block: Add Error to blk_set_aio_context()

Add an Error parameter to blk_set_aio_context() and use
bdrv_child_try_set_aio_context() internally to check whether all
involved nodes can actually support the AioContext switch.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

3 files changed, 20 insertions, 8 deletions

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 8c37bd3..158c78f 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -173,6 +173,7 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
     unsigned i;
     unsigned nvqs = s->conf->num_queues;
+    Error *local_err = NULL;
     int r;
 
     if (vblk->dataplane_started || s->starting) {
@@ -212,7 +213,11 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
     vblk->dataplane_started = true;
     trace_virtio_blk_data_plane_start(s);
 
-    blk_set_aio_context(s->conf->conf.blk, s->ctx);
+    r = blk_set_aio_context(s->conf->conf.blk, s->ctx, &local_err);
+    if (r < 0) {
+        error_report_err(local_err);
+        goto fail_guest_notifiers;
+    }
 
     /* Kick right away to begin processing requests already in vring */
     for (i = 0; i < nvqs; i++) {
@@ -281,8 +286,9 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
     aio_context_acquire(s->ctx);
     aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
 
-    /* Drain and switch bs back to the QEMU main loop */
-    blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context());
+    /* Drain and try to switch bs back to the QEMU main loop. If other users
+     * keep the BlockBackend in the iothread, that's ok */
+    blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context(), NULL);
 
     aio_context_release(s->ctx);
 
diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c
index bb8f118..f7ad452 100644
--- a/hw/block/dataplane/xen-block.c
+++ b/hw/block/dataplane/xen-block.c
@@ -682,7 +682,8 @@ void xen_block_dataplane_stop(XenBlockDataPlane *dataplane)
     }
 
     aio_context_acquire(dataplane->ctx);
-    blk_set_aio_context(dataplane->blk, qemu_get_aio_context());
+    /* Xen doesn't have multiple users for nodes, so this can't fail */
+    blk_set_aio_context(dataplane->blk, qemu_get_aio_context(), &error_abort);
     aio_context_release(dataplane->ctx);
 
     xendev = dataplane->xendev;
@@ -811,7 +812,8 @@ void xen_block_dataplane_start(XenBlockDataPlane *dataplane,
     }
 
     aio_context_acquire(dataplane->ctx);
-    blk_set_aio_context(dataplane->blk, dataplane->ctx);
+    /* If other users keep the BlockBackend in the iothread, that's ok */
+    blk_set_aio_context(dataplane->blk, dataplane->ctx, NULL);
     aio_context_release(dataplane->ctx);
     return;
 
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 839f120..01c2b85 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -795,6 +795,7 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
     VirtIODevice *vdev = VIRTIO_DEVICE(hotplug_dev);
     VirtIOSCSI *s = VIRTIO_SCSI(vdev);
     SCSIDevice *sd = SCSI_DEVICE(dev);
+    int ret;
 
     if (s->ctx && !s->dataplane_fenced) {
         AioContext *ctx;
@@ -808,9 +809,11 @@ static void virtio_scsi_hotplug(HotplugHandler *hotplug_dev, DeviceState *dev,
             return;
         }
         virtio_scsi_acquire(s);
-        blk_set_aio_context(sd->conf.blk, s->ctx);
+        ret = blk_set_aio_context(sd->conf.blk, s->ctx, errp);
         virtio_scsi_release(s);
-
+        if (ret < 0) {
+            return;
+        }
     }
 
     if (virtio_vdev_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG)) {
@@ -839,7 +842,8 @@ static void virtio_scsi_hotunplug(HotplugHandler *hotplug_dev, DeviceState *dev,
 
     if (s->ctx) {
         virtio_scsi_acquire(s);
-        blk_set_aio_context(sd->conf.blk, qemu_get_aio_context());
+        /* If other users keep the BlockBackend in the iothread, that's ok */
+        blk_set_aio_context(sd->conf.blk, qemu_get_aio_context(), NULL);
         virtio_scsi_release(s);
     }