[pve-devel] [PATCH-SERIES v3 pve-storage/qemu-server/pve-qemu] add external qcow2 snapshot support

[Fiona Ebner]

Am 13.01.25 um 11:57 schrieb DERUMIER, Alexandre via pve-devel:
>> Hmm, sounds like it might a bug, I can look into it. If really
>> required
>> to make it work, we can still set fixed node-names on the
>> commandline,
>> but also query them before usage to be sure we have the correct, i.e.
>> currently inserted node.
> 
>>> AFAICT, this is because the node name is not set in the original
>>> options
>>> for the block driver state and then it wrongly detects an attempt to
>>> change the node name (even if specifying the correct auto-generated
>>> one
>>> during reopen). However, it is rather ugly to try and use a -drive
>>> together with blockdev-reopen in any case, blockdev-reopen is really
>>> written with -blockdev in mind and -blockdev necessarily requires
>>> setting node-name up front.
> 
> you are too fast ^_^
> 
>>> I don't think it's even worth fixing that bug. We should use
>>> blockdev-reopen only after switching to -blockdev, it's much nicer
>>> like
>>> that 🙂
>>>
>>> I'd still be in favor of querying the node-name of drives with
>>> query-block before doing QMP operations though. Like that, we can
>>> warn/error if it doesn't match what we expect for example, to catch
>>> unexpected situations.
> 
> ok, so the question is : how to query to node-noname of different disk
> (+snapshot chain).
> 
> Fabian is against the use of the path.
> 
> So, I'm a little bit out of idea ^_^
> 

For almost all QMP commands, we only need to care about the node that's
inserted for the drive. And for your use-case, checking that the top
node of the chain matches what we expect is already a good first step.
The lookup itself is a different question, I'll also answer to the other
mail.