linux-ext4 - Re: e4defrag and immutable files

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Message-ID: <20100609014438.GB6529@thunk.org>
Date:	Tue, 8 Jun 2010 21:44:38 -0400
From:	tytso@....edu
To:	"H. Peter Anvin" <hpa@...or.com>,
	Sunil Mushran <sunil.mushran@...cle.com>,
	linux-ext4@...r.kernel.org, Mark Fasheh <mfasheh@...e.com>
Subject: Re: e4defrag and immutable files

On Tue, Jun 08, 2010 at 06:10:28PM -0700, Joel Becker wrote:
> 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.

Umm, what I think is being proposed --- and certainly what I think
makes sense --- is that immutable just means the data contents (just
as it has always meant), and we add two new flags, one which means
"fixed mappings", or that the location on disk must not change, and
"fixed metadata" which means all of the file metadata (not including
the mappings) must not change.

					- Ted
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