linux-ext4 - Re: e4defrag and immutable files

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Message-ID: <20100609011028.GD6795@mail.oracle.com>
Date:	Tue, 8 Jun 2010 18:10:28 -0700
From:	Joel Becker <Joel.Becker@...cle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Sunil Mushran <sunil.mushran@...cle.com>, tytso@....edu,
	linux-ext4@...r.kernel.org, Mark Fasheh <mfasheh@...e.com>
Subject: Re: e4defrag and immutable files

On Tue, Jun 08, 2010 at 03:12:04PM -0700, H. Peter Anvin wrote:
> On 06/02/2010 11:02 AM, Sunil Mushran wrote:
> > "Immutable" means the contents do not change. But the file mappings
> > could change.
> > 
> > "Fixed mapping" means the mappings do not change but contents
> > could (as long as the ondisk mappings don't).
> > 
> > "Fixed metadata" means the entire inode (mappings included) cannot
> > change but the contents could (as long as the ondisk mappings don't).
> > (This does have the side effect of allowing writes without touching the
> > mtime. Like XFS' invisible i/o.)
> > 
> 
> Actually, if you're going to have three flags you might as well make
> them orthogonal.  That is, separate "fixed contents", "fixed mappings",
> "fixed metadata" -- and don't consider the mapping as metadata for this
> purpose.

	I think Sunil was defining terms, not suggesting three flags ;-)
That said, it does allow all the possible characteristics in the
discussion.  The only ugly think I can see is that we'll have three new
flags, plus the old immutable flag that means the same as setting all
three new flags.

Joel

-- 

"But all my words come back to me
 In shades of mediocrity.
 Like emptiness in harmony
 I need someone to comfort me."

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@...cle.com
Phone: (650) 506-8127
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