Syslinux - Dec 2008 - Custom MBR

Hi,

Is it possible to always load syslinux from whichever partition it?s installed
on, regardless of whether it?s active or not (and even if it?s a logical
partition), just like grub?

The MBR code that ships with syslinux (much like dos/windows default MBR) would
only boot the active primary partition. It would be nice if you could provide a
custom MBR such that one could set one byte in the MBR indicating which
partition should be booted (0,1,2,3 for primary/extended and 4,5,6,? for
logical) and install it in the sector 0. Thereafter, upon system restart,
instead of searching for active partitions, the MBR could would just load the
correct boot sector and execute it. The code to read each successive extended
partition table (in case of logical partitions) would need to be added, but I
see that there?s already some unused space available.

Is this possible to do this using just 440 bytes? If not, maybe, the CHS code
could be knocked off since most people use newer bios now-a-days?

Thanks,
YYZ

--On Friday, December 12, 2008 11:22:29 AM -0800 YYZ <yyz01 at yahoo.com> 
wrote:
> Hi,
>
> Is it possible to always load syslinux from whichever partition it?s
> installed on, regardless of whether it?s active or not (and even if
> it?s a logical partition), just like grub?
>
> The MBR code that ships with syslinux (much like dos/windows default MBR)
> would only boot the active primary partition. It would be nice if you
> could provide a custom MBR such that one could set one byte in the MBR
> indicating which partition should be booted (0,1,2,3 for primary/extended
> and 4,5,6,? for logical) and install it in the sector 0. Thereafter,
> upon system restart, instead of searching for active partitions, the MBR
> could would just load the correct boot sector and execute it.
So in other words, the MBR would boot a partition designated by data stored 
on the disk, but instead of using the standard mechanism for this, you'd 
have it use some new, nonstandard mechanism that nothing else supports.

Why?

> So in other words, the MBR would boot a partition designated by data stored
> on the disk, but instead of using the standard mechanism for this,
you'd
> have it use some new, nonstandard mechanism that nothing else supports.
> Why?
Which partition to boot is encoded within the MBR itself during the
installation.

There is nothing non-standard about this and this is not incompatible with any
other software (grub already does this). This ?standard? approach dates back to
the time when one had to rely solely on MBR code as boot manager and use fdisk
or similar tool while booted in one OS to switch to the other OS by activating
the other partition. With modern multi-boot managers, you can decide at boot
time which partition to boot and they don?t rely on the active flag in MBR at
all. The catch is that whenever you start your system, the control should
somehow get transferred to the boot manager wherever it resides (unused sectors
of track0, a dedicated boot partition, etc.). This is what I?m asking for ? I
would like to install syslinux on any partition of my choice and would like to
boot into syslinux regardless of which partition is active. From syslinux, I can
always boot any partition I want by loading its boot sector.