Question about skipping virDomainDiskDefAssignAddress

[Laine Stump]

On 7/16/21 8:51 AM, Daniel P. Berrangé wrote:
> On Fri, Jul 16, 2021 at 09:49:40PM +0900, Motohiro Kawahito wrote:
>>> From: "Daniel P. Berrangé" <berrange at redhat.com>
>>> To: Motohiro Kawahito <JL25131 at jp.ibm.com>
>>> Cc: libvir-list at redhat.com
>>> Date: 2021/07/16 17:22
>>> Subject: [EXTERNAL] Re: Question about skipping
>> virDomainDiskDefAssignAddress
>>>
>>> On Fri, Jul 16, 2021 at 01:01:50PM +0900, Motohiro Kawahito wrote:
>>>>> From: "Daniel P. Berrangé" <berrange at redhat.com>
>>>>> To: Motohiro Kawahito <JL25131 at jp.ibm.com>
>>>>> Cc: libvir-list at redhat.com
>>>>> Date: 2021/07/16 00:42
>>>>> Subject: [EXTERNAL] Re: Question about skipping
>>>> virDomainDiskDefAssignAddress
>>>>>
>>>>
>>>>> With the exception of paravirtualized Xen guests, this field in
>>>>> libvirt XML is *completely* independant of the guest assigned
>>>>> device name.
>>>>>
>>>>> eg the XML might say /dev/vda, but the guest might decde to
>>>>> call it /dev/sda, or /dev/whatever or really absolutely
>>>>> anything.
>>>>
>>>> Thank you very much for this information! I understand it.
>>>> However, I don't understand how we can pass the target device
>> information
>>>> (e.g. 0A80) without an error. Do you know how to do it?
>>>>
>>>> My question was not good, so I opened another thread (How do we
>> specify
>>>> disk device names for non-Linux VMs in XML?).
>>>
>>> There is nothing that needs passing. The guest OS decides its naming
>>> however it wants to.
>>
>> We need to control device number from user. This device number would be
>> used later, such as detach-disk. Can we pass device number from outside?
> 
> Detach-disk requires the same information that is provided when the
> disk is first configured in libvir. This is completely separate to the
> device number / name seen inside the guest.

To expand on that, in the case of detaching a disk, you could 1) provide 
the target dev in the XML you give to "virsh detach-device", 2) give the 
target dev name that you provided in the original XML when you call 
"virsh detach-disk", or 3) you could specify a custom alias in the 
original XML ("<alias name='ua-somename'/>" - note that the leading 
"ua-" is *required* for a custom alias name) and then give that same 
alias to "virsh detach-device-alias". All three will allow you to 
reliably select the disk you want, and have the same result.