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Re: [Qemu-block] block: Dirty bitmaps and COR in bdrv_move_feature_field

From: Kevin Wolf
Subject: Re: [Qemu-block] block: Dirty bitmaps and COR in bdrv_move_feature_fields()
Date: Wed, 2 Mar 2016 17:19:29 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

Am 02.03.2016 um 17:06 hat Eric Blake geschrieben:
> On 03/02/2016 02:31 AM, Kevin Wolf wrote:
> > 
> > Seriously, if you need back references from BDS to BB, watch graph
> > modifications above the node, automatically creating new names for
> > bitmaps while taking a snapshot and similar things, then you're doing
> > something wrong. I don't even want to start thinking about persistent
> > bitmaps floating towards the top.
> > 
> > So I think what we need to do is simple: Keep the bitmaps at the node
> > for which they were created. For the cases where we must change what a
> > bitmap tracks, we can provide a QMP command to move it. If any name
> > change or anything like that is involved, it needs to be explicitly
> > requested by the management tool and not automatically be done by qemu
> > magic.
> > 
> > Eric, does this look reasonable for libvirt?
> Yes, I think it will be manageable to consistently track bitmaps by
> node, with the ability to explicitly move them if needed (preferably
> during the same transaction doing whatever else to the node graph that
> makes it worth moving the bitmap).

Making it transactionable shouldn't be a big deal for in-memory bitmaps.
I'm not sure what we should do with persistent ones, though. Or maybe
those aren't supposed to move in the first place.


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