Re: [Qemu-devel] [patch] non-blocking disk IO

[John Coiner <jcoiner@stanfordalumni.org>]

Brad Campbell wrote:
> With this patch qemu will not boot the qcow files but will boot the base 
> images (I copy them and then try to boot to test). As soon as I patch -R 
> && make, qemu will boot the qcow files no problems..
> 
> Let me clarify that..
> qemu-img create -f qcow xp.img 4G
> qemu -cdrom xp.iso -hda xp.img -boot d (Install XP from scratch)
> qemu-img create -b xp.img -f qcow xp2.img
> qemu -hda xp2.img
> 
> This gives me an invalid hard disk error. If I revert the patch I can 
> boot from xp2.img with no issues. With or without the patch I can boot 
> from xp.img.
> 
> I have tried installing XP with and without the patch and that works fine..
> 
> Regards,
> Brad

Thanks for the report. I was able to reproduce this.

The problem was due to missing Makefile dependencies. The patch modifies 
'block_int.h', which is #included in several '.c' files. The file 
'block.c' recompiled at 'make' time, but 'block-qcow.c' didn't. The 
resulting '.o' files had different opinions about what a 
BlockDriverState struct looked like, which broke the qcow code.

Unaware of this, I added a printf to 'block-qcow.c', and the printf 
fixed the problem! The man page for printf doesn't mention this... and 
then I was enlightened. :P

To be safe, try a 'make clean ; make install' and you should be all 
good. Let me know if not.

-- John