Re: chained grub2 derivative bootauto system

[Brendan Trotter]

Hi,

On Fri, Aug 31, 2012 at 11:59 PM, Lennart Sorensen
<address@hidden> wrote:
> On Fri, Aug 31, 2012 at 09:19:43AM +1000, Philip Rhoades wrote:
>> Ivo,
>>
>> Interesting idea - I particularly like the idea of booting from
>> arbitrary isos.
>
> Too bad that accessing an iso on a usb key is nothing like an actual cd
> or dvd and the sytem you boot must have support for the fact you put the
> iso on the usb key rather than as a real disc.  Nothing the boot loader
> can do to change that.
>
> If it was really that simple, someone would already have made such a
> boot loader for use on usb keys.  The reason it doesn't exist yet is
> that it can't exist.

For "PC BIOS", having a USB with multiple ISO images would actually be
relatively easy.

The USB's boot code would need to hook Int 0x15 to steal some memory,
then install code that emulates a CD (and El Torito) into the stolen memory.
Obviously you'd also hook "Int 0x13" so that the BIOS disk services are
redirected to your CD emulation code.

I'd expect that similar would be possible for UEFI (e.g. create a special
UEFI driver that emulates CD/s).

The main problem is after the OS on the ISO tries to take control of hardware
and fails to find its (emulated) CD. For some OSs this may not be a problem -
e.g. MS-DOS and FreeDOS (which continue to use the BIOS services
and don't take control of hardware), Linux (as long as the root
partition isn't on
the emulated CD), etc. For other OS's (Windows) it can't work.

However, someone that wants to create a USB like this might not care about
those "unsupportable" OSs anyway.

Finally; I'm not sure how a scheme like this would involve GRUB - you'd want
relatively specialised USB boot code (not GRUB). GRUB could (potentially)
be installed inside one or more of the ISOs, but this would be a normal
"El Torito" (or UEFI) boot as far as GRUB would know.


Cheers,

Brendan