vbox + gpxe + pxeboot = fail

[Daniel Braniss]

Hi Lawrence,
> Hi All,
> 
> I had some frustration trying to get FreeBSD to pxeboot inside a vbox VM
> a while back. The thread is available here:
> 
> http://lists.freebsd.org/pipermail/freebsd-emulation/2010-April/007681.html
> 
> I left things for a while and came back to them yesterday with some
> fresh resolve to nut the problem out. I have some new insights I wanted
> to share.
> 
> I'm using gpxe 1.0.1 from
> http://kernel.org/pub/software/utils/boot/gpxe/ and doing the builds on
> a Debian VM. To create a rom for the vbox AMD adapter types, I'm
> following the details at:
> 
> http://www.etherboot.org/wiki/romburning/vbox
> 
> I turned the instructions to pad the rom into a python script you can
> grab from here:
> 
> http://people.freebsd.org/~lstewart/misc/vbox/rompad.py
> 
> 
> 
> Here's what I've figured out so far:
> 
> - The problem stems from the pxe boot rom environment provided by gpxe.
> It sends and receives packets correctly, but somehow the IP addresses
> get mangled (I think this happens inside gpxe) so it thinks the replies
> it is waiting for should be coming in on one IP address when they
> actually arrive on the real valid IP address.
> 
> - Using the binary only vbox on Win XP which uses the Intel pxe boot rom
> has no problems and works perfectly i.e. further evidence this is
> isolated to gpxe
> 
> - By changing the line
> "if (udpread_p->status > 0) {"
> to
> "if (udpread_p->status > 1) {"
> in sys/boot/i386/libi386/pxe.c, our pxeboot is able to work around the
> problem and I can pxeboot FreeBSD just fine. gpxe therefore is correctly
> reading the packets off the wire and passing them to our pxeboot code.
> gpxe just sets the failure status code because it thinks the packet is
> not the one we were waiting for because of the IP address being mismatched.
> 
> 
> 
> The file in the gpxe distribution that I've been adding debug printf's
> to is: src/arch/i386/interface/pxe/pxe_udp.c
> By doing a "%s/DBG/dbg_printf/g" in that file, you get debugging output
> that shows you the failures and the IP address it thinks the pkt should
> be coming in on. In my case, it correctly sends UDP packets to
> 172.16.7.21, and then waits for the reply on 172.16.7.50 (but sees that
> the reply actually comes in on 172.16.7.43 which is the IP of the VM).
> Because .43 != .50, gpxe returns status failure (i.e. 1) but does still
> correctly read the pkt and pass it to our pxeboot hence why my hack of
> ignoring the status actually allows things to work.
> 
> I've put an unmodified copy of pxe_udp.c at:
> 
> http://people.freebsd.org/~lstewart/misc/vbox/pxe_udp.c
> 
> If anyone is able to see any obvious problems in that file I'd love to
> hear about it. I suspect the problem is embedded somewhere a bit deeper
> in the gpxe code though so I'll ping the gpxe folks and see what they
> have to say.
> 
> Cheers,
> Lawrence

as far as i remember, the gpxe rom only worked with direct connected, no bridge
nor nat, so I guess you figured out why :-)

danny