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Re: booting from disk image

From: Jochen Hoenicke
Subject: Re: booting from disk image
Date: Fri, 10 Nov 2000 15:18:23 +0100 (MET)

On Nov 10, Vesa Jääskeläinen wrote:
> On Fri, 10 Nov 2000, Albert Max Lai wrote:
> > Ideally, I'd like to be able to boot an image by dd'ing to read in the
> > bootable dos floppy. This seems to be close but not quite there. I am
> > able to chainload the boot loader. However, after the boot loader
> > loads, the subsequent I/O calls look at the floppy drive. What would
> > be nice is to map the I/O calls to the image that was just
> > bootstrapped. Are there any reasons why this can't be done? I know
> > that etherboot and netboot are able to do this with netboot images
> > (which seem to have some assembly code to patch the bios at the
> > beginning of the images.)
> maybe this could be done by doing it sameway as CD-boot floppy 
> emulation is done. (load image to memory and call couple of BIOS calls)

You have to provide a ramdisk driver that simulates a floppy from a
ram image.  There is a program mknbi that creates netboot images from
floppy disks.  This netboot image contains the floppy contents and a
ramdisk driver.

There are two possible ways:  

1: Add netboot image support to grub.  All that has to be done is
   to load the different chunks of the netboot images to fixed
   addresses and jump to it.  The difficult part is, that netboot
   only reserves a small chunk in low memory for the boot loader.  You
   have to handle the high memory in an intelligent way, so you can
   temporarily store the part of the image that would overwrite grub
   in a free chunk of high memory.

2: Make a program similar to mknbi that produces multiboot
   compliant images.  One can probably reuse the ramdisk driver.


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