linux-kernel - Re: [xfs-masters] Re: freeze vs freezer

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Date:	Mon, 30 Jun 2008 02:11:50 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Dave Chinner <david@...morbit.com>, xfs-masters@....sgi.com,
	Elias Oltmanns <eo@...ensachen.de>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Kyle Moffett <mrmacman_g4@....com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	David Chinner <dgc@....com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [xfs-masters] Re: freeze vs freezer

On Mon, Jun 30, 2008 at 01:22:47AM +0200, Rafael J. Wysocki wrote:
> > > Actually, I believe requirements are same.
> > > 
> > > 'don't do i/o in dangerous period'.
> > > 
> > > swsusp will just do sync() before entering dangerous period. That
> > > provides consistent-enough state...
> > 
> > As I've said many times before - if the requirement is "don't do
> > I/O" then you have to freeze the filesystem. In no way does 'sync'
> > prevent filesystems from doing I/O.....
> 
> Well, it seems we can handle this on the block layer level, by temporarily
> replacing the elevator with something that will selectively prevent fs I/O
> from reaching the layers below it.
> 
> I talked with Jens about it on a very general level, but it seems doable at
> first sight.

Why would you hack the blok layer when we already have a perfectly fine
facility to archive what you want?  freeze_bdev is there exactly for the
purpose to make the filesystem consistant on disk and then freeze all
I/O.
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