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

From: Pierre Morel
Subject: Re: [Qemu-devel] [PATCH v2] qdev/core: Can not replug device on bus that allows one device
Date: Fri, 14 Dec 2018 10:16:04 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

On 13/12/2018 17:26, Tony Krowiak 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.

I think that the root of the problem is that the max_index is not the right measure to determine the number of devices currently plugged.

With the comment amended in this direction:

Reviewed-by: Pierre Morel<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 
              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);
@@ -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;
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;


Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany

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