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

From: Tony Krowiak
Subject: Re: [Qemu-devel] [PATCH v2] qdev/core: Can not replug device on bus that allows one device
Date: Fri, 14 Dec 2018 09:36:08 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1

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 
              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;

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