Useful additional functions for libvirt

["Richard W.M. Jones" <rjones@xxxxxxxxxx>]

[I haven't implemented any of these yet, but if people think they're a 
good idea, or at least not an actively bad idea, then I'll post a patch.]

virDomainGetConnection
virNetworkGetConnection

  Purpose: Given a virDomainPtr or virNetworkPtr, obtain the virConnectPtr.

  Reason: All the language bindings to libvirt need to keep the 
virConnectPtr separately alongside the virDomain/NetworkPtr, in the main 
so that they can query if an error has happened from inside some deep 
call.  This is wasteful since the connection pointer is already included 
in the virDomain or virNetwork structure, so we should just provide a 
call to get it.

virConnectGetHostname
virConnectGetTransport
virConnectGetURI

  Purpose: Get the remote hostname, remote transport (tls, ssh, etc.), 
and URI.

  Reason: In virt-manager it would be nice to display the remote 
hostname.  However doing this at the moment requires parsing the 
connection URI, which is duplicated code and also significantly 
complicated.  Instead, allow the remote driver to just give us this 
information, and in non-remote cases default to something sensible.  The 
case for the other two calls is weaker, but it might still be useful to 
know something about the security of the actual transport selected, and 
also to not have to keep the URI around with the connection (we might 
also canonicalise the transport for the user).

virConnectPing

  Purpose: "Ping" the hypervisor to see if its up.

  Reason: Since we now support remote connections, there is a much more 
signficant chance that we will lose contact with the hypervisor, for 
example if the host goes down.  This will do some very minimal operation 
to cheaply test whether the hypervisor can be contacted.  Of course we 
could do something like 'virConnectNumOfDomains', but it's not clear to 
me that this operation would always be cheap (eg. if we had to implement 
it through xend).

Rich.

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