[libvirt] Attempting to pivot disk with incomplete mirror results in hang

[Scott Sullivan]

I have what appears to be a bug when pivoting a disk during a block copy that is not yet 100% finished, resulting in the pivot command hanging. I have verified this problem on libvirt 1.2.10.

Here's what Im seeing (transient guest):

1.) Start the block copy:

[root at host ~]# virsh blockcopy f20-SPICE vda /dev/sdc --format=raw --blockdev
Block Copy started
[root at host ~]#

2.) Query status to see it works/is started

[root at host ~]# virsh blockjob --info f20-SPICE vda
Block Copy: [  1 %]

[root at host ~]#

3.) Attempt the pivot before mirror reaches 100% (this makes cmd hang)

[root at test-parent-kvm ~]# virsh blockjob f20-SPICE vda --pivot
^^^ cmd is now hanging

-------------------------------------------------------------

When its hanging, I see this in /var/log/libvirt/libvirtd.log

19:29:33.376+0000: 1845: error : qemuDomainBlockPivot:15367 : block copy still active: disk 'vda' not ready for pivot yet
19:30:31.000+0000: 1842: warning : qemuDomainObjBeginJobInternal:1376 : Cannot start job (query, none) for domain f20-SPICE; current job is (modify, none) owned by (1845, 0)
19:30:31.000+0000: 1842: error : qemuDomainObjBeginJobInternal:1381 : Timed out during operation: cannot acquire state change lock

This then makes other commands querying this domain hang as well, such as:

virsh blockjob --info f20-SPICE vda

With this being put into log:

19:30:31.000+0000: 1842: error : qemuDomainObjBeginJobInternal:1381 : Timed out during operation: cannot acquire state change lock
19:34:45.568+0000: 1841: error : virNetSocketReadWire:1571 : End of file while reading data: Input/output error

Is this expected behavior? It would be nice if on step #3 instead of hanging the command returned in an error state saying cannot pivot because the mirror is not yet 100% or similar. I am happy to test later versions or patches as needed.