In this chapter, we look at the history and development of Linux, and cover the user and programmer interfaces that Linux presents interfaces that owe a great deal to the UNIX tradition. We also discuss the internal methods by which Linux implements these interfaces. However, since Linux has been designed to run as many standard UNIX applications as possible, it has much in common with existing UNIX implementations. We do not duplicate the basic description of UNIX given in the previous chapter. | CSC 322 Operating Systems Concepts Lecture - 21: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-4) Silberschatz, Galvin and Gagne 2002, Operating System Concepts, Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 Chapter 4 File System File system Implementation (Contd) File System Management Lecture-21 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 Implementing Directories How do we deal with variable length names? Problem is that names have become very long Two approaches Fixed header followed by variable length names Heap-pointer points to names Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 3 Two ways of handling long file names in a directory. In-line. In a heap. Implementing Directories Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 4 File system containing a shared file. File systems is a Directed Acyclic Graph/tree (DAG) Shared Files Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 5 Shared files If B or | CSC 322 Operating Systems Concepts Lecture - 21: by Ahmed Mumtaz Mustehsan Special Thanks To: Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. (Chapter-4) Silberschatz, Galvin and Gagne 2002, Operating System Concepts, Ahmed Mumtaz Mustehsan, CIIT, Islamabad 1 Chapter 4 File System File system Implementation (Contd) File System Management Lecture-21 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 2 Implementing Directories How do we deal with variable length names? Problem is that names have become very long Two approaches Fixed header followed by variable length names Heap-pointer points to names Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 3 Two ways of handling long file names in a directory. In-line. In a heap. Implementing Directories Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 4 File system containing a shared file. File systems is a Directed Acyclic Graph/tree (DAG) Shared Files Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 5 Shared files If B or C adds new blocks, how does other owner find out? Use special i-node for shared files indicates that file is shared Use symbolic link a special file put in B’s directory if C is the owner. Contains the path name of the file to which it is linked Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 6 I-node problem If C removes file, B’s directory still points to i-node for shared file If i-node is re-used for another file, B’s entry points to wrong i-node Solution: Leave i-node and reduce number of owners Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 7 Situation prior to linking. After the link is created. After the original owner removes the file. I node problem and solution Lecture-20 Ahmed Mumtaz Mustehsan, CIIT, Islamabad 8 Symbolic links Symbolic link solves problem Can have too many symbolic links and they take time to follow Backup programs must be intelligent. Otherwise will duplicate the linked files while backup and restore. Big advantage ; Can point to files on other .
