Xen domain save file should be deleted/renamed after successful restore operation

Xen domain save file should be deleted/renamed after successful restore operation

[Michal Novotny]

Hello everybody,
I have found a problem about the checkpoint file (saved domain file) 
that has been already used to restore a domain. The second time 
restoring domain from the same saved domain file will result in disk 
corruption and kernel of VM saved in this save file is in an 
inconsistent state then.

You can replicate this by eg. creating some PV domain, saving it using 
`xm save` command to /var/lib/xen/save directory and restoring it again. 
The domain save file is not deleted or anything so when rebooting dom0 
`xendomains` script starts this machine again but this results in disk 
corruption of disk used for this guest.

It would be better if we either delete a domain save file after 
successful restore process or at least rename it to some name that won't 
be run automatically using `xendomains` script (maybe we can append a 
dot before file name itself so it won't be restored automatically by 
this script) or, maybe better, there could be an option in 
xend-config.sxp to allow user choose what he would like to do.

Thanks,
Michal

Re: Xen domain save file should be deleted/renamed after successful restore operation

[Ian Jackson]

Michal Novotny writes ("[Xen-devel] Xen domain save file should be deleted/renamed after successful restore operation"):
> Hello everybody,
> I have found a problem about the checkpoint file (saved domain file) 
> that has been already used to restore a domain. The second time 
> restoring domain from the same saved domain file will result in disk 
> corruption and kernel of VM saved in this save file is in an 
> inconsistent state then.

Yes.  Don't do that then.

> You can replicate this by eg. creating some PV domain, saving it using 
> `xm save` command to /var/lib/xen/save directory and restoring it again. 
> The domain save file is not deleted or anything so when rebooting dom0 
> `xendomains` script starts this machine again but this results in disk 
> corruption of disk used for this guest.

In particular, the /var/lib/xen/save directory is for use by the
automatic domain management scripts like `xendomains'.  Do not
manually save a domain into it and absolutely do not restore a domain
from it manually!

Ian.