vdpa: Add eventfd for the vdpa callback

Add eventfd for the vdpa callback so that user
can signal it directly instead of triggering the
callback. It will be used for vhost-vdpa case.
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Message-Id: <20230323053043.35-9-xieyongji@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vhost/vdpa.c

@@ -599,9 +599,11 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 		if (vq->call_ctx.ctx) {
 			cb.callback = vhost_vdpa_virtqueue_cb;
 			cb.private = vq;
+			cb.trigger = vq->call_ctx.ctx;
 		} else {
 			cb.callback = NULL;
 			cb.private = NULL;
+			cb.trigger = NULL;
 		}
 		ops->set_vq_cb(vdpa, idx, &cb);
 		vhost_vdpa_setup_vq_irq(v, idx);

drivers/virtio/virtio_vdpa.c

@@ -196,6 +196,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
 	/* Setup virtqueue callback */
 	cb.callback = callback ? virtio_vdpa_virtqueue_cb : NULL;
 	cb.private = info;
+	cb.trigger = NULL;
 	ops->set_vq_cb(vdpa, index, &cb);
 	ops->set_vq_num(vdpa, index, virtqueue_get_vring_size(vq));
 

include/linux/vdpa.h

@@ -13,10 +13,16 @@
  * struct vdpa_calllback - vDPA callback definition.
  * @callback: interrupt callback function
  * @private: the data passed to the callback function
+ * @trigger: the eventfd for the callback (Optional).
+ *           When it is set, the vDPA driver must guarantee that
+ *           signaling it is functional equivalent to triggering
+ *           the callback. Then vDPA parent can signal it directly
+ *           instead of triggering the callback.
  */
 struct vdpa_callback {
 	irqreturn_t (*callback)(void *data);
 	void *private;
+	struct eventfd_ctx *trigger;
 };
 
 /**