[syslinux] Re: Problem with memdisk and Free FDISK

Brian E. Reifsnyder reifsnyderb at mindspring.com
Sat Jul 5 17:02:14 PDT 2003


> Sorry for the cross-post, but I do not know whether this is a bug in
> Free FDISK, memdisk, or neither.
> It then exits with status 5.
> However, if I do:
>     set FFD_VERSION=6
>     fdisk /info
> ...it correctly displays the partition table for the virtual drive.

This indicates that the problem is with the BIOS (virtual BIOS?).  When
FFD_VERSION=6 is set, Free FDISK only accesses the hard disks via legacy
interrupt 0x13.  Support for hard disks > 8GB is disabled.

> If I then do "fdisk /info 2", it displays the partition table for the
> physical disk, but only the first 8 gigabytes (not surprisingly).  So
> setting FFD_VERSION=6 is only a partial workaround, because sometimes
> I need to partition the entire drive.
> Browsing the fdisk source code, I suspect I could work around this
> problem by setting "EMULATE_DISK=1", but since my copy of fdisk.exe
> does not have debugging enabled, this option is not recognized.

Nope.  The EMULATE_DISK function only creates a fake simulation of a hard
disk in the buffers used by Free FDISK.  This "emulated drive" is used in
order to debug a partitioning issue when a test hard disk is not available.
(i.e.  I originally used it when I re-wrote Free FDISK on a laptop....no
test hard drive was available.)  Over 90% of all partitioning problems could
be resolved without another hard drive once the functions to physically
access the hard disk were working.

> Questions:
>   1) Where can I obtain a copy of fdisk.exe with DEBUG enabled?  (Do I
>      have to purchase Borland C++ and build it myself?)

If you would like, I could compile one for you.

>   2) This appears to be some sort of bug with INT13 extensions.  Is it
>      most likely a bug in fdisk, memdisk, or my BIOS?  Just curious.

My first thought would be that it is in memdisk.  But, I am not familiar
with PXELINUX.  My guess, from your description, is that you are attempting
to run Free FDISK from within an emulated DOS machine (DOS Emu?  Bochs?).

>   3) What can I do to help fix this?

I suppose that it would be possible to add the capability to selectively
support interupt 0x13 extensions.  For example, change Free FDISK such that
you could instruct it to use interrupt 0x13 extensions with disk 1 but not
with disk 2.  I don't think it would be too hard to do this.  What do you


Brian Reifsnyder
reifsnyderb at mindspring.com

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