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Bug 1144922

Summary:	wrong backingStore info after blockpull and destroy/start guest
Product:	Red Hat Enterprise Linux 7	Reporter:	Shanzhi Yu <shyu>
Component:	libvirt	Assignee:	Peter Krempa <pkrempa>
Status:	CLOSED ERRATA	QA Contact:	Virtualization Bugs <virt-bugs>
Severity:	high	Docs Contact:
Priority:	high
Version:	7.1	CC:	dyuan, mzhan, pkrempa, rbalakri, yanyang
Target Milestone:	rc
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	libvirt-1.2.8-4.el7	Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2015-03-05 07:44:58 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Shanzhi Yu 2014-09-22 02:44:44 UTC

Description of problem:

wrong backingStore info after blockpull and destroy/start guest

Version-Release number of selected component (if applicable):

libvirt-1.2.8-3.el7.x86_64

How reproducible:

100%

Steps to Reproduce:

1. Prepare a running guest

# virsh list
 Id    Name                           State
----------------------------------------------------
 32    rh7-l                          running

2. Create four external disk snapshot

# for i in 1 2 3 4 ;do virsh snapshot-create-as rh7-l s$i --disk-only --diskspec vda,file=/tmp/rh7-l.s$i;done
Domain snapshot s1 created
Domain snapshot s2 created
Domain snapshot s3 created
Domain snapshot s4 created

# virsh dumpxml rh7-g
..
<disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/tmp/rh7-l.s4'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/tmp/rh7-l.s3'/>
        <backingStore type='file' index='2'>
          <format type='qcow2'/>
          <source file='/tmp/rh7-l.s2'/>
          <backingStore type='file' index='3'>
            <format type='qcow2'/>
            <source file='/tmp/rh7-l.s1'/>
            <backingStore type='block' index='4'>
              <format type='raw'/>
              <source dev='/dev/vg01/lv01'/>
              <backingStore/>
            </backingStore>
          </backingStore>
        </backingStore>
      </backingStore>
      <target dev='vda' bus='virtio'/>
..
#qemu-img info /tmp/rh7-l.s4 --backing-chain

rh7-l.s4-> rh7-l.s3->rh7-l.s2->rh7-l.s1->/dev/vg01/lv01

3. Do blockpull from middle to top
# virsh blockpull rh7-l vda --base vda[2] --verbose --wait
Block Pull: [100 %]
Pull complete

or

# virsh blockpull rh7-l vda --base /tmp/rh7-l.s3 --verbose --wait

4. Check snapshot file backing chain and guest xml
#qemu-img info /tmp/rh7-l.s4 --backing-chain

rh7-l.s4->rh7-l.s2->rh7-l.s1->/dev/vg01/lv01
# virsh dumpxml rh7-l|grep disk -A 16
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/tmp/rh7-l.s4'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/tmp/rh7-l.s2'/>
        <backingStore type='file' index='2'>
          <format type='qcow2'/>
          <source file='/tmp/rh7-l.s1'/>
          <backingStore type='block' index='3'>
            <format type='raw'/>
            <source dev='/dev/vg01/lv01'/>
            <backingStore/>
          </backingStore>
        </backingStore>
      </backingStore>
      <target dev='vda' bus='virtio'/>
..

5. Destroy/start guest then re-check guest xml
# virsh destroy rh7-l;virsh start rh7-l;
Domain rh7-l destroyed

Domain rh7-l started

# virsh dumpxml rh7-l
..
 <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/tmp/rh7-l.s4'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/tmp/rh7-l.s3'/>
        <backingStore type='file' index='2'>
          <format type='qcow2'/>
          <source file='/tmp/rh7-l.s2'/>
          <backingStore type='file' index='3'>
            <format type='qcow2'/>
            <source file='/tmp/rh7-l.s1'/>
            <backingStore type='block' index='4'>
              <format type='raw'/>
              <source dev='/dev/vg01/lv01'/>
              <backingStore/>
            </backingStore>
          </backingStore>
        </backingStore>
      </backingStore>
      <target dev='vda' bus='virtio'/>
..

6. Do blockpull again

# virsh blockpull rh7-l vda --base vda[1] --verbose --wait
error: internal error: Unexpected error: (GenericError) 'Base '/tmp/rh7-l.s3' not found'


Actual results:


Expected results:

/tmp/rh7-l.s3 should not appear in guest xml since it already pull into rh7-l.s4

Additional info:

Comment 1 Peter Krempa 2014-09-26 07:41:25 UTC

Fixed upstream:

commit fe7ef7b112b3b4d6f9c9edf499a79683fb0b7edb
Author: Peter Krempa <pkrempa>
Date:   Thu Sep 25 17:30:28 2014 +0200

    qemu: Always re-detect backing chain
    
    Since 363e9a68 we track backing chain metadata when creating snapshots
    the right way even for the inactive configuration. As we did not yet
    update other code paths that modify the backing chain (blockpull) the
    newDef backing chain gets out of sync.
    
