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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.bugs.4bsd,net.unix-wizards
Subject: EXCL without CREAT
Message-ID: <6220@utzoo.UUCP>
Date: Thu, 12-Dec-85 15:59:43 EST
Article-I.D.: utzoo.6220
Posted: Thu Dec 12 15:59:43 1985
Date-Received: Thu, 12-Dec-85 15:59:43 EST
References: <5507@allegra.UUCP>
Organization: U of Toronto Zoology
Lines: 24

>	It is most unfortunate that open() flag O_EXCL only applies
>	when O_CREAT is also in effect.  If there were a flag that
>	meant ``succeed only if you can get me the file with nobody
>	else having it opened, and nobody else able to open it,''
>	then that atomic operation could have been used here.
>	...Such a mechanism
>	would save a lot of misguided hacking to achieve exclusive
>	use of a resource.

It would also create problems of its own.  Consider the following:

	main() {
		int foo;

		foo = open("/etc/passwd", O_READ|O_EXCL);
		for (;;)
			sleep(30000);
	}

The CREAT-only restriction is there for a reason.

In any case, removing this limitation (assuming that the security problems
could be solved) would amount to re-inventing flock(); why not just add an
advisory/mandatory flag to flock()?