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To: Alfred Perlstein <bright@wintelcom.net>
Subject: Re: versioned files via snapshot evilness. 
Cc: Terry Lambert <tlambert@primenet.com>, fs@FreeBSD.ORG
In-Reply-To: Your message of "Thu, 26 Apr 2001 11:10:11 PDT."
             <20010426111010.M18676@fw.wintelcom.net> 
Date: Thu, 10 May 2001 19:31:50 -0700
From: Kirk McKusick <mckusick@mckusick.com>
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	Date: Thu, 26 Apr 2001 11:10:11 -0700
	From: Alfred Perlstein <bright@wintelcom.net>
	To: Terry Lambert <tlambert@primenet.com>
	Cc: mckusick@FreeBSD.ORG, fs@FreeBSD.ORG
	Subject: Re: versioned files via snapshot evilness.

	* Terry Lambert <tlambert@primenet.com> [010426 10:46] wrote:
	> > I'm wondering if it might be possible to abuse the ffs snapshot
	> > stuff to do file versioning ala VMS.
	> 
	> Not really, IMO.
	> 
	> Versioning ala VMS requires kernel globbing, or amazingly
	> intrusive library modifications, coupled with a guarantee
	> by programmers that they will only use the preferred APIs
	> in their applications.
	> 
	> Consider how you would make:
	> 
	> 	fd = open( "foo", O_RDWR, 0);
	> 
	> open version 17 of the file "foo", as opposed to an earlier version,
	> and how you would tag versions into the file names, without stealing
	> a character (e.g. ";").  Also note that "/" is valid in a UTF-8
	> filename today, if it is part of a multibyte sequence (but FreeBSD
	> can not handle this).

	It would be nice if "foo" was the "HEAD" version of
	the file and each new open for write _could_ cause a foo;#ver or
	something to be created.

	I was asking more to find out the capabilities that snapshots
	brings versus the pre-existing limitations in the namespace code
	currently in place.

	More, can we snapshot individual files?

	-- 
	-Alfred Perlstein - [alfred@freebsd.org]
	Represent yourself, show up at BABUG http://www.babug.org/

The way that snapshots are implemented, they only work for filesystems
as a whole, not for individual files.

	Kirk

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