the rest of file system interface tree and still not have their reference counts reduced to zero. Periodic garbage collection is required to detect and resolve this problem.

Disconnected disk blocks that are not marked as free are added back to the file systems with made-up file names, and can usually be safely deleted.