[libvirt-users] Attaching disks with external snapshots

Erlon Cruz sombrafam at gmail.com
Mon Aug 22 17:26:12 UTC 2016 

If that was the case I wouldn't be able to attach a volume without
snapshots. But just in case I did the following test, before attaching the
file, I copied all the file to a local folder and changed the path in XML
with the new paths. The problem repeats:

*2016-08-22 17:14:19.795+0000: 3799: info : qemuMonitorIOProcess:423 :
QEMU_MONITOR_IO_PROCESS: mon=0x7f68f800c4c0 buf={"return": "Could not open
backing file: Could not open
'/home/ubuntu/volumes/volume-d81f7e7e-4215-4433-aad2-50adcd31b29d.7a9ea169-a3ab-48bd-bd9d-e7585860abe4':
Permission denied\r\n", "id": "libvirt-30"}*

But, if I use the top backing file with same permissions
(/home/ubuntu/volumes/volume-d81f7e7e-4215-4433-aad2-50adcd31b29d), the
operation suceeds. Can this be a libvirt/QEMU bug?

Han, can you tell me more details about the commands you used and the
versions of or libvirt/qemu? I couldn't reproduce from the steps you
outlined.

On Fri, Aug 19, 2016 at 12:02 AM, Han Han <hhan at redhat.com> wrote:

