[Engine-devel] Floating Disks implementation in REST-API

[Ori Liel]

>
>>> Floating disks should be both in the root context, and also in the VM
>>> context for each VM the floating disk is attached to, right? So floating
>>> disks would appear 1+N_attach times in the API, once in the root
>>> context, and once for each VM they are attached to.
>>>
>>
>> IIUC a floating disk is not associated with the VM in any way, and should
>> not appear in that VM's collection of disks. There's a similar feature of
>> activate/deactivate disk (http://www.ovirt.org/wiki/Features/HotPlug).
>> A deactivated disk is still associated with the VM, and should appear in
>> the VM's collection of disks. Perhaps this is the source of confusion.
>
>No that isn't it. I think have a bit of terminology mismatch. According to:
>
>http://www.ovirt.org/wiki/Features/DetailedFloatingDisk
>
>i think your use of the word floating is correct. I got confused as i
>thought that any disk could be floating, whether it was attached to 0
>VMs, 1 VM, or 2 or more VMs.
>
>So before we go further, let's get things straight:
>
>  - disk without any VMs => floating. It appears in the root context.
>  - disk attached to 1 VM => normal state. It appears in the VM context.

I think this type of disk should be shown in both contexts. 

If a user is looking at http://{host:port}/disks, I think he intuitively 
expects to see all disks (attached or unattached). A disk will contain 
reference to the VMs which it is attached to, and thus:

- No VM-ids          -->    floating disk. 
- One VM-id          -->    regular disk.
- Multiple VM-ids    -->    shared disk. 

>  - disk attached to 2 VMs => shared disk. It appears in both VM contexts.
>
>Is that correct?
>
>Also can someone explain on how floating and shared disks are actually
>implemented in the BE? I imagine it's one of two ways:
>
>  => The BE keep a global list of disks, each disk with zero or more
>references to a VM.
>  => The BE keeps a special "floating" state independent of the number
>of VMs that it is attached to.
>
>Thanks,
>Geert