Hmm interesting, so without adding backing_fmt, if i enable the below in /etc/libvirt/qemu.conf, will it work ? # If allow_disk_format_probing is enabled, libvirt will probe disk # images to attempt to identify their format, when not otherwise # specified in the XML. This is disabled by default. # # WARNING: Enabling probing is a security hole in almost all # deployments. It is strongly recommended that users update their # guest XML <disk> elements to include <driver type='XXXX'/> # elements instead of enabling this option. # #allow_disk_format_probing = 1 On Wed, Mar 18, 2015 at 5:33 PM, Shanzhi Yu <shyu@redhat.com> wrote:

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*From: *"Deepak Shetty" <dpkshetty@gmail.com> *To: *libvir-list@redhat.com *Sent: *Wednesday, March 18, 2015 7:19:05 PM *Subject: *[libvirt] Domain XML isn't dumping full backing chain

Hi, I am using libvirt version 1.2.9.2 on F21 and i am unable to get the complete backing chain info in the virsh dumpxml output. Details below :

*My backing chain per qemu-img :*

[stack@devstack-f21 test]$ qemu-img info --backing-chain snap4.qcow2 image: snap4.qcow2 file format: qcow2 virtual size: 1.0G (1073741824 bytes) disk size: 196K cluster_size: 65536 backing file: ./snap3.qcow2 Format specific information: compat: 1.1 lazy refcounts: false

image: ./snap3.qcow2 file format: qcow2 virtual size: 1.0G (1073741824 bytes) disk size: 196K cluster_size: 65536 backing file: ./snap2.qcow2 (actual path: ././snap2.qcow2) Format specific information: compat: 1.1 lazy refcounts: false

image: ././snap2.qcow2 file format: qcow2 virtual size: 1.0G (1073741824 bytes) disk size: 196K cluster_size: 65536 backing file: ./snap1.qcow2 (actual path: ./././snap1.qcow2) Format specific information: compat: 1.1 lazy refcounts: false

image: ./././snap1.qcow2 file format: qcow2 virtual size: 1.0G (1073741824 bytes) disk size: 196K cluster_size: 65536 backing file: ./base.qcow2 (actual path: ././././base.qcow2) Format specific information: compat: 1.1 lazy refcounts: false

image: ././././base.qcow2 file format: qcow2 virtual size: 1.0G (1073741824 bytes) disk size: 196K cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false

If you want prepare the backing chain yourself, you should add "-o backing_fmt=$farmat" options, like "qemu-img create -f qcow2 base.s1 -b base.qcow2 -o backing_fmt=qcow2"

I created 4 snapshots using commands (similar to the below, just dumping the last one here ):

[stack@devstack-f21 test]$ virsh snapshot-create-as test-domain on-test-snap4 --disk-only --reuse-external --diskspec hda,snapshot=external,file=/home/stack/test/snap4.qcow2 Domain snapshot on-test-snap4 created

[stack@devstack-f21 test]$ virsh domblklist test-domain Target Source ------------------------------------------------ hda /home/stack/test/snap4.qcow2

virsh dumpxml test-domain|more ....

<disk type='file' device='disk'> <driver name='qemu' type='qcow2' cache='none'/> <source file='/home/stack/test/snap4.qcow2'/> <backingStore type='file' index='1'> <format type='raw'/>

If you don't add "-o backing_fmt=qcow2", it will treat backing file format as raw format. Since a raw format file doesn't have a backing file, so you only see snap4.qcow2 and snap3.qcow2

<source file='/home/stack/test/./snap3.qcow2'/> <backingStore/> </backingStore> <target dev='hda' bus='ide'/> <alias name='ide0-0-0'/> <address type='drive' controller='0' bus='0' target='0' unit='0'/> </disk>

.....

I think thats happening beccause the backingStore format is coming as 'raw' What am i missing ?

thanx, deepak

-- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list

-- Regards shyu

On Wed, Mar 18, 2015 at 07:21:22AM -0600, Eric Blake wrote:

On 03/18/2015 07:03 AM, Deepak Shetty wrote:

[please don't top-post on technical lists]

...

Hmm interesting, so without adding backing_fmt, if i enable the below in /etc/libvirt/qemu.conf, will it work ?

# If allow_disk_format_probing is enabled, libvirt will probe disk # images to attempt to identify their format, when not otherwise # specified in the XML. This is disabled by default. # # WARNING: Enabling probing is a security hole in almost all # deployments. It is strongly recommended that users update their # guest XML <disk> elements to include <driver type='XXXX'/> # elements instead of enabling this option. # #allow_disk_format_probing = 1

Along with what Eric says, here's some detailed description of issues (that are fixed) from Daniel Berrange: https://www.redhat.com/archives/libvir-list/2010-July/msg00221.html

It _might_ work in that libvirt will then probe the backing chain as qcow2, rather than treating it as raw; on the other hand, the upcoming qemu 2.3 is trying to deprecate probing altogether because of the security problems it represented, and so you may reach a point where even if you tell libvirt it is okay to probe, that qemu will refuse to open your image if you didn't specify backing format.

-- /kashyap