[libvirt] Using external ceph.conf for RBD pools and disks

[Eric Blake]

On 11/01/2013 08:31 AM, Michael Chapman wrote:
> On Fri, 1 Nov 2013, Daniel P. Berrange wrote:
>> We have always taken the position that we do not want to rely on host
>> configuration in this way. The goal of the XML configs is that they
>> fully describe the functional setup of the resource in question. This
>> is to ensure that if you put the same XML config on two different hosts
>> you can be sure that they will operate in the same way. If you leave out
>> a bunch of config information and rely on the host ceph.conf file, then
>> you can no longer ever be sure if two hosts are configured the same way
>> with libvirt.
> 
> I suspected that might be the case -- half the reason I sent my email,
> really!
> 
> If it's desireable to not rely on any host configuration at all, should
> we be explicitly be passing conf=/dev/null to QEMU when setting up a RBD
> device?

Sure sounds like it to me.

> As I mentioned before, without that QEMU will implicitly try to
> find a system ceph.conf file using a built-in librados search path.
> Would this actually be backwards-incompatible change given it was never
> documented by libvirt?

The old behavior is broken, so we can bill this as a bug fix
(previously, qemu would behave differently than what the XML defined,
which is not supposed to happen) rather than a backwards-incompatible
change.  Can you propose a patch in time for inclusion in 1.1.4?

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

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