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Re: [Qemu-discuss] QEMU ARM test image: modifying arm_root.img

From: Jakob Bohm
Subject: Re: [Qemu-discuss] QEMU ARM test image: modifying arm_root.img
Date: Tue, 21 Jan 2014 16:40:35 +0100
User-agent: Mozilla/5.0 (Windows NT 5.2; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0

On 1/11/2014 2:18 PM, jmf list wrote:

I'm trying to modify the initrd (arm_root.img) for the QEMU ARM test image (http://wiki.qemu.org/Testing#QEMU_disk_images). I am able to extract it using gunzip and cpio, but I can't recreate the archive so that the VM will boot properly (I get a kernel panic). I believe my problem is with how I am invoking cpio: if I simply gunzip/zip the existing initrd cpio archive the VM boots properly, but if I extract and re-create the cpio archive (without modification) the boot fails. So, I was wondering: could you tell me what cpio options you used to create the arm_root.img archive?

Pardon for any obvious issues I might be overlooking. I've never delved into initrd before; I am actually just trying to set up automated testing for some ARM code that was contributed to one of my open source projects. I am a bit far down the rabbit hole, I'm afraid. I've googled and searched the mailing lists but wasn't able to find a solution to my problem.

Thanks for all the great work regardless,


Here is how I am extracting the archive, after gunzip:
$ cpio -i -vd -H newc < ../arm_root

Here is how I am creating it, before gzipping it:
$ rm ../arm_root
$ find . -depth -print | cpio -o --format=newc > ../arm_root

Hmm, have you tried without "-depth" ?, I am not sure the kernel can
successfully unpack rootfs files to a directory which has not yet
been created
Here is a snippet from the console when the kernel panic occurs:
802.1Q VLAN Support v1.8 Ben Greear <address@hidden <mailto:address@hidden>> All bugs added by David S. Miller <address@hidden <mailto:address@hidden>>
VFP support v0.3: implementor 41 architecture 1 part 10 variant 9 rev 0
Root-NFS: No NFS server available, giving up.
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "<NULL>" or unknown-block(2,0)
Please append a correct "root=" boot option
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)


Jakob Bohm, CIO, Partner, WiseMo A/S.  http://www.wisemo.com
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