Re: [Qemu-devel] Citrix VHD implementation

[Daniel P. Berrange]

On Mon, Mar 02, 2009 at 11:41:25AM +0000, Stefano Stabellini wrote:
> Philipp Schmid wrote:
> 
> > Hi,
> > 
> > as some of you might know, citrix has open sourced the library they  
> > use to read and write to VHD disk images.
> > 
> > I'm trying to implementing a block-vhd driver on top of libvhd, but my  
> > C knowledge is very limited as I haven't written any code in C for a  
> > long time.
> > 
> > What I already have is a git repo with the libvhd code extracted from  
> > the xen-unstable tree with the blocktap2 patches applied.
> > libvhd also comes with vhd-util, a utility to create and modify vhd  
> > images.
> > I have only tried to compile it on ubuntu 8.10, so it might not work  
> > on your system.
> > 
> > The git repo is hosted on github: 
> > http://github.com/schmidp/libvhd/tree/master
> > 
> > Are there any docs about how to implement a block driver for qemu?
> > As far as I have seen from the qemu code, block_int.h defines the  
> > interface and you register your driver in block.c, but that is all  
> > I've found out so far.
> > 
> > I will try to implement a synchrones driver first as it seems more  
> > simple...
> 
> Why don't you just use blktap2 to create a raw device from the vhd file
> and then open the raw device in qemu?

There is no blktap unless you have Xen userspace and the Xen kernel
installed. Having a native vhd QEMU driver would avoid the need to
install Xen just to use VHD format images under non-Xen QEMU/KVM.

Daniel
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