> Hi Erlon,
> Since you say you got Permission denied error while the ACL mode is 777， I
> guess it is due to security system like selinux or apparmor.
> As I know, selinux defaultly will disable qemu to use volume based on NFS.
> We need to use 'setsebool virt_use_nfs 1' to enable it.
> Well, your OS is ubuntu, so I think apparmor causes the permission
> problem. Try to find a way to enable virt_use_nfs or disable apparmor. Then
> check if the problem can be reproduced.
>
> Han
>
> ----- Original Message -----
> From: "Erlon Cruz" <sombrafam at gmail.com>
> To: "Han Han" <hhan at redhat.com>
> Cc: "Yang Yang" <yanyang at redhat.com>, "Yuan Dan" <dyuan at redhat.com>,
> "Xuesong Zhang" <xuzhang at redhat.com>, libvirt-users at redhat.com
> Sent: Thursday, 18 August, 2016 12:44:36 PM
> Subject: Re: [libvirt-users] Attaching disks with external snapshots
>
> Hi Han,
>
> Any update on this?
>
> Erlon
>
> On Wed, Aug 17, 2016 at 9:58 AM, Erlon Cruz <sombrafam at gmail.com> wrote:
>
> > Han,
> >
> > Did the same test again with libvirt debug enabled. This time I added the
> > disk[1] without snaps (OK), and then added the disk[2] with snapshots.
> The
> > libvirt log[3] (line 320) says:
> >
> > *Could not open
> > '/opt/stack/data/nova/mnt/a3b4c6ddd9bf82edd4f726872be58d
> 05/volume-a75b42e8-8175-4516-b724-43ee6f3d2520':
> > Permission denied\r\n", "id": "libvirt-33"}]*
> >
> > But this file has 777 permissions. I can access it with any user I
> > tried[4]. Tough its mounted over NFS, the permissions seems to be right.
> >
> > Erlon
> >
> > [1]  http://paste.openstack.org/show/556055/
> > [2]  http://paste.openstack.org/show/556056/
> > [3]  http://pastebin.com/CCFcKq5b
> > [4]  http://paste.openstack.org/show/559018/
> >
> >
> > On Tue, Aug 16, 2016 at 2:41 PM, Erlon Cruz <sombrafam at gmail.com> wrote:
> >
> >> Hi Han,
> >>
> >> Thanks for helping. What is the XML before the snapshot is created? Can
> >> you post the XML files you used too? The files are in the links pointed
> by
> >> the numbers [1], [2] etc.
> >>
> >> The versions are:
> >> qemu-system-x86_64 --version
> >> QEMU emulator version 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.4), Copyright
> >> (c) 2003-2008 Fabrice Bellard
> >>
> >> libvirtd --version
> >> libvirtd (libvirt) 1.3.1
> >>
> >>
> >>
> >> Erlon
> >>
> >> On Mon, Aug 15, 2016 at 12:56 AM, Han Han <hhan at redhat.com> wrote:
> >>
> >>> Hi，Erlon
> >>> I was not able to reproduce your problem. It is ok to attach disk with
> >>> external snapshot.
> >>> I did it with following steps:
> >>> # qemu-img create /tmp/vdb 100M
> >>> Formatting '/tmp/vdb', fmt=raw size=104857600
> >>> # virsh start snap
> >>> Domain snap started
> >>> # virsh snapshot-create-as snap s1 --disk-only --diskspec
> >>> vdb,file=/tmp/vdb.s1 --quiesce
> >>> Domain snapshot s1 created
> >>> # virsh dumpxml snap|awk '/<disk/,/<\/disk/'
> >>>     <disk type='file' device='disk'>
> >>>       <driver name='qemu' type='qcow2' cache='none'/>
> >>>       <source file='/var/lib/libvirt/images/snap.s1'/>
> >>>       <backingStore type='file' index='1'>
> >>>         <format type='qcow2'/>
> >>>         <source file='/var/lib/libvirt/images/snap.qcow2'/>
> >>>         <backingStore/>
> >>>       </backingStore>
> >>>       <target dev='vda' bus='virtio'/>
> >>>       <alias name='virtio-disk0'/>
> >>>       <address type='pci' domain='0x0000' bus='0x00' slot='0x07'
> >>> function='0x0'/>
> >>>     </disk>
> >>>     <disk type='file' device='disk'>
> >>>       <driver name='qemu' type='qcow2'/>
> >>>       <source file='/tmp/vdb.s1'/>
> >>>       <backingStore type='file' index='1'>
> >>>         <format type='raw'/>
> >>>         <source file='/tmp/vdb'/>
> >>>         <backingStore/>
> >>>       </backingStore>
> >>>       <target dev='vdb' bus='virtio'/>
> >>>       <alias name='virtio-disk1'/>
> >>>       <address type='pci' domain='0x0000' bus='0x00' slot='0x0c'
> >>> function='0x0'/>
> >>>     </disk>
> >>>
> >>> Save the dumped vdb's xml to /tmp/vdb.xml
> >>> # virsh detach-device snap /tmp/vdb.xml
> >>> Device detached successfully
> >>> # virsh attach-device snap /tmp/vdb.xml
> >>> Device attached successfully
> >>> # virsh dumpxml snap|awk '/<disk/,/<\/disk/'
> >>>     <disk type='file' device='disk'>
> >>>       <driver name='qemu' type='qcow2' cache='none'/>
> >>>       <source file='/var/lib/libvirt/images/snap.s1'/>
> >>>       <backingStore type='file' index='1'>
> >>>         <format type='qcow2'/>
> >>>         <source file='/var/lib/libvirt/images/snap.qcow2'/>
> >>>         <backingStore/>
> >>>       </backingStore>
> >>>       <target dev='vda' bus='virtio'/>
> >>>       <alias name='virtio-disk0'/>
> >>>       <address type='pci' domain='0x0000' bus='0x00' slot='0x07'
> >>> function='0x0'/>
> >>>     </disk>
> >>>     <disk type='file' device='disk'>
> >>>       <driver name='qemu' type='qcow2'/>
> >>>       <source file='/tmp/vdb.s1'/>
> >>>       <backingStore type='file' index='1'>
> >>>         <format type='raw'/>
> >>>         <source file='/tmp/vdb'/>
> >>>         <backingStore/>
> >>>       </backingStore>
> >>>       <target dev='vdb' bus='virtio'/>
> >>>       <alias name='virtio-disk1'/>
> >>>       <address type='pci' domain='0x0000' bus='0x00' slot='0x0c'
> >>> function='0x0'/>
> >>>     </disk>
> >>>
> >>> So I managed to attach disks with snapshot.
> >>> I want to know what is your libvirt and qemu-kvm version?
> >>> And can you provide your files: /tmp/disk.xml[1],
> >>> /tmp/snap-from-disk.xml[2], /tmp/disk-with-snap.xml[4],
> >>> /tmp/disk-with-snap.xml . I need more details.
> >>>
> >>> Han Han
> >>>
> >>> ----- Original Message -----
> >>> From: "Erlon Cruz" <sombrafam at gmail.com>
> >>> To: libvirt-users at redhat.com
> >>> Sent: Friday, August 12, 2016 10:23:24 AM
> >>> Subject: [libvirt-users] Attaching disks with external snapshots
> >>>
> >>> Hi folks,
> >>>
> >>> I'm trying to to attach a disk to an instance using libvirt. The
> problem
> >>> is, this disk has external snapshots. The process tried was:
> >>>
> >>> 1 - Attach a disk in the domain:
> >>> virsh# attach-device instance-00000006 /tmp/disk.xml[1] --live
> >>>
> >>> 2 - Snapshot the disk[2]:
> >>> virsh# snapshot-create instance-00000006 --quiesce --xmlfile
> >>> /tmp/snap-from-disk.xml[2] --disk-only
> >>>
> >>> 3 - Dump the domain XML and create a new disk file from it:
> >>> virsh# dumpxml instance-00000006
> >>> ... [3]
> >>>
> >>> 4 - Dettach the device and re-add it using the new disk file:
> >>> virsh# detach-device instance-00000006 /tmp/disk-with-snap.xml[4]
> >>> Device detached successfully
> >>> virsh# attach-device instance-00000006 /tmp/disk-with-snap.xml
> >>> error: Failed to attach device from /tmp/disk-with-snap.xml
> >>> error: internal error: unable to execute QEMU command 'device_add':
> >>> Property 'virtio-blk-device.drive' can't find value
> 'drive-virtio-disk1'
> >>>
> >>> Question, is this operation supported? If yes, how is the correct
> >>> procedure?
> >>>
> >>> Erlon
> >>>
> >>>
> >>> [1] http://paste.openstack.org/show/556055/
> >>> [2] http://paste.openstack.org/show/556056/
> >>> [3] http://paste.openstack.org/show/556063/
> >>> [4] http://paste.openstack.org/show/556064/
> >>>
> >>> _______________________________________________
> >>> libvirt-users mailing list
> >>> libvirt-users at redhat.com
> >>> https://www.redhat.com/mailman/listinfo/libvirt-users
> >>>
> >>
> >>
> >
>
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