[ovirt-devel] Re: implementing hotplugCd/hotunplugCd in vdsm
So from what I was able to see in hotplugDisk example, for CDs I would have to do
similar:
1. parse disk params from stored xml metadata
2. call prepareVolumePath with these params
(skip normalizeVdsmImg)
3. call updateDriveIndex
(skip validating whether volume has leases)
4. drive.getXML() and then hooks.before_disk_hotplug with it
5. call attachDevice with drive XML and handle possible errors
I am not sure, however, whether we need what "else" does in hotplugDisk (vm.py
line 3468)...
Looking forward to hearing your opinions,
Fedor
----- Original Message -----
From: "Fedor Gavrilov" <fgavrilo(a)redhat.com>
To: "devel" <devel(a)ovirt.org>
Sent: Monday, June 22, 2020 4:37:59 PM
Subject: [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
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