linux-ext4 - Re: [PATCH 3/3] Add timeout feature

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Date:	Wed, 9 Jul 2008 16:59:50 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Miklos Szeredi <miklos@...redi.hu>, hch@...radead.org,
	tytso@....edu, pavel@...e.cz, t-sato@...jp.nec.com,
	akpm@...ux-foundation.org, viro@...IV.linux.org.uk,
	linux-ext4@...r.kernel.org, xfs@....sgi.com, dm-devel@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	axboe@...nel.dk, mtk.manpages@...glemail.com
Subject: Re: [PATCH 3/3] Add timeout feature

On Tue, Jul 08, 2008 at 11:41:20PM -0700, Arjan van de Ven wrote:
> On Wed, 09 Jul 2008 08:22:56 +0200
> Miklos Szeredi <miklos@...redi.hu> wrote:
> > > On Wed, Jul 09, 2008 at 08:13:21AM +0200, Miklos Szeredi wrote:
> > > > This would mean that freeze and thaw will have to be done on the
> > > > same file descriptor, but this isn't unreasonable to expect, is
> > > > it?
> > > 
> > > It is certainly not the current use case, where you run one command
> > > to freeze the filesystem and another one to unfreeze it.
> > 
> > So instead of
> > 
> >   freeze_fs mountpoint
> >   backup-command
> >   unfreeze_fs mountpoint
> > 
> > the user would have do to
> > 
> >   run_freezed mountpoint backup-command
> > 
> > I find the second one nicer, regardless of any reliability issues.
> 
> nah he needs to do
> 
> make_snapshot ; backup-command ; unref_snapshot.
> 
> freezing isn't the right solution for the backup problem ;)

You're forgetting that to take a snapshot you generally need to
freeze the filesystem. ;) i.e:

freeze; make_snapshot; unfreeze
backup-command
unref_snapshot

Yes, dm_snapshot does the freeze/snapshot/unfreeze for you, but the
point is there is a freeze in the example you gave.

The argument against Miklos' version is that there may be multiple
commands to execute while the fs is frozen.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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