[Qemu-devel] [PATCH v2 11/13] virtio-blk: Don't handle output when backend is locked

[Fam Zheng <famz@redhat.com>]

virtio-blk now listens to locking and unlocking of the associated block
backend.

Up on locking:

  non-dataplane:
   1) Set VirtIOBlock.paused
   2) In virtio_blk_handle_output, do nothing if VirtIOBlock.paused

  dataplane:
   1) Clear the host event notifier
   2) In handle_notify, do nothing if VirtIOBlock.paused

Up on unlocking:

  non-dataplane:
   1) Clear VirtIOBlock.paused
   2) Schedule a BH on the AioContext of the backend, which calls
   virtio_blk_handle_output, so that the previous unhandled kicks can
   make progress

  dataplane:
   1) Set the host event notifier
   2) Notify the host event notifier so that unhandled events are
   processed

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 hw/block/dataplane/virtio-blk.c | 25 +++++++++++++++++-
 hw/block/virtio-blk.c           | 57 +++++++++++++++++++++++++++++++++++++++--
 include/hw/virtio/virtio-blk.h  |  8 +++++-
 3 files changed, 86 insertions(+), 4 deletions(-)

diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index ec0c8f4..d6c943c 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -87,8 +87,28 @@ static void complete_request_vring(VirtIOBlockReq *req, unsigned char status)
     qemu_bh_schedule(s->bh);
 }
 
+static void virtio_blk_data_plane_pause(VirtIOBlock *vblk)
+{
+    VirtIOBlockDataPlane *s = vblk->dataplane;
+
+    event_notifier_test_and_clear(&s->host_notifier);
+    aio_set_event_notifier(s->ctx, &s->host_notifier, NULL);
+}
+
+static void handle_notify(EventNotifier *e);
+static void virtio_blk_data_plane_resume(VirtIOBlock *vblk)
+{
+    VirtIOBlockDataPlane *s = vblk->dataplane;
+
+    aio_set_event_notifier(s->ctx, &s->host_notifier, handle_notify);
+
+    event_notifier_set(&s->host_notifier);
+}
+
 static const VirtIOBlockOps virtio_blk_data_plane_ops = {
-    .complete_request = complete_request_vring,
+    .complete_request           = complete_request_vring,
+    .pause                      = virtio_blk_data_plane_pause,
+    .resume                     = virtio_blk_data_plane_resume,
 };
 
 static void handle_notify(EventNotifier *e)
@@ -98,6 +118,9 @@ static void handle_notify(EventNotifier *e)
     VirtIOBlock *vblk = VIRTIO_BLK(s->vdev);
 
     event_notifier_test_and_clear(&s->host_notifier);
+    if (vblk->paused) {
+        return;
+    }
     blk_io_plug(s->conf->conf.blk);
     for (;;) {
         MultiReqBuffer mrb = {};
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index af20e78..d485a40 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -59,8 +59,38 @@ static void virtio_blk_complete_request(VirtIOBlockReq *req,
     virtio_notify(vdev, s->vq);
 }
 
+typedef struct {
+    QEMUBH *bh;
+    VirtIOBlock *s;
+} VirtIOBlockResumeData;
+
+static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq);
+static void virtio_blk_resume_bh_cb(void *opaque)
+{
+    VirtIOBlockResumeData *data = opaque;
+    qemu_bh_delete(data->bh);
+    virtio_blk_handle_output(VIRTIO_DEVICE(data->s), data->s->vq);
+}
+
+static void virtio_blk_pause(VirtIOBlock *vblk)
+{
+    /* TODO: stop ioeventfd */
+}
+
+static void virtio_blk_resume(VirtIOBlock *vblk)
+{
+    VirtIOBlockResumeData *data = g_new(VirtIOBlockResumeData, 1);
+    data->bh = aio_bh_new(blk_get_aio_context(vblk->blk),
+            virtio_blk_resume_bh_cb, data);
+    data->s = vblk;
+    data->s->paused = false;
+    qemu_bh_schedule(data->bh);
+}
+
 static const VirtIOBlockOps virtio_blk_ops = (VirtIOBlockOps) {
-    .complete_request = virtio_blk_complete_request,
+    .complete_request           = virtio_blk_complete_request,
+    .pause                      = virtio_blk_pause,
+    .resume                     = virtio_blk_resume,
 };
 
 static void virtio_blk_req_complete(VirtIOBlockReq *req, unsigned char status)
@@ -597,6 +627,9 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
     VirtIOBlockReq *req;
     MultiReqBuffer mrb = {};
 
+    if (s->paused) {
+        return;
+    }
     /* Some guests kick before setting VIRTIO_CONFIG_S_DRIVER_OK so start
      * dataplane here instead of waiting for .set_status().
      */
@@ -787,7 +820,7 @@ static void virtio_blk_save(QEMUFile *f, void *opaque)
 
     virtio_save(vdev, f);
 }
-    
+
 static void virtio_blk_save_device(VirtIODevice *vdev, QEMUFile *f)
 {
     VirtIOBlock *s = VIRTIO_BLK(vdev);
@@ -875,6 +908,22 @@ static void virtio_blk_migration_state_changed(Notifier *notifier, void *data)
     }
 }
 
+static void virtio_blk_pause_handler(Notifier *notifier, void *opaque)
+{
+    BdrvLockEvent *event = opaque;
+    VirtIOBlock *s = container_of(notifier, VirtIOBlock,
+                                  pause_notifier);
+
+    if (event->locking == s->paused) {
+        return;
+    }
+    if (event->locking) {
+        s->ops->pause(s);
+    } else {
+        s->ops->resume(s);
+    }
+}
+
 static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
@@ -926,6 +975,9 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
     blk_set_guest_block_size(s->blk, s->conf.conf.logical_block_size);
 
     blk_iostatus_enable(s->blk);
+
+    s->pause_notifier.notify = virtio_blk_pause_handler;
+    blk_add_lock_unlock_notifier(s->blk, &s->pause_notifier);
 }
 
 static void virtio_blk_device_unrealize(DeviceState *dev, Error **errp)
@@ -933,6 +985,7 @@ static void virtio_blk_device_unrealize(DeviceState *dev, Error **errp)
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VirtIOBlock *s = VIRTIO_BLK(dev);
 
+    notifier_remove(&s->pause_notifier);
     remove_migration_state_change_notifier(&s->migration_state_notifier);
     virtio_blk_data_plane_destroy(s->dataplane);
     s->dataplane = NULL;
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index 28b3436..4b6246f 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -42,12 +42,16 @@ struct VirtIOBlkConf
 };
 
 struct VirtIOBlockDataPlane;
-
+struct VirtIOBlock;
 struct VirtIOBlockReq;
 
 typedef struct {
     /* Function to push to vq and notify guest */
     void (*complete_request)(struct VirtIOBlockReq *req, unsigned char status);
+
+    /* Functions to pause/resume request handling */
+    void (*pause)(struct VirtIOBlock *vblk);
+    void (*resume)(struct VirtIOBlock *vblk);
 } VirtIOBlockOps;
 
 typedef struct VirtIOBlock {
@@ -62,6 +66,8 @@ typedef struct VirtIOBlock {
     VMChangeStateEntry *change;
     const VirtIOBlockOps *ops;
     Notifier migration_state_notifier;
+    Notifier pause_notifier;
+    bool paused;
     struct VirtIOBlockDataPlane *dataplane;
 } VirtIOBlock;
 
-- 
2.4.1