EECS 1012 Lecture 9: EECS 1012 Lecture 9 Notes
13 Jun 2018
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EECS 1012 Lecture 9 Notes
Introduction
Individual user
• An individual user can even create multiple paths to a file, if so desired.
• This capability could be useful if the file is associated with two different directories, and
the user would like to place it as an entry in both for more convenient access.
• One difficulty with implementation of an acyclic-graph directory is assuring that the links
do not connect in such a way that it is possible to cycle through a path more than once
when tracing out the path to a file.
• The links between current and projects and between projects and im woman complete
a cycle.
• Thus, the file name PROJ1.TXT can be reached by an infinite number of paths, including
• IMWOMAN/CURRENT/PROJECTS/2008/PROJ1.TXT
• IMWOMAN/CURRENT/PROJECTS/IMWOMAN/CURRENT/ PROJECTS/2008/PROJ1.TXT
• IMWOMAN/CURRENT/PROJECTS/IMWOMAN/CURRENT/
• PROJECTS/IMWOMAN/CURRENT/PROJECTS/ and so on.
• This is obviously an unsatisfactory situation.
• When the file system is searching for files, it will encounter an infinite number of paths
that it believes must be checked.
• The system must assure that the addition of a link does not create a cycle.
• An additional difficulty is establishing a policy for the deletion of files that have multiple
links.
• Removing a file without removing the links leaves dangling links, links that point to
nowhere.
• It is also possible on some systems to remove all links to the file, leaving file space that
a’t e relaied y the syste.
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