Question about skipping virDomainDiskDefAssignAddress

[Motohiro Kawahito]

Laine Stump <laine at laine.org> wrote on 2021/07/17 00:01:36:

> From: Laine Stump <laine at laine.org>
> To: Libvirt <libvir-list at redhat.com>
> Cc: Motohiro Kawahito <JL25131 at jp.ibm.com>, "Daniel P. Berrangé" 
> <berrange at redhat.com>
> Date: 2021/07/17 00:01
> Subject: [EXTERNAL] Re: Question about skipping 
virDomainDiskDefAssignAddress
> 
> 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.
> 

Laine and Daniel, thank you very much for your comments. It's good to know 
the flexibility in the naming convention. However, I found libvirtd 
rejects a non-Linux device (i.e. '0A84') as a target device. The following 
two commands return an error message, "Unknown disk name '0A84'". Can you 
let me know how we specify an unusual name, like '0A84'?

$ virsh attach-disk sample_domain /volumes/user.qcow2 0A84
$ virsh detach-disk sample_domain 0A84

If we should use an alias, could you advise me how to specify? Thank you 
so much again for your help.

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