[syslinux] Booting ISO images over PXE

[Andreas Kotes]

Hello Peter,

* H. Peter Anvin <hpa at zytor.com> [20071002 19:52]:
> It used to be that *no* operating system (including DOS) would continue 
> to use El Torito, but I think there is an ELTORITO.SYS for DOS now, 
> which would actually continue to work.  The question is if anything 
> would actually use it.

.. not by itself, i.e. you'd have to touch it in any case, which makes
it a moot point again .. I wonder why companies like Dell don't deliver
PXE images like they deliver ISO and HDD images for updates and the
like. strange.

> On the latest hardware (VMX/SVM capable) one could, at least in theory, 
> implement a thin hypervisor and virtualize the relevant I/O ports to 
> make it appear that a real CD-ROM is out there.  Needless to say, that's 
> a big effort.

... and it would work on a comparatively small range of computers as
well.

Another idea I had once was some something along the lines of memdisk
installing something like a fake MSCDEX driver which uses the TCP/IP
stack left over from PXE to fetch the block requested from the CD-ROM
over the network ... most of the CD-ROM-drivers I know fail when they
encounter another driver already using the MSCDEX-name they're trying to
register themselves as - but DOS continues to boot, so the MSCDEX.EXE
might be able to use the fake CD-ROM .. you might run into memory
problems later on, and e.g. TFTP doesn't support requesting specific
blocks, so you'd have to implement something else (block ranges via
HTTP, for example, but you might have more luck extenting tftp-hpa, so
you don't need to do TCP and be really networking-interactive) ..

.. maybe feasible, but wouldn't help with linux images, or anything else
which doesn't use the (rather aged) MSCDEX ..

Br,

   Andreas

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