[syslinux] PXE Booting EFI

[Gene Cumm]

On Mon, Jan 19, 2015 at 3:09 PM, Patrick Masotta <masottaus at yahoo.com> wrote:
>
>> EFI has proven to be more robust.  The catch
>> here is order.  The
>> ProxyOffer data must
>> take precedence over the PxeReply data but both
>> of them probably need to be parsed.
>
> Not really; If you parse both "next server" from the
> last parsed packet (PxeReply) will overwrite
> the value gathered from the ProxyOffer and that leads
> to "Nest-server"= DHCP Server IP (wrong)

Order:

at syslinux-6.03/efi/pxe.c

void net_parse_dhcp(void)
{
...

    parse_dhcp(&mode->PxeReply.Dhcpv4, pkt_len);
//genemod start
    if(&mode->ProxyOfferReceived)
        parse_dhcp(&mode->ProxyOffer.Dhcpv4, pkt_len);
//genemod end
   Print(L"\n");

...

}


Though I'm trying to think of a DHCP option that wouldn't be in the
earlier packets.

> Fore some reason I think there might be also a bug on EFI firmware code:
> If the DHCP server provides an answer with "next server" populated
> but no file field populated nor the corresponding option either that's not
> a PxeReply then that structure should be empty..

Which sounds like a server operator error.

> Reading the standard does not say much about how/when these structures
> really get populated.

If they're the on-wire frames, it's the server.  If it's the packet
buffer in RAM, it's the server.  If it's how Syslinux variants use the
packet buffer, that's up to the Syslinux variant to (hopefully) follow
the standards to utilize them.

-- 
-Gene