"Dr. David Alan Gilbert" <dgilb...@redhat.com> writes:
> * Markus Armbruster (arm...@redhat.com) wrote:
>> "Dr. David Alan Gilbert" <dgilb...@redhat.com> writes:
[...]
>> > I'm confused why we need a 'reset to default' - all we need is the ability
>> > to change each parameter, and for the new value of that parameter
>> > to be an empty string.
>>
>> You argue syntax, I'm arguing semantics.
>>
>> The command means "set parameter P to value V". *Except* when V is "",
>> it means something else, namely "reset parameter P to its default,
>> whatever that may be".
>>
>> This is (a) not general, because it won't do for cases where "" may
>> occur as value, and (b) ugly.
>>
>> Ugliness is the eye of the beholder. Lack of generality isn't.
>
> No, I'm questioning why it's defined as 'reset parameter P to its default';
> why do we need a way to do that?
Dan's commit message explains:
Some of the migration parameters are strings, which default to NULL,
eg tls_hostname and tls_creds.
The mgmt app will set the tls_creds parameter on both source and target
QEMU instances, in order to trigger use of TLS for migration.
After performing a TLS encrypted migration though, migration might be
used for other reasons - for example, to save the QEMU state to a file.
We need TLS turned off when doing this, but the migrate-set-parameters
QAPI command does not provide any facility to clear/reset parameters
to their default state.
If you simply ommit the tls_creds parameter in migrate-set-parameters,
then 'has_tls_creds' will be false and so no action will be taken. The
only option that works with migrate-set-parameters is to treat "" on
the wire as equivalent to requesting NULL. Failing that we would have
to create a new 'migrate-reset-parameters' method to explicitly put
a parameter back to its default value.
