Re: [PATCH v2 00/10] mirror: allow switching from background to active mode

[Peter Krempa]

On Thu, Mar 07, 2024 at 22:42:56 +0300, Vladimir Sementsov-Ogievskiy wrote:
> On 04.03.24 14:09, Peter Krempa wrote:
> > On Mon, Mar 04, 2024 at 11:48:54 +0100, Kevin Wolf wrote:
> > > Am 28.02.2024 um 19:07 hat Vladimir Sementsov-Ogievskiy geschrieben:
> > > > On 03.11.23 18:56, Markus Armbruster wrote:
> > > > > Kevin Wolf<kwolf@redhat.com>  writes:

[...]

> 
> I only see the following differencies:
> 
> 1. block-job-complete documents that it completes the job synchronously.. But 
> looking at mirror code I see it just set s->should_complete = true, which 
> will be then handled asynchronously.. So I doubt that documentation is 
> correct.
> 
> 2. block-job-complete will trigger final graph changes. block-job-cancel will 
> not.
> 
> Is [2] really useful? Seems yes: in case of some failure before starting 
> migration target, we'd like to continue executing source. So, no reason to 
> break block-graph in source, better keep it unchanged.
> 
> But I think, such behavior better be setup by mirror-job start parameter, 
> rather then by special option for cancel (or even compelete) command, useful 
> only for mirror.

Libvirt's API design was based on the qemu quirk and thus we allow users
to do the decision after starting the job, thus anything you pick needs
to allow us to do this at "completion" time.

Libvirt can adapt to any option that will give us the above semantics
(extra parameter at completion time, different completion command or
extra command to switch job properties right before completion), but to
be honest all of these feel like they would be more hassle than keeping
'block-job-cancel' around from qemu's side.