Re: [Qemu-devel] qcow2, lazy_refcounts and killing qemu

[Markus Armbruster]

"Richard W.M. Jones" <address@hidden> writes:

> On Fri, Sep 05, 2014 at 04:39:51PM +0100, Stefan Hajnoczi wrote:
>> Did you try older QEMU versions?  I'm curious if this is something that
>> crept in later or is fundamentally broken in lazy_refcounts=on.
>
> At your prompting, I've done a bit more investigation.
>
> I was basing my observations on qemu 2.1.0.  However I tried my test
> against qemu from git today and the bug has gone.  Good!
>
> For my entertainment, I bisected the problem, and the commit which
> *fixes* it is:
>
>   commit 91af7014125895cc74141be6b60f3a3e882ed743
>   Author: Max Reitz <address@hidden>
>   Date:   Fri Jul 18 20:24:56 2014 +0200
>
>     block: Add bdrv_refresh_filename()
>
> I didn't believe this either, but I have checked the result manually
> and I'm pretty sure that whatever this commit does, it does end up
> fixing the lazy_refcounts problem as a side-effect.

Weird.  Maybe Max (cc'ed) has an idea.

> ----------------------------------------------------------------------
>
> I've updated the test script (attached), so you can now run it against
> your own qemu, and also to improve the output.