[Libvir] RFC 'xen like scripts'

[Daniel P. Berrange]

On Mon, May 05, 2008 at 10:15:19PM +0200, Stefan de Konink wrote:
> Currently in Xen it is very easy to prototype a certain function related
> to binding host hardware to virtual hardware. The script gets an argument,
> can do anything it wants and returns another argument, or better: writes
> it to the xen-store.
> 
> I was reviewing the current iSCSI code, because I cannot switch to libvirt
> with the current implementation. (From OpenSolaris, I migrated to NetApp.)
> 
> 
> So I pose a simple request: would anyone be able to create a xen-like
> storage backend that in principle passes the URI to a script (that runs as
> a fork) this script sets for example an envirionment variable or text
> output, the code uses this envirionment variable as path to the storage
> area. And a great prototypable system has been created.

This kind of plugin functionality is delibrately not exposed in libvirt. 
The XML configuration for a guest is intended to provide a description of 
a guest with guarenteed semantics which is portable to any machine using
libvirt. If we were to enable arbitrary admin provided scripts on the
backend the semantics could not longer be guarenteed.

> It could be a question by some: 'why doesn't he write a simple
> implementation in C?' basically: I'll will do this, no worries about that
> one, but I would like to be able to prototype my programs first.

While I understand your desire to be able to prototype things quickly
I don't want to expose a generic scriptable plugin in the libvirt backend

BTW, if you want any hints / advise / help with making the iSCSI stuff work
on OpenSolaris let me know. I'm assuming the iSCSI admin tools on Linux are
rather differnent in calling conventions, but the general principles of
the Linux impl should still apply.

Dan.
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