qdev: unplug blocker for devices

Add blocker to prevent hot-unplug of devices

TYPE_VFIO_USER_SERVER, which is introduced shortly, attaches itself to a
PCIDevice on which it depends. If the attached PCIDevice gets removed
while the server in use, it could cause it crash. To prevent this,
TYPE_VFIO_USER_SERVER adds an unplug blocker for the PCIDevice.

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>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: c41ef80b7cc063314d629737bed2159e5713f2e0.1655151679.git.jag.raman@oracle.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

3 files changed, 57 insertions, 0 deletions

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 84f3019..0806d8f 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -468,6 +468,28 @@ char *qdev_get_dev_path(DeviceState *dev)
     return NULL;
 }
 
+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;
+}
+
 static bool device_get_realized(Object *obj, Error **errp)
 {
     DeviceState *dev = DEVICE(obj);
@@ -704,6 +726,8 @@ static void device_finalize(Object *obj)
 
     DeviceState *dev = DEVICE(obj);
 
+    g_assert(!dev->unplug_blockers);
+
     QLIST_FOREACH_SAFE(ngl, &dev->gpios, node, next) {
         QLIST_REMOVE(ngl, node);
         qemu_free_irqs(ngl->in, ngl->num_in);
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 92c3d65..98774e2 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 {
@@ -420,6 +421,34 @@ void qdev_machine_creation_done(void);
 bool qdev_machine_modified(void);
 
 /**
+ * qdev_add_unplug_blocker: Add 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: Remove 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: Confirm 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
  *
  * GPIO lines use either positive (active-high) logic,
diff --git a/softmmu/qdev-monitor.c b/softmmu/qdev-monitor.c
index bb5897f..4b0ef65 100644
--- a/softmmu/qdev-monitor.c
+++ b/softmmu/qdev-monitor.c
@@ -899,6 +899,10 @@ void qdev_unplug(DeviceState *dev, Error **errp)
     HotplugHandlerClass *hdc;
     Error *local_err = NULL;
 
+    if (qdev_unplug_blocked(dev, errp)) {
+        return;
+    }
+
     if (dev->parent_bus && !qbus_is_hotpluggable(dev->parent_bus)) {
         error_setg(errp, QERR_BUS_NO_HOTPLUG, dev->parent_bus->name);
         return;