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

[Fiona Ebner]

Am 13.01.25 um 12:58 schrieb DERUMIER, Alexandre:
> 
> 
>>> For almost all QMP commands, we only need to care about the node
>>> that's
>>> inserted for the drive.
> (yes, that the throttle group in my implementation, and I have a fixed
> name, I'm reusing the "drive-(ide|scsi|virtio)x naming"
> 

This assumption might not always hold, see my earlier replies. To avoid
relying on the assumption, we can use query-block and warn if the name
doesn't match the fixed one we expect. This usually shouldn't happen,
but who knows what the future brings and what else touches the block
graph. Querying is cheap and will immediately give us a good idea
what/when something goes wrong. Such a situation might even just be a
valid edge case or third-party use case. I don't want to break those for
no reason.

Let me illustrate what I mean with an example: say that a user requests
move storage for drive scsi0. Then we can:
1. use query-block to get the node name of what's inserted in drive
scsi0 right now
2. warn if the node-name doesn't match the expected drive-scsi0 name
3. run blockdev-mirror with the node name we queried, because that is
the node name with that data that the guest also sees right now

We could also error out instead of warn in step 2, but that might break
some third-party use cases or edge cases we are not aware of right now.

The problem for how to name the nodes in the backing chain is
independent from this. I'll answer the other mail where you discussed
this with Fabian.