On Mon, Sep 25, 2017 at 03:46:47PM +0200, Igor Mammedov wrote: > On Mon, 25 Sep 2017 10:31:53 -0300 > Eduardo Habkost <ehabk...@redhat.com> wrote: > > > On Mon, Sep 25, 2017 at 01:53:16PM +0200, Cornelia Huck wrote: > > > On Fri, 22 Sep 2017 11:16:34 +0200 > > > Thomas Huth <th...@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 <th...@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? > > > > I've seen a similar case broken by "[PATCH] hw/core/qdev: Do not > > allow hot-plugging without hotplug controller", because we're > > blocking creation of devices created internally by other devices, > > not just the ones created by device_add. I need to find the > > exact reproducer again. > > > > It would probably simplify things if we move the check for > > DeviceClass::hotpluggable to qmp_device_add(), instead of > > device_set_realized(). > if we would have to do that, than we are probably doing > something wrong and not using property right. Perhaps we > should fix property instead of trying find a place to check > it where it would hurt less.
I disagree. It depends on the purpose and semantics we define for DeviceClass::hotpluggable. My goal is to have a reliable way to tell the user if a device really supports device_add, and I think it wouldn't make sense to report hotpluggable=true on a device that is never instantiated directly by the user and only used internally. -- Eduardo
