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

On Wed, Mar 01, 2017 at 01:39:18PM +0100, Jiri Denemark wrote: > 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. If you don't have TLS enabled, then whether tls-hostname is set or not is irrelevant - it'll never be used. So the fact that tls-hostname may be still mistakenly set, when you later save to a file is harmless, as long as tls-creds is unset.

> > 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.