On Fri, Mar 03, 2017 at 06:05:15PM +0100, Markus Armbruster wrote: > "Daniel P. Berrange" <berra...@redhat.com> writes: > > > On Fri, Mar 03, 2017 at 03:44:12PM +0100, Markus Armbruster wrote: > >> "Daniel P. Berrange" <berra...@redhat.com> writes: > >> > >> > On Wed, Mar 01, 2017 at 08:36:03AM -0600, Eric Blake wrote: > >> >> On 03/01/2017 06:32 AM, Daniel P. Berrange wrote: > >> >> > } > >> >> > if (params->has_tls_creds) { > >> >> > g_free(s->parameters.tls_creds); > >> >> > - s->parameters.tls_creds = g_strdup(params->tls_creds); > >> >> > + if (*params->tls_creds == '\0') { > >> >> > + s->parameters.tls_creds = NULL; > >> >> > >> >> I'm wondering if you should also do s->parameters.has_tls_creds = false > >> >> at this point? The visitors expect that if has_tls_creds is true, then > >> >> the string is non-NULL. > >> > > >> > The fact that s->parameters contains has_* fields is completely ignored > >> > by the migration code afaict. IOW the code behaves as if all the has_* > >> > fields are hardwired to true in s->parameters, even though that is not > >> > the case :-) The has_* fields are only used when the various migration > >> > QMP methods are executed, and those all use a separate > >> > MigrationParameters > >> > struct instance. > >> > >> Not keeping the has_ members up-to-date is harmless as long as you don't > >> pass the thing to visitors, including the one hiding in qapi_free_FOO(). > >> That one ignores scalars, though. > >> > >> > >> From a more abstract point of view, we have two related data types: one > >> for the state, and one for state changes requests. > >> > >> In state, members are always present. > >> > >> A state change request is a bag of state member change requests, and > >> each request can either specify the new value or ask for a reset to > >> default. Absent member means no change. > >> > >> We press the same QAPI type into service for both by making all members > >> optional. > >> > >> For the state case, we hardwire the has_ to true. Or even ignore them > >> completely. > >> > >> For the state change request, we use has_ = false for "no change", has_ > >> = true with a special value for "reset to default" (new in this patch) > >> and has_ = true with a non-special value for "set to this value". > >> > >> Requires a special value outside the set of non-special values. The > >> obvious one is JSON null, but the QAPI generator doesn't quite support > >> that, yet. "" works here, but is not general. > >> > >> I think I can get you null support in 2.10. Would that work for you? > > > > Not really - we need this fix so libvirt can enable TLS migration, > > in addition we'll be wanting to add it to stable branches upstream > > and downstream. > > Alternatives: > > (a) We support null in 2.9, and use it to solve this problem. > > (b) We use "", support null in 2.10, immediately deprecate "" in favor > of null. > > PRO (a): Less churn, less variation, less overall work. > > PRO (b): Might be easier to backport to really old versions. Soft > freeze. > > Non-alternative: use "" forever. Sorry, I hate it.
I don't see a problem with accepting both "" & nil forever, as there's no reason to need to distinguish them here. "" is never a valid ID for a qobject, and "" is never a valid hostname, so treating "" as a synonym for NULL/nil is fine. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|