[ipxe-devel] Xen netfront support

[Shao Miller]

On 7/29/2014 18:20, Michael Brown wrote:
> I'm please to announce that iPXE now natively supports Xen netfront
> virtual NICs.  This may be of interest to anyone wanting to use iPXE
> running in a Xen PV-HVM domain.
>

Awesome! :)

> I have one issue which I'm not sure how to handle, and would appreciate
> feedback from anyone who frequently uses Xen:
>
> For each configured NIC, Xen exposes both an emulated PCI NIC (for OSes
> with no native Xen drivers) and a netfront virtual NIC (for OSes with
> native Xen drivers).  Xen provides a mechanism for OSes to "unplug" the
> emulated PCI NICs.  Operating systems with native Xen drivers will
> typically unplug the emulated PCI NICs to prevent confusion.
>
> iPXE could easily unplug the emulated PCI NICs.  However, this operation
> is irreversible.  If the loaded OS does not include native Xen drivers,
> then it will not be able to see any network devices.  This is undesirable.
>

Personally, I don't think seeing both NICs is a huge deal, as a Xen user 
should be aware of the dual-NIC thing.

But: are there any ordering guarantees about which NIC of the pair is 
going to be first (net0) in iPXE?

Also: Would the unplugging happen before any NIC-detection, if it were 
going to happen?  If so, that wouldn't suggest a 'xen-unplug' command, 
at least.

Maybe it could just sit as a build option and those who desire the 
guaranteed unplugging can build such.  That seems to be the special 
scenario; better confused with the possibility of poorer performance 
with the emulated NIC than NICless at OS time, perhaps.

+$0.02

- Shao Miller