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

[Tony Krowiak <akrowiak@linux.ibm.com>]

On 12/14/18 7:09 AM, Halil Pasic wrote:
> On Thu, 13 Dec 2018 11:26:42 -0500
> Tony Krowiak <akrowiak@linux.ibm.com> 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 <pasic@linux.ibm.com>

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

> 
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> ---
>>   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;
>>   }
>>   
>>   /*
>