[libvirt] [PATCH 0/12] Standardized device addressing & SCSI controller/disk hotplug

[Wolfgang Mauerer]

Daniel P. Berrange wrote:
> On Thu, Dec 10, 2009 at 10:22:20PM +0000, Daniel P. Berrange wrote:
>> The XML for each address type looks like
>>
>>       <address type='pci' mode='static' domain='0x0000' bus='0x1e' slot='0x07' function='0x0'/>
>>       <address type='usb' mode='dynamic' bus='007' dev='003'/>
>>       <address type='drive' mode='dynamic' controller='1' bus='0' unit='5'/>
>>
>>
>> The 'mode' attribute for any of them is allowed to be either
>> 'static' or 'dynamic'. A static address is one specified by
>> the end user when defining the XML, while a dynamic address is
>> one automatically chosen by libvirt/QEMU every time a guest
>> boots. The idea of static addresses is to allow management
>> apps to guarentee that PCI device & drive numbering never
>> changes. This series does not actually implement static
>> addressing for PCI yet, because it requires that we change
>> the way we generate QEMU command line arguments. It does
>> do static addressing for disks.
> 
> I'm now wondering whether we actually truely need the 'dynamic'
> option. It already doesn't really make sense for disks. For PCI
> though I'm not sure anyone would ever want the dynamic mode, 
> where addresses can change at every boot. I think I should just
> remove the 'mode' attribute here, and just have libvirt detect
> PCI addresses the first time, and keep them the same thereafter.

Maybe there are two things to distinguish: If you read "dynamic"
in the sense of "I don't care which address the device/disk/whatever
uses, and I don't want to specify it explicitely", then having the
option is reasonable . I agree that  it does not make any sense
to have dynamic in the sense "explicitely assign new addresses every
time system boots", but that would not happen any way: Given the same
set of devices, the underlying hypervisor should assign the same
addresses.

Your suggestion would essentially imply that an initial "dynamic"
specification is converted into a static one after the first boot.
You are only referring to the in-memory configuration of libvirt
when you talk about subsequent boots, or are you also thinking
about modifying the persistent configuration?

> The second thought is whether we should put the <address>
> data inside a <device> element, so it looked like
> 
>   <device type='pci'>
>      <address domain='0x0000' bus='0x1e' slot='0x07' function='0x0'/>
>   </device>
> 
> The reason being, that I think it might be interesting to  also add in
> the vendor / product info at a later date 
> 
>   <device type='pci'>
>      <vendor id='0x8086'/>
>      <product id='0x1234'/>
>      <address domain='0x0000' bus='0x1e' slot='0x07' function='0x0'/>
>   </device>

Can't certainly do any harm to keep the format extensible.

Regards,

Wolfgang