From: utzoo!decvax!microsof!uw-beave!black
Newsgroups: net.unix-wizards
Title: File Protection and Deletion
Article-I.D.: uw-beave.236
Posted: Fri Dec  3 10:59:21 1982
Received: Sun Dec  5 04:25:29 1982



I'm suprised that "Unix Wizards" are missing the difference between the three
different kinds of file deletion.  They are:

	(1) DeleteBody  - i.e. make the file 0 bytes long
 	(2) DeleteEntry - An operation on a directory, not on the file
			  at all.  The file is unchanged, but there is
			  one less directory entry which points to it.
	(3) DeleteFile  - Remove the file heading, as well as the body.

On unix, (1) is available by doing an open for reading and a close, and
requires write permission on the file to be DeleteBodied.  (2) is available
by doing an Unlink on the directory concerned, and requires write permission
on the directory.  So Unix does distinguish between these things rather well.

(3) is not available at all, on the other hand!  I used to use a system where
it was available, and it was very handy.  For example, if I have my own link
to a large system file, and the administrator creates a new version and
unlinks the old one, I am unaware of what has happened and continue to hog
disk space as well as use an out of date file.  If the old file was
DeleteFile'd instead, when I next tried to access it I would get "Attempt to
Open Deleted File" and would thus be given a warning of what had happened.
 
If Unix was to add DeleteFile, then there is a strong argument for needing
different permissions to DeleteBody and to DeleteFile.  However, I don't
beleive that it makes sense to make DeleteBody different from any other kind
of write.

    Andrew Black