[Qemu-devel] [PATCH 1/2] virtio: add aio handler

["Michael S. Tsirkin" <mst@redhat.com>]

In addition to handling IO in vcpu thread and
in io thread, blk dataplane introduces yet another mode:
handling it by aio.

This reuses the same handler as previous modes,
which triggers races as these were not designed to be reentrant.

As a temporary fix, add a separate handler just for aio, this will make
it possible to disable regular handlers when dataplane is active.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 include/hw/virtio/virtio.h |  4 ++++
 hw/virtio/virtio.c         | 36 ++++++++++++++++++++++++++++++++----
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 2b5b248..c032067 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -142,6 +142,9 @@ VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
                             void (*handle_output)(VirtIODevice *,
                                                   VirtQueue *));
 
+void virtio_set_queue_aio(VirtQueue *vq,
+                          void (*handle_output)(VirtIODevice *, VirtQueue *));
+
 void virtio_del_queue(VirtIODevice *vdev, int n);
 
 void *virtqueue_alloc_element(size_t sz, unsigned out_num, unsigned in_num);
@@ -253,6 +256,7 @@ void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign,
 void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext *ctx,
                                                 bool assign, bool set_handler);
 void virtio_queue_notify_vq(VirtQueue *vq);
+void virtio_queue_notify_aio_vq(VirtQueue *vq);
 void virtio_irq(VirtQueue *vq);
 VirtQueue *virtio_vector_first_queue(VirtIODevice *vdev, uint16_t vector);
 VirtQueue *virtio_vector_next_queue(VirtQueue *vq);
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 08275a9..182bc56 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -94,6 +94,7 @@ struct VirtQueue
 
     uint16_t vector;
     void (*handle_output)(VirtIODevice *vdev, VirtQueue *vq);
+    void (*handle_aio_output)(VirtIODevice *vdev, VirtQueue *vq);
     VirtIODevice *vdev;
     EventNotifier guest_notifier;
     EventNotifier host_notifier;
@@ -1086,6 +1087,16 @@ void virtio_queue_set_align(VirtIODevice *vdev, int n, int align)
     virtio_queue_update_rings(vdev, n);
 }
 
+void virtio_queue_notify_aio_vq(VirtQueue *vq)
+{
+    if (vq->vring.desc && vq->handle_aio_output) {
+        VirtIODevice *vdev = vq->vdev;
+
+        trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
+        vq->handle_aio_output(vdev, vq);
+    }
+}
+
 void virtio_queue_notify_vq(VirtQueue *vq)
 {
     if (vq->vring.desc && vq->handle_output) {
@@ -1141,10 +1152,19 @@ VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
     vdev->vq[i].vring.num_default = queue_size;
     vdev->vq[i].vring.align = VIRTIO_PCI_VRING_ALIGN;
     vdev->vq[i].handle_output = handle_output;
+    vdev->vq[i].handle_aio_output = NULL;
 
     return &vdev->vq[i];
 }
 
+void virtio_set_queue_aio(VirtQueue *vq,
+                          void (*handle_output)(VirtIODevice *, VirtQueue *))
+{
+    assert(vq->handle_output);
+
+    vq->handle_aio_output = handle_output;
+}
+
 void virtio_del_queue(VirtIODevice *vdev, int n)
 {
     if (n < 0 || n >= VIRTIO_QUEUE_MAX) {
@@ -1778,11 +1798,11 @@ EventNotifier *virtio_queue_get_guest_notifier(VirtQueue *vq)
     return &vq->guest_notifier;
 }
 
-static void virtio_queue_host_notifier_read(EventNotifier *n)
+static void virtio_queue_host_notifier_aio_read(EventNotifier *n)
 {
     VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
     if (event_notifier_test_and_clear(n)) {
-        virtio_queue_notify_vq(vq);
+        virtio_queue_notify_aio_vq(vq);
     }
 }
 
@@ -1791,14 +1811,22 @@ void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext *ctx,
 {
     if (assign && set_handler) {
         aio_set_event_notifier(ctx, &vq->host_notifier, true,
-                               virtio_queue_host_notifier_read);
+                               virtio_queue_host_notifier_aio_read);
     } else {
         aio_set_event_notifier(ctx, &vq->host_notifier, true, NULL);
     }
     if (!assign) {
         /* Test and clear notifier before after disabling event,
          * in case poll callback didn't have time to run. */
-        virtio_queue_host_notifier_read(&vq->host_notifier);
+        virtio_queue_host_notifier_aio_read(&vq->host_notifier);
+    }
+}
+
+static void virtio_queue_host_notifier_read(EventNotifier *n)
+{
+    VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
+    if (event_notifier_test_and_clear(n)) {
+        virtio_queue_notify_vq(vq);
     }
 }
 
-- 
MST