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Re: [Libvir] Remote daemon & virDomainFree interaction

On Tue, Jul 24, 2007 at 03:41:32AM +0100, Daniel P. Berrange wrote:
> On Tue, Jul 24, 2007 at 02:38:40AM +0100, Daniel P. Berrange wrote:
> > In looking at a problem with domain object cleanup in virt-manager I came 
> > across a problem in the remote driver, well the internal driver API itself
> > actually. Specifically the implmenetation of virDomainFree() never calls
> > into the driver API - it simply uses virFreeDomain() release the memory
> > associated with the virDomainPtr object. 
> > 
> > Couple this with the remote driver though, and virDomainPtr objects in the
> > remote daemon never get released, because the virDomainFree call is never
> > propagated over the wire to the server.
> > 
> > Its quite easy to see this in practice. Simply add a printf to the impl
> > of virDomainLookupByName which prints out the ref count. Then run either
> > virsh or virt-manager for a while
> > 
> >   Get info QEMUGuest1 69 c7a5fdbd-edaf-9455-926a-d65c16db1809
> >   Get info QEMUGuest1 70 c7a5fdbd-edaf-9455-926a-d65c16db1809
> >   Get info QEMUGuest1 71 c7a5fdbd-edaf-9455-926a-d65c16db1809
> > 
> > We need to make virDomainFree call into the driver API, and also make sure
> > that the remote driver implements it.
> Actually I was wrong in this. It is not just that the virDomainLookupByName 
> which cause virDomainPtr objects to be allocated. Every single API call into
> the daemon which uses get_nonnull_domain() causes a virDomainPtr object
> to have its ref count increased. So we don't want to pass the virDomainFree
> API through the driver API at all.
> Instead in the server side of the remote driver, any API call which returns 
> a virDomainPtr *and* any call which accepts a virDomainPtr needs to have a
> corresponding call to virDomainFree to reduce the ref-count in all of its
> exit paths. The same goes for virNetwork objects & its calls.
> I'm attaching a patch which I believe hits all the neccessary codepaths.
> With a few prints in virGetDomain, I can see the refcount correctly being
> incremented & decremented per API call, rather than growing without bound.

  Dohh, giant memory leak ! Good catch !
  A couple more may be needed and not in the list for the upcoming 
DomainMigrate entry points, 



Red Hat Virtualization group http://redhat.com/virtualization/
Daniel Veillard      | virtualization library  http://libvirt.org/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine  http://rpmfind.net/

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