virtio: introduce virtio_device_ioeventfd_enabled

This will be used to forbid iothread configuration when the
proxy does not allow using ioeventfd.  To simplify the implementation,
change the direction of the ioeventfd_disabled callback too.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/s390x/virtio-ccw.c

@@ -59,11 +59,11 @@ static void virtio_ccw_stop_ioeventfd(VirtioCcwDevice *dev)
     virtio_bus_stop_ioeventfd(&dev->bus);
 }
 
-static bool virtio_ccw_ioeventfd_disabled(DeviceState *d)
+static bool virtio_ccw_ioeventfd_enabled(DeviceState *d)
 {
     VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
 
-    return !(dev->flags & VIRTIO_CCW_FLAG_USE_IOEVENTFD);
+    return (dev->flags & VIRTIO_CCW_FLAG_USE_IOEVENTFD) != 0;
 }
 
 static int virtio_ccw_ioeventfd_assign(DeviceState *d, EventNotifier *notifier,
@@ -1589,7 +1589,7 @@ static void virtio_ccw_bus_class_init(ObjectClass *klass, void *data)
     k->pre_plugged = virtio_ccw_pre_plugged;
     k->device_plugged = virtio_ccw_device_plugged;
     k->device_unplugged = virtio_ccw_device_unplugged;
-    k->ioeventfd_disabled = virtio_ccw_ioeventfd_disabled;
+    k->ioeventfd_enabled = virtio_ccw_ioeventfd_enabled;
     k->ioeventfd_assign = virtio_ccw_ioeventfd_assign;
 }
 

hw/virtio/virtio-bus.c

@@ -193,7 +193,7 @@ int virtio_bus_start_ioeventfd(VirtioBusState *bus)
     VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
     int r;
 
-    if (!k->ioeventfd_assign || k->ioeventfd_disabled(proxy)) {
+    if (!k->ioeventfd_assign || !k->ioeventfd_enabled(proxy)) {
         return -ENOSYS;
     }
     if (bus->ioeventfd_started || bus->ioeventfd_disabled) {
@@ -223,6 +223,14 @@ void virtio_bus_stop_ioeventfd(VirtioBusState *bus)
     bus->ioeventfd_started = false;
 }
 
+bool virtio_bus_ioeventfd_enabled(VirtioBusState *bus)
+{
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
+    DeviceState *proxy = DEVICE(BUS(bus)->parent);
+
+    return k->ioeventfd_assign && k->ioeventfd_enabled(proxy);
+}
+
 /*
  * This function switches from/to the generic ioeventfd handler.
  * assign==false means 'use generic ioeventfd handler'.

hw/virtio/virtio-mmio.c

@@ -92,9 +92,9 @@ typedef struct {
     bool format_transport_address;
 } VirtIOMMIOProxy;
 
-static bool virtio_mmio_ioeventfd_disabled(DeviceState *d)
+static bool virtio_mmio_ioeventfd_enabled(DeviceState *d)
 {
-    return !kvm_eventfds_enabled();
+    return kvm_eventfds_enabled();
 }
 
 static int virtio_mmio_ioeventfd_assign(DeviceState *d,
@@ -531,7 +531,7 @@ static void virtio_mmio_bus_class_init(ObjectClass *klass, void *data)
     k->save_config = virtio_mmio_save_config;
     k->load_config = virtio_mmio_load_config;
     k->set_guest_notifiers = virtio_mmio_set_guest_notifiers;
-    k->ioeventfd_disabled = virtio_mmio_ioeventfd_disabled;
+    k->ioeventfd_enabled = virtio_mmio_ioeventfd_enabled;
     k->ioeventfd_assign = virtio_mmio_ioeventfd_assign;
     k->has_variable_vring_alignment = true;
     bus_class->max_dev = 1;

hw/virtio/virtio-pci.c

@@ -262,11 +262,11 @@ static int virtio_pci_load_queue(DeviceState *d, int n, QEMUFile *f)
     return 0;
 }
 
-static bool virtio_pci_ioeventfd_disabled(DeviceState *d)
+static bool virtio_pci_ioeventfd_enabled(DeviceState *d)
 {
     VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
 
-    return !(proxy->flags & VIRTIO_PCI_FLAG_USE_IOEVENTFD);
+    return (proxy->flags & VIRTIO_PCI_FLAG_USE_IOEVENTFD) != 0;
 }
 
 #define QEMU_VIRTIO_PCI_QUEUE_MEM_MULT 0x1000
@@ -2516,7 +2516,7 @@ static void virtio_pci_bus_class_init(ObjectClass *klass, void *data)
     k->device_plugged = virtio_pci_device_plugged;
     k->device_unplugged = virtio_pci_device_unplugged;
     k->query_nvectors = virtio_pci_query_nvectors;
-    k->ioeventfd_disabled = virtio_pci_ioeventfd_disabled;
+    k->ioeventfd_enabled = virtio_pci_ioeventfd_enabled;
     k->ioeventfd_assign = virtio_pci_ioeventfd_assign;
 }
 

hw/virtio/virtio.c

@@ -2247,6 +2247,14 @@ static void virtio_device_class_init(ObjectClass *klass, void *data)
     vdc->stop_ioeventfd = virtio_device_stop_ioeventfd_impl;
 }
 
+bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev)
+{
+    BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
+    VirtioBusState *vbus = VIRTIO_BUS(qbus);
+
+    return virtio_bus_ioeventfd_enabled(vbus);
+}
+
 static const TypeInfo virtio_device_info = {
     .name = TYPE_VIRTIO_DEVICE,
     .parent = TYPE_DEVICE,

include/hw/virtio/virtio-bus.h

@@ -71,10 +71,10 @@ typedef struct VirtioBusClass {
     int (*query_nvectors)(DeviceState *d);
     /*
      * ioeventfd handling: if the transport implements ioeventfd_assign,
-     * it must implement ioeventfd_disabled as well.
+     * it must implement ioeventfd_enabled as well.
      */
-    /* Returns true if the ioeventfd has been disabled for the device. */
-    bool (*ioeventfd_disabled)(DeviceState *d);
+    /* Returns true if the ioeventfd is enabled for the device. */
+    bool (*ioeventfd_enabled)(DeviceState *d);
     /*
      * Assigns/deassigns the ioeventfd backing for the transport on
      * the device for queue number n. Returns an error value on
@@ -131,6 +131,8 @@ static inline VirtIODevice *virtio_bus_get_device(VirtioBusState *bus)
     return (VirtIODevice *)qdev;
 }
 
+/* Return whether the proxy allows ioeventfd.  */
+bool virtio_bus_ioeventfd_enabled(VirtioBusState *bus);
 /* Start the ioeventfd. */
 int virtio_bus_start_ioeventfd(VirtioBusState *bus);
 /* Stop the ioeventfd. */

include/hw/virtio/virtio.h

@@ -273,6 +273,7 @@ void virtio_queue_set_guest_notifier_fd_handler(VirtQueue *vq, bool assign,
                                                 bool with_irqfd);
 int virtio_device_start_ioeventfd(VirtIODevice *vdev);
 void virtio_device_stop_ioeventfd(VirtIODevice *vdev);
+bool virtio_device_ioeventfd_enabled(VirtIODevice *vdev);
 EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq);
 void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
                                                bool set_handler);