This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] A migration framework for external devices

To: "Mike D. Day" <ncmike@xxxxxxxxxx>
Subject: Re: [Xen-devel] A migration framework for external devices
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Thu, 09 Feb 2006 12:45:11 -0600
Cc: "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Stefan Berger <stefanb@xxxxxxxxxx>, "Scarlata, Vincent R" <vincent.r.scarlata@xxxxxxxxx>, Ronald Perez <ronpz@xxxxxxxxxx>
Delivery-date: Thu, 09 Feb 2006 18:56:46 +0000
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <43EB8B89.80909@xxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <OF8A30427C.48305C4F-ON85257110.005AFDA3-85257110.005CA9EB@xxxxxxxxxx> <43EB766A.30701@xxxxxxxxxx> <43EB8B89.80909@xxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mail/News 1.5 (X11/20060119)
Mike D. Day wrote:
Anthony Liguori wrote:
all). It also allows you to do clever things like vary the port which should add to the security of migration.

Allowing the target to choose the port is good practice but not added security.
If the Xend is always listening for migrations on a well-known port, it is trivially easy to start migrating domains to that host. If the port number isn't decided until the time of migration (and better yet, is decided through a secure channel like SSH), it makes it difficult to determine when a port is open to migrate to and which port that is.

It's not perfect, but no security mechanism is. It's definitely better than what we have now as it means you have to authenticate to a host before you can migrate to it.
Why do plugins have to exist? The only reason to have a plugin mechanism is to be able to maintain plugins outside of the Xend tree which would require a stable plugin interface. I don't think we're at a point where we can do that.

No, you are missing an important point. The plugin mechanism is necessary to isolate specialized device migration code from general-purpose migration code. I don't think it has anything to do with where the plugins are maintained.
All devices have to have their state migrated in some form. There's already code to handle that in Xend (via the S-Expression configuration file). The only reason TPM migration doesn't just work is that the current state migration is unidirectional and TPM requires bidirectional state synchronization.

All that's strictly required here is the ability to transfer the TPM state. This is just a little bit of additional code in XendCheckpoint that ran after suspend to transfer the TPM state.

You certainly don't need to have a plugin mechanism to handle TPM devices. I don't know of any other devices that need this logic either today so it would be creating a lot of complexity with a plugin mechanism and extensible protocol when it's not necessary.


Anthony Liguori

Xen-devel mailing list