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Fixed upstream:
commit 865421c94a63f43c0164d598a73226d0e4231c93
Author: Peter Krempa <pkrempa>
Date: Tue Sep 16 12:55:32 2014 +0200
util: storage: Copy driver type when initializing chain element
virStorageSourceInitChainElement initializes a new storage chain element
for use as a new disk source. If the new element doesn't contain the
driver name, copy it from the old source.
This fixes issue where a disk would forget the driver after a snapshot.
Verify this bug with libvirt-1.2.8-3.el7.x86_64.
Steps as comment 0.
line "<driver name='qemu' type='qcow2' cache='none'/>" doesn't change after create external disk snapshot
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://rhn.redhat.com/errata/RHSA-2015-0323.html
Description of problem: sub-element in <disk>...</disk> change after create external disk snapshot Version-Release number of selected component (if applicable): libvirt-1.2.7-2.el7.x86_64 libvirt-client-1.2.7-2.el7.x86_64 How reproducible: 100% Steps to Reproduce: 1. Prepare a running guest # virsh dumpxml rhel7-qcow2 |grep disk -A 5 .. <disk type='file' device='disk'> <driver name='qemu' type='qcow2' cache='none'/> <source file='/var/lib/libvirt/images/rhel7-qcow2.img'/> <backingStore/> <target dev='vda' bus='virtio'/> <alias name='virtio-disk0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/> </disk> .. 2. create external disk snapshot # virsh snapshot-create-as rhel7-qcow2 ss --disk-only 3. check guest xml # virsh dumpxml rhel7-qcow2 |grep disk -A 8 <disk type='file' device='disk'> <driver type='qcow2' cache='none'/> <source file='/var/lib/libvirt/images/rhel7-qcow2.ss'/> <backingStore type='file' index='1'> <format type='qcow2'/> <source file='/var/lib/libvirt/images/rhel7-qcow2.img'/> <backingStore/> </backingStore> <target dev='vda' bus='virtio'/> <alias name='virtio-disk0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/> </disk> 4. validate xml for running guest #virsh dumpxml rhel7-qcow2 > r7.xml # virt-xml-validate r7.xml Relax-NG validity error : Extra element devices in interleave r7.xml:1: element domain: Relax-NG validity error : Element domain failed to validate content r7.xml fails to validate 5. destroy/start guest and re-check guest xml # virsh destroy rhel7-qcow2;virsh start rhel7-qcow2 Domain rhel7-qcow2 destroyed Domain rhel7-qcow2 started #virsh dumpxml rhel7-qcow2 ... <disk type='file' device='disk'> <driver type='qcow2' cache='none'/> <source file='/var/lib/libvirt/images/rhel7-qcow2.ss'/> <backingStore type='file' index='1'> <format type='qcow2'/> <source file='/var/lib/libvirt/images/rhel7-qcow2.img'/> <backingStore/> </backingStore> <target dev='vda' bus='virtio'/> <alias name='virtio-disk0'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/> </disk> ... Actual results: In step 3, <driver name='qemu' type='qcow2' cache='none'/> change to <driver type='qcow2' cache='none'/> Expected results: driver name='qemu' type='qcow2' should not change in step 3 or virt-xml-validate pass in step 4 Additional info: # grep "driverFormat" docs/schemas/*.rng -A 12 docs/schemas/domaincommon.rng: <ref name="driverFormat"/> docs/schemas/domaincommon.rng- </optional> docs/schemas/domaincommon.rng- <optional> docs/schemas/domaincommon.rng- <ref name="driverCache"/> docs/schemas/domaincommon.rng- </optional> docs/schemas/domaincommon.rng- <optional> docs/schemas/domaincommon.rng- <ref name="driverErrorPolicy"/> docs/schemas/domaincommon.rng- </optional> docs/schemas/domaincommon.rng- <optional> docs/schemas/domaincommon.rng- <ref name="driverRerrorPolicy"/> docs/schemas/domaincommon.rng- </optional> docs/schemas/domaincommon.rng- <optional> docs/schemas/domaincommon.rng- <ref name="driverIO"/> -- docs/schemas/domaincommon.rng: <define name="driverFormat"> docs/schemas/domaincommon.rng- <attribute name="name"> docs/schemas/domaincommon.rng- <ref name="genericName"/> docs/schemas/domaincommon.rng- </attribute> docs/schemas/domaincommon.rng- <optional> docs/schemas/domaincommon.rng- <attribute name='type'> docs/schemas/domaincommon.rng- <choice> docs/schemas/domaincommon.rng- <ref name='storageFormat'/> docs/schemas/domaincommon.rng- <value>aio</value> <!-- back-compat for 'raw' --> docs/schemas/domaincommon.rng- </choice> docs/schemas/domaincommon.rng- </attribute> docs/schemas/domaincommon.rng- </optional> docs/schemas/domaincommon.rng- </define>