qdev: Track runtime machine modifications

Create a trivial interface to track whether the machine has been
modified since boot.  Adding or removing devices will trigger this
to return true.  An example usage scenario for such an interface is
the rtl8139 driver which includes a cpu_register_io_memory() value
in it's migration stream.  For the majority of migrations, where
no hotplug has occured in the machine, this works correctly.  Once
the machine is modified, we can use this interface to detect that
and include a subsection for the device to prevent migrations to
rtl8139 versions with this bug.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 11 insertions, 0 deletions

diff --git a/hw/qdev.c b/hw/qdev.c
index 31eb464f23..5b8d3742ec 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -32,6 +32,8 @@
 #include "blockdev.h"
 
 static int qdev_hotplug = 0;
+static bool qdev_hot_added = false;
+static bool qdev_hot_removed = false;
 
 /* This is a nasty hack to allow passing a NULL bus to qdev_create.  */
 static BusState *main_system_bus;
@@ -93,6 +95,7 @@ static DeviceState *qdev_create_from_info(BusState *bus, DeviceInfo *info)
     if (qdev_hotplug) {
         assert(bus->allow_hotplug);
         dev->hotplugged = 1;
+        qdev_hot_added = true;
     }
     dev->instance_id_alias = -1;
     dev->state = DEV_STATE_CREATED;
@@ -294,6 +297,8 @@ int qdev_unplug(DeviceState *dev)
     }
     assert(dev->info->unplug != NULL);
 
+    qdev_hot_removed = true;
+
     return dev->info->unplug(dev);
 }
 
@@ -395,6 +400,11 @@ void qdev_machine_creation_done(void)
     qdev_hotplug = 1;
 }
 
+bool qdev_machine_modified(void)
+{
+    return qdev_hot_added || qdev_hot_removed;
+}
+
 /* Get a character (serial) device interface.  */
 CharDriverState *qdev_init_chardev(DeviceState *dev)
 {
diff --git a/hw/qdev.h b/hw/qdev.h
index 2be775f9e8..e520aaa786 100644
--- a/hw/qdev.h
+++ b/hw/qdev.h
@@ -132,6 +132,7 @@ int qdev_unplug(DeviceState *dev);
 void qdev_free(DeviceState *dev);
 int qdev_simple_unplug_cb(DeviceState *dev);
 void qdev_machine_creation_done(void);
+bool qdev_machine_modified(void);
 
 qemu_irq qdev_get_gpio_in(DeviceState *dev, int n);
 void qdev_connect_gpio_out(DeviceState *dev, int n, qemu_irq pin);