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Bug 1523261

Summary:	block commit with --keep-relative does not work after libvirtd restart
Product:	Red Hat Enterprise Linux 7	Reporter:	Peter Krempa <pkrempa>
Component:	libvirt	Assignee:	Peter Krempa <pkrempa>
Status:	CLOSED ERRATA	QA Contact:	Han Han <hhan>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	7.4	CC:	dyuan, lmen, lmiksik, meili, rbalakri, salmy, xuzhang
Target Milestone:	rc	Keywords:	Regression
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	libvirt-3.9.0-7.el7	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2018-04-10 11:02:08 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 Peter Krempa 2017-12-07 14:36:14 UTC

Description of problem:
Libvirt does not re-detect or store necessary metadata for --keep-relative to work after restart.

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


How reproducible:
100%

Steps to Reproduce:
1. Create few snapshots with relative backing paths (using --reuse-external)
2. Restart libvirtd
3. try virsh block-commit --keep-relative

Actual results:
error: Requested operation is not valid: can't keep relative backing relationship

Expected results:
Block commit successful

Additional info:

Comment 3 Han Han 2017-12-08 09:39:30 UTC

Reproduced on qemu-kvm-rhev-2.10.0-11.el7.x86_64 libvirt-3.9.0-5.el7.x86_64:
Run script:
```
+ set -o nounset
+ VM=q35
+ DISK=vdb
+ cd /var/lib/libvirt/images
+ mkdir b c d -p
+ cd /var/lib/libvirt/images/b
+ qemu-img create /var/lib/libvirt/images/b 100M -f qcow2
Formatting '/var/lib/libvirt/images/b', fmt=qcow2 size=104857600 cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img: /var/lib/libvirt/images/b: Could not create file: Is a directory
+ cd ../c
+ qemu-img create -b ../b/b -o backing_fmt=qcow2 c -f qcow2
Formatting 'c', fmt=qcow2 size=104857600 backing_file=../b/b backing_fmt=qcow2 cluster_size=65536 lazy_refcounts=off refcount_bits=16
+ cd ../d
+ qemu-img create -b ../c/c -o backing_fmt=qcow2 d -f qcow2
Formatting 'd', fmt=qcow2 size=104857600 backing_file=../c/c backing_fmt=qcow2 cluster_size=65536 lazy_refcounts=off refcount_bits=16
+ virsh start q35
Domain q35 started

+ sleep 10
+ virsh attach-disk q35 /var/lib/libvirt/images/d/d vdb --subdriver qcow2
Disk attached successfully

+ systemctl restart libvirtd
+ virsh blockcommit q35 vdb --top 'vdb[1]' --shallow --keep-relative
error: Requested operation is not valid: can't keep relative backing relationship

➜  ~ virsh destroy q35    
vDomain q35 destroyed

➜  ~ vim /tmp/reproduce.sh
➜  ~ /tmp/reproduce.sh
+ set -o nounset
+ VM=q35
+ DISK=vdb
+ cd /var/lib/libvirt/images
+ mkdir b c d -p
+ cd /var/lib/libvirt/images/b
+ qemu-img create /var/lib/libvirt/images/b 100M -f qcow2
Formatting '/var/lib/libvirt/images/b', fmt=qcow2 size=104857600 cluster_size=65536 lazy_refcounts=off refcount_bits=16
qemu-img: /var/lib/libvirt/images/b: Could not create file: Is a directory
+ cd ../c
+ qemu-img create -b ../b/b -o backing_fmt=qcow2 c -f qcow2
Formatting 'c', fmt=qcow2 size=104857600 backing_file=../b/b backing_fmt=qcow2 cluster_size=65536 lazy_refcounts=off refcount_bits=16
+ cd ../d
+ qemu-img create -b ../c/c -o backing_fmt=qcow2 d -f qcow2
Formatting 'd', fmt=qcow2 size=104857600 backing_file=../c/c backing_fmt=qcow2 cluster_size=65536 lazy_refcounts=off refcount_bits=16
+ virsh start q35
Domain q35 started

+ sleep 10
+ virsh attach-disk q35 /var/lib/libvirt/images/d/d vdb --subdriver qcow2
Disk attached successfully

+ systemctl restart libvirtd
+ virsh blockcommit q35 vdb --top 'vdb[1]' --shallow --keep-relative
error: Requested operation is not valid: can't keep relative backing relationship

+ virsh dumpxml q35
+ awk '/<disk/,/<\/disk/'
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/q35.qcow2'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x04' slot='0x00' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/d/d'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/var/lib/libvirt/images/d/../c/c'/>
        <backingStore type='file' index='2'>
          <format type='qcow2'/>
          <source file='/var/lib/libvirt/images/d/../c/../b/b'/>
          <backingStore type='file' index='3'>
            <format type='qcow2'/>
            <source file='/var/lib/libvirt/images/d/../c/../b/../V.qcow2'/>
            <backingStore/>
          </backingStore>
        </backingStore>
      </backingStore>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x09' slot='0x00' function='0x0'/>
    </disk>
```
As the result 'error: Requested operation is not valid: can't keep relative backing relationship'

Comment 4 Peter Krempa 2017-12-14 13:18:40 UTC

Fixed upstream by:

commit b3d0270c44b85944f91906225b27bca6700a6333 
Author: Peter Krempa <pkrempa>
Date:   Wed Dec 13 17:06:00 2017 +0100

    qemu: domain: Parse and format relPath into disk source private data
    
    Register the helpers directly to format and parse the data.
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1523261

commit cd31709351142a2770d2b9baa7755eaed672710a
Author: Peter Krempa <pkrempa>
Date:   Wed Dec 13 17:04:54 2017 +0100

    util: storage: Add helpers to parse and format relPath into privateData
    
    This will be the first private piece of data that will need to be stored
    in the XML for some drivers. Add helpers which will do it.

commit aed3d038a6565f3b0e916bdb004ca90b302b200d
Author: Peter Krempa <pkrempa>
Date:   Tue Dec 12 17:55:03 2017 +0100

    conf: Add infrastructure for disk source private data XML
    
    VM drivers may need to store additional private data to the status XML
    so that it can be restored after libvirtd restart. Since not everything
    is needed add a callback infrastructure, where VM drivers can add only
    stuff they need.
    
