Question about skipping virDomainDiskDefAssignAddress

[Daniel P. Berrangé]

On Mon, Jul 19, 2021 at 11:00:33AM +0900, Motohiro Kawahito wrote:
> 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

Do no use these names, they are irrelevant. Use the normal 
linux-style name, regardless of what the guest OS does.


Regards,
Daniel
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