Re: [PATCH 2/2] Support monitor chardev hotswap with QMP

[Markus Armbruster]

Li Zhang <zhlcindy@gmail.com> writes:

> On Tue, Apr 13, 2021 at 8:41 AM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Li Zhang <zhlcindy@gmail.com> writes:
>>
>> > From: Li Zhang <li.zhang@cloud.ionos.com>
>> >
>> > For some scenarios, it needs to hot-add a monitor device.
>> > But QEMU doesn't support hotplug yet. It also works by adding
>> > a monitor with null backend by default and then change its
>> > backend to socket by QMP command "chardev-change".
>> >
>> > So this patch is to support monitor chardev hotswap with QMP.
>> >
>> > Signed-off-by: Li Zhang <li.zhang@cloud.ionos.com>
>>
>> I think what what you're trying to say is that chardev-change does not
>> work when the character device changes is used by a QMP monitor.
>> Correct?
>>
> I mean that when the character device is a monitor device, it doesn't
> work with a QMP monitor.
> For example, I add 2 QMP monitors and change one of the monitor's
> backends from socket to a null device.
> It doesn't work because it needs the monitor device to support chardev-change.
>
>> If yes, how exactly does it misbehave?
> This command chardev-change needs specific device's change callback function.

Yes, but what happens if you try anyway?  I'm asking, because I'd like
the answer to be worked into the commit message.

>> Does it work with an HMP monitor?
> No, it doesn't work.