[gPXE] A Late gPXE Shutdown

[Miller, Shao]

Oooh.  I found an [mildly] interesting one today.

Lately I've been making use of a small Windows via MEMDISK.  It goes:

Native PXE -> PXELINUX -> gPXE (undionly.kkpxe) -> SAN-boot -> SYSLINUX
-> MEMDISK -> Windows

Today I [roughly] determined the point of failure for one particular
model of computer...  When I do:

SYSLINUX -> MEMDISK -> Windows

everything is fine.  However in the former scenario, the computer
freezes as soon as the NIC driver is installed (or in other tests where
it's already installed, when the driver is started).  Kernel debugging
shows lots of interrupts.  I was able to avoid the freeze by manually
uninstalling and re-installing various PCI bus devnodes, which I assume
passed along a reset of some kind of the NIC.

The singular change of removing this NIC driver allows for correct
operation.

I am going to guess that this particular Windows driver doesn't deal
well with having the NIC in whatever state gPXE has left it in.  Too
bad, because we have no idea when the OS will take control and not need
gPXE again.

Anyway, we might come across similar buggy Windows drivers in SAN-boot
scenarios again.  This one was for:
3Com 3C920 Integrated Fast Ethernet Controller (3C905C-TX Compatible)
Vendor ID: 10B7
Device ID: 9200
Windows driver: EL90XBC5.SYS

One possible solution would involve having some code in the MEMDISK
image to inform gPXE to shut down the NIC.  In my case, once the MEMDISK
has booted, the work of the SAN connection is done.

- Shao Miller