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

[Daniel Berrange]

There is really no such concept as "NIC order" at the hardware level in
QEMU. NIC naming order is something that operating systems invent
according to some policy they have. As far as libvirt & QEMU are
concerned, you only have control over the PCI device slot numbering.
The operating system may choose to number NICs based on their PCI device
slot number, or something else entirely. Further after an OS has been
booted once, they often record the original mapping of MAC <-> NIC
names, so even if you change the PCI slot ordering on later boots, the
naming won't change.

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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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