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Re: [Qemu-devel] [PATCH] migration: allow clearing migration string para
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters |
Date: |
Wed, 15 Mar 2017 10:36:35 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
* Markus Armbruster (address@hidden) wrote:
> "Dr. David Alan Gilbert" <address@hidden> writes:
>
> > * Markus Armbruster (address@hidden) wrote:
> >> "Dr. David Alan Gilbert" <address@hidden> 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.
OK, I thought the default was empty string.
IMHO the problem here is we're just being too clever; lets just make
the default "" rather than NULL, and make that parameter always be
a string.
Dave
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters, (continued)
- Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters, Dr. David Alan Gilbert, 2017/03/14
- Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters, Markus Armbruster, 2017/03/15
- Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters, Dr. David Alan Gilbert, 2017/03/15
- Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters, Markus Armbruster, 2017/03/15
- Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters,
Dr. David Alan Gilbert <=
- Re: [Qemu-devel] [PATCH] migration: allow clearing migration string parameters, Daniel P. Berrange, 2017/03/15