Re: 5.5 discussion

On Apr 13, 2005, at 10:45 AM, Michael Brown wrote:
>> I've supported this on http://rom-o-matic.net/ for a long time, and
>> while I don't think it should be on by default, I don't mind it being 
>> an
>> option.  It should be well-documented as to what the downsides of
>> enabling it are, but if people need it, they should not have to hack 
>> the
>> source to get it.

> Since we'll be writing proper ProxyDHCP support at some time, can we 
> use
> that opportunity to obviate that patch?

I think we were talking about:

ZPXE_SUFFIX_STRIP
If the last 5 characters of the filename passed to Etherboot is ".zpxe" 
then strip it off. This is useful in cases where a DHCP server is not 
able to be configured to support conditionals. The way it works is that 
the DHCP server is configured with a filename like "foo.nbi.zpxe" so 
that when PXE asks for a filename it gets that, and loads Etherboot 
from that file. Etherboot then starts up and once again asks the DHCP 
server for a filename and once again gets foo.nbi.zpxe, but with this 
option turned on loads "foo.nbi" instead. This allows people to use 
Etherboot who might not otherwise be able to because their DHCP servers 
won't let them.

I'm not sure how ProxyDHCP support would help here, but maybe I don't 
understand fully.

The situation this patch addresses seems to be where someone has 
another PXE stack and they want to chain Etherboot to use the Etherboot 
stack instead(?).  Since Etherboot now has a PXE stack, So, I'm 
guessing the filename that would be passed would be something like:

     pxelinux.0.zpxe

So, their PXE stack loads Etherboot, which then loads pxelinux.0, which 
presumably loads a kernel.  This might be useful in cases where the 
first PXE stack is good enough to load .zpxe files, but not good enough 
to work well with PXELINUX.

The other possibility, where people give a filename of:

     vmlinux.nbi.zpxe

Works around the situation where people want to load an NBI file, but 
can't do:

      if substring (option vendor-class-identifier, 0, 9) = "PXEClient"
      {
         # NOTE: kernels are specified in /tftpboot/lts/pxe/pxelinux.cfg/
         filename      "/lts/pxe/pxelinux.0";
      }
      # default to an i386 BOOTP image
      else
      {
         filename      "/lts/vmlinuz.ltsp";
      }

Because they're running a DHCP server that does not allow this kind of 
conditional construct.

That's my understanding of the utility of this suffix-stripping option. 
  I don't see a problem with having it as a non-default option, since it 
potentially helps people, in certain circumstances.

If there is something I am missing here, I would very much appreciate 
any illumination or clarification, as always.

Thanks,

Marty



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