Subject: Re: how to bring a mounted filesystem to an almost clean state?
To: Daniel Carosone <>
From: Christian Limpach <>
List: tech-kern
Date: 02/15/2003 15:55:27
Quoting Daniel Carosone <>:

> Even without addressing the filesystem issues at the layer above,
> I'd be interested in such a device.  Is this something you'll be
> able to release when you're done?

Yes.  The driver is available as an LKM for 1.6_STABLE.  I have a pkgsrc 
package which builds the LKM and includes some rc.d files to load it early 
enough, before fsck wants to run:
There's only a very rough setup tool included, you almost definitely want to 
get some volume manager software[1].

> At the upper layer, it's probably something that will need direct
> support from the filesystems. In the softdep case, something that
> can be inserted in the dependency chain as a barrier - and when it
> finally hits the lower layer device in order, it triggers the actual
> snapshot to happen. That should avoid the need for locking, which
> you need to avoid so your snapshots remain transparent.

is there really such a single ordered dependency chain (in the softdep case) 
and does it include non-metadata accesses?

Christian Limpach <>