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Re: [PATCH v7 07/13] monitor: Make current monitor a per-coroutine prope
From: |
Markus Armbruster |
Subject: |
Re: [PATCH v7 07/13] monitor: Make current monitor a per-coroutine property |
Date: |
Mon, 28 Sep 2020 09:47:00 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) |
Kevin Wolf <kwolf@redhat.com> writes:
> Am 14.09.2020 um 17:11 hat Markus Armbruster geschrieben:
>> Kevin Wolf <kwolf@redhat.com> writes:
>>
>> > This way, a monitor command handler will still be able to access the
>> > current monitor, but when it yields, all other code code will correctly
>> > get NULL from monitor_cur().
>> >
>> > This uses a hash table to map the coroutine pointer to the current
>> > monitor of that coroutine. Outside of coroutine context, we associate
>> > the current monitor with the leader coroutine of the current thread.
>>
>> In qemu-system-FOO, the hash table can have only these entries:
>>
>> * (OOB) One mapping @mon_iothread's thread leader to a QMP monitor, while
>> executing a QMP command out-of-band.
>>
>> * (QMP-CO) One mapping @qmp_dispatcher_co (a coroutine in the main
>> thread) to a QMP monitor, while executing a QMP command in-band and in
>> coroutine context.
>>
>> * (QMP) One mapping the main thread's leader to a QMP monitor, while
>> executing a QMP command in-band and out of coroutine context, in a
>> bottom half.
>>
>> * (HMP) One mapping the main thread's leader to an HMP monitor, while
>> executing an HMP command out of coroutine context.
>>
>> * (HMP-CO) One mapping a transient coroutine in the main thread to an
>> HMP monitor, while executing an HMP command in coroutine context.
>>
>> In-band execution is one command after the other.
>>
>> Therefore, at most one monitor command can be executing in-band at any
>> time.
>>
>> Therefore, the hash table has at most *two* entries: one (OOB), and one
>> of the other four.
>>
>> Can you shoot any holes into my argument?
>
> I think with human-monitor-command, you can have three mappings:
>
> 1. The main thread's leader (it is a non-coroutine QMP command) to the
> QMP monitor
This is (QMP).
> 2. With a coroutine HMP command, one mapping from the transient HMP
> coroutine to the transient HMP monitor (with a non-coroutine HMP
> command, we'd instead temporarily change the mapping from 1.)
This is (HMP-CO).
> 3. The OOB entry
This is (OOB).
To get 1. (QMP) and 2, (HMP-CO) at the same time, the in-band,
non-coroutine QMP command needs to execute interleaved with the in-band,
coroutine HMP command.
Such an interleaving contradicts "In-band execution is one command after
the other", which is a fundamental assumption in-band commands may make.
If the assumption is invalid, we got a problem. Is it?
>> I suspect there's a simpler solution struggling to get out. But this
>> solution works, so in it goes. Should the simpler one succeed at
>> getting out, it can go in on top. If not, I'll probably add even more
>> comments to remind myself of these facts.
>
> I think the simple approach you had posted could work if you can fill in
> the HMP part, but I think it wasn't completely trivial and you told me
> not to bother for now,
Correct. I decided to go with the code you already tested.
> so I didn't. It may still be a viable path
> forward if you like it better.
- Re: [PATCH v7 06/13] qmp: Call monitor_set_cur() only in qmp_dispatch(), (continued)
- Re: [PATCH v7 06/13] qmp: Call monitor_set_cur() only in qmp_dispatch(), Kevin Wolf, 2020/09/25
- Re: [PATCH v7 06/13] qmp: Call monitor_set_cur() only in qmp_dispatch(), Markus Armbruster, 2020/09/28
- Re: [PATCH v7 06/13] qmp: Call monitor_set_cur() only in qmp_dispatch(), Kevin Wolf, 2020/09/28
- Re: [PATCH v7 06/13] qmp: Call monitor_set_cur() only in qmp_dispatch(), Markus Armbruster, 2020/09/30
- Re: [PATCH v7 06/13] qmp: Call monitor_set_cur() only in qmp_dispatch(), Kevin Wolf, 2020/09/30
- Re: [PATCH v7 06/13] qmp: Call monitor_set_cur() only in qmp_dispatch(), Markus Armbruster, 2020/09/30
- Re: [PATCH v7 06/13] qmp: Call monitor_set_cur() only in qmp_dispatch(), Kevin Wolf, 2020/09/30
[PATCH v7 07/13] monitor: Make current monitor a per-coroutine property, Kevin Wolf, 2020/09/09
[PATCH v7 08/13] qapi: Add a 'coroutine' flag for commands, Kevin Wolf, 2020/09/09
[PATCH v7 09/13] qmp: Move dispatcher to a coroutine, Kevin Wolf, 2020/09/09