On Thu, Mar 07, 2013 at 08:00:29PM +0100, Andreas Färber wrote: > Am 07.03.2013 19:12, schrieb Michael S. Tsirkin: > > On Thu, Mar 07, 2013 at 06:23:46PM +0100, Markus Armbruster wrote: > >> "Michael S. Tsirkin" <m...@redhat.com> writes: > >> > >>> On Thu, Mar 07, 2013 at 03:14:15PM +0100, Markus Armbruster wrote: > >>>> Andreas Färber <afaer...@suse.de> writes: > >>>> > >>>>> Am 07.03.2013 11:07, schrieb Michael S. Tsirkin: > >>>>>> On Thu, Mar 07, 2013 at 10:55:23AM +0100, Markus Armbruster wrote: > >>>>>>> "Michael S. Tsirkin" <m...@redhat.com> writes: > >>>>>>> > >>>>>>>> On Wed, Mar 06, 2013 at 02:57:22PM +0100, Andreas Färber wrote: > >>>>>>>>> Am 06.03.2013 14:00, schrieb Michael S. Tsirkin: > >>>>>>>>>> libvirt has a long-standing bug: when removing the device, > >>>>>>>>>> it can request removal but does not know when does the > >>>>>>>>>> removal complete. Add an event so we can fix this in a robust way. > >>>>>>>>>> > >>>>>>>>>> Signed-off-by: Michael S. Tsirkin <m...@redhat.com> > >>>>>>>>> > >>>>>>>>> Sounds like a good idea to me. :) > >>>>>>>>> > >>>>>>>>> [...] > >>>>>>>>>> diff --git a/hw/qdev.c b/hw/qdev.c > >>>>>>>>>> index 689cd54..f30d251 100644 > >>>>>>>>>> --- a/hw/qdev.c > >>>>>>>>>> +++ b/hw/qdev.c > >>>>>>>>>> @@ -29,6 +29,7 @@ > >>>>>>>>>> #include "sysemu/sysemu.h" > >>>>>>>>>> #include "qapi/error.h" > >>>>>>>>>> #include "qapi/visitor.h" > >>>>>>>>>> +#include "qapi/qmp/qjson.h" > >>>>>>>>>> > >>>>>>>>>> int qdev_hotplug = 0; > >>>>>>>>>> static bool qdev_hot_added = false; > >>>>>>>>>> @@ -267,6 +268,11 @@ void qdev_init_nofail(DeviceState *dev) > >>>>>>>>>> /* Unlink device from bus and free the structure. */ > >>>>>>>>>> void qdev_free(DeviceState *dev) > >>>>>>>>>> { > >>>>>>>>>> + if (dev->id) { > >>>>>>>>>> + QObject *data = qobject_from_jsonf("{ 'device': %s }", > >>>>>>>>>> dev->id); > >>>>>>>>>> + monitor_protocol_event(QEVENT_DEVICE_DELETED, data); > >>>>>>>>>> + qobject_decref(data); > >>>>>>>>>> + } > >>>>>>>>>> object_unparent(OBJECT(dev)); > >>>>>>>>>> } > >>>>>>>>>> > >>>>>>>>> > >>>>>>>>> I'm pretty sure this is the wrong place to fire the notification. We > >>>>>>>>> should rather do this when the device is actually deleted - which > >>>>>>>>> qdev_free() does *not* actually guarantee, as criticized in the > >>>>>>>>> s390x > >>>>>>>>> and unref'ing contexts. > >>>>>>>>> I would suggest to place your code into device_unparent() instead. > >>>>>>>>> > >>>>>>>>> Another thing to consider is what data to pass to the event: Not all > >>>>>>>>> devices have an ID. > >>>>>>>> > >>>>>>>> If they don't they were not created by management so management is > >>>>>>>> probably not interested in them being removed. > >>>>>>>> > >>>>>>>> We could always add a 'path' key later if this assumption > >>>>>>>> proves incorrect. > >>>>>>> > >>>>>>> In old qdev, ID was all we had, because paths were busted. Thus, > >>>>>>> management had no choice but use IDs. > >>>>>>> > >>>>>>> If I understand modern qdev correctly, we got a canonical path. Old > >>>>>>> APIs like device_del still accept only ID. Should new APIs still be > >>>>>>> designed that way? Or should they always accept / provide the > >>>>>>> canonical > >>>>>>> path, plus optional ID for convenience? > >>>>>> > >>>>>> What are advantages of exposing the path to users in this way? > >>>> > >>>> The path is the device's canonical name. Canonical means path:device is > >>>> 1:1. Path always works. Qdev ID only works when the user assigned one. > >>>> > >>>> Funny case: board creates a hot-pluggable device by default (thus no > >>>> qdev ID), guest ejects it, what do you put into the event? Your code > >>>> simply doesn't emit one. > >>>> > >>>> You could blame the user; after all he could've used -nodefaults, and > >>>> added the device himself, with an ID. > >>>> > >>>> I blame your design instead, which needlessly complicates the event's > >>>> semantics: it gets emitted only for devices with a qdev ID. Which you > >>>> neglected to document clearly, by the way. > >>> > >>> Good point, I'll document this. > >>> > >>>> If you put the path into the event, you can emit it always, which is > >>>> simpler. Feel free to throw in the qdev ID. > >>> > >>> I don't blame anyone. User not assigning an id is a clear indication > >>> that user does not care about the lifetime of this device. > >>> > >>>>>> Looks like maintainance hassle without real benefits? > >>>> > >>>> I can't see path being a greater maintenance hassle than ID. > >>> > >>> Sure, the less events we emit the less we need to support. > >>> You want to expose all kind of internal events, > >>> then management will come to depend on it and > >>> we'll have to maintain them forever. > >> > >> Misunderstanding. I'm *not* asking for more events. I'm asking for the > >> DEVICE_DELETED event to carry the device's canonical name: its QOM path. > >> > >>>>> Anthony had rejected earlier QOM patches by Paolo related to qdev id, > >>>>> saying it was deprecated in favor of those QOM paths. > >>>> > >>>> More reason to put the path into the event, not just the qdev ID. > >>> > >>> libvirt does not seems to want it there. We'll always be able to > >>> add info but will never be able to remove info, keep it minimal. > >> > >> Yes, adding members to an event is easy. Doesn't mean we should do it > >> just for the heck of it. If we don't need a member now, and we think > >> there's a chance we won't need in the future, then we probably shouldn't > >> add it now. > >> > >> I believe the chance of not needing the QOM path is effectively zero. > >> > >> Moreover, we'd add not just a member in this case, we'd add a *trigger*. > >> > >> Before: the event gets emitted only for devices with a qdev ID. > >> > >> After: the event gets emitted for all devices. > >> > >> I very much prefer the latter, because it's simpler. > >> > >> [...] > > > > I still don't see why it's useful for anyone. For now I hear from the > > libvirt guys that this patch does exactly what they need so I'll keep it > > simple. You are welcome to send a follow-up patch adding a path > > and more triggers, I won't object. > > Well, the libvirt guys have been told to poll using qom-list, which > needs the path, not an ID. Using it in both places would make it > symmetrical - that may qualify as useful. > (I'm not aware of any id -> path lookup QMP command.) > > Nontheless, you can retain my Reviewed-by on v4+ as long as the code in > hw/qdev.c doesn't change. > > Andreas
I suggested retrying device_del, this has an advantage of working on more qemu version. > -- > SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany > GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg