Re: [Qemu-devel] [PATCH v2] qdev/core: Can not replug device on bus that allows one device

[Tony Krowiak]

On 12/14/18 7:09 AM, Halil Pasic wrote:
> On Thu, 13 Dec 2018 11:26:42 -0500
> Tony Krowiak <address@hidden> wrote:
>
> > If the maximum number of devices allowed on a bus is 1 and a device
> > which is plugged into the bus is subsequently unplugged, attempting to replug
> > the device fails with error "Bus 'xxx' does not support hotplugging".
> > The "error" is detected in the qbus_is_full(BusState *bus) function
> > (qdev_monitor.c) because bus->max_index >= bus_class->max_dev. The
> > root of the problem is that the bus->max_index is not decremented when a device
> > is unplugged from the bus. This patch fixes that problem.
>
> As Pierre has pointed out, the commit message is stale and inaccurate.
> Subject could be better as well. I mean the problem is not limited to
> buses that allow only one device. Each bus that can get full looses
> capacity with every plug/unplug op pair. With that fixed:
>
> Reviewed-by: Halil Pasic <address@hidden>

I'll make the changes recommended by you and Pierre.

> > Signed-off-by: Tony Krowiak <address@hidden>
> > ---
> >   hw/core/qdev.c         | 3 +++
> >   include/hw/qdev-core.h | 1 +
> >   qdev-monitor.c         | 2 +-
> >   3 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> > index 6b3cc55b27c2..956923f33520 100644
> > --- a/hw/core/qdev.c
> > +++ b/hw/core/qdev.c
> > @@ -59,6 +59,8 @@ static void bus_remove_child(BusState *bus, DeviceState 
> > *child)
> >               snprintf(name, sizeof(name), "child[%d]", kid->index);
> >               QTAILQ_REMOVE(&bus->children, kid, sibling);
> >   
> > +            bus->num_children--;
> > +
> >               /* This gives back ownership of kid->child back to us.  */
> >               object_property_del(OBJECT(bus), name, NULL);
> >               object_unref(OBJECT(kid->child));
> > @@ -73,6 +75,7 @@ static void bus_add_child(BusState *bus, DeviceState *child)
> >       char name[32];
> >       BusChild *kid = g_malloc0(sizeof(*kid));
> >   
> > +    bus->num_children++;
> >       kid->index = bus->max_index++;
> >       kid->child = child;
> >       object_ref(OBJECT(kid->child));
> > diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
> > index a24d0dd566e3..521f0a947ead 100644
> > --- a/include/hw/qdev-core.h
> > +++ b/include/hw/qdev-core.h
> > @@ -206,6 +206,7 @@ struct BusState {
> >       HotplugHandler *hotplug_handler;
> >       int max_index;
> >       bool realized;
> > +    int num_children;
> >       QTAILQ_HEAD(ChildrenHead, BusChild) children;
> >       QLIST_ENTRY(BusState) sibling;
> >   };
> > diff --git a/qdev-monitor.c b/qdev-monitor.c
> > index 07147c63bf8b..45a8ba49644c 100644
> > --- a/qdev-monitor.c
> > +++ b/qdev-monitor.c
> > @@ -414,7 +414,7 @@ static DeviceState *qbus_find_dev(BusState *bus, char *elem)
> >   static inline bool qbus_is_full(BusState *bus)
> >   {
> >       BusClass *bus_class = BUS_GET_CLASS(bus);
> > -    return bus_class->max_dev && bus->max_index >= bus_class->max_dev;
> > +    return bus_class->max_dev && bus->num_children >= bus_class->max_dev;
> >   }
> >   
> >   /*