[libvirt] [PATCH v3 0/5] Next round of active commit support

[Kashyap Chamarthy]

On Mon, Jun 23, 2014 at 09:39:08AM -0600, Eric Blake wrote:
> On 06/21/2014 04:34 AM, Kashyap Chamarthy wrote:
> > I just tried to test this series built from Eric's libvirt git repo, and
> > QEMU built from its git.
> > 
> > On a live (or offline guest) I see the below:
> > 
> >     $ virsh blockcommit f20vm1 vda --shallow --wait \
> >         --verbose --pivot --active
> >      error: unsupported flags (0x4) in function qemuDomainBlockCommit 
> > 
> > I also tried:
> > 
> >     $ virsh blockcommit --domain f20vm1 vda \
> >         --base /home/kashyap/vmimages/snap3-f20vm1.qcow2 \
> >         --top /home/kashyap/vmimages/snap4-f20vm1.qcow2  \
> >         --wait --verbose --pivot --active
> >     error: unsupported flags (0x4) in function qemuDomainBlockCommit
> > 
> > Is that expected?
> 
> Unfortunately, yes, unless you have also applied Jeff's pending patches
> for qemu that actually enable optional 'top':
> 
> https://lists.gnu.org/archive/html/qemu-devel/2014-06/msg04060.html

Yep, I just applied the above patch to today's QEMU git and tested with
same libvirt (from your repos.or.cz instance) commit ID that I pointed
to in my earlier email in this thread, and active blockcommit w/ 'virsh'
works for me. 

Following are details of a simple test I did.


Before active blockcommit
-------------------------

  - I had a chain like that:

    [base] <-- [snap1] <-- [snap2] <-- [snap3] <-- [snap4] (current-active)

  - Current active block device in use:

    $ virsh domblklist f20vm1
    Target     Source
    ------------------------------------------------
    vda        /home/kashyap/vmimages/snap4.qcow2


Perform active blockcommit
--------------------------

The below commmand will commit contents of [snap4] into [snap3] and
makes [snap3] as the current active image invalidating [snap4]:

    $ virsh blockcommit f20vm1 vda --shallow --wait \
        --verbose --pivot --active
    Block Commit: [100 %]
    Successfully pivoted


After active blockcommit
------------------------

The chain has reduced to below (shortened by one image):

    [base] <-- [snap1] <-- [snap2] <-- [snap3] (current-active)

Again, check what's the current active block device via 'virsh' (it
should reflect 'snap3'):

    $ virsh domblklist f20vm1                                                                                                              
    Target     Source
    ------------------------------------------------
    vda        /home/kashyap/vmimages/snap3.qcow2

Also, it updated the 'virsh dumpxml' output just fine.

Lastly, I ran active blockcommit again (w/ --shallow), so the chain is
now reduced to

    [base] <-- [snap1] <-- [snap2] (current-active)

And, here's its associated 'virsh dumpxml' output showing the uppdated
backing store (chain reduced by two):

    $ virsh dumpxml f20vm1 | grep "snap2.qcow2" -A10 -B2
        <disk type='file' device='disk'>
          <driver name='qemu' type='qcow2'/>
          <source file='/home/kashyap/vmimages/snap2.qcow2'/>
          <backingStore type='file' index='1'>
            <format type='qcow2'/>
            <source file='/home/kashyap/vmimages/snap1.qcow2'/>
            <backingStore type='file' index='2'>
              <format type='qcow2'/>
              <source file='/home/kashyap/vmimages/f20vm1.qcow2'/>
              <backingStore/>
            </backingStore>
          </backingStore>
          <target dev='vda' bus='virtio'/>

 
So, works as described in the patch titled "blockcommit: turn on active
commit" (on libvir-list). Will test more once patches are committed to git.

> You're very bleeding edge; I won't push my patches to libvirt.git until
> qemu.git also has matching patches, so in the meantime, you have to
> carry patches on both repos.  Peter has been doing some rpm builds of
> the bits and pieces for integration testing, but I'm not sure if he is
> planning on publishing them for public consumption yet.

No worries, I can test manually apply patches ('git am
-3') from the list to test.

--
/kashyap