[Qemu-devel] [PATCH 6/9] virtio-blk: use aio handler for data plane

[Paolo Bonzini <pbonzini@redhat.com>]

From: "Michael S. Tsirkin" <mst@redhat.com>

In addition to handling IO in vcpu thread and in io thread, 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.

Use a separate handler just for aio, and disable regular handlers when
dataplane is active.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 13 +++++++++++++
 hw/block/virtio-blk.c           | 27 +++++++++++++++++----------
 include/hw/virtio/virtio-blk.h  |  2 ++
 3 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 378feb3..4a137df 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -183,6 +183,17 @@ void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
     g_free(s);
 }
 
+static void virtio_blk_data_plane_handle_output(VirtIODevice *vdev,
+                                                VirtQueue *vq)
+{
+    VirtIOBlock *s = (VirtIOBlock *)vdev;
+
+    assert(s->dataplane);
+    assert(s->dataplane_started);
+
+    virtio_blk_handle_vq(s, vq);
+}
+
 /* Context: QEMU global mutex held */
 void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
 {
@@ -225,6 +236,7 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
 
     /* Get this show started by hooking up our callbacks */
     aio_context_acquire(s->ctx);
+    virtio_set_queue_aio(s->vq, virtio_blk_data_plane_handle_output);
     virtio_queue_aio_set_host_notifier_handler(s->vq, s->ctx, true, true);
     aio_context_release(s->ctx);
     return;
@@ -261,6 +273,7 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
 
     /* Stop notifications for new requests from guest */
     virtio_queue_aio_set_host_notifier_handler(s->vq, s->ctx, true, false);
+    virtio_set_queue_aio(s->vq, NULL);
 
     /* Drain and switch bs back to the QEMU main loop */
     blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context());
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index 77221c1..47ad9ed 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -577,20 +577,11 @@ void virtio_blk_handle_request(VirtIOBlockReq *req, MultiReqBuffer *mrb)
     }
 }
 
-static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
+void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq)
 {
-    VirtIOBlock *s = VIRTIO_BLK(vdev);
     VirtIOBlockReq *req;
     MultiReqBuffer mrb = {};
 
-    /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
-     * dataplane here instead of waiting for .set_status().
-     */
-    if (s->dataplane && !s->dataplane_started) {
-        virtio_blk_data_plane_start(s->dataplane);
-        return;
-    }
-
     assert(atomic_fetch_inc(&s->reentrancy_test) == 0);
     blk_io_plug(s->blk);
 
@@ -606,6 +597,22 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
     atomic_dec(&s->reentrancy_test);
 }
 
+static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
+{
+    VirtIOBlock *s = (VirtIOBlock *)vdev;
+
+    if (s->dataplane) {
+        /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
+         * dataplane here instead of waiting for .set_status().
+         */
+        virtio_blk_data_plane_start(s->dataplane);
+        if (!s->dataplane_disabled) {
+            return;
+        }
+    }
+    virtio_blk_handle_vq(s, vq);
+}
+
 static void virtio_blk_dma_restart_bh(void *opaque)
 {
     VirtIOBlock *s = opaque;
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 073c632..b5117a8 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -87,4 +87,6 @@ void virtio_blk_handle_request(VirtIOBlockReq *req, MultiReqBuffer *mrb);
 
 void virtio_blk_submit_multireq(BlockBackend *blk, MultiReqBuffer *mrb);
 
+void virtio_blk_handle_vq(VirtIOBlock *s, VirtQueue *vq);
+
 #endif
-- 
1.8.3.1