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Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices |
Date: |
Mon, 29 Nov 2021 19:55:30 +0000 |
User-agent: |
Mutt/2.1.3 (2021-09-10) |
* Markus Armbruster (armbru@redhat.com) wrote:
> Damien Hedde <damien.hedde@greensocs.com> writes:
> > Patches 1, 3 and 5 miss a review.
> >
> > The series is organized as follow:
> >
> > + Patches 1 and 2 converts the MachinePhase enum to a qapi definition
> > and add the 'query-machine-phase'. It allows to introspect the
> > current machine phase during preconfig as we will now be able to
> > reach several machine phases using QMP.
>
> If we fold MachinePhase into RunState, we can reuse query-status.
>
> Having two state machines run one after the other feels like one too
> many.
Be careful, the RunState is API and things watch for events on it, so
any changes to it are delicate.
Dave
> > + Patch 3 adds the 'x-machine-init' QMP command to stop QEMU at
> > machine-initialized phase during preconfig.
> > + Patch 4 allows issuing device_add QMP command during the
> > machine-initialized phase.
> > + Patch 5 improves the doc about preconfig in consequence.
>
> I understand you want to make progress towards machine configuration
> with QMP. However, QEMU startup is (in my educated opinion) a hole, and
> we should be wary of digging deeper.
>
> The "timeline" you gave above illustrates this. It's a complicated
> shuffling of command line options and QMP commands that basically nobody
> can keep in working memory. We have reshuffled it / made it more
> complicated quite a few times already to support new features. Based on
> your cover letter, I figure you're making it more complicated once more.
>
> At some point, we need to stop digging us deeper into the hole. This is
> not an objection to merging your work. It's a call to stop and think.
>
> Let me quote the sketch I posted to the "Stabilize preconfig" thread:
>
> 1. Start event loop
>
> 2. Feed it CLI left to right. Each option runs a handler just like each
> QMP command does.
>
> Options that read a configuration file inject the file into the feed.
>
> Options that create a monitor create it suspended.
>
> Options may advance the phase / run state, and they may require
> certain phase(s).
>
> 3. When we're done with CLI, resume any monitors we created.
>
> 4. Monitors now feed commands to the event loop. Commands may advance
> the phase / run state, and they may require certain phase(s).
>
> Users can do as much or as little with the CLI as they want. You'd
> probably want to set up a QMP monitor and no more.
>
> device_add becomes possible at a certain state of the phase / run state
> machine. It changes from cold to hot plug at a certain later state.
>
> > [1]:
> > https://lore.kernel.org/qemu-devel/b31f442d28920447690a6b8cee865bdbacde1283.1635160056.git.mprivozn@redhat.com
> >
> > Thanks for your feedback.
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
- [RFC PATCH v3 3/5] qapi: Implement x-machine-init QMP command, (continued)
- [RFC PATCH v3 3/5] qapi: Implement x-machine-init QMP command, Damien Hedde, 2021/11/17
- [RFC PATCH v3 4/5] qapi: Allow device_add to execute in machine initialized phase, Damien Hedde, 2021/11/17
- [RFC PATCH v3 5/5] docs/system: improve doc about preconfig, Damien Hedde, 2021/11/17
- Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices, Markus Armbruster, 2021/11/20
- Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices, Damien Hedde, 2021/11/23
- Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices, Markus Armbruster, 2021/11/24
- Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices, Daniel P . Berrangé, 2021/11/24
- Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices, Markus Armbruster, 2021/11/24
- Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices, Damien Hedde, 2021/11/25
- Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices, Daniel P . Berrangé, 2021/11/25
Re: [RFC PATCH v3 0/5] QMP support for cold-plugging devices,
Dr. David Alan Gilbert <=