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

[Li Zhang]

When I tried chardev-change, it reports this error:

{
    "error": {
        "class": "GenericError",
        "desc": "Chardev user does not support chardev hotswap"
    }
}

On Fri, Apr 16, 2021 at 11:33 AM Markus Armbruster <armbru@redhat.com> wrote:
>
> 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.
>


-- 

Best Regards
-Li