    After stopping of a VM the new definition gets copied to the next start
    one. The new VM then has incorrect backing chain info. This patch
    switches the backing chain detector to always purge the existing backing
    chain and forces re-detection to avoid this issue until we'll have full
    backing chain tracking support.

v1.2.9-rc1-9-gfe7ef7b

Comment 4 Yang Yang 2014-10-11 06:59:01 UTC

Verified on libvirt-1.2.8-5.el7.x86_64 and qemu-kvm-rhev-2.1.2-1.el7.x86_64

Steps:
1. Create 4 external disk only snapshots
# for i in s1 s2 s3 s4; do virsh snapshot-create-as qe-con $i --disk-only --diskspec vda,file=/tmp/qe-con.$i; done
Domain snapshot s1 created
Domain snapshot s2 created
Domain snapshot s3 created
Domain snapshot s4 created

# virsh snapshot-list qe-con
 Name                 Creation Time             State
------------------------------------------------------------
 s1                   2014-10-11 14:42:10 +0800 disk-snapshot
 s2                   2014-10-11 14:42:10 +0800 disk-snapshot
 s3                   2014-10-11 14:42:11 +0800 disk-snapshot
 s4                   2014-10-11 14:42:11 +0800 disk-snapshot

2. check the xml
# virsh dumpxml qe-con | grep disk -a16
<disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/tmp/qe-con.s4'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/tmp/qe-con.s3'/>
        <backingStore type='file' index='2'>
          <format type='qcow2'/>
          <source file='/tmp/qe-con.s2'/>
          <backingStore type='file' index='3'>
            <format type='qcow2'/>
            <source file='/tmp/qe-con.s1'/>
            <backingStore type='file' index='4'>
              <format type='qcow2'/>
              <source file='/var/lib/libvirt/images/qe-con.qcow2'/>
              <backingStore/>
            </backingStore>
          </backingStore>
        </backingStore>
      </backingStore>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>
3. check the image chain
# qemu-img info /tmp/qe-con.s4 --backing-chain
image: /tmp/qe-con.s4
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 3.3M
cluster_size: 65536
backing file: /tmp/qe-con.s3
backing file format: qcow2
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /tmp/qe-con.s3
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 196K
cluster_size: 65536
backing file: /tmp/qe-con.s2
backing file format: qcow2
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /tmp/qe-con.s2
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 196K
cluster_size: 65536
backing file: /tmp/qe-con.s1
backing file format: qcow2
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /tmp/qe-con.s1
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 196K
cluster_size: 65536
backing file: /var/lib/libvirt/images/qe-con.qcow2
backing file format: qcow2
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /var/lib/libvirt/images/qe-con.qcow2
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 1.2G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false

4. do blockpull
# virsh blockpull qe-con vda --base /tmp/qe-con.s2 --verbose --wait
Block Pull: [100 %]
Pull complete

5. check the image chain again
# qemu-img info /tmp/qe-con.s4 --backing-chainimage: /tmp/qe-con.s4
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 3.4M
cluster_size: 65536
backing file: /tmp/qe-con.s2
backing file format: qcow2
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /tmp/qe-con.s2
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 196K
cluster_size: 65536
backing file: /tmp/qe-con.s1
backing file format: qcow2
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /tmp/qe-con.s1
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 196K
cluster_size: 65536
backing file: /var/lib/libvirt/images/qe-con.qcow2
backing file format: qcow2
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /var/lib/libvirt/images/qe-con.qcow2
file format: qcow2
virtual size: 5.0G (5368709120 bytes)
disk size: 1.2G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false

6. check xml
# virsh dumpxml qe-con | grep disk -a16
<disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/tmp/qe-con.s4'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/tmp/qe-con.s2'/>
        <backingStore type='file' index='2'>
          <format type='qcow2'/>
          <source file='/tmp/qe-con.s1'/>
          <backingStore type='file' index='3'>
            <format type='qcow2'/>
            <source file='/var/lib/libvirt/images/qe-con.qcow2'/>
            <backingStore/>
          </backingStore>
        </backingStore>
      </backingStore>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>
7. destroy/start the domain and check xml again
# virsh destroy qe-con; virsh start qe-con
Domain qe-con destroyed

Domain qe-con started

# virsh dumpxml qe-con | grep disk -a16
<disk type='file' device='disk'>
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/tmp/qe-con.s4'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/tmp/qe-con.s2'/>
        <backingStore type='file' index='2'>
          <format type='qcow2'/>
          <source file='/tmp/qe-con.s1'/>
          <backingStore type='file' index='3'>
            <format type='qcow2'/>
            <source file='/var/lib/libvirt/images/qe-con.qcow2'/>
            <backingStore/>
          </backingStore>
        </backingStore>
      </backingStore>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>

Since the results are as expected, I'd like to set it to verified

Comment 6 errata-xmlrpc 2015-03-05 07:44:58 UTC

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