qom: Make QOM link property unref optional

Some object_property_add_link() callers expect property deletion to
unref the link property object.  Other callers expect to manage the
refcount themselves.  The former are currently broken and therefore leak
the link property object.

This patch adds a flags argument to object_property_add_link() so the
caller can specify which refcount behavior they require.  The new
OBJ_PROP_LINK_UNREF_ON_RELEASE flag causes the link pointer to be
unreferenced when the property is deleted.

This fixes refcount leaks in qdev.c, xilinx_axidma.c, xilinx_axienet.c,
s390-virtio-bus.c, virtio-pci.c, virtio-rng.c, and ui/console.c.

Rationale for refcount behavior:

 * hw/core/qdev.c
   - bus children are explicitly unreferenced, don't interfere
   - parent_bus is essentially a read-only property that doesn't hold a
     refcount, don't unref
   - hotplug_handler is leaked, do unref

 * hw/dma/xilinx_axidma.c
   - rx stream "dma" links are set using set_link, therefore they
     need unref
   - tx streams are set using set_link, therefore they need unref

 * hw/net/xilinx_axienet.c
   - same reasoning as hw/dma/xilinx_axidma.c

 * hw/pcmcia/pxa2xx.c
   - pxa2xx bypasses set_link and therefore does not use refcounts

 * hw/s390x/s390-virtio-bus.c
 * hw/virtio/virtio-pci.c
 * hw/virtio/virtio-rng.c
 * ui/console.c
   - set_link is used and there is no explicit unref, do unref

Cc: Peter Crosthwaite <peter.crosthwaite@petalogix.com>
Cc: Alexander Graf <agraf@suse.de>
Cc: Anthony Liguori <aliguori@amazon.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>

11 files changed, 85 insertions, 22 deletions

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 9f0a522ee8..a182917222 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -97,8 +97,7 @@ static void bus_add_child(BusState *bus, DeviceState *child)
     snprintf(name, sizeof(name), "child[%d]", kid->index);
     object_property_add_link(OBJECT(bus), name,
                              object_get_typename(OBJECT(child)),
-                             (Object **)&kid->child,
-                             NULL);
+                             (Object **)&kid->child, 0, NULL);
 }
 
 void qdev_set_parent_bus(DeviceState *dev, BusState *bus)
@@ -824,7 +823,8 @@ static void device_initfn(Object *obj)
     } while (class != object_class_by_name(TYPE_DEVICE));
 
     object_property_add_link(OBJECT(dev), "parent_bus", TYPE_BUS,
-                             (Object **)&dev->parent_bus, &error_abort);
+                             (Object **)&dev->parent_bus, 0,
+                             &error_abort);
 }
 
 static void device_post_init(Object *obj)
@@ -944,7 +944,9 @@ static void qbus_initfn(Object *obj)
     QTAILQ_INIT(&bus->children);
     object_property_add_link(obj, QDEV_HOTPLUG_HANDLER_PROPERTY,
                              TYPE_HOTPLUG_HANDLER,
-                             (Object **)&bus->hotplug_handler, NULL);
+                             (Object **)&bus->hotplug_handler,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             NULL);
     object_property_add_bool(obj, "realized",
                              bus_get_realized, bus_set_realized, NULL);
 }
diff --git a/hw/dma/xilinx_axidma.c b/hw/dma/xilinx_axidma.c
index 19f07b3b25..c8fda39122 100644
--- a/hw/dma/xilinx_axidma.c
+++ b/hw/dma/xilinx_axidma.c
@@ -537,9 +537,13 @@ static void xilinx_axidma_realize(DeviceState *dev, Error **errp)
     Error *local_errp = NULL;
 
     object_property_add_link(OBJECT(ds), "dma", TYPE_XILINX_AXI_DMA,
-                             (Object **)&ds->dma, &local_errp);
+                             (Object **)&ds->dma,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &local_errp);
     object_property_add_link(OBJECT(cs), "dma", TYPE_XILINX_AXI_DMA,
-                             (Object **)&cs->dma, &local_errp);
+                             (Object **)&cs->dma,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &local_errp);
     if (local_errp) {
         goto xilinx_axidma_realize_fail;
     }
@@ -571,10 +575,14 @@ static void xilinx_axidma_init(Object *obj)
     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
 
     object_property_add_link(obj, "axistream-connected", TYPE_STREAM_SLAVE,
-                             (Object **)&s->tx_data_dev, &error_abort);
+                             (Object **)&s->tx_data_dev,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &error_abort);
     object_property_add_link(obj, "axistream-control-connected",
                              TYPE_STREAM_SLAVE,
-                             (Object **)&s->tx_control_dev, &error_abort);
+                             (Object **)&s->tx_control_dev,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &error_abort);
 
