An Operating Systems Vade Mecum

190 File Structures Chapter 6Master directorysoftwaresmith.thesissmith.coursestroyuser file directoriesfortran.runsimulate.forsimulate.runchapter1.textmailmailslide1.textJIR.textsmith.textfilesFigure 6.2 Two-level directory/smith.thesis/chapter1.textFileslide1.textmail/smith.thesis/simulate.for/smith.thesis/simulate.run/smith.thesis/chapter1.text/troy/JIR.text/software/fortran.runAlso called/smith.courses/slide1.text/smith.courses/mail/smith.thesis/mail/troy/smith.textAliases raise several issues pertaining to naming, deletion and accounting.Naming: A file with several aliases no longer seems to have a ‘‘true’’ name. Is themail file really /smith.courses/mail or /smith.thesis/mail? Wecan increase the confusion by giving the same file different local names in the twodirectories, such as mail and letters. We could even put the two aliases inthe same directory, as long as the local names are different.If we are willing to distinguish files from names, as our figures show, wecan find this situation useful. A file may have multiple names. For example, everystudent in a class might be expected to build a file called project.mod. Theteacher may wish to build an alias for each of these files in the teacher’s directory.The local name for each file in the teacher’s directory could refer to the student:brown.mod, asaithambi.mod, and mogolescu.mod.Deletion: If the file is deleted under one of its aliases, should it disappear under allaliases? If so, then it is necessary to find all the directories that contain aliases forthe deleted file and remove those aliases as well. To make this search efficient, all