Syslinux - Aug 2002 - memdisk possible bug

I just wanted to pass on some information regarding the behavior of memdisk 
that I was observing.  I have been trying to set up pxelinux/memdisk on a 
network with a series of machines.  I am trying to boot a 2.88MB DOS image.  
This image worked fine on all but one of our machines.  The machine had a usb 
floppy device.  Now the machine would boot the DOS image fine if the usb 
floppy device was properly attached to the machine.  However, if the USB 
floppy was not attached to the machine when memdisk would boot the image it 
would return with the "Non-system disk or disk error" message.

On further investigation it looks like this could be caused by the mbr on the 
dos image calling the drive reset subfunction.  It didn't look like this 
subfunction was hooked by memdisk and so it is relying on the floppy drive 
connected to the machine.

We modified the MBR of the DOS image to skip this drive reset call and are now 
able to boot the DOS image without the floppy drive attached to the machine.  
I am curious if you have observed or heard about this behavior before?

Regards,
Brian Jaeger

brjaeger wrote:
> I just wanted to pass on some information regarding the behavior of memdisk
> that I was observing.  I have been trying to set up pxelinux/memdisk on a 
> network with a series of machines.  I am trying to boot a 2.88MB DOS image.
> This image worked fine on all but one of our machines.  The machine had a
usb
> floppy device.  Now the machine would boot the DOS image fine if the usb 
> floppy device was properly attached to the machine.  However, if the USB 
> floppy was not attached to the machine when memdisk would boot the image it
> would return with the "Non-system disk or disk error" message.
> 
> On further investigation it looks like this could be caused by the mbr on
the
> dos image calling the drive reset subfunction.  It didn't look like
this
> subfunction was hooked by memdisk and so it is relying on the floppy drive 
> connected to the machine.
> 
> We modified the MBR of the DOS image to skip this drive reset call and are
now
> able to boot the DOS image without the floppy drive attached to the
machine.
> I am curious if you have observed or heard about this behavior before?
> 
I have heard about this; unfortunately there is preciously little that
can be done about this.  The reset calls aren't specific to a drive, but
to a drive *type* (floppy vs hard disk), so I have to chain back to the
BIOS to make sure all drives get reset.

I could make it ignore errors, but that would be potentially dangerous too.

	-hpa