     object_initialize(&s->rx_data_dev, sizeof(s->rx_data_dev),
                       TYPE_XILINX_AXI_DMA_DATA_STREAM);
diff --git a/hw/net/xilinx_axienet.c b/hw/net/xilinx_axienet.c
index 0bd5eda199..7ecf9251a7 100644
--- a/hw/net/xilinx_axienet.c
+++ b/hw/net/xilinx_axienet.c
@@ -945,9 +945,13 @@ static void xilinx_enet_realize(DeviceState *dev, Error **errp)
     Error *local_errp = NULL;
 
     object_property_add_link(OBJECT(ds), "enet", "xlnx.axi-ethernet",
-                             (Object **) &ds->enet, &local_errp);
+                             (Object **) &ds->enet,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &local_errp);
     object_property_add_link(OBJECT(cs), "enet", "xlnx.axi-ethernet",
-                             (Object **) &cs->enet, &local_errp);
+                             (Object **) &cs->enet,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &local_errp);
     if (local_errp) {
         goto xilinx_enet_realize_fail;
     }
@@ -982,10 +986,14 @@ static void xilinx_enet_init(Object *obj)
     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
 
     object_property_add_link(obj, "axistream-connected", TYPE_STREAM_SLAVE,
-                             (Object **) &s->tx_data_dev, &error_abort);
+                             (Object **) &s->tx_data_dev,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &error_abort);
     object_property_add_link(obj, "axistream-control-connected",
                              TYPE_STREAM_SLAVE,
-                             (Object **) &s->tx_control_dev, &error_abort);
+                             (Object **) &s->tx_control_dev,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &error_abort);
 
     object_initialize(&s->rx_data_dev, sizeof(s->rx_data_dev),
                       TYPE_XILINX_AXI_ENET_DATA_STREAM);
diff --git a/hw/pcmcia/pxa2xx.c b/hw/pcmcia/pxa2xx.c
index 8f17596cc3..6949214df3 100644
--- a/hw/pcmcia/pxa2xx.c
+++ b/hw/pcmcia/pxa2xx.c
@@ -198,7 +198,7 @@ static void pxa2xx_pcmcia_initfn(Object *obj)
     s->slot.irq = qemu_allocate_irqs(pxa2xx_pcmcia_set_irq, s, 1)[0];
 
     object_property_add_link(obj, "card", TYPE_PCMCIA_CARD,
-                             (Object **)&s->card, NULL);
+                             (Object **)&s->card, 0, NULL);
 }
 
 /* Insert a new card into a slot */
diff --git a/hw/s390x/s390-virtio-bus.c b/hw/s390x/s390-virtio-bus.c
index e4fc35366b..930b4f7cd0 100644
--- a/hw/s390x/s390-virtio-bus.c
+++ b/hw/s390x/s390-virtio-bus.c
@@ -313,7 +313,8 @@ static void s390_virtio_rng_instance_init(Object *obj)
     object_initialize(&dev->vdev, sizeof(dev->vdev), TYPE_VIRTIO_RNG);
     object_property_add_child(obj, "virtio-backend", OBJECT(&dev->vdev), NULL);
     object_property_add_link(obj, "rng", TYPE_RNG_BACKEND,
-                             (Object **)&dev->vdev.conf.rng, NULL);
+                             (Object **)&dev->vdev.conf.rng,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE, NULL);
 }
 
 static uint64_t s390_virtio_device_vq_token(VirtIOS390Device *dev, int vq)
diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index a01801e342..aebb2dec6d 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -1272,7 +1272,8 @@ static void virtio_ccw_rng_instance_init(Object *obj)
     object_initialize(&dev->vdev, sizeof(dev->vdev), TYPE_VIRTIO_RNG);
     object_property_add_child(obj, "virtio-backend", OBJECT(&dev->vdev), NULL);
     object_property_add_link(obj, "rng", TYPE_RNG_BACKEND,
-                             (Object **)&dev->vdev.conf.rng, NULL);
+                             (Object **)&dev->vdev.conf.rng,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE, NULL);
 }
 
 static Property virtio_ccw_rng_properties[] = {
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 7b91841a1d..eebb819d98 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1517,7 +1517,8 @@ static void virtio_rng_initfn(Object *obj)
     object_initialize(&dev->vdev, sizeof(dev->vdev), TYPE_VIRTIO_RNG);
     object_property_add_child(obj, "virtio-backend", OBJECT(&dev->vdev), NULL);
     object_property_add_link(obj, "rng", TYPE_RNG_BACKEND,
-                             (Object **)&dev->vdev.conf.rng, NULL);
+                             (Object **)&dev->vdev.conf.rng,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE, NULL);
 
