[Sheepdog] The 's' flag

[MORITA Kazutaka]

At Tue, 23 Aug 2011 18:00:36 +0100,
Brian Candler wrote:
> 
> On Mon, Aug 22, 2011 at 03:18:07PM +0900, MORITA Kazutaka wrote:
> > > However, in my tests the 's' flag is applied to everything except the last
> > > snapshot:
> > > 
> > > brian at x100:~$ collie vdi list
> > >   name        id    size    used  shared    creation time   vdi id
> > > ------------------------------------------------------------------
> > > s Test         1  2.0 GB  472 MB  0.0 MB 2011-08-16 21:00   ec9f05
> > > s Test         2  2.0 GB  0.0 MB  472 MB 2011-08-16 22:44   ec9f06
> > > s Test         3  2.0 GB   48 MB  424 MB 2011-08-16 22:46   ec9f07
> > > s Test         4  2.0 GB   56 MB  416 MB 2011-08-16 22:46   ec9f08
> > > s Test         5  2.0 GB   44 MB  428 MB 2011-08-16 23:04   ec9f09
> > >   Test         6  2.0 GB   48 MB  424 MB 2011-08-16 23:05   ec9f0a
> > > 
> > > This suggest to me that 's' means 'shared'?
> > 
> > No, the 's' flag means a snapshot.  I think you ran
> > "qemu-img snapshot -c tag sheepdog:Test" five times, no?
> 
> Not exactly. I can't remember the exact sequence of what I did to get to
> that point but it includes the following:
> 
> * I created a vdi and booted with an Ubuntu cd-rom image, and did the
>   install. This gave me image id 1 (size 2.0GB, used 472MB)
> 
> * I created at least one snapshot from it
> 
> * I tried booting the original image and the snapshot. As far as I can see,
>   booting the snapshot caused a new snapshot to be created.

Thanks for your report, but this operation is not allowed.  You cannot
open the same "name" vdi at the same time.  You need to create another
name vdi from the snapshot
(e.g. qemu-img create -b sheepdog:Test:1 sheepdog:NewVdi).

> 
> * I tried booting the original image (id 1) more than once. It allowed me
>   to do so; both VMs had writable access to the same underlying block
>   device (e.g. if I overwrite an unused file in /etc from one VM with a
>   test message, and then cat it from the other, I can see the data I wrote).

Unfortunately, this can happen if you open the same name vdi at the
same time.


Thanks,

Kazutaka


> 
> This last thing seems like a bug, but I haven't reported it yet because
> I need to confirm the exact steps to reproduce.
> 
> Regards,
> 
> Brian.
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