vhost-user-scsi: reset the device if supported

If the vhost-user-scsi backend supports the VHOST_USER_F_RESET_DEVICE
protocol feature, then the device can be reset when requested.

If this feature is not supported, do not try a reset as this will send
a VHOST_USER_RESET_OWNER that the backend is not expecting,
potentially putting into an inoperable state.

Signed-off-by: David Vrabel <david.vrabel@nutanix.com>
Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <1572385083-5254-3-git-send-email-raphael.norwitz@nutanix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/scsi/vhost-user-scsi.c

@@ -39,6 +39,10 @@ static const int user_feature_bits[] = {
     VHOST_INVALID_FEATURE_BIT
 };
 
+enum VhostUserProtocolFeature {
+    VHOST_USER_PROTOCOL_F_RESET_DEVICE = 13,
+};
+
 static void vhost_user_scsi_set_status(VirtIODevice *vdev, uint8_t status)
 {
     VHostUserSCSI *s = (VHostUserSCSI *)vdev;
@@ -62,6 +66,25 @@ static void vhost_user_scsi_set_status(VirtIODevice *vdev, uint8_t status)
     }
 }
 
+static void vhost_user_scsi_reset(VirtIODevice *vdev)
+{
+    VHostSCSICommon *vsc = VHOST_SCSI_COMMON(vdev);
+    struct vhost_dev *dev = &vsc->dev;
+
+    /*
+     * Historically, reset was not implemented so only reset devices
+     * that are expecting it.
+     */
+    if (!virtio_has_feature(dev->protocol_features,
+                            VHOST_USER_PROTOCOL_F_RESET_DEVICE)) {
+        return;
+    }
+
+    if (dev->vhost_ops->vhost_reset_device) {
+        dev->vhost_ops->vhost_reset_device(dev);
+    }
+}
+
 static void vhost_dummy_handle_output(VirtIODevice *vdev, VirtQueue *vq)
 {
 }
@@ -182,6 +205,7 @@ static void vhost_user_scsi_class_init(ObjectClass *klass, void *data)
     vdc->get_features = vhost_scsi_common_get_features;
     vdc->set_config = vhost_scsi_common_set_config;
     vdc->set_status = vhost_user_scsi_set_status;
+    vdc->reset = vhost_user_scsi_reset;
     fwc->get_dev_path = vhost_scsi_common_get_fw_dev_path;
 }