On Fri, May 29, 2020 at 7:03 AM Markus Armbruster <arm...@redhat.com> wrote: > > We commonly plug devices into their bus right when we create them, > like this: > > dev = qdev_create(bus, type_name); > > Note that @dev is a weak reference. The reference from @bus to @dev > is the only strong one. > > We realize at some later time, either with > > object_property_set_bool(OBJECT(dev), true, "realized", errp); > > or its convenience wrapper > > qdev_init_nofail(dev); > > If @dev still has no QOM parent then, realizing makes the > /machine/unattached/ orphanage its QOM parent. > > Note that the device returned by qdev_create() is plugged into a bus, > but doesn't have a QOM parent, yet. Until it acquires one, > unrealizing the bus will hang in bus_unparent(): > > while ((kid = QTAILQ_FIRST(&bus->children)) != NULL) { > DeviceState *dev = kid->child; > object_unparent(OBJECT(dev)); > } > > object_unparent() does nothing when its argument has no QOM parent, > and the loop spins forever. > > Device state "no QOM parent, but plugged into bus" is dangerous. > > Paolo suggested to delay plugging into the bus until realize. We need > to plug into the parent bus before we call the device's realize > method, in case it uses the parent bus. So the dangerous state still > exists, but only within realization, where we can manage it safely. > > This commit creates infrastructure to do this: > > dev = qdev_new(type_name); > ... > qdev_realize_and_unref(dev, bus, errp) > > Note that @dev becomes a strong reference here. > qdev_realize_and_unref() drops it. There is also plain > qdev_realize(), which doesn't drop it. > > The remainder of this series will convert all users to this new > interface. > > Cc: Michael S. Tsirkin <m...@redhat.com> > Cc: Marcel Apfelbaum <marcel.apfelb...@gmail.com> > Cc: Alistair Francis <alist...@alistair23.me> > Cc: Gerd Hoffmann <kra...@redhat.com> > Cc: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk> > Cc: David Gibson <da...@gibson.dropbear.id.au> > Signed-off-by: Markus Armbruster <arm...@redhat.com> > Acked-by: Gerd Hoffmann <kra...@redhat.com>
Reviewed-by: Alistair Francis <alistair.fran...@wdc.com> Alistair > --- > include/hw/qdev-core.h | 11 +++++- > hw/core/bus.c | 14 +++++++ > hw/core/qdev.c | 90 ++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 114 insertions(+), 1 deletion(-) > > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h > index b870b27966..fba29308f7 100644 > --- a/include/hw/qdev-core.h > +++ b/include/hw/qdev-core.h > @@ -57,7 +57,7 @@ typedef void (*BusUnrealize)(BusState *bus); > * After successful realization, setting static properties will fail. > * > * As an interim step, the #DeviceState:realized property can also be > - * set with qdev_init_nofail(). > + * set with qdev_realize() or qdev_init_nofail(). > * In the future, devices will propagate this state change to their children > * and along busses they expose. > * The point in time will be deferred to machine creation, so that values > @@ -322,7 +322,13 @@ compat_props_add(GPtrArray *arr, > > DeviceState *qdev_create(BusState *bus, const char *name); > DeviceState *qdev_try_create(BusState *bus, const char *name); > +DeviceState *qdev_new(const char *name); > +DeviceState *qdev_try_new(const char *name); > void qdev_init_nofail(DeviceState *dev); > +bool qdev_realize(DeviceState *dev, BusState *bus, Error **errp); > +bool qdev_realize_and_unref(DeviceState *dev, BusState *bus, Error **errp); > +void qdev_unrealize(DeviceState *dev); > + > void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id, > int required_for_version); > HotplugHandler *qdev_get_bus_hotplug_handler(DeviceState *dev); > @@ -411,6 +417,9 @@ typedef int (qdev_walkerfn)(DeviceState *dev, void > *opaque); > void qbus_create_inplace(void *bus, size_t size, const char *typename, > DeviceState *parent, const char *name); > BusState *qbus_create(const char *typename, DeviceState *parent, const char > *name); > +bool qbus_realize(BusState *bus, Error **errp); > +void qbus_unrealize(BusState *bus); > + > /* Returns > 0 if either devfn or busfn