[libvirt] [BUG] Re: [2/6] loadvm: improve tests before bdrv_snapshot_goto()

[Philipp Hahn]

Hello,

Am Dienstag 03 August 2010 06:44:26 schrieb Kevin Wolf:
> From: Miguel Di Ciurcio Filho <miguel.filho at gmail.com>
>
> This patch improves the resilience of the load_vmstate() function, doing
> further and better ordered tests.

This patch broke restoring not-running VMs using libvirt-0.8.7 with qemu-0.14: 
When the domain is not running while taking a snpshot, the sn.vm_state_size 
== 0:

2021        } else if (sn.vm_state_size == 0) {
(gdb) print sn
$6 = {id_str = "1", '\0' <repeats 126 times>, name = "pre-update-flash", '\0' 
<repeats 239 times>, vm_state_size = 0, date_sec = 1302698007, date_nsec = 
711909000, 
  vm_clock_nsec = 0}

> The [old] process:
...
> - run bdrv_snapshot_goto() on devices
>     - if fails, give an warning and goes to the next (not good!)
>     - if fails on the VM state device, return zero (not good!)
> - check if the requested snapshot exists on the device that saves the VM
> state and the state is not zero
>     - if fails return -error

Previously the qcow2 image was still reverted to the old state, so on the next 
start of the domain the qcow2 image would be in the state of the snapshot

> New behavior:
...
> - check if the requested snapshot exists on the device that saves the VM
> state and the state is not zero
>     - if fails return -error
...
> - run snapshot_goto() on devices

Now the qcow2 image is not reverted and when the domain is started, it is NOT 
in the state of the snapshot.

I can't decide if this regression is an Qemu bug or libvirt should be adapted 
to this new behavior.

I found the Bug also reported with Ubuntu and created a Bug in our own German 
bugtracker:
<https://bugs.launchpad.net/qemu/+bug/726619>
<https://forge.univention.org/bugzilla/show_bug.cgi?id=22221>

Sincerely
Philipp Hahn
-- 
Philipp Hahn           Open Source Software Engineer      hahn at univention.de
Univention GmbH        Linux for Your Business        fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/
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