Re: [Qemu-block] [Qemu-devel] [PATCH v2 21/40] job: Convert block_job_cancel_async() to Job

[Kevin Wolf]

Am 24.05.2018 um 19:42 hat John Snow geschrieben:
> 
> 
> On 05/24/2018 04:24 AM, Kevin Wolf wrote:
> > Am 24.05.2018 um 01:18 hat John Snow geschrieben:
> >>> diff --git a/include/qemu/job.h b/include/qemu/job.h
> >>> index 3e817beee9..2648c74281 100644
> >>> --- a/include/qemu/job.h
> >>> +++ b/include/qemu/job.h
> >>> @@ -97,6 +97,12 @@ typedef struct Job {
> >>>       */
> >>>      bool cancelled;
> >>>  
> >>> +    /**
> >>> +     * Set to true if the job should abort immediately without waiting
> >>> +     * for data to be in sync.
> >>> +     */
> >>> +    bool force_cancel;
> >>> +
> >>
> >> Does this comment need an update now, though?
> >>
> >> Actually, in terms of "new jobs" API, it'd be really nice if cancel
> >> *always meant cancel*.
> >>
> >> I think "cancel" should never be used to mean "successful completion,
> >> but different from the one we'd get if we used job_complete."
> >>
> >> i.e., either we need a job setting:
> >>
> >> job-set completion-mode=[pivot|no-pivot]
> >>
> >> or optional parameters to pass to job-complete:
> >>
> >> job-complete mode=[understood-by-job-type]
> >>
> >> or some other mechanism that accomplishes the same type of behavior. It
> >> would be nice if it did not have to be determined at job creation time
> >> but instead could be determined later.
> > 
> > I agree. We already made sure that job-cancel really means cancel on the
> > QAPI level, so we're free to do that. We just need to keep supporting
> > block-job-cancel with the old semantics, so what I have is the easy
> > conversion. We can change the internal implementation when we actually
> > implement the selection of a completion mode.
> > 
> > Kevin
> > 
> 
> We need this before 3.0 though, yeah? unless we make job-cancel
> x-job-cancel or some other warning that the way it works might change, yeah?
> 
> Or do I misunderstand our leeway to change this at a later point in time?
> 
> (can job-cancel apply to block jobs created with the legacy
> infrastructure? My reading was "yes.")

It can, and it already has its final semantics, so nothing has to change
before 3.0. job-cancel is equivalent to block-job-cancel with fixed
force=true. If you want the complete-by-cancel behaviour of mirror, you
have to use block-job-cancel for now, because job-cancel doesn't provide
that functionality.

So what we can change later is adding a way to initiate this secondary
completion mode with a job-* command (probably with a new option for
job-complete). But we wouldn't change the semantics of exisiting
commands.

Kevin