[syslinux] memdisk possible bug

H. Peter Anvin hpa at zytor.com
Wed Aug 28 14:13:41 PDT 2002

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.


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