Re: [Qemu-devel] [PATCH] hw/core/qdev: Do not allow hot-plugging without hotplug controller

[Eduardo Habkost <ehabkost@redhat.com>]

On Tue, Sep 26, 2017 at 12:05:47PM +0200, Thomas Huth wrote:
> On 21.09.2017 19:56, Eduardo Habkost wrote:
> > On Thu, Sep 07, 2017 at 11:22:42AM +0200, Thomas Huth wrote:
> >> qdev_unplug() bails out with an assertion if the user tries to device_del
> >> a hot-plugged device that does not have a hotplug controller. Unfortunately,
> >> our devices are all marked with hotpluggable = true by default (see the
> >> device_class_init() function in qdev.c), so it currently can happen that
> >> the user runs into this situation and QEMU gets terminated unexpectedly:
> >>
> >> $ qemu-system-aarch64 -M virt -nographic -nodefaults -monitor stdio -S
> >> QEMU 2.10.50 monitor - type 'help' for more information
> >> (qemu) device_add aux-to-i2c-bridge,id=x
> >> (qemu) device_del x
> >> **
> >> ERROR:qdev-monitor.c:872:qdev_unplug: assertion failed: (hotplug_ctrl)
> >> Aborted (core dumped)
> >>
> >> Hotplugging devices without a hotplug controller does not make much sense,
> >> so we should disallow this during the device_add process already!
> >>
> >> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> >> Signed-off-by: Thomas Huth <thuth@redhat.com>
> > 
> > I'm queueing this on machine-next.  We still want it even if we
> > apply the patch that changes TYPE_DEVICE to hotpluggable=false by
> > default, right?
> 
> OK, just to be sure: Please de-queue it again. As you already mentioned
> in another mail, there are situations where this does not work (e.g.
> when one hot-pluggable device wants to instantiate another hot-pluggable
> device internally).

I just dequeued it.

> 
> But maybe we could add the test for the availability of a hot-plug
> controller to qmp_device_add() instead? (I haven't had a closer look at
> that yet, though).

I'm unsure about this.  Now we know we have some devices that
work without a hotplug controller, so what's the reason
device_add must always require one?

-- 
Eduardo