[libvirt-users] blockcopy for libvirt and version compatibility

[Eric Blake]

On 12/20/2013 11:45 AM, Mark Trinh wrote:
> I'm currently running:
> virsh --version
> 1.0.2
> 
> libvirtd --version
> libvirtd (libvirt) 1.0.2
> 
> I have a couple questions.
> 
> 1. Can I upgrade my libvirt.so version to use with an older libvirtd?  In
> other words, does the versions of libvirt and libvirtd need to be in lock
> step?

No, they do not have to be in lockstep.  libvirt.so communicates to a
local libvirtd the same way it communicates to a remote machine, and we
took great care in the design to ensure that things error out nicely if
the libvirt.so client is newer than the remote server; conversely, if
the client is older, the changes have always been back-compat so that a
newer server will always talk to the client correctly (although the
client being older means that you can't take full advantage of the server).

> 
> 
> 2. I'm able to use virsh blockcopy, but I want to do it programmatically
> via C.  I looked through the API and was not able to see any references to
> that.  I did see mention of virDomainBlockCopy on the TIP of the git
> repository, but no other references to it.

The source code to virsh shows the APIs that we used; this is a good
starting point for any other C binding, and also for any other language
binding if you can map the C bindings over to your language bindings.
In particular, tools/virsh-domain.c:cmdBlockCopy() is currently
implemented atop the virDomainBlockRebase() API call with the
VIR_DOMAIN_BLOCK_REBASE_COPY flag (but the door is open to also
implement it atop a newer more-powerful virDomainBlockCopy() once we
start targetting some of qemu 1.7 or 2.0's newer features).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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