skip walk somewhere in cursion, > * < 0 if either devfn or busfn terminate walk somewhere in cursion, > * 0 otherwise. */ > diff --git a/hw/core/bus.c b/hw/core/bus.c > index 33a4443217..6f6071f5fa 100644 > --- a/hw/core/bus.c > +++ b/hw/core/bus.c > @@ -164,6 +164,20 @@ BusState *qbus_create(const char *typename, DeviceState > *parent, const char *nam > return bus; > } > > +bool qbus_realize(BusState *bus, Error **errp) > +{ > + Error *err = NULL; > + > + object_property_set_bool(OBJECT(bus), true, "realized", &err); > + error_propagate(errp, err); > + return !err; > +} > + > +void qbus_unrealize(BusState *bus) > +{ > + object_property_set_bool(OBJECT(bus), false, "realized", &error_abort); > +} > + > static bool bus_get_realized(Object *obj, Error **errp) > { > BusState *bus = BUS(obj); > diff --git a/hw/core/qdev.c b/hw/core/qdev.c > index a68ba674db..f2c5cee278 100644 > --- a/hw/core/qdev.c > +++ b/hw/core/qdev.c > @@ -176,6 +176,32 @@ DeviceState *qdev_try_create(BusState *bus, const char > *type) > return dev; > } > > +/* > + * Create a device on the heap. > + * A type @name must exist. > + * This only initializes the device state structure and allows > + * properties to be set. The device still needs to be realized. See > + * qdev-core.h. > + */ > +DeviceState *qdev_new(const char *name) > +{ > + return DEVICE(object_new(name)); > +} > + > +/* > + * Try to create a device on the heap. > + * This is like qdev_new(), except it returns %NULL when type @name > + * does not exist. > + */ > +DeviceState *qdev_try_new(const char *name) > +{ > + if (!object_class_by_name(name)) { > + return NULL; > + } > + > + return DEVICE(object_new(name)); > +} > + > static QTAILQ_HEAD(, DeviceListener) device_listeners > = QTAILQ_HEAD_INITIALIZER(device_listeners); > > @@ -427,6 +453,66 @@ void qdev_init_nofail(DeviceState *dev) > object_unref(OBJECT(dev)); > } > > +/* > + * Realize @dev. > + * @dev must not be plugged into a bus. > + * Plug @dev into @bus if non-null, else into the main system bus. > + * This takes a reference to @dev. > + * If @dev has no QOM parent, make one up, taking another reference. > + * On success, return true. > + * On failure, store an error through @errp and return false. > + */ > +bool qdev_realize(DeviceState *dev, BusState *bus, Error **errp) > +{ > + Error *err = NULL; > + > + assert(!dev->realized && !dev->parent_bus); > + > + if (!bus) { > + /* > + * Assert that the device really is a SysBusDevice before we > + * put it onto the sysbus. Non-sysbus devices which aren't > + * being put onto a bus should be realized with > + * object_property_set_bool(OBJECT(dev), true, "realized", > + * errp); > + */ > + g_assert(object_dynamic_cast(OBJECT(dev), TYPE_SYS_BUS_DEVICE)); > + bus = sysbus_get_default(); > + } > + > + qdev_set_parent_bus(dev, bus); > + > + object_property_set_bool(OBJECT(dev), true, "realized", &err); > + if (err) { > + error_propagate(errp, err); > + } > + return !err; > +} > + > +/* > + * Realize @dev and drop a reference. > + * This is like qdev_realize(), except the caller must hold a > + * (private) reference, which is dropped on return regardless of > + * success or failure. Intended use: > + * dev = qdev_new(); > + * [...] > + * qdev_realize_and_unref(dev, bus, errp); > + * Now @dev can go away without further ado. > + */ > +bool qdev_realize_and_unref(DeviceState *dev, BusState *bus, Error **errp) > +{ > + bool ret; > + > + ret = qdev_realize(dev, bus, errp); > + object_unref(OBJECT(dev)); > + return ret; > +} > + > +void qdev_unrealize(DeviceState *dev) > +{ > + object_property_set_bool(OBJECT(dev), false, "realized", &error_abort); > +} > + > static int qdev_assert_realized_properly(Object *obj, void *opaque) > { > DeviceState *dev = DEVICE(object_dynamic_cast(obj, TYPE_DEVICE)); > @@ -1002,6 +1088,10 @@ post_realize_fail: > fail: > error_propagate(errp, local_err); > if (unattached_parent) { > + /* > + * Beware, this doesn't just revert > + * object_property_add_child(), it also runs bus_remove()! > + */ > object_unparent(OBJECT(dev)); > unattached_count--; > } > -- > 2.21.3 > >