[PATCH v3 2/2] vhost-user-blk: delay vhost_user_blk_disconnect

[Dima Stepanov]

A socket write during vhost-user communication may trigger a disconnect
event, calling vhost_user_blk_disconnect() and clearing all the
vhost_dev structures holding data that vhost-user functions expect to
remain valid to roll back initialization correctly. Delay the cleanup to
keep vhost_dev structure valid.
There are two possible states to handle:
1. RUN_STATE_PRELAUNCH: skip bh oneshot call and perform disconnect in
the caller routine.
2. RUN_STATE_RUNNING: delay by using bh

BH changes are based on the similar changes for the vhost-user-net
device:
  commit e7c83a885f865128ae3cf1946f8cb538b63cbfba
  "vhost-user: delay vhost_user_stop"

Signed-off-by: Dima Stepanov <address@hidden>
---
 hw/block/vhost-user-blk.c | 49 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 43 insertions(+), 6 deletions(-)

diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
index 9d8c0b3..447fc9c 100644
--- a/hw/block/vhost-user-blk.c
+++ b/hw/block/vhost-user-blk.c
@@ -337,11 +337,6 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VHostUserBlk *s = VHOST_USER_BLK(vdev);
 
-    if (!s->connected) {
-        return;
-    }
-    s->connected = false;
-
     if (s->dev.started) {
         vhost_user_blk_stop(vdev);
     }
@@ -349,6 +344,19 @@ static void vhost_user_blk_disconnect(DeviceState *dev)
     vhost_dev_cleanup(&s->dev);
 }
 
+static void vhost_user_blk_event(void *opaque, QEMUChrEvent event);
+
+static void vhost_user_blk_chr_closed_bh(void *opaque)
+{
+    DeviceState *dev = opaque;
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    VHostUserBlk *s = VHOST_USER_BLK(vdev);
+
+    vhost_user_blk_disconnect(dev);
+    qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, vhost_user_blk_event,
+            NULL, opaque, NULL, true);
+}
+
 static void vhost_user_blk_event(void *opaque, QEMUChrEvent event)
 {
     DeviceState *dev = opaque;
@@ -363,7 +371,28 @@ static void vhost_user_blk_event(void *opaque, 
QEMUChrEvent event)
         }
         break;
     case CHR_EVENT_CLOSED:
-        vhost_user_blk_disconnect(dev);
+        /*
+         * A close event may happen during a read/write, but vhost
+         * code assumes the vhost_dev remains setup, so delay the
+         * stop & clear. There are two possible paths to hit this
+         * disconnect event:
+         * 1. When VM is in the RUN_STATE_PRELAUNCH state. The
+         * vhost_user_blk_device_realize() is a caller.
+         * 2. In tha main loop phase after VM start.
+         *
+         * For p2 the disconnect event will be delayed. We can't
+         * do the same for p1, because we are not running the loop
+         * at this moment. So just skip this step and perform
+         * disconnect in the caller function.
+         */
+        if (s->connected && runstate_is_running()) {
+            AioContext *ctx = qemu_get_current_aio_context();
+
+            qemu_chr_fe_set_handlers(&s->chardev, NULL, NULL, NULL, NULL,
+                    NULL, NULL, false);
+            aio_bh_schedule_oneshot(ctx, vhost_user_blk_chr_closed_bh, opaque);
+        }
+        s->connected = false;
         break;
     case CHR_EVENT_BREAK:
     case CHR_EVENT_MUX_IN:
@@ -428,6 +457,14 @@ reconnect:
 
     ret = vhost_dev_get_config(&s->dev, (uint8_t *)&s->blkcfg,
                                sizeof(struct virtio_blk_config));
+    if (!s->connected) {
+        /*
+         * Perform disconnect before making reconnect. More detailed
+         * comment why it was delayed is in the vhost_user_blk_event()
+         * routine.
+         */
+        vhost_user_blk_disconnect(dev);
+    }
     if (ret < 0) {
         error_report("vhost-user-blk: get block config failed");
         goto reconnect;
-- 
2.7.4