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Re: [PATCH 3/3] Add timeout feature

To: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Subject: Re: [PATCH 3/3] Add timeout feature
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 9 Jul 2008 16:59:50 +1000
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>, hch@xxxxxxxxxxxxx, tytso@xxxxxxx, pavel@xxxxxxx, t-sato@xxxxxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, dm-devel@xxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, axboe@xxxxxxxxx, mtk.manpages@xxxxxxxxxxxxxx
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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@xxxxxxxxxx> 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@xxxxxxxxxxxxx


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