[syslinux] EFI: PXE: "My IP is 0.0.0.0"

[Patrick Masotta]

>>>
 > 1) There's not "any" SB protocol present (Elitebook 8460p/2560p)
 
 The only solution for these is to use our own stack (likely full
 TCP/IP like lwIP) and connect to the Net GUID (EFI_SIMPLE_NETWORK_PROTOCOL). 
 Does the handle for Pxebc contain a Net? 
>>>

It does contain a Net but there are 2 issues with SNP:
1) The interface is different than UDPv4/TCPv4 protocols; this imply lot of code.
2) SNP has its non-blocking transmit issues ; see "Flaws in the design" at
https://wiki.linaro.org/LEG/Engineering/Kernel/UEFI/UEFI_Network_Driver



>>>
I found out that my EFI shell on VMware VMs can also handle output redirection like:
 guid > fs0:\efi-guid.txt
 dh > fs0:\efi-dh.txt
 dh bd >> fs0:\efi-dh.txt
 
 fs0 being the EFI boot partition on the hard drive of the VM.
<<<

Yes, but I use empty virtual clients when testing Syslinux PXE then I prefer redirecting 
console commands to a USB pendrive


 >>>
 > 2) SB protocols are loaded under a different that LoadeImage's DeviceHandle,
 > while Pxebc is loaded under the LoadeImage's DeviceHandle. (Elitebook 8470p/2570p)
 
 a) Hunt for a Sb.
 b) use Net
<<<

I do a hunt for either UDPv4Sb or TCPv4Sb 


>>>
 > 3) SB protocols and Pxebc are loaded under the LoadeImage's DeviceHandle (VMware Workstation 10).
 
 a) use Sb on Pxebc handle
 b) use Net
 <<<
I reuse the "Hunt for a Sb" approach (the overhead is not much) but I could easily use a)


>>>
 > About MNPSb; even when it presents the same interface than all the Service Binding protocols
 > remember we have to create a child of the particular matching protocol and those do not have
 > the same interface.
 
 Correct, different interface but it seems dominantly the same EFI_HANDLE.
 <<<

So far I've seen MNPSb is only available when the rest of SBs are also present then
it makes no sense embracing a new MNP protocol when UDPv4Sb and TCPv4Sb are also 
available.


>>>
 > I kept testing my patch and so far it proved to work in a multi-NIC environment:
 > I've set a VMware EFI client with 2 NICs connected to the same network,
 > using the VMware  DHCP server and Serva as proxyDHCP.
 > Setting a MAC filter in Serva I forced the client not receiving PXE redirection parameters
 > alternative on NIC_1 or NIC_2; the client always booted correctly from the NIC that received the
 > full set of PXE parameters. It seems to work.
 
 This sounds positive
 for cases 2&3 but still leaves #1 high and dry.
<<<

Case #1 is really a problem; the only alternative would be implementing SNP but as I've
mentioned before this approach also has its issues...
I also wonder if UEFI firmware w/o SB protocols is really UEFI compliant...
i.e the Elitebook 8460p is an early 2011 model that probably should receive a firmware update
including the missing SB protocols...
I think the best alternative would be implementing SNP and use it as last resort
"only" for Case #1.

 
 >>>
 Debating if this hunting should be more persistent so we don't go
 hunting at every binding.  It shouldn't affect large files but could
 affect lots of tiny files if we're hunting every time.  If it's to
 be more persistent, a table of known GUIDs to match to a handle should be stored.
 
 -- 
 -Gene
 <<<
I thought of it but I do not know if there's really much to get here;
i.e. in a 4 NIC PC the parsing only involves 4 UDPv4Sb (or TCPv4Sb) handles.
Anyway it can definitely be done if necessary.

Best
Patrick