[coreboot] questions about "QEMU Build Tutorial"

Myles Watson mylesgw at gmail.com
Fri May 2 17:12:46 CEST 2008

> http://www.coreboot.org/QEMU_Build_Tutorial
> My test versions:
> coreboot v2- revision 3275
> filo - v0.5- revision 45
> qemu- v0.9.1
> I followed steps described in that wiki page, and I got:
> "
>   1 init_drive: Probing for hda
>   2 init_drive: LBA mode, sectors=409600
>   3 init_drive: LBA48 mode, sectors=409600
>   4 init_drive: Init device params... ok
>   5 hda: LBA48 209MB: QEMU HARDDISK
>   6 init_controller: MASTER CHECK: master yes
>   7 init_controller: /*slave */ -- drive is 0
>   8 open_pc_partition: pc partition magic number not found
> "
> Have I missed anything? Seems 'qemu-create img'  not produce the correct
> image?
> here is my xxd result:
> $ head disk.img | xxd | vi -
> "
>     1 0000000: 0000 0000 0000 0000 0000 0000 0000 0000  ................
>     2 0000010: 0000 0000 0000 0000 0000 0000 0000 0000  ................

I don't know how this tutorial is supposed to work.  Disk.img is supposed to
be the whole hard drive, and you're treating it like a partition with
mkfs.ext2.  Here is something that should work:

1. Create the raw image like it says in the tutorial
2. Boot QEMU with a rescue disk from your favorite OS
3. Run fdisk and create a single partition on the drive that takes up the
whole drive
4. Quit and write the partition to disk
5. Run mkfs.ext2fs on that partition
6. Exit QEMU

You now have a partitioned disk with an ext2 fs.  You could have put in a
second partition for swap while you were there, but lets keep this simple.

Now you have a hard drive image with a partition and you need to mount that
partition to copy the files you want.


mount -o loop,skip=32256 disk.img /mnt/rootfs 

(Thanks to http://wiki.archlinux.org/index.php/Qemu)

and continue the tutorial.

To restate:  The problem is that when you run mkfs.ext2 on the disk.img,
you're formatting it as if it were a partition, not a drive, and you don't
have a valid partition table.

There are many other ways to get this done, I think this is the easiest.  If
you can't get it to work you might also try:

1. Stealing the first 32256 bytes (63 * 512B sectors) from a known good
image of the same size and concatenating it to the front of a partition like
you made in the tutorial (- 63 sectors)

Hope that helps,


PS The page I referenced above has other advanced tips too.

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