linux-kernel - Re: Versioning file system

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Date:	Tue, 19 Jun 2007 15:07:40 -0700 (PDT)
From:	david@...g.hm
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
cc:	Chris Snook <csnook@...hat.com>,
	Jack Stone <jack@...keye.stone.uk.eu.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	akpm@...ux-foundation.org, viro@...iv.linux.org.uk, hpa@...or.com,
	alan <alan@...eserver.org>
Subject: Re: Versioning file system

On Tue, 19 Jun 2007, Lennart Sorensen wrote:

> On Tue, Jun 19, 2007 at 02:03:07PM -0400, Chris Snook wrote:
>> I pointed out NetApp's .snapshot directories because that's a method that
>> uses legal path character, but doesn't break anything.  With this method,
>> userspace tools will have to be taught that : is suddenly a special
>> character.  Userspace already knows that files beginning with . are special
>> and treat them specially. We don't need a new special character for every
>>  new feature.  We've got one, and it's flexible enough to do what you want,
>> as proven by NetApp's extremely successful implementation.  Perhaps you
>> want a slightly different interface from what NetApp has implemented, but
>> what you're suggesting will change the default behavior of basic tools like
>> tar and ls.  This is not a good thing.
>
> I think I used one of those systems once (or at least another one with
> .snapshot feature).  It managed to completely avoid user space problems
> by never actually showing .snapshot in directory listings, but you could
> always cd to it or refer to it explicitly.  You never risked having tar
> or find or anything else accidentally pick it up.  Very nice interface.

since anything starting with . is considered a 'hidden' file per *nix 
tradition it's ignored by many programs and optionally ignored by most 
others (and anything that doesn't ignore . files when presending files to 
the user has many other problems on modern desktop systems anyway ;-)

the only trouble I ever had with the .snapshot approach is when tar or 
find would decend down into the .snapshot when I didn't really intend for 
it to do so.

David Lang
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