virtio: explicit enable_cb/disable_cb rather than callback return.

It seems that virtio_net wants to disable callbacks (interrupts) before
calling netif_rx_schedule(), so we can't use the return value to do so.

Rename "restart" to "cb_enable" and introduce "cb_disable" hook: callback
now returns void, rather than a boolean.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/block/virtio_blk.c

@@ -36,7 +36,7 @@ struct virtblk_req
 	struct virtio_blk_inhdr in_hdr;
 };
 
-static bool blk_done(struct virtqueue *vq)
+static void blk_done(struct virtqueue *vq)
 {
 	struct virtio_blk *vblk = vq->vdev->priv;
 	struct virtblk_req *vbr;
@@ -65,7 +65,6 @@ static bool blk_done(struct virtqueue *vq)
 	/* In case queue is stopped waiting for more buffers. */
 	blk_start_queue(vblk->disk->queue);
 	spin_unlock_irqrestore(&vblk->lock, flags);
-	return true;
 }
 
 static bool do_req(struct request_queue *q, struct virtio_blk *vblk,

drivers/lguest/lguest_device.c

@@ -191,7 +191,7 @@ static void lg_notify(struct virtqueue *vq)
  * So we provide devices with a "find virtqueue and set it up" function. */
 static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
 				    unsigned index,
-				    bool (*callback)(struct virtqueue *vq))
+				    void (*callback)(struct virtqueue *vq))
 {
 	struct lguest_device *ldev = to_lgdev(vdev);
 	struct lguest_vq_info *lvq;

drivers/net/virtio_net.c

@@ -52,13 +52,12 @@ static inline void vnet_hdr_to_sg(struct scatterlist *sg, struct sk_buff *skb)
 	sg_init_one(sg, skb_vnet_hdr(skb), sizeof(struct virtio_net_hdr));
 }
 
-static bool skb_xmit_done(struct virtqueue *rvq)
+static void skb_xmit_done(struct virtqueue *rvq)
 {
 	struct virtnet_info *vi = rvq->vdev->priv;
 
 	/* In case we were waiting for output buffers. */
 	netif_wake_queue(vi->dev);
-	return true;
 }
 
 static void receive_skb(struct net_device *dev, struct sk_buff *skb,
@@ -161,12 +160,14 @@ static void try_fill_recv(struct virtnet_info *vi)
 	vi->rvq->vq_ops->kick(vi->rvq);
 }
 
-static bool skb_recv_done(struct virtqueue *rvq)
+static void skb_recv_done(struct virtqueue *rvq)
 {
 	struct virtnet_info *vi = rvq->vdev->priv;
-	netif_rx_schedule(vi->dev, &vi->napi);
-	/* Suppress further interrupts. */
-	return false;
+	/* Schedule NAPI, Suppress further interrupts if successful. */
+	if (netif_rx_schedule_prep(vi->dev, &vi->napi)) {
+		rvq->vq_ops->disable_cb(rvq);
+		__netif_rx_schedule(vi->dev, &vi->napi);
+	}
 }
 
 static int virtnet_poll(struct napi_struct *napi, int budget)
@@ -192,7 +193,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 	/* Out of packets? */
 	if (received < budget) {
 		netif_rx_complete(vi->dev, napi);
-		if (unlikely(!vi->rvq->vq_ops->restart(vi->rvq))
+		if (unlikely(!vi->rvq->vq_ops->enable_cb(vi->rvq))
 		    && netif_rx_reschedule(vi->dev, napi))
 			goto again;
 	}

drivers/virtio/virtio_ring.c

@@ -220,7 +220,17 @@ static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len)
 	return ret;
 }
 
