Re: [Qemu-devel] [PATCH 2/8] qcow2: add dirty-bitmaps feature

[Stefan Hajnoczi]

On Fri, Jun 12, 2015 at 03:02:33PM -0400, John Snow wrote:
> 
> 
> On 06/10/2015 10:30 AM, Stefan Hajnoczi wrote:
> > On Mon, Jun 08, 2015 at 06:21:20PM +0300, Vladimir Sementsov-Ogievskiy 
> > wrote:
> > 
> > I noticed a corner case, it's probably not a problem in practice:
> > 
> > Since the dirty bitmap is stored with the help of a BlockDriverState
> > (and its bs->file), it's possible that writing the bitmap will cause
> > bits in the bitmap to be dirtied!
> > 
> 
> But since it's metadata and not stored within a disk sector, can this
> actually happen? Do you have an example of a scenario where this might
> come up?

The persistent dirty bitmap for bs->file is storeed in the qcow2 BDS.
This results in recursion.

This is a misconfiguration but I just want to understand what happens
when someone does this by mistake.

Stefan

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