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

[Halil Pasic]

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>

> 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;
>  }
>  
>  /*