On Fri, Sep 25, 2009 at 02:27:23PM +0100, Daniel P. Berrange wrote:
> On Tue, Sep 22, 2009 at 02:43:20PM +0200, Daniel Veillard wrote:
> > [ Sending again due to mail output problems ]
> >
> > On Thu, Sep 17, 2009 at 06:25:01PM +0100, Daniel P. Berrange wrote:
> > > Introduces several new public API options for migration
> > >
> > > - VIR_MIGRATE_PEER2PEER: With this flag the client only
> > > invokes the virDomainMigratePerform method, expecting
> > > the source host driver to do whatever is required to
> > > complete the entire migration process.
> > > - VIR_MIGRATE_TUNNELLED: With this flag the actual data
> > > for migration will be tunnelled over the libvirtd RPC
> > > channel. This requires that VIR_MIGRATE_PEER2PEER is
> > > also set.
> >
> > Hum, I would rather add that when entering libvirt.c entry point
> > set explicitely VIR_MIGRATE_PEER2PEER if VIR_MIGRATE_TUNNELLED is asked
> > for, that's an internal impl. detail.
>
> I didn't do that, because I wanted to leave open the option
> to supporting TUNNELLED mode, without PEER2PEER mode. I
> don't really know what that would look like, but I think it
> is better future proofing to not presume one implies the other.
Okay, let's go for this.
> > > - virDomainMigrateToURI: This is variant of the existing
> > > virDomainMigrate method which can be used when the
> > > VIR_MIGRATE_PEER2PEER flag is set. The benefit of this
> > > method is that no virConnectPtr object is required for
> > > the destination host, only a destination URI.
> >
> > Sounds good if we have proper error handling. I'm also wondering
> > how authentification and access control can be handled in that mode,
> > the normal method of access somehow garantee that the user credentials
> > can be checked in some ways, but if it's direct daemon to daemon
> > talking how can this be performed ?
>
> The client application authenticates with the source libvirtd
> in the normal manner. The source libvirtd will authenticate
> with the destination libvirtd directly.
>
> The client application will not be authenticating with the
> destination libvirtd itself.
>
> While this may sound like a security issue, I don't think it
> really is. It is more of an authorization problem - eg the
> admin needs to declare somewhere which libvirtd instances
> are allowed to migrate guests between then. This authorization
> problem is really outside the scope of the client application
> or our public app API
Okay, as soon as you want to allow automatic migrations that
will be considered normal.
> > >
> > > +int virDomainMigrateToURI (virDomainPtr domain, const char *duri,
> > > + unsigned long flags, const char *dname,
> > > + unsigned long bandwidth);
> > > +
> >
> > s/duri/dest/ or target, the fact it's a connection URI should be made
> > obvious in the function comment.
>
> Yep, the function comment later only clearly describes what URIs are
> acceptable.
>
> > [...]
> > > + } else {
> > > + if (flags & VIR_MIGRATE_TUNNELLED) {
> > > + virLibConnError(domain->conn, VIR_ERR_OPERATION_INVALID,
> > > + _("cannot perform tunnelled migration without using peer2peer flag"));
> > > + goto error;
> > > + }
> >
> > I don't really agree, we should just or the flag and hide this from
> > the API user.
>
> I really did want to leave open the option of relaxing this restriction
> in the future, and thus didn't want to automatically set the PEER2PEER
> flag - once its set we can never unset it in the future.
>
> > > +
> > > +
> > > /*
> > > * Not for public use. This function is part of the internal
> > > * implementation of migration in the remote case.
> > > diff --git a/src/libvirt_internal.h b/src/libvirt_internal.h
> > > index 5913798..5f1a7fe 100644
> > > --- a/src/libvirt_internal.h
> > > +++ b/src/libvirt_internal.h
> > > @@ -17,6 +17,7 @@
> > > * License along with this library; if not, write to the Free Software
> > > * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
> > > *
> > > + * NB This file is (secret) ABI sensitive. Append only
> >
> > Huh ???
>
> The methods here are encoded in the wire protocol ABI,
> but not included in the public libvirt.h header. Hence
> they are ABI sensitive, but secret & thus append only
> like the rest of our API
>
> > > diff --git a/src/xen_unified.c b/src/xen_unified.c
> > > index dfa9ca5..954b187 100644
> > > --- a/src/xen_unified.c
> > > +++ b/src/xen_unified.c
> > > @@ -455,8 +455,11 @@ static int
> > > xenUnifiedSupportsFeature (virConnectPtr conn ATTRIBUTE_UNUSED, int feature)
> > > {
> > > switch (feature) {
> > > - case VIR_DRV_FEATURE_MIGRATION_V1: return 1;
> > > - default: return 0;
> > > + case VIR_DRV_FEATURE_MIGRATION_V1:
> > > + case VIR_DRV_FEATURE_MIGRATION_P2P:
> > > + return 1;
> > > + default:
> > > + return 0;
> > > }
> > > }
> > >
> > > diff --git a/src/xend_internal.c b/src/xend_internal.c
> > > index 7f55116..da5c039 100644
> > > --- a/src/xend_internal.c
> > > +++ b/src/xend_internal.c
> > > @@ -4400,6 +4400,12 @@ xenDaemonDomainMigratePerform (virDomainPtr domain,
> > > strcpy (live, "1");
> > > flags &= ~VIR_MIGRATE_LIVE;
> > > }
> > > + /* Trivially support this in Xen, since XenD on dest is always
> > > + * ready to accept incoming migration */
> > > + if ((flags & VIR_MIGRATE_PEER2PEER)) {
> > > + flags &= ~VIR_MIGRATE_PEER2PEER;
> > > + }
> > > + /* XXX we could easily do tunnelled migration too if we want to */
> > > if (flags != 0) {
> > > virXendError (conn, VIR_ERR_NO_SUPPORT,
> > > "%s", _("xenDaemonDomainMigrate: unsupported flag"));
> >
> > Sounds and looks good to me, with the small caveat of the required
> > VIR_MIGRATE_PEER2PEER flag and making sure it would work later with
> > QEmu/KVM before commiting this.
> >
> > I must admit peer-2-peer left me a bit puzzled at the beginning
> > it wasn't obvious what kind of transfer it actually meant. Only de
> > the documentation clarified it but I have no better suggestion :-)
> > "direct" maybe ...
>
> I called it peer-2-peer, because the 2 libvirtd instances are talking
> to each other p2p, rather than having all communcation go via
> the client application.
it's just that p2p raises the idea of a mesh of machines in my mind
and I'm probably not the only one :-) No problem !
ACK
Daniel
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Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/
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