Re: [Etherboot-developers] PXELINUX on top of Etherboot?

[H. P. A. <hp...@zy...>]

Eric W. Biederman wrote:
> 
> The short answer is that the code in at least one place was not
> integrated cleanly and a working version has never made it into an
> etherboot release. 
> 
> That said I surveyed the code a while ago and fixing it up does not
> look too difficult.  The concept are at least clean.
> 
> With respect to stomping memory except for a small real mode
> trampoline the development version of etherboot 5.1.x lives at the
> high end of memory below 4GB, so the code should be safe.
> 

OK; it really should hook INT 15h (and move the low DOS memory ceiling 
BIOS variable at physical address 0x413) to make itself invisible -- 
PXELINUX will actually avoid touching the top 128K of memory just in 
case a PXE stack doesn't do that, but that's the "right thing" to do.

When you get the cleanup command (unload stack) then you remove the 
hooks, of course.

> It has been observed before that getting pxelinux running should not
> be too difficult, and no one was opposed.  But so far no one has
> volunteered to debug it into operation.
> 
> Besides the missing functions there are two significant stumbling blocks.
> 1) The callbacks are currently 32bit only.

OK... not sure what you mean with callbacks here.  Are you referring to 
the 32-bit PXE entrypoint, or the 32-bit PXE status callback?  PXELINUX 
doesn't use the status callbacks, but it does use the 16-bit PXENV+ or 
!PXE entrypoints.

> 2) The pxe entry points depend on freebsd headers so the does not
>    currently compile on linux.

<nod> that doesn't sound too hard to fix.

> Looking through the actual pxe wrappers the code should continue to
> work.  But there was at least one location where the fact that
> etherboot can now live above 1MB breaks the code.  But for
> the short term that can be worked around by just disabling -DRELOCATION
> though etherboot stomps on to much memory in that case.

How much memory is "too much"?  As far as I know, some actual PXE stacks 
will hog memory down to near the 448K mark.  PXELINUX only requires 384K 
of conventional (low 1M) memory, although I might move that mark up to 
448K in a future version in order to allow the use of large blocks 
through the TFTP blksize option.

I'll see if I have a chance to look at this.  If the learning curve 
isn't too steep I might be able to make it work.

	-hpa