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Article #477Re: mv not atomic in dynix
From: Jim Reid
Date: Tue, 19 Feb 1991 16:23
Date: Tue, 19 Feb 1991 16:23
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In article <1991Feb16.000101.4149@ux1.cso.uiuc.edu> phil@ux1.cso.uiuc.edu (Phil Howard KA9WGN) writes: When two (or more) "mv" commands try to rename the same file OR DIRECTORY to two DIFFERENT names at the same time, the result can be two separate hard links to the same inode. In the case of directories, "ln" (or the underlying system call) will refuse to allow this to happen except if the uid is root. This is not unreasonable on a multi-processor with a re-entrant kernel. On a uniprocessor, the rename() system call is "atomic" because no other process can be executing kernel code (and renaming the same files) at the same time. In DYNIX, it is possible for several processes to be executing rename() at the same time on different processors. Although hardware locks are used to synchronise access to the inodes as their link counts are changed, this will not prevent the behaviour you describe from happening. Jim
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!usc!samsung!sdd.hp.com!spool.mu.edu!uunet!mcsun!ukc!strath-cs!baird!jim From: jim@cs.strath.ac.uk (Jim Reid) Newsgroups: comp.sys.sequent Subject: Re: mv not atomic in dynix Message-ID: <JIM.91Feb19162349@baird.cs.strath.ac.uk> Date: 19 Feb 91 16:23:49 GMT References: <1991Feb16.000101.4149@ux1.cso.uiuc.edu> Sender: jim@cs.strath.ac.uk Organization: Computer Science Dept., Strathclyde Univ., Glasgow, Scotland. Lines: 18 In-reply-to: phil@ux1.cso.uiuc.edu's message of 16 Feb 91 00:01:01 GMT