 }
 
diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
index a16e3bc52e..2efda8b443 100644
--- a/hw/virtio/virtio-rng.c
+++ b/hw/virtio/virtio-rng.c
@@ -223,7 +223,8 @@ static void virtio_rng_initfn(Object *obj)
     VirtIORNG *vrng = VIRTIO_RNG(obj);
 
     object_property_add_link(obj, "rng", TYPE_RNG_BACKEND,
-                             (Object **)&vrng->conf.rng, NULL);
+                             (Object **)&vrng->conf.rng,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE, NULL);
 }
 
 static const TypeInfo virtio_rng_info = {
diff --git a/include/qom/object.h b/include/qom/object.h
index 4cd77049e4..9feb441986 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -1067,12 +1067,18 @@ Object *object_resolve_path_component(Object *parent, const gchar *part);
 void object_property_add_child(Object *obj, const char *name,
                                Object *child, Error **errp);
 
+typedef enum {
+    /* Unref the link pointer when the property is deleted */
+    OBJ_PROP_LINK_UNREF_ON_RELEASE = 0x1,
+} ObjectPropertyLinkFlags;
+
 /**
  * object_property_add_link:
  * @obj: the object to add a property to
  * @name: the name of the property
  * @type: the qobj type of the link
  * @child: a pointer to where the link object reference is stored
+ * @flags: additional options for the link
  * @errp: if an error occurs, a pointer to an area to store the area
  *
  * Links establish relationships between objects.  Links are unidirectional
@@ -1084,10 +1090,13 @@ void object_property_add_child(Object *obj, const char *name,
  * Ownership of the pointer that @child points to is transferred to the
  * link property.  The reference count for <code>*@child</code> is
  * managed by the property from after the function returns till the
- * property is deleted with object_property_del().
+ * property is deleted with object_property_del().  If the
+ * <code>@flags</code> <code>OBJ_PROP_LINK_UNREF_ON_RELEASE</code> bit is set,
+ * the reference count is decremented when the property is deleted.
  */
 void object_property_add_link(Object *obj, const char *name,
                               const char *type, Object **child,
+                              ObjectPropertyLinkFlags flags,
                               Error **errp);
 
 /**
diff --git a/qom/object.c b/qom/object.c
index cc946d9dac..9e22f11e21 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -1023,10 +1023,16 @@ out:
     g_free(type);
 }
 
+typedef struct {
+    Object **child;
+    ObjectPropertyLinkFlags flags;
+} LinkProperty;
+
 static void object_get_link_property(Object *obj, Visitor *v, void *opaque,
                                      const char *name, Error **errp)
 {
-    Object **child = opaque;
+    LinkProperty *lprop = opaque;
+    Object **child = lprop->child;
     gchar *path;
 
     if (*child) {
@@ -1081,7 +1087,8 @@ static void object_set_link_property(Object *obj, Visitor *v, void *opaque,
                                      const char *name, Error **errp)
 {
     Error *local_err = NULL;
-    Object **child = opaque;
+    LinkProperty *prop = opaque;
+    Object **child = prop->child;
     Object *old_target = *child;
     Object *new_target = NULL;
     char *path = NULL;
@@ -1107,18 +1114,41 @@ static void object_set_link_property(Object *obj, Visitor *v, void *opaque,
     }
 }
 
+static void object_release_link_property(Object *obj, const char *name,
+                                         void *opaque)
+{
+    LinkProperty *prop = opaque;
+
+    if ((prop->flags & OBJ_PROP_LINK_UNREF_ON_RELEASE) && *prop->child) {
+        object_unref(*prop->child);
+    }
+    g_free(prop);
+}
+
 void object_property_add_link(Object *obj, const char *name,
                               const char *type, Object **child,
+                              ObjectPropertyLinkFlags flags,
                               Error **errp)
 {
+    Error *local_err = NULL;
+    LinkProperty *prop = g_malloc(sizeof(*prop));
     gchar *full_type;
 
+    prop->child = child;
+    prop->flags = flags;
+
     full_type = g_strdup_printf("link<%s>", type);
 
     object_property_add(obj, name, full_type,
                         object_get_link_property,
                         object_set_link_property,
-                        NULL, child, errp);
+                        object_release_link_property,
+                        prop,
+                        &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        g_free(prop);
+    }
 
     g_free(full_type);
 }
diff --git a/ui/console.c b/ui/console.c
index 4df251d579..9974212409 100644
--- a/ui/console.c
+++ b/ui/console.c
@@ -1180,7 +1180,9 @@ static QemuConsole *new_console(DisplayState *ds, console_type_t console_type)
     obj = object_new(TYPE_QEMU_CONSOLE);
     s = QEMU_CONSOLE(obj);
     object_property_add_link(obj, "device", TYPE_DEVICE,
-                             (Object **)&s->device, &local_err);
+                             (Object **)&s->device,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE,
+                             &local_err);
     object_property_add_uint32_ptr(obj, "head",
                                    &s->head, &local_err);