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

[Mark Wagner]

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 ?

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.

Doesn't it make more sense to just put a stake in the ground and say version
X.Y of libvirt will only work with version A.B of (insert your favorite
hypervisor here)

Perhaps you keep multiple branches of libvirt "mostly" aligned with a
generation of hypervisor and only back port the critical changes from the
head.

-mark