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Re: [Qemu-block] [Qemu-devel] [PATCH v2 02/11] blockjob: centralize QMP

From: Kevin Wolf
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v2 02/11] blockjob: centralize QMP event emissions
Date: Thu, 6 Oct 2016 09:44:27 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 05.10.2016 um 20:49 hat John Snow geschrieben:
> On 10/05/2016 09:43 AM, Kevin Wolf wrote:
> >Am 01.10.2016 um 00:00 hat John Snow geschrieben:
> >>@@ -3136,10 +3111,10 @@ void qmp_block_commit(bool has_job_id, const char 
> >>*job_id, const char *device,
> >>             goto out;
> >>         }
> >>         commit_active_start(has_job_id ? job_id : NULL, bs, base_bs, speed,
> >>-                            on_error, block_job_cb, bs, &local_err, false);
> >>+                            on_error, NULL, bs, &local_err, false);
> >
> >Here we have an additional caller in block/replication.c and qemu-img,
> >so the parameters must stay. For qemu-img, nothing changes. For
> >replication, the block job events are added as a side effect.
> >
> >Not sure if we want to emit such events for an internal block job, but
> >if we do want the change, it should be explicit.
> >
> Hmm, do we want to make it so some jobs are invisible and others are
> not? Because as it stands right now, neither case is strictly true.
> We only emit cancelled/completed events if it was started via QMP,
> however we do emit events for error and ready regardless of who
> started the job.
> That didn't seem particularly consistent to me; either all events
> should be controlled by the job layer itself or none of them should
> be.

Yes, I agree. The use of block jobs in replication is rather broken and
we should change it one way or another. But I'd prefer to do so
explicitly instead of doing it as a side-effect of a patch like this

> I opted for "all."
> For "internal" jobs that did not previously emit any events, is it
> not true that these jobs still appear in the block job list and are
> effectively public regardless? I'd argue that these messages may be
> of value for management utilities who are still blocked by these
> jobs whether or not they are 'internal' or not.
> I'll push for keeping it mandatory and explicit. If it becomes a
> problem, we can always add a 'silent' job property that silences ALL
> qmp events, including all completion, error, and ready notices.

Actually, there is at least one other reason why the block jobs in
replication are a bad a idea as they are today: Job naming. Currently
they use a fixed string, conflicting with the user-controlled job
namespace and with itself (i.e. restricting replication to a single

And are we really prepared to handle cases where the user decides to
pause, complete or cancel an internal job?

I think we should really hide them from the user. And maybe the way to
do so isn't a bool job->user flag, but actually job->id = NULL. Then it
would work the same way as named/internal BlockBackends do and we would
get rid of the naming problem, too.


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