Is this a bug in qemu-img?

Is this a bug in qemu-img?

[walt]

I do a fresh install of Windows vista on qcow2 which works
perfectly.  Thereafter I use that image as a backing file
to make all kinds of updates to Vista, and all that works
perfectly too.

Then I use 'qemu-img commit' to commit all the changes I've
made to Vista.  The problem is that the updated base image
doesn't work quite right if I try to run Vista from it --
there are minor malfunctions which indicate that the commit
was incomplete or maybe just wrong.

Does this sound like a bug, or are my expectations wrong?

Thanks.

Re: Is this a bug in qemu-img?

[Avi Kivity]

walt wrote:
> I do a fresh install of Windows vista on qcow2 which works
> perfectly.  Thereafter I use that image as a backing file
> to make all kinds of updates to Vista, and all that works
> perfectly too.
>
> Then I use 'qemu-img commit' to commit all the changes I've
> made to Vista.  The problem is that the updated base image
> doesn't work quite right if I try to run Vista from it --
> there are minor malfunctions which indicate that the commit
> was incomplete or maybe just wrong.

What's your sequence of commands?  Are you using -snapshot?

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

Re: Is this a bug in qemu-img?

[walt]

On Sun, 23 Nov 2008, Avi Kivity wrote:

> walt wrote:
> > I do a fresh install of Windows vista on qcow2 which works
> > perfectly.  Thereafter I use that image as a backing file
> > to make all kinds of updates to Vista, and all that works
> > perfectly too.
> >
> > Then I use 'qemu-img commit' to commit all the changes I've
> > made to Vista.  The problem is that the updated base image
> > doesn't work quite right if I try to run Vista from it --
> > there are minor malfunctions which indicate that the commit
> > was incomplete or maybe just wrong.
>
> What's your sequence of commands?  Are you using -snapshot?

No, not using -snapshot anywhere.  I'm not sure how much detail
you want, but here's from the beginning:

#qemu-img create -f qcow2 vista 20G
#qemu-system-x86_64 -m 2048 -cdrom vistasp1.iso vista
[install vista without updating and exit]
#qemu-img create -f qcow2 -b vista vista.delta
#qemu-system-x86_64 -m 2048 vista.delta
[update vista with all the recent patches and exit]

Everything above works perfectly.  I can reboot vista,
check for new updates, create user accounts, all the
normal stuff.  Now comes the trouble:

#qemu-img commit vista.delta [takes >1 hour]

Now, IIUC the base image vista should be entirely
useable by itself, i.e. I can delete vista.delta
and everyting should still work correctly?

But it doesn't.  For example, when I boot vista and
try to look for windows updates, the updates page is
almost blank and completely non-functional. There
may be other problems too, but I haven't bothered
to look.

BTW, I've been through the same steps twice and
get the same results, so I don't think it's flakey
hardware. OTOH today is a new day, so I'll try it
again to triple check.

Any thoughts?

Thanks.

Re: Is this a bug in qemu-img?

[walt]

walt wrote:
>
> ...
> BTW, I've been through the same steps twice and
> get the same results, so I don't think it's flakey
> hardware. OTOH today is a new day, so I'll try it
> again to triple check.

Tried again all the way from the beginning and got
the same result.  The commit step is where things go
wrong every time.

I know qcow2 is not considered quite ready for prime
time, but having that commit feature is important to
me so I'd love to see it work correctly.

Any chance that 'commit' could be added to raw as
well as qcow2?

Thanks.

Re: Is this a bug in qemu-img?

[Charles Duffy]

walt wrote:
> Any chance that 'commit' could be added to raw as
> well as qcow2?

Raw images by their nature can't contain metadata -- they have only the 
exact contents of the virtual drive, which is what makes them "raw" -- 
so they by definition can't support copy-on-write (and thus commit) or 
other functionality requiring metadata.

Re: Is this a bug in qemu-img?

[Aurelien Jarno]

On Sun, Nov 23, 2008 at 09:29:48AM -0800, walt wrote:
> 
> Everything above works perfectly.  I can reboot vista,
> check for new updates, create user accounts, all the
> normal stuff.  Now comes the trouble:
> 
> #qemu-img commit vista.delta [takes >1 hour]
> 

The facts it takes very long is fixed in QEMU SVN. It will be fixed in
KVM as soon as the QEMU SVN is pulleD.

-- 
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