Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!ogicse!unicorn!phil
From: phil@unicorn.cc.wwu.edu (Phil Nelson)
Newsgroups: comp.os.minix
Subject: fs "bug" (rename) and "fix"
Keywords: fs rename
Message-ID: <1990Nov28.001925.24250@unicorn.cc.wwu.edu>
Date: 28 Nov 90 00:19:25 GMT
Organization: Western Washington University, Bellingham WA.
Lines: 42

Recently, I was working with a program that used the rename system call
to make backup files.  It used calls like rename("file","file~").  This
call failed every time.  After tracking down what was happening, I
discovered that fs (the code for rename) checks to make sure that the
old file name (file) is not a prefix of the new file name (file~).  If
it is a prefix, then the rename is denied.  This means many rename
calls will fail when it is safe to do the rename.  I don't have the
POSIX definition, but I presume that is not a POSIX requirement.

After looking at the fs code, I decided that the "correct" test was to
see if the old file name is a DIRECTORY prefix in the new name.  If it
is, then the rename is trying to move a directory into a subdirectory
of itself.  This is something that should not work.

I changed the code to test for the directory prefix problem.  The uuencoded,
compressed cdiff follows.


--Phil Nelson
(phil@cs.wwu.edu, Western Washington University, Bellingham, WA)


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