[libvirt] Determining domain job kind from job stats?

[Milan Zamazal]

Jiri Denemark <jdenemar at redhat.com> writes:

> On Tue, Feb 21, 2017 at 15:38:22 +0100, Milan Zamazal wrote:
>> [Starting to move to the development list.]
>> 
>> Milan Zamazal <mzamazal at redhat.com> writes:
>> 
>> > Jiri Denemark <jdenemar at redhat.com> writes:
>> >
>> >> On Fri, Feb 17, 2017 at 12:38:24 +0100, Milan Zamazal wrote:
>> >>> 
>> >>> There are basically two problems:
>> >>> 
>> >>> - When the job completion callback is called, I need to distinguish what
>> >>>   kind of job was it to perform the appropriate actions.  It would be
>> >>>   easier if I knew the job type directly in the callback (no need to
>> >>>   coordinate anything), but "external" job tracking is also possible.
>> >>
>> >> An immediate answer would be: "don't rely on the completion callback and
>> >> just check the return value of the API which started the job", but I
>> >> guess you want it because checking the return value is not possible when
>> >> the process which started the job is not running anymore as described
>> >> below.
>> >
>> > Well, avoiding using the completion callback is probably OK for me.
>> 
>> Thinking about it more, it's not very nice: I have to use the callback
>> to get the completed job stats (I'm not guaranteed the domain still
>> exists on the source host when I ask it for the stats explicitly) *and*
>> to track the jobs outside the callback to know whether the callback is
>> related to the type of domain jobs I'm going to handle.
>> 
>> Although not absolutely necessary, it would be much nicer if the job
>> type was identified in the callback.
>
> The job completed event uses type parameters so adding a new parameter
> describing the just completed job should not be a problem.

Great, so all what remains to solve the problem is to add the
parameter :-).  (And I'd like to have the same info available when a job
is still running for reasons already discussed.)

I looked how the change could be implemented.  Could you please help me
clarify some things?

- I think a new member should be added to _virDomainJobInfo for the
  purpose.  What would be a good name for it?  Maybe "operation"?
- Do I need to care about backends other than QEMU?
- Jobs are classified by qemuDomainAsyncJob, which is a QEMU specific
  type.  Is it OK to use such structures in virsh-domain.c or is there
  any additional abstraction needed?
- Are there any libvirt-python updates needed or will all the things
  propagate to it automatically?
- I think there are no documentation updates needed to perform manually
  for this change, right?
- Should I be aware of anything else?

Thanks,
Milan