[libvirt] RE: Re: kvm-81: save / restore does not work - missing incoming stdio feature

[Daniel P. Berrange]

On Mon, Jan 19, 2009 at 07:20:07PM -0500, Mark Wagner wrote:
> Daniel P. Berrange wrote:
> >On Mon, Jan 19, 2009 at 01:53:48PM +0100, Daniel Schwager wrote:
> >>Hi Daniel,
> >>
> >>Charles Duffy (thanks Charles !) told me how to fix libvirt for using
> >>the
> >>new "-incoming" API - yust replace "stdio" with "exec:cat" ..
> >>
> >>Works like a charm,  tested with FC9, libvirt.0.5.1-2 and KVM-83
> >
> >Unfortunately things are not that simple. This will work for new KVM, but
> >break for older KVM which only supports 'stdio:', 'file://' and 'tcp://'
> >for incoming migration. There needs to be some kind of version / support
> >check here to decide which syntax to use.
> >
> >Daniel
> 
> So are there guidelines posted somewhere for the backwards compatibility
> that must be maintained ?

The code is written to work with all QEMU >= 0.8.2, which includes
basically all KVM (bugs aside). In this case we've long supported
the existing KVM migrate syntax and cannot break our existing users
of it.

> If you try to support every older version of each hypervisor / product
> you will quickly have a test matrix that will make it darn near impossible
> to actually release a new version of libvirt w/o a tremendously long test
> cycle.

This is why we have an extensive test suite to cover generation of
command line arguments & explicitly test these kind of scenarios
where one version changes the command line syntax.

Daniel
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