[Qemu-devel] [PATCH RFC 1/6] virtio-bus: common ioeventfd infrastructure

[Cornelia Huck]

Introduce a set of ioeventfd callbacks on the virtio-bus level
that can be implemented by the individual transports. At the
virtio-bus level, do common handling for host notifiers (which
is actually most of it).

Two things of note:
- We always iterate over all possible virtio queues, even though
ccw (currently) has a lower limit. It does not really matter in
this place.
- We allow for the virtio-bus caller to pass an "assign" argument
down when stopping ioeventfd, which the old interface did not allow.

Signed-off-by: Cornelia Huck <address@hidden>
---
 hw/virtio/virtio-bus.c         | 108 +++++++++++++++++++++++++++++++++++++++++
 include/hw/virtio/virtio-bus.h |  14 ++++++
 2 files changed, 122 insertions(+)

diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index 574f0e2..501300f 100644
--- a/hw/virtio/virtio-bus.c
+++ b/hw/virtio/virtio-bus.c
@@ -146,6 +146,114 @@ void virtio_bus_set_vdev_config(VirtioBusState *bus, 
uint8_t *config)
     }
 }
 
+static int set_host_notifier_internal(DeviceState *proxy, VirtioBusState *bus,
+                                      int n, bool assign, bool set_handler)
+{
+    VirtIODevice *vdev = virtio_bus_get_device(bus);
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
+    VirtQueue *vq = virtio_get_queue(vdev, n);
+    EventNotifier *notifier = virtio_queue_get_host_notifier(vq);
+    int r = 0;
+
+    if (assign) {
+        r = event_notifier_init(notifier, 1);
+        if (r < 0) {
+            error_report("%s: unable to init event notifier: %d", __func__, r);
+            return r;
+        }
+        virtio_queue_set_host_notifier_fd_handler(vq, true, set_handler);
+        r = k->ioeventfd_assign(proxy, notifier, n, assign);
+        if (r < 0) {
+            error_report("%s: unable to assign ioeventfd: %d", __func__, r);
+            virtio_queue_set_host_notifier_fd_handler(vq, false, false);
+            event_notifier_cleanup(notifier);
+            return r;
+        }
+    } else {
+        virtio_queue_set_host_notifier_fd_handler(vq, false, false);
+        k->ioeventfd_assign(proxy, notifier, n, assign);
+        event_notifier_cleanup(notifier);
+    }
+    return r;
+}
+
+void virtio_bus_start_ioeventfd(VirtioBusState *bus)
+{
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
+    DeviceState *proxy = DEVICE(BUS(bus)->parent);
+    VirtIODevice *vdev;
+    int n, r;
+
+    if (!k->ioeventfd_started || k->ioeventfd_started(proxy)) {
+        return;
+    }
+    if (!k->ioeventfd_disabled(proxy)) {
+        return;
+    }
+    vdev = virtio_bus_get_device(bus);
+    for (n = 0; n < VIRTIO_QUEUE_MAX; n++) {
+        if (!virtio_queue_get_num(vdev, n)) {
+            continue;
+        }
+        r = set_host_notifier_internal(proxy, bus, n, true, true);
+        if (r < 0) {
+            goto assign_error;
+        }
+    }
+    k->ioeventfd_set_started(proxy, true, false);
+    return;
+
+assign_error:
+    while (--n >= 0) {
+        if (!virtio_queue_get_num(vdev, n)) {
+            continue;
+        }
+
+        r = set_host_notifier_internal(proxy, bus, n, false, false);
+        assert(r >= 0);
+    }
+    k->ioeventfd_set_started(proxy, false, true);
+    error_report("%s: failed. Fallback to userspace (slower).", __func__);
+}
+
+void virtio_bus_stop_ioeventfd(VirtioBusState *bus, bool assign)
+{
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
+    DeviceState *proxy = DEVICE(BUS(bus)->parent);
+    VirtIODevice *vdev;
+    int n, r;
+
+    if (!k->ioeventfd_started || !k->ioeventfd_started(proxy)) {
+        return;
+    }
+    vdev = virtio_bus_get_device(bus);
+    for (n = 0; n < VIRTIO_QUEUE_MAX; n++) {
+        if (!virtio_queue_get_num(vdev, n)) {
+            continue;
+        }
+        r = set_host_notifier_internal(proxy, bus, n, assign, false);
+        assert(r >= 0);
+    }
+    k->ioeventfd_set_started(proxy, false, false);
+}
+
+int virtio_bus_set_host_notifier(VirtioBusState *bus, int n, bool assign)
+{
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(bus);
+    DeviceState *proxy = DEVICE(BUS(bus)->parent);
+
+    if (!k->ioeventfd_started) {
+        return -ENOSYS;
+    }
+    /* Stop using the generic ioeventfd, we are doing eventfd handling
+     * ourselves below */
+    k->ioeventfd_set_disabled(proxy, assign);
+    if (assign) {
+        virtio_bus_stop_ioeventfd(bus, assign);
+    }
+    return set_host_notifier_internal(proxy, bus, n, assign, false);
+}
+
 static char *virtio_bus_get_dev_path(DeviceState *dev)
 {
     BusState *bus = qdev_get_parent_bus(dev);
diff --git a/include/hw/virtio/virtio-bus.h b/include/hw/virtio/virtio-bus.h
index 3f2c136..0281cbf 100644
--- a/include/hw/virtio/virtio-bus.h
+++ b/include/hw/virtio/virtio-bus.h
@@ -71,6 +71,16 @@ typedef struct VirtioBusClass {
     void (*device_unplugged)(DeviceState *d);
     int (*query_nvectors)(DeviceState *d);
     /*
+     * ioeventfd handling: if the transport implements ioeventfd_started,
+     * it must implement the other ioeventfd callbacks as well
+     */
+    bool (*ioeventfd_started)(DeviceState *d);
+    void (*ioeventfd_set_started)(DeviceState *d, bool started, bool err);
+    bool (*ioeventfd_disabled)(DeviceState *d);
+    void (*ioeventfd_set_disabled)(DeviceState *d, bool disabled);
+    int (*ioeventfd_assign)(DeviceState *d, EventNotifier *notifier,
+                            int n, bool assign);
+    /*
      * Does the transport have variable vring alignment?
      * (ie can it ever call virtio_queue_set_align()?)
      * Note that changing this will break migration for this transport.
@@ -111,4 +121,8 @@ static inline VirtIODevice 
*virtio_bus_get_device(VirtioBusState *bus)
     return (VirtIODevice *)qdev;
 }
 
+void virtio_bus_start_ioeventfd(VirtioBusState *bus);
+void virtio_bus_stop_ioeventfd(VirtioBusState *bus, bool assign);
+int virtio_bus_set_host_notifier(VirtioBusState *bus, int n, bool assign);
+
 #endif /* VIRTIO_BUS_H */
-- 
2.6.5