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From: lm@snafu.Sun.COM (Larry McVoy)
Newsgroups: comp.unix.questions,comp.unix.wizards,comp.lang.c
Subject: Re: what does O_EXCL open flag do?
Message-ID: <129748@sun.Eng.Sun.COM>
Date: 30 Dec 89 00:13:29 GMT
References: <479@dios.hf.intel.com>
Sender: news@sun.Eng.Sun.COM
Reply-To: lm@sun.UUCP (Larry McVoy)
Organization: Sun Microsystems, Mountain View
Lines: 16

In article <479@dios.hf.intel.com> martin@clubmed.hf.intel.com (Martin Wilde) writes:
>Does anyone know what the O_EXCL flag for the open call is
>supposed to do?  I have read the POSIX spec, but I don't quite
>understand what the flag is for.  The only thing that
>the POSIX spec says is that if O_EXCL and O_CREAT are set, open()
>shall fail if the file exists.  What if just O_EXCL is set?

Yeah, it's a misnomer.  As far as I know, it's only generic use is the one
you describe (commonly used to implement a crude form of semaphore).

I think that some device drivers may also look at this flag to mean exclusive 
(i.e, one user).  
---
What I say is my opinion.  I am not paid to speak for Sun, I'm paid to hack.

Larry McVoy, Sun Microsystems     (415) 336-7627       ...!sun!lm or lm@sun.com