TCK regression from blockdev change

[Jim Fehlig]

Hi all,

I noticed libvirt-tck test 207-disk-media-change.t is failing with 6.1.0, 
although I _think_ the failure has actually been around since the change to 
using blockdev in the qemu driver. The test essentially creates a minimal domain 
with a cdrom disk device, then calls attach_device a few times, changing the 
<source> of the disk. The last attach_device uses the same <source> as when the 
domain was created and expects the initial and final XML to be the same. For 
reference, here's a link to the test

https://libvirt.org/git/?p=libvirt-tck.git;a=blob;f=scripts/domain/207-disk-media-change.t;h=dfef7c95c9d062e0f20dd2ed53d4dfb12cca0ab3;hb=HEAD

However the test fails since the 'index' attribute of the <source> element is 
not the same between initial XML (index='1') and final XML (index='5'). Indeed 
with each attach operation the index is incremented. Should libvirt be fixed to 
always provide an index of 1 for this disk config? Or should we adjust the test 
case? I'm not so familiar with this functionality but I lean towards the former 
since attaching a disk with a missing source (no media) results in odd looking 
disk config

     <disk type='file' device='cdrom'>
       <driver name='qemu' type='raw' cache='none'/>
       <source index='4'/>
       <target dev='hdc' bus='ide'/>
       <readonly/>
       <alias name='ide0-1-0'/>
       <address type='drive' controller='0' bus='1' target='0' unit='0'/>
     </disk>

Regards,
Jim