[syslinux] [syslinux:disklib] disklib: make CHS calculation match core/fs/diskio.c

[Shao Miller]

 > On 10/14/2010 09:08 AM, Shao Miller wrote:
 >>
 >> Somewhat unrelated: Some day in the far, far future, it might be nice to
 >> "re-image"[1] computers using INT 13h via one or more COMBOOT32
 >> programs.  - Shao
 >>
 >> [1] Apply a disk or filesystem snapshot/saved-state.
 >
 > That's not even very hard at all, at least not for the whole-disk case.

Andrew Bobulsky wrote:
> Hello Shao, hpa,
>

Hello.

> I thought it was really ironic that you guys mentioned this.  I 
> remember back when I was imaging XP, I was trying to work out 
> specifically what I'd want to do to get gPXE/PXELINUX/COMBOOT to 
> simplify our imaging process which at the time was using a very clunky 
> XP live CD that took forever to boot up...  I ultimately ended up 
> booting DOS from iSCSI and imaging via INT13 with Ghost 8, which 
> worked pretty well.

That seems very familiar...  Until (for Windows) working out a 210 MB 
non-PE XP RAM disk image and including NIC and SATA drivers; then there 
was a definite gain from 32-bit network drivers.

> Still, while I was wrapping my head around the concepts I was trying 
> to exploit, I was browsing through all of these com32 modules in the 
> SYSLINUX package then hopped on IRC and said, "Hey guys, is there a 
> COM32 module for imaging disks?  Something like DD.c32?"

That seems interesting, and as H. Peter mentions, probably fairly 
straight-forward to implement for sector imaging.  FS manipulation would 
be a different story. :S

> While several people (you guys included I think) remarked that it was 
> an interesting idea, I never found anything...  Hence the Ghost 8 use :-D

Well if we [Syslinux users/enthusiasts] had a DD.C32 COMBOOT32 module 
that did something useful like write an image from the Syslinux 
filesystem (TFTP: hmm...) to a disk via INT 0x13, that might be a tiny 
start.  There might be a challenge if a RAID/SCSI adapter was a BEV 
device and if the user PXE-boots but if that prevents the adapter's ROM 
from establishing an INT 0x13 hook.  I guess there's one way to find out.

> I do think it would be really nifty to have a DVD with ISOLINUX that 
> boots to a menu and images all via COM32...   no HAL issues or 
> hardware compatibility issues, no need to wait for a "thick" protected 
> mode OS to load.  Making modern operating systems easier to deploy by 
> exploiting the ubiquity of the "modern" BIOS implementations has a 
> high geek-sexiness factor to it ;)

For Windows, HAL/kernel injection might require an FS driver (I'm 
thinking of NTFS) and write support.  A sneaky way might be to put magic 
in a BOOT.INI file with known contiguity and a known length, then 
overwrite it with a particular HAL/kernel choice...  What a hack.  But 
we don't know Windows XP Setup's logic for HAL/kernel choice (though 
perhaps we could guess).

With Linux, of course, it's possible (and easy) to get a minimal 
environment with just what you need for re-imaging.  There is a project 
called "DeployStudio"[1] whose PC support happens to use PXELINUX and 
Linux for re-imaging, but I believe the environment supports Windows 
images, as well.

There is definitely something nice about pre-OS control, where Syslinux 
and its wonderful shuffler can "get out of the way" and boot an OS after 
doing other useful things...  And of course UNDI+PXE and INT 0x13 are 
handy where one doesn't wish to manage tracking down and injecting 
drivers for a proper OS.

- Shao Miller

[1] http://www.deploystudio.com/Home.html