[Qemu-devel] [PATCH RFC 2/4] qdev/machine: Introduce hotplug_allowed hook

[Peter Xu <peterx@redhat.com>]

Introduce this new per-machine hook to give any machine class a chance
to do a sanity check on the to-be-hotplugged device as a sanity test.
This will be used for x86 to try to detect some illegal configuration
of devices, e.g., possible conflictions between vfio-pci and x86
vIOMMU.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/core/qdev.c         | 17 +++++++++++++++++
 include/hw/boards.h    |  9 +++++++++
 include/hw/qdev-core.h |  1 +
 qdev-monitor.c         |  7 +++++++
 4 files changed, 34 insertions(+)

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 94ebc0a4a1..d792b43c37 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -236,6 +236,23 @@ HotplugHandler *qdev_get_machine_hotplug_handler(DeviceState *dev)
     return NULL;
 }
 
+bool qdev_hotplug_allowed(DeviceState *dev, Error **errp)
+{
+    MachineState *machine;
+    MachineClass *mc;
+    Object *m_obj = qdev_get_machine();
+
+    if (object_dynamic_cast(m_obj, TYPE_MACHINE)) {
+        machine = MACHINE(m_obj);
+        mc = MACHINE_GET_CLASS(machine);
+        if (mc->hotplug_allowed) {
+            return mc->hotplug_allowed(machine, dev, errp);
+        }
+    }
+
+    return true;
+}
+
 HotplugHandler *qdev_get_bus_hotplug_handler(DeviceState *dev)
 {
     if (dev->parent_bus) {
diff --git a/include/hw/boards.h b/include/hw/boards.h
index a71d1a53a5..1cf63be45d 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -166,6 +166,13 @@ typedef struct {
  *    The function pointer to hook different machine specific functions for
  *    parsing "smp-opts" from QemuOpts to MachineState::CpuTopology and more
  *    machine specific topology fields, such as smp_dies for PCMachine.
+ * @hotplug_allowed:
+ *    If the hook is provided, then it'll be called for each device
+ *    hotplug to check whether the device hotplug is allowed.  Return
+ *    true to grant allowance or false to reject the hotplug.  When
+ *    false is returned, an error must be set to show the reason of
+ *    the rejection.  If the hook is not provided, all hotplug will be
+ *    allowed.
  */
 struct MachineClass {
     /*< private >*/
@@ -223,6 +230,8 @@ struct MachineClass {
 
     HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
                                            DeviceState *dev);
+    bool (*hotplug_allowed)(MachineState *state, DeviceState *dev,
+                            Error **errp);
     CpuInstanceProperties (*cpu_index_to_instance_props)(MachineState *machine,
                                                          unsigned cpu_index);
     const CPUArchIdList *(*possible_cpu_arch_ids)(MachineState *machine);
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 136df7774c..88e7ec4b60 100644
--- a/include/hw/qdev-core.h
+++ b/include/hw/qdev-core.h
@@ -284,6 +284,7 @@ void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
                                  int required_for_version);
 HotplugHandler *qdev_get_bus_hotplug_handler(DeviceState *dev);
 HotplugHandler *qdev_get_machine_hotplug_handler(DeviceState *dev);
+bool qdev_hotplug_allowed(DeviceState *dev, Error **errp);
 /**
  * qdev_get_hotplug_handler: Get handler responsible for device wiring
  *
diff --git a/qdev-monitor.c b/qdev-monitor.c
index 58222c2211..6c80602771 100644
--- a/qdev-monitor.c
+++ b/qdev-monitor.c
@@ -614,6 +614,13 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
     /* create device */
     dev = DEVICE(object_new(driver));
 
+    /* Check whether the hotplug is allowed by the machine */
+    if (qdev_hotplug && !qdev_hotplug_allowed(dev, &err)) {
+        /* Error must be set in the machine hook */
+        assert(err);
+        goto err_del_dev;
+    }
+
     if (bus) {
         qdev_set_parent_bus(dev, bus);
     } else if (qdev_hotplug && !qdev_get_machine_hotplug_handler(dev)) {
-- 
2.21.0