svn commit: r185562 - head/sys/boot/i386/boot0

[John Baldwin]

On Tuesday 02 December 2008 09:57:48 am Luigi Rizzo wrote:
> Author: luigi
> Date: Tue Dec  2 14:57:48 2008
> New Revision: 185562
> URL: http://svn.freebsd.org/changeset/base/185562
> 
> Log:
>   This commits brings in a lot of documentation and some enhancement
>   of the boot0.S code, with a number of compile-time selectable options,
>   the most interesting one being the ability to select PXE booting.
>   
>   The code is completely compatible with the previous one, and with
>   the boot0cfg program. Even the actual code is largely unmodified,
>   with only minor rearrangements or fixes to make room for the new
>   features.
>   
>   The behaviour of the standard build differs from the previous
>   version in the following, minor things:
>   
>   + 'noupdate' is the default, which means the code does not
>     write back the selection to disk. You can enable the feature
>     at runtime with boot0cfg, or changing the flags in the Makefile.
>   
>   + a drive number of 0x00 (floppy, or USB in floppy emulation) is
>     now accepted as valid. Previously, it was overridden with 0x80,
>     meaning that the partition table coming from the media was
>     used to access sectors on a possibly different media.
>     You can revert to the previous mode building with -DCHECK_DRIVE,
>     and you can always use the 'setdrv' option in boot0cfg

I would flip this back to the original default.  This was there to workaround 
certain broken BIOSes that incorrectly specified a drive of 0x00 when you 
booted from the hard drive (at least according to the comments).  On such 
systems they will now fail to boot.  MBR's aren't really supported on 
floppies, so you shouldn't ever have a legitmate %dl of 0x00.  In the rare 
case that you do you could use the 'setdrv' option to boot0cfg.

-- 
John Baldwin