qdev/core: fix qbus_is_full()

The qbus_is_full(BusState *bus) function (qdev_monitor.c) compares the max_index
value of the BusState structure with the max_dev value of the BusClass structure
to determine whether the maximum number of children has been reached for the
bus. The problem is, the max_index field of the BusState structure does not
necessarily reflect the number of devices that have been plugged into
the bus.

Whenever a child device is plugged into the bus, the bus's max_index value is
assigned to the child device and then incremented. If the child is subsequently
unplugged, the value of the max_index does not change and no longer reflects the
number of children.

When the bus's max_index value reaches the maximum number of devices
allowed for the bus (i.e., the max_dev field in the BusClass structure),
attempts to plug another device will be rejected claiming that the bus is
full -- even if the bus is actually empty.

To resolve the problem, a new 'num_children' field is being added to the
BusState structure to keep track of the number of children plugged into the
bus. It will be incremented when a child is plugged, and decremented when a
child is unplugged.

Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Pierre Morel<pmorel@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Message-Id: <1545062250-7573-1-git-send-email-akrowiak@linux.ibm.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index d59071b8ed..00a5a39c76 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));