    Note that the private data is formatted as a <privateData> sub-element
    of the <disk> or <backingStore> <source> sub-element. This is done since
    storing it out of band (in the VM private data) would require a complex
    matching process to allow to put the data into correct place.

Comment 7 Han Han 2018-01-13 14:48:09 UTC

Verified in libvirt-3.9.0-7.el7.x86_64 qemu-kvm-rhev-2.10.0-15.el7.x86_64:
Try to do blockcommit on a relative backing chain after restart libvirt:
Run following script:
```
#!/bin/bash -x
VM=V-raw
DISK=vdb
cd /var/lib/libvirt/images
mkdir b c d -p
cd /var/lib/libvirt/images/b
qemu-img create b 100M -f qcow2
cd ../c
qemu-img create -b ../b/b -o backing_fmt=qcow2 c -f qcow2
cd ../d
qemu-img create -b ../c/c -o backing_fmt=qcow2 d -f qcow2
virsh start $VM
sleep 10
virsh attach-disk $VM /var/lib/libvirt/images/d/d $DISK --subdriver qcow2
virsh dumpxml $VM|awk '/<disk/,/<\/disk/'
systemctl restart libvirtd
diff <( virsh dumpxml $VM ) /tmp/$VM.xml
virsh blockcommit $VM $DISK --top "$DISK[1]" --shallow --keep-relative
virsh dumpxml $VM|awk '/<disk/,/<\/disk/'
```
The result:
+ VM=V-raw                                                                                                                                                                                                                                                                                                                                                                         [1/462]
+ DISK=vdb
+ cd /var/lib/libvirt/images
+ mkdir b c d -p
+ cd /var/lib/libvirt/images/b
+ qemu-img create b 100M -f qcow2
Formatting 'b', fmt=qcow2 size=104857600 cluster_size=65536 lazy_refcounts=off refcount_bits=16
+ cd ../c
+ qemu-img create -b ../b/b -o backing_fmt=qcow2 c -f qcow2
Formatting 'c', fmt=qcow2 size=104857600 backing_file=../b/b backing_fmt=qcow2 cluster_size=65536 lazy_refcounts=off refcount_bits=16
+ cd ../d
+ qemu-img create -b ../c/c -o backing_fmt=qcow2 d -f qcow2
Formatting 'd', fmt=qcow2 size=104857600 backing_file=../c/c backing_fmt=qcow2 cluster_size=65536 lazy_refcounts=off refcount_bits=16
+ virsh start V-raw
Domain V-raw started

+ sleep 10
+ virsh attach-disk V-raw /var/lib/libvirt/images/d/d vdb --subdriver qcow2
Disk attached successfully

+ virsh dumpxml V-raw
+ awk '/<disk/,/<\/disk/'
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/mapper/rhel-V'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/d/d'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/var/lib/libvirt/images/d/../c/c'/>
        <backingStore type='file' index='2'>
          <format type='qcow2'/>
          <source file='/var/lib/libvirt/images/d/../c/../b/b'/>
          <backingStore/>
        </backingStore>
      </backingStore>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
    </disk>
+ systemctl restart libvirtd
+ diff /dev/fd/63 /tmp/V-raw.xml
++ virsh dumpxml V-raw
1c1
< <domain type='kvm' id='63'>
---
> <domain type='kvm' id='60'>
109c109
<       <source path='/dev/pts/5'/>
---
>       <source path='/dev/pts/3'/>
115,116c115,116
<     <console type='pty' tty='/dev/pts/5'>
<       <source path='/dev/pts/5'/>
---
>     <console type='pty' tty='/dev/pts/3'>
>       <source path='/dev/pts/3'/>
126c126
<       <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-63-V-raw/org.qemu.guest_agent.0'/>
---
>       <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-60-V-raw/org.qemu.guest_agent.0'/>
164,165c164,165
<     <label>system_u:system_r:svirt_t:s0:c67,c822</label>
<     <imagelabel>system_u:object_r:svirt_image_t:s0:c67,c822</imagelabel>
---
>     <label>system_u:system_r:svirt_t:s0:c703,c726</label>
>     <imagelabel>system_u:object_r:svirt_image_t:s0:c703,c726</imagelabel>
+ virsh blockcommit V-raw vdb --top 'vdb[1]' --shallow --keep-relative
Block Commit started
+ virsh dumpxml V-raw
+ awk '/<disk/,/<\/disk/'
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/mapper/rhel-V'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/d/d'/>
      <backingStore type='file' index='1'>
        <format type='qcow2'/>
        <source file='/var/lib/libvirt/images/d/../c/../b/b'/>
        <backingStore/>
      </backingStore>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/>
    </disk>

Blockcommit works well after libvirt restarted. Bug fixed.

Comment 11 errata-xmlrpc 2018-04-10 11:02:08 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://access.redhat.com/errata/RHEA-2018:0704