Xen Domain Configuration file issue

[Elliott Mitchell <ehem+undef@xxxxxxx>]

I've been considering weaknesses with the `xendomains` script and how one
might address them.  In the process I've run head-on into some rather odd
design choices with Xen domain configuration handling.

The obvious place to dump domain start/stop configuration information is
into the domain.cfg files themselves.  One favored way to do this is to
stick the configuration information into comment sections.  This has
advantages and disadvantages.  Another way is if the file format syntax
allows it, simply stick the information into the main portion of the
files.

This lead to two observations.  First, domain.cfg files can have
arbitrary extra sections added and `xl create` doesn't complain about
unknown sections.  Second, unrecognized settings in domain.cfg files are
*completely* ignored.  Having these two characteristics combined is
extremely odd.

Complaining about unknown settings is the most common UI choice.  This
alerts users they've misconfigured things.  Sticking "colonel=XEN_EFI.fd"
is likely a configuration error.

On the flip side, since `xenstored` can hold more or less arbitrary
values, depositing unrecognized options there also seems reasonable.

Might the best behavior be for `xl create` to default to producing an
error if unrecognized options are found?  Then add a "-U" option to
`xl create` which places unrecognized options into the XenStore?

A replacement for `xendomains` script could then use `xl create -U` to
load domain.cfg files.  Configuration options it recognized could then be
consumed and if unrecognized options were left it would then complain.

Either approach is going to need some work on libxlutil.


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