[et-mgmt-tools] 'arch' in image XML

[Daniel P. Berrange]

On Fri, Jul 04, 2008 at 04:29:16PM +0100, John Levon wrote:
> 
> What is the purpose of this option exactly? From a quick look it only
> seems to be used to select which RPMs to use when doing an install. Is
> there some extra semantics to it?

The 'arch' is refering to the architecture of the guest OS kernel, eg one
of i686, x86_64, ppc, sparc, etc, etc.  The 'virsh capabilities' XML for
a hypervisor driver declares what architectures the driver supports and
thus allows virt-image to determine whether it is capable of executing
the OS being requested. Some drivers like QEMU supported a whole suite
of architectures by virtue of doing emulation, others only support matching
host arch (eg Xen).

Basically the idea behind the virt-image XML in general is to declare the
requirements for its execution. This is matched  up with capabilities of
hosts.  So things which are deployment specific are not included in the
virt-image XML. As an example we declare the filessytem format (eg raw
or qcow) but don't declare the full path or driver (eg tap vs phy vs file)
since those are deployment details

> Another question: it seems that virt-image always insists on an install
> step. What was the intent behind using virt-convert (nee virt-unpack)
> with virt-image output, in this case?

I'm not sure what you mean by 'install step' here. The idea is that the
disk image associated with the XML doc contains a pre-installed operating
system (or 'appliance' in marketing buzzword bingo), so there isn't
really any install step. We're merely validating requirements against
capabilities, and configuring deployment specific details.

The idea behind the virt-image/virt-unpack  association is that the 
virt-image XML defines a portable format for 'appliance' metadata
information (cf OVF) but not the distribution format (ZIP, tar.gz,
etc). So the virt-pack tool would doing bundling into ZIP files. 

Regards,
Daniel
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