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

[Anthony Liguori <aliguori@xxxxxxxxxx>]

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.
Regards,

Anthony Liguori

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