[ovirt-devel] implementing hotplugCd/hotunplugCd in vdsm
Hey,
So in an attempt to fix change CD functionality we discovered a few other potential issues
and what Nir suggested was to implement two [somewhat] new functions in VDSM: hotplug and
hotunplug for CDs similar to how it works for normal disks now. Existing changeCD function
will be left as is for backwards compatibility.
As I found out, engine already calculates iface and index before invoking VDSM functions,
so we will just pass these along with PDIV to the VDSM.
Suggested flow is, let me quote:
So the complete change CD flow should be:
1. get the previous drivespec from vm metadata
2. prepare new drivespec
3. add new drivespec to vm metadata
4. attach a new device to vm
5. teardown the previous drivespec
6. remove previous drivespec from vm metadata
When the vm is stopped, it must do:
1. get drive spec from vm metadata
2. teardown drivespec
During attach, there are interesting races:
- what happens if vdsm crashes after step 2? who will teardown the volume?
maybe you need to add the new drivespec to the metadata first,
before preparing it.
- what happens if attach failed? who will remove the new drive from
the metadata?
Now, what makes hotplugDisk/hotunplugDisk different? From what I understand, the flow is
same there, so what difference is there as far as VDSM is concerned? If none, this means
if I more or less copy that code, changing minor details and data accordingly for CDs,
this should work, shouldn't it?
Thanks!
Fedor