[RFC v2 01/15] qdev: Add pointer to BusChild in DeviceState

[Zhao Liu <zhao1.liu@xxxxxxxxx>]

The device topology structures based on buses are unidirectional: the
parent device can access the child device through the BusChild within
the bus, but not vice versa.

For the CPU topology tree constructed on the device-bus, it is necessary
for the child device to be able to access the parent device via the
parent bus. To address this, introduce a pointer to the BusChild, named
bus_node.

This pointer also simplifies the logic of bus_remove_child(). Instead of
the parent bus needing to traverse the children list to locate the
corresponding BusChild, it can now directly find it using the bus_node
pointer.

Signed-off-by: Zhao Liu <zhao1.liu@xxxxxxxxx>
---
 hw/core/qdev.c          | 29 ++++++++++++++---------------
 include/hw/qdev-core.h  |  4 ++++
 include/qemu/typedefs.h |  1 +
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index db36f54d914a..4429856eaddd 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -57,25 +57,23 @@ static void bus_free_bus_child(BusChild *kid)
 
 static void bus_remove_child(BusState *bus, DeviceState *child)
 {
-    BusChild *kid;
-
-    QTAILQ_FOREACH(kid, &bus->children, sibling) {
-        if (kid->child == child) {
-            char name[32];
+    BusChild *kid = child->bus_node;
+    char name[32];
 
-            snprintf(name, sizeof(name), "child[%d]", kid->index);
-            QTAILQ_REMOVE_RCU(&bus->children, kid, sibling);
+    if (!kid) {
+        return;
+    }
 
-            bus->num_children--;
+    snprintf(name, sizeof(name), "child[%d]", kid->index);
+    QTAILQ_REMOVE_RCU(&bus->children, kid, sibling);
+    child->bus_node = NULL;
+    bus->num_children--;
 
-            /* This gives back ownership of kid->child back to us.  */
-            object_property_del(OBJECT(bus), name);
+    /* This gives back ownership of kid->child back to us.  */
+    object_property_del(OBJECT(bus), name);
 
-            /* free the bus kid, when it is safe to do so*/
-            call_rcu(kid, bus_free_bus_child, rcu);
-            break;
-        }
-    }
+    /* free the bus kid, when it is safe to do so*/
+    call_rcu(kid, bus_free_bus_child, rcu);
 }
 
 static void bus_add_child(BusState *bus, DeviceState *child)
@@ -86,6 +84,7 @@ static void bus_add_child(BusState *bus, DeviceState *child)
     bus->num_children++;
     kid->index = bus->max_index++;
     kid->child = child;
+    child->bus_node = kid;
     object_ref(OBJECT(kid->child));
 
     QTAILQ_INSERT_HEAD_RCU(&bus->children, kid, sibling);
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index aa97c34a4be7..85c7d462dfba 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -253,6 +253,10 @@ struct DeviceState {
      * @parent_bus: bus this device belongs to
      */
     BusState *parent_bus;
+    /**
+     * @bus_node: bus node inserted in parent bus
+     */
+    BusChild *bus_node;
     /**
      * @gpios: QLIST of named GPIOs the device provides.
      */
diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
index 9d222dc37628..aef41c4e67ce 100644
--- a/include/qemu/typedefs.h
+++ b/include/qemu/typedefs.h
@@ -32,6 +32,7 @@ typedef struct BdrvDirtyBitmapIter BdrvDirtyBitmapIter;
 typedef struct BlockBackend BlockBackend;
 typedef struct BlockBackendRootState BlockBackendRootState;
 typedef struct BlockDriverState BlockDriverState;
+typedef struct BusChild BusChild;
 typedef struct BusClass BusClass;
 typedef struct BusState BusState;
 typedef struct Chardev Chardev;
-- 
2.34.1