vhost: allow per device message handler

This patch allow device to register its own message handler during
vhost_dev_init(). vDPA device will use it to implement its own DMA
mapping logic.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20200326140125.19794-3-jasowang@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index f44340b..8e9e234 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -457,7 +457,9 @@ static size_t vhost_get_desc_size(struct vhost_virtqueue *vq,
 
 void vhost_dev_init(struct vhost_dev *dev,
 		    struct vhost_virtqueue **vqs, int nvqs,
-		    int iov_limit, int weight, int byte_weight)
+		    int iov_limit, int weight, int byte_weight,
+		    int (*msg_handler)(struct vhost_dev *dev,
+				       struct vhost_iotlb_msg *msg))
 {
 	struct vhost_virtqueue *vq;
 	int i;
@@ -473,6 +475,7 @@ void vhost_dev_init(struct vhost_dev *dev,
 	dev->iov_limit = iov_limit;
 	dev->weight = weight;
 	dev->byte_weight = byte_weight;
+	dev->msg_handler = msg_handler;
 	init_llist_head(&dev->work_list);
 	init_waitqueue_head(&dev->wait);
 	INIT_LIST_HEAD(&dev->read_list);
@@ -1178,7 +1181,12 @@ ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
 		ret = -EINVAL;
 		goto done;
 	}
-	if (vhost_process_iotlb_msg(dev, &msg)) {
+
+	if (dev->msg_handler)
+		ret = dev->msg_handler(dev, &msg);
+	else
+		ret = vhost_process_iotlb_msg(dev, &msg);
+	if (ret) {
 		ret = -EFAULT;
 		goto done;
 	}