[PATCH v6 03/19] qdev: unplug blocker for devices

[Jagannathan Raman]

Add blocker to prevent hot-unplug of devices

Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
---
 include/hw/qdev-core.h | 35 +++++++++++++++++++++++++++++++++++
 softmmu/qdev-monitor.c | 26 ++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 92c3d65208..4b1d77f44a 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -193,6 +193,7 @@ struct DeviceState {
     int instance_id_alias;
     int alias_required_for_version;
     ResettableState reset;
+    GSList *unplug_blockers;
 };
 
 struct DeviceListener {
@@ -419,6 +420,40 @@ void qdev_simple_device_unplug_cb(HotplugHandler 
*hotplug_dev,
 void qdev_machine_creation_done(void);
 bool qdev_machine_modified(void);
 
+/**
+ * Device Unplug blocker: prevents a device from being unplugged. It could
+ * be used to indicate that another object depends on the device.
+ *
+ * qdev_add_unplug_blocker: Adds an unplug blocker to a device
+ *
+ * @dev: Device to be blocked from unplug
+ * @reason: Reason for blocking
+ *
+ */
+void qdev_add_unplug_blocker(DeviceState *dev, Error *reason);
+
+/**
+ * qdev_del_unplug_blocker: Removes an unplug blocker from a device
+ *
+ * @dev: Device to be unblocked
+ * @reason: Pointer to the Error used with qdev_add_unplug_blocker.
+ *          Used as a handle to lookup the blocker for deletion.
+ *
+ */
+void qdev_del_unplug_blocker(DeviceState *dev, Error *reason);
+
+/**
+ * qdev_unplug_blocked: Confirms if a device is blocked from unplug
+ *
+ * @dev: Device to be tested
+ * @reason: Returns one of the reasons why the device is blocked,
+ *          if any
+ *
+ * Returns: true if device is blocked from unplug, false otherwise
+ *
+ */
+bool qdev_unplug_blocked(DeviceState *dev, Error **errp);
+
 /**
  * GpioPolarity: Polarity of a GPIO line
  *
diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
index 01f3834db5..69d9cf3f25 100644
--- a/softmmu/qdev-monitor.c
+++ b/softmmu/qdev-monitor.c
@@ -945,10 +945,36 @@ void qmp_device_del(const char *id, Error **errp)
             return;
         }
 
+        if (qdev_unplug_blocked(dev, errp)) {
+            return;
+        }
+
         qdev_unplug(dev, errp);
     }
 }
 
+void qdev_add_unplug_blocker(DeviceState *dev, Error *reason)
+{
+    dev->unplug_blockers = g_slist_prepend(dev->unplug_blockers, reason);
+}
+
+void qdev_del_unplug_blocker(DeviceState *dev, Error *reason)
+{
+    dev->unplug_blockers = g_slist_remove(dev->unplug_blockers, reason);
+}
+
+bool qdev_unplug_blocked(DeviceState *dev, Error **errp)
+{
+    ERRP_GUARD();
+
+    if (dev->unplug_blockers) {
+        error_propagate(errp, error_copy(dev->unplug_blockers->data));
+        return true;
+    }
+
+    return false;
+}
+
 void hmp_device_add(Monitor *mon, const QDict *qdict)
 {
     Error *err = NULL;
-- 
2.20.1