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Re: [Qemu-devel] [RFC] qcow2 journalling draft
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [RFC] qcow2 journalling draft |
Date: |
Fri, 6 Sep 2013 18:02:39 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Fri, 09/06 11:57, Kevin Wolf wrote:
> Am 06.09.2013 um 11:20 hat Fam Zheng geschrieben:
> > On Wed, 09/04 11:39, Kevin Wolf wrote:
> > > First of all, excuse any inconsistencies in the following mail. I wrote
> > > it from top to bottom, and there was some thought process involved in
> > > almost every paragraph...
> > >
> > > Am 04.09.2013 um 10:03 hat Stefan Hajnoczi geschrieben:
> > > > On Tue, Sep 03, 2013 at 03:45:52PM +0200, Kevin Wolf wrote:
> > > > > @@ -103,7 +107,11 @@ in the description of a field.
> > > > > write to an image with unknown auto-clear
> > > > > features if it
> > > > > clears the respective bits from this field first.
> > > > >
> > > > > - Bits 0-63: Reserved (set to 0)
> > > > > + Bit 0: Journal valid bit. This bit
> > > > > indicates that the
> > > > > + image contains a valid main journal
> > > > > starting at
> > > > > + journal_offset.
> > > >
> > > > Whether the journal is used can be determined from the journal_offset
> > > > value (header length must be large enough and journal offset must be
> > > > valid).
> > > >
> > > > Why do we need this autoclear bit?
> > >
> > > Hm, I introduced this one first and the journal dirty incompatible bit
> > > later, perhaps it's unnecessary now. Let's check...
> > >
> > > The obvious thing we need to protect against is applying stale journal
> > > data to an image that has been changed by an older version. As long as
> > > the journal is clean, this can't happen, and the journal dirty bit will
> > > ensure that the old version can only open the image if it is clean.
> > >
> > > However, what if we run 'qemu-img check -r leaks' with an old qemu-img
> > > version? It will reclaim the clusters used by the journal, and if we
> > > continue using the journal we'll corrupt whatever new data is there
> > > now.
> > >
> > Why can old version qemu-img open the image with dirty journal in the first
> > place? It's incompatible bit.
>
> This is about a clean journal.
>
Ah yes, I get it, thanks.
Fam
- Re: [Qemu-devel] [RFC] qcow2 journalling draft, (continued)
- Re: [Qemu-devel] [RFC] qcow2 journalling draft, Stefan Hajnoczi, 2013/09/05
- Re: [Qemu-devel] [RFC] qcow2 journalling draft, Kevin Wolf, 2013/09/05
- Re: [Qemu-devel] [RFC] qcow2 journalling draft, Stefan Hajnoczi, 2013/09/05
- Re: [Qemu-devel] [RFC] qcow2 journalling draft, Kevin Wolf, 2013/09/05
- Re: [Qemu-devel] [RFC] qcow2 journalling draft, Eric Blake, 2013/09/05
- Re: [Qemu-devel] [RFC] qcow2 journalling draft, Fam Zheng, 2013/09/06
- Re: [Qemu-devel] [RFC] qcow2 journalling draft, Kevin Wolf, 2013/09/06
- Re: [Qemu-devel] [RFC] qcow2 journalling draft,
Fam Zheng <=
Re: [Qemu-devel] [RFC] qcow2 journalling draft, Max Reitz, 2013/09/04
Re: [Qemu-devel] [RFC] qcow2 journalling draft, Stefan Hajnoczi, 2013/09/05
Re: [Qemu-devel] [RFC] qcow2 journalling draft, Fam Zheng, 2013/09/06