[Qemu-devel] [Bug 1089006] Re: Qemu scrambles order of eth devices in vm

[john fisher]

Thank you Daniel.
I understand what you say and agree. However when presented with a mapping and 
an order by libvirt, shouldn't the order be preserved by default? If the OS 
scrambles it, then fine, not your problem...

Are we on the right track here, is there some way to control the order
as presented by Qemu when the VM's OS boots?

If its at all helpful to understand the issue, here is our current proposed 
workaround:
=start 32 fresh VMs, each with 8 bridged connections and 4 82599 virtual 
connections=
take one generic xml file
qemu-img one default disk image
examine the HV's lspci output to find out bus numbering for the 82599 virtuals
add correct bus numbering in xml file
virsh create the xml to get randomized MAC addresses ( better ways  to do 
this...)
save  xml again
shutdown VM
> heres where the workaround occurs <
mount VM
write to /etc/udev/rules.d file to capture MAC vs PCI numbering in order of 
presentation for booting
etc etc

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https://bugs.launchpad.net/bugs/1089006

Title:
  Qemu scrambles order of eth devices in vm

Status in QEMU:
  New

Bug description:
  HV = 12.04 LTS plus libvirt 1.0x
  VM = 12.04 LTS

  On the HV there are 12 eth interfaces which we make available to the
  VM. We have 4 10G virtual function interfaces, and 8 1G conventionally
  bridged interfaces. No matter what order we present the interfaces in
  the xml file, they come up in eth0-eth11 order on the VM as follows:
  ( the interfcaes do work, once you figure out which is which)

  eth0-eth7 not in order as compoared to the bridges on the HV (interfaces 
file) or compared to the xml file for the VM, or compared to the bus numbers. 
MAC addresses are random.
  eth8-eth11 show up in the VM  in order of PCU bus numbers just as you'd 
expect, always after the bridged interfaces.

  Consulting the libvirt mailing list, the developer says they present
  the list in bus order to qemu, but qemu scrambles that order. That
  appears to me too, to be the case.

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