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Re: [Qemu-devel] monitor: enable OOB by default

From: Markus Armbruster
Subject: Re: [Qemu-devel] monitor: enable OOB by default
Date: Thu, 28 Jun 2018 09:04:19 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)

Eric Blake <address@hidden> writes:

> On 06/27/2018 07:07 AM, Peter Xu wrote:
>>>> Worse than that - broadcasting to all monitors is categorically broken.
>>>> Different monitors make use the same "id" formatting scheme, so if you
>>>> broadcast COMMAND_DROPPED to a different monitor you might have clashing
>>>> "id" and thus incorrectly tell a client its command was dropped when in
>>>> fact it was processed. You'd have to be fairly unlucky in timing, but
>>>> it could happen.
>>> Right.  Must fix bug.
>> My current plan is that I can touch up scripts/qapi/events.py and
>> related stuff to allow QMPEventFuncEmit to take a monitor parameter,
>> then we pass in NULL when we want to send the event to all monitors.
>> Would that work?
> Makes sense to me. Also, right now, ALL callers of qapi_event_send_*
> pass &error_abort as their final parameter. If you're refactoring
> everything anyways, you could get rid of that parameter on the
> presumption that it doesn't buy us anything.

Let me try to turn presumption into fact :)

The generated qapi_event_send_FOO() can detect the following error

* Visitor fails.  But the QObject output visitor can't actually fail.

  Since the errp parameter is part of the abstract visitor interface, we
  can't eliminate it.  We can pass &error_abort.

* emit() function fails.  Can't happen, either.

  Let's eliminate the unused errp parameter of QMPEventFuncEmit.

  If we can eliminate the somewhat silly indirection through
  qmp_event_get_func_emit(), even better.

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