[libvirt-users] Efficient live disk backup with active blockcommit : Failed 'block-commit': Could not reopen file: Permission denied

[Keyur Bhalerao]

Hi ,

Working on the simple POC : Advanced snapshot using libvirt and qemu .
Following are the exact steps which are followed .

1. Created as base VM - Ubuntu 15.10 with following libvirt and qemu
versions
   Using library: libvirt 1.2.16
   Using API: QEMU 1.2.16
   Running hypervisor: QEMU 2.3.0

   QEMU emulator version 2.3.0 (Debian 1:2.3+dfsg-5ubuntu9.1), Copyright
(c) 2003-2008 Fabrice
   Bellard

2.Created nested VM (vm-01) using VirtManager on base VM.
3.Used following commands to take the multiple snapshots -

virsh # list
 Id    Name                           State
----------------------------------------------------
 7     vm-01                          running

virsh # domblklist vm-01
Target     Source
------------------------------------------------
vda        /home/ubuntu/vm-01.img
hda        /dev/sr0

snapshot-create-as --domain vm-01 snap1 --diskspec
vda,file=/var/lib/libvirt/sn1.qcow2 --disk-only --atomic
snapshot-create-as --domain vm-01 snap2 --diskspec
vda,file=/var/lib/libvirt/sn2.qcow2 --disk-only --atomic

virsh #snapshot-list vm-01

------------------------------------------------------------
 snap1                2015-12-07 11:51:51 -0800 disk-snapshot
 snap2                2015-12-07 11:52:28 -0800 disk-snapshot

virsh # snapshot-list vm-01 --tree
snap1
  |
  +- snap2

List the current block device in use, again. It can be noticed, the new
overlay 'sn2.qcow2' is the current disk in use:

virsh # domblklist vm-01

Target     Source
------------------------------------------------
vda        /var/lib/libvirt/sn2.qcow2
hda        /dev/sr0

Now that the backup is finished, perform active blockcommit by live
mergning contents of sn2 into base:

ubuntu at keyurubuntu:~$ virsh blockcommit vm-01 vda --active --verbose --pivot
error: internal error: unable to execute QEMU command 'block-commit': Could
not reopen file: Permission denied

I am not sure why this is getting as permission denied. I have tried couple
of times reinstalling and creating new VMs . Every time when i have tried
to block-commit getting landed into  same error.

Is there any troubleshooting or solution to this issue. Stuck on this issue
for last 2 days.
Quick help much appreciated.

Thanks,
Keyur Bhalerao

Reference used -
http://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit
                        -
http://kashyapc.com/2012/09/14/externaland-live-snapshots-with-libvirt/
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