libvirt users - Jul 2014 - snapshot-create error

Hi,

What's the difference between QEMU snapshot and libvirt snapshot? 

# qemu-img create -f qcow2 disk.img 512
Formatting 'disk.img', fmt=qcow2 size=512 encryption=off
cluster_size=65536 lazy_refcounts=off

# qemu-img info disk.img
image: disk.img
file format: qcow2
virtual size: 512 (512 bytes)
disk size: 136K
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false

# /usr/bin/qemu-system-ppc -M ppce500 -enable-kvm -m 512 -nographic -kernel
/dev/shm/uImage -initrd /dev/shm/ramdisk -append "root=/dev/ram rw
console=ttyS0,115200" -serial tcp::4444,server,telnet -snapshot -hda
disk.img
QEMU 1.7.0 monitor - type 'help' for more information
(qemu) QEMU waiting for connection on: telnet:0.0.0.0:4444,server

(qemu) savevm
(qemu) info snapshot
unknown command: 'info snapshot'
(qemu) info snapshots
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         vm-20140709035738      173M 2014-07-09 03:57:38   00:00:07.401


Is there any special qemu command options or kernel configurations to allow
libvirt create snapshot?

I got the error as below:

virsh # snapshot-create snap
error: unsupported configuration: internal snapshots and checkpoints require all
disks to be selected for snapshot

The domain XML file is converted as below steps.
# cat >snap.args <<EOF
/usr/bin/qemu-system-ppc -name snap -M ppce500 -enable-kvm -m 512 -nographic
-kernel /dev/shm/uImage -initrd /dev/shm/ramdisk -append "root=/dev/ram rw
console=ttyS0,115200" -serial pty

# virsh domxml-from-native qemu-argv snap.args >snap.xml

# cat sdk.xml
<domain type='kvm'>
    <name>sdk</name>
    <memory unit='KiB'>524288</memory>
    <currentMemory unit='KiB'>524288</currentMemory>
    <vcpu placement='static'>1</vcpu>
    <os>
      <type arch='ppc' machine='ppce500'>hvm</type>
      <kernel>/dev/shm/uImage</kernel>
      <initrd>/dev/shm/ramdisk</initrd>
      <cmdline>root=/dev/ram rw console=ttyS0,115200</cmdline>
      <boot dev='hd'/>
    </os>
    <clock offset='utc'/>
    <on_poweroff>destroy</on_poweroff>
    <on_reboot>restart</on_reboot>
    <on_crash>destroy</on_crash>
    <devices>
      <emulator>/usr/bin/qemu-system-ppc</emulator>
      <controller type='usb' index='0'/>
      <controller type='pci' index='0'
model='pci-root'/>
      <serial type='pty'>
        <target port='0'/>
      </serial>
      <console type='pty'>
        <target type='serial' port='0'/>
      </console>
      <memballoon model='virtio'>
        <address type='pci' domain='0x0000'
bus='0x00' slot='0x02' function='0x0'/>
      </memballoon>
    </devices>
</domain>


Best Regards,
Olivia

On 07/10/2014 01:15 AM, Hong-Hua.Yin@freescale.com
wrote:
> Hi,
> 
> What's the difference between QEMU snapshot and libvirt snapshot? 
> 
> # qemu-img create -f qcow2 disk.img 512
> Formatting 'disk.img', fmt=qcow2 size=512 encryption=off
cluster_size=65536 lazy_refcounts=off
This created an offline internal snapshot.  You can do the same with
libvirt (which basically calls qemu-img under the hood for an offline
guest).
> 
> Is there any special qemu command options or kernel configurations to allow
libvirt create snapshot?
No, if you are using libvirt to create the snapshot, then it should just
work, provided you used libvirt correctly.
> 
> I got the error as below:
> 
> virsh # snapshot-create snap
> error: unsupported configuration: internal snapshots and checkpoints
require all disks to be selected for snapshot
This says to create a default snapshot of the domain named 'snap'; since
you didn't specify any xml file, that default implies an internal
snapshot.  Is your guest running or offline at the time you attempted this?
> # cat sdk.xml
> <domain type='kvm'>
...
>     <devices>
>       <emulator>/usr/bin/qemu-system-ppc</emulator>
>       <controller type='usb' index='0'/>
>       <controller type='pci' index='0'
model='pci-root'/>
What? No <disk> element?  You have to have a qcow2 disk associated with
your domain before you can create an internal snapshot, regardless of
whether the guest is online or offline.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org