[libvirt-users] avoiding PCI bus 8 / using PCI function / virt-install

[Laine Stump]

On 12/26/18 6:59 PM, b f31415 wrote:
> Thanks.  Maybe I'm missing something but when I try virt-install 
> --dry-run --print-xml it generates this snippet of XML:
> 
> <interface type="bridge">
> 
> <source bridge="ge_0_0_0_77"/>
> 
> <mac address="52:54:00:01:00:4e"/>
> 
> <model type="virtio"/>
> 
> </interface>
> 
> 
> but what i need (and get from virsh dumpxml) has this extra PCI line.
> 
> <interface type='bridge'>
> 
> <mac address='52:54:00:01:00:4e'/>
> 
> <source bridge='ge_0_0_0_77'/>
> 
> <target dev='vnet78'/>
> 
> <model type='virtio'/>
> 
> <alias name='net78'/>
> 
> <address type='pci' domain='0x0000' bus='0x01' slot='0x0a' function='0x6' />
> 
> </interface>
> 
> 
> Did I miss something?  Do you see PCI in the XML when you do the 
> virt-install --dryrun approach?

virt-install never explicitly specifies a PCI address in the XML it 
creates and sends to libvirt, and what you're seeing as the output from 
--print-xml is the XML before it has been sent to libvirt.

Additionally, in response to a question in the original mail, there is 
no way to tell virt-install (or libvirt itself) to use non-0 functions 
for devices (except to manually specify the entire PCI address).

Since 99 44/100% of users (probably much higher, but that number has 
such a nice ring to anyone who recalls the old Ivory Soap commercials 
:-) never need more devices than are possible using only function 0, 
there has been no effort made to automate assignment of non-0 functions.

So if you need this many devices, you should probably consider just 
using virt-install once to generate proto-template XML, then "virsh 
define" that template to get an XML that has an <address...> element for 
every device that needs it, write a script that condenses all the device 
PCI addresses into less slots by using non-0 functions (and saves that 
as the "final" template), and finally modify your installation to do a 
series of virsh commands using that template XML as a start.


I know it sounds awkward, but there is really nothing in libvirt or 
virt-install to automate assignment of PCI devices to non-0 functions.


> On Wed, Dec 26, 2018 at 2:57 PM Peter Crowther 
> <peter.crowther at melandra.com <mailto:peter.crowther at melandra.com>> wrote:
> 
>     On Wed, 26 Dec 2018 at 16:26, b f31415 <bf31415 at gmail.com
>     <mailto:bf31415 at gmail.com>> wrote:
> 
>         If not, is there a way with one of the virt command line tools
>         to create the XML (with the PCI addresses specified) so that I
>         can process that XML and re-write the PCI addressing values? 
>         Right now the only way I’ve been able to get that detailed XML
>         file is to 1) virt-install and let the VM begin the boot process
>         and then do a 2) virsh dumpxml and then 3) virsh
>         destroy/undefine that VM, 4) modify the XML and then 5) virsh
>         create ./modified.xml.  Is there a cleaner way to do this?
> 
> 
>     It won't do everything you want, but check out virt-install
>     --print-step --dry-run.  This should at least allow you to get at
>     the XML for the intermediate steps and remove the brittleness of
>     defining, destroying, undefining the VM.
> 
>     Cheers,
> 
>     - Peter
> 
> 
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