Re: [libvirt] [PATCH v2 00/14] Add TLS support for migration

On Wed, Mar 01, 2017 at 12:18:23 +0000, Daniel P. Berrange wrote: > Hmm, I see this is a limitation of the migrate-set-parameters method. You > can set new parameters for tls_creds / tls_hostname, but you can't fully > delete the old parameters. > > The tls_hostname is only set on the source host of the migration and that > VM will be killed off upon successful migration. The problem only arises > if you have a migration that fails, and you then try to migrate that same > VM again later, *and* you don't have tls_hostname set. I don't think that'd > hit libvirt, since libvirt will always need to set tls-hostname as it uses > fd: migrate method. IOW, I don't see any need to be able to clear > tls-hostname when used with libvirt. But we will only set it if TLS is turned on. We certainly don't want to use this parameter when saving a domain to a file, making a snapshot, or migrating without TLS.

> For TLS creds it would be a problem if we do a TLS migration and then need > to migrate the target QEMU again later, but don't want TLS used, as that > would require us to fully clear the tls_creds parameter. At best we can > set it to empty string, which is not good enough. So seems we need a QEMU > fix here. Another problem (I mentioned in another email in this series) is query-migrate-parameters does not show the tls parameters unless they are set. So it looks like we need to invent a special value which can be reported when they are unset and we could use the same special value to reset them. An empty string sounds like an obvious candidate.