[ARMedslack] qemu raw image partition offset calculation

[Davide]

Not sure what you're not digesting but if I can help make things more clear I will ... just tell me what's not so clear.

I wanted to do hings in the other direction: from a miniroot fs image (or my microroot system) to a qemu disk image so that I can do testing without having the dockstar around in the office.

I had trouble starting from a blank disk image created with the qemu-img 
tool and populating it with what I wanted without going trough any installation. 

Regards
David
--- Lun 9/5/11, Stuart Winter <m-lists at biscuit.org.uk> ha scritto:

> Da: Stuart Winter <m-lists at biscuit.org.uk>
> Oggetto: Re: [ARMedslack] qemu raw image partition offset calculation
> A: "Slackware ARM port" <armedslack at lists.armedslack.org>
> Data: Lunedì 9 maggio 2011, 08:22
> 
> Yep this is all good stuff.
> ftp://ftp.armedslack.org/armedslack/armedslack-devtools/sheevaplug/qemu-to-sheeva.txt
> 
> I haven't digested everything you've put down but the above
> URL is how I
> bootstrapped armedslack onto the sheevaplug -- converting a
> qemu
> installation back to a bootable hard disk.
> 
> On Fri, 6 May 2011, Davide wrote:
> 
> > It's often handy to know the physical offset of the
> first partition of a qemu raw disk image.
> > If you do not use raw images you can convert it to raw
> ... do what you need and convert it back.
> > I've not yet found a reliable way of mounting non raw
> images from ordinary linux OS.
> > You can use this trick to populate a qemu disk image
> with an armedslack miniroot sistem image directky from your
> linux x86 box.
> >
> > Unfortunatelly the offset depends on the geometry of
> the disk image.
> > Here's how I guess the correct offset:
> >
> > the firs block of the firs partition is located in:
> > the first sector of the second track
> > it will be located in <sectors per track> * 512
> >
> > example:
> > fdisk -l qemu_hdu.raw
> > Disk qemu_hdu.raw: 0 MB, 0 bytes
> > 5 heads, 54 sectors/track, 0 cylinders
> > Units = cylinders of 270 * 512 = 138240 bytes
> > Sector size (logical/physical): 512 bytes / 512 bytes
> > I/O size (minimum/optimal): 512 bytes / 512 bytes
> > Disk identifier: 0x00000000
> >
> >        Device Boot   
>   Start         End 
>     Blocks   Id  System
> > qemu_hdu.raw1           
>    1        1016 
>     137133   83  Linux
> >
> > the firs partition of this image (qemu_hdu.raw1) will
> begin:
> > (54 * 512) = 27648
> >
> >
> >
> > Ho do you go about creating the filesystem from the
> x86 linux box:
> >
> > What folows creates an ext2 filesystem on the first
> partition of the
> > qemu raw disk image and subsequently mount is so that
> you can polulate it.
> >
> > # losetup -o <previously calculated offset>
> /dev/loop0  qemu_hdu.raw
> > # mke2fs -b 4096 -i 16384 -m 1 -L surap_root
> /dev/loop0
> > # mount /dev/loop0 /mnt/tmp/
> >
> > Hope this helps
> > David
> >
> >
> > _______________________________________________
> > ARMedslack mailing list
> > ARMedslack at lists.armedslack.org
> > http://lists.armedslack.org/mailman/listinfo/armedslack
> >
> 
> -- 
> Stuart Winter
> Slackware ARM: www.armedslack.org
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