-static bool vring_restart(struct virtqueue *_vq)
+static void vring_disable_cb(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	START_USE(vq);
+	BUG_ON(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT);
+	vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
+	END_USE(vq);
+}
+
+static bool vring_enable_cb(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
@@ -254,8 +264,8 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 		return IRQ_HANDLED;
 
 	pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
-	if (vq->vq.callback && !vq->vq.callback(&vq->vq))
-		vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
+	if (vq->vq.callback)
+		vq->vq.callback(&vq->vq);
 
 	return IRQ_HANDLED;
 }
@@ -264,7 +274,8 @@ static struct virtqueue_ops vring_vq_ops = {
 	.add_buf = vring_add_buf,
 	.get_buf = vring_get_buf,
 	.kick = vring_kick,
-	.restart = vring_restart,
+	.disable_cb = vring_disable_cb,
+	.enable_cb = vring_enable_cb,
 	.shutdown = vring_shutdown,
 };
 
@@ -272,7 +283,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
 				      struct virtio_device *vdev,
 				      void *pages,
 				      void (*notify)(struct virtqueue *),
-				      bool (*callback)(struct virtqueue *))
+				      void (*callback)(struct virtqueue *))
 {
 	struct vring_virtqueue *vq;
 	unsigned int i;

include/linux/virtio.h

@@ -11,15 +11,13 @@
 /**
  * virtqueue - a queue to register buffers for sending or receiving.
  * @callback: the function to call when buffers are consumed (can be NULL).
- *    If this returns false, callbacks are suppressed until vq_ops->restart
- *    is called.
  * @vdev: the virtio device this queue was created for.
  * @vq_ops: the operations for this virtqueue (see below).
  * @priv: a pointer for the virtqueue implementation to use.
  */
 struct virtqueue
 {
-	bool (*callback)(struct virtqueue *vq);
+	void (*callback)(struct virtqueue *vq);
 	struct virtio_device *vdev;
 	struct virtqueue_ops *vq_ops;
 	void *priv;
@@ -41,7 +39,9 @@ struct virtqueue
  *	vq: the struct virtqueue we're talking about.
  *	len: the length written into the buffer
  *	Returns NULL or the "data" token handed to add_buf.
- * @restart: restart callbacks after callback returned false.
+ * @disable_cb: disable callbacks
+ *	vq: the struct virtqueue we're talking about.
+ * @enable_cb: restart callbacks after disable_cb.
  *	vq: the struct virtqueue we're talking about.
  *	This returns "false" (and doesn't re-enable) if there are pending
  *	buffers in the queue, to avoid a race.
@@ -65,7 +65,8 @@ struct virtqueue_ops {
 
 	void *(*get_buf)(struct virtqueue *vq, unsigned int *len);
 
-	bool (*restart)(struct virtqueue *vq);
+	void (*disable_cb)(struct virtqueue *vq);
+	bool (*enable_cb)(struct virtqueue *vq);
 
 	void (*shutdown)(struct virtqueue *vq);
 };

include/linux/virtio_config.h

@@ -61,7 +61,7 @@ struct virtio_config_ops
 	void (*set_status)(struct virtio_device *vdev, u8 status);
 	struct virtqueue *(*find_vq)(struct virtio_device *vdev,
 				     unsigned index,
-				     bool (*callback)(struct virtqueue *));
+				     void (*callback)(struct virtqueue *));
 	void (*del_vq)(struct virtqueue *vq);
 };
 

include/linux/virtio_ring.h

@@ -114,7 +114,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
 				      struct virtio_device *vdev,
 				      void *pages,
 				      void (*notify)(struct virtqueue *vq),
-				      bool (*callback)(struct virtqueue *vq));
+				      void (*callback)(struct virtqueue *vq));
 void vring_del_virtqueue(struct virtqueue *vq);
 
 irqreturn_t vring_interrupt(int irq, void *_vq);

net/9p/trans_virtio.c

@@ -199,14 +199,12 @@ static void p9_virtio_close(struct p9_trans *trans)
 	kfree(trans);
 }
 
-static bool p9_virtio_intr(struct virtqueue *q)
+static void p9_virtio_intr(struct virtqueue *q)
 {
 	struct virtio_chan *chan = q->vdev->priv;
 
 	P9_DPRINTK(P9_DEBUG_TRANS, "9p poll_wakeup: %p\n", &chan->wq);
 	wake_up_interruptible(&chan->wq);
-
-	return true;
 }
 
 static int p9_virtio_probe(struct virtio_device *dev)