Re: [Qemu-devel] [PATCH v2] qdev: Mark devices as non-hotpluggable by default

[Cornelia Huck <cohuck@redhat.com>]

On Fri, 22 Sep 2017 11:16:34 +0200
Thomas Huth <thuth@redhat.com> wrote:

> Historically we've marked all devices as hotpluggable by default. However,
> most devices are not hotpluggable, and you also need a HotplugHandler to
> support these devices. So if the user tries to "device_add" or "device_del"
> such a non-hotpluggable device during runtime, either nothing really usable
> happens, or QEMU even crashes/aborts unexpectedly (see for example commit
> 84ebd3e8c7d4fe955b - "Mark diag288 watchdog as non-hotpluggable").
> So let's change this dangerous default behaviour and mark the devices as
> non-hotpluggable by default. Certain parent devices classes which are known
> as hotpluggable (e.g. PCI, USB, etc.) are marked with "hotpluggable = true",
> so that devices that are derived from these classes continue to work as
> expected.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  v2: Add missing devices and dropped "RFC" status. See Eduardo's reply on
>  the previous version of this patch for the rationale which devices need
>  to be hotpluggable:
>  https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg06128.html
> 
>  hw/char/virtio-serial-bus.c   |  1 +
>  hw/core/qdev.c                | 10 ++++------
>  hw/mem/nvdimm.c               |  3 +++
>  hw/mem/pc-dimm.c              |  1 +
>  hw/pci/pci.c                  |  1 +
>  hw/ppc/spapr_cpu_core.c       |  1 +
>  hw/s390x/ccw-device.c         |  1 +
>  hw/scsi/scsi-bus.c            |  1 +
>  hw/usb/bus.c                  |  1 +
>  hw/usb/dev-smartcard-reader.c |  1 +
>  hw/xen/xen_backend.c          |  1 +
>  target/i386/cpu.c             |  4 ++--
>  target/s390x/cpu.c            |  1 +
>  13 files changed, 19 insertions(+), 8 deletions(-)

Hm, this seems to break hotplug of virtio devices:

(qemu) device_add virtio-net-pci,id=xxx
Device 'virtio-net-device' does not support hotplugging

(qemu) device_add virtio-net-ccw,id=yyy
Device 'virtio-net-device' does not support hotplugging

We probably need to enable hotplug for virtio devices as well?