xen-netback: add control ring boilerplate

My recent patch to include/xen/interface/io/netif.h defines a new shared
ring (in addition to the rx and tx rings) for passing control messages
from a VM frontend driver to a backend driver.

This patch adds the necessary code to xen-netback to map this new shared
ring, should it be created by a frontend, but does not add implementations
for any of the defined protocol messages. These are added in a subsequent
patch for clarity.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/common.h

@@ -260,6 +260,11 @@ struct xenvif {
 	struct dentry *xenvif_dbg_root;
 #endif
 
+	struct xen_netif_ctrl_back_ring ctrl;
+	struct task_struct *ctrl_task;
+	wait_queue_head_t ctrl_wq;
+	unsigned int ctrl_irq;
+
 	/* Miscellaneous private stuff. */
 	struct net_device *dev;
 };
@@ -285,10 +290,15 @@ struct xenvif *xenvif_alloc(struct device *parent,
 int xenvif_init_queue(struct xenvif_queue *queue);
 void xenvif_deinit_queue(struct xenvif_queue *queue);
 
-int xenvif_connect(struct xenvif_queue *queue, unsigned long tx_ring_ref,
+int xenvif_connect_data(struct xenvif_queue *queue,
-		   unsigned long rx_ring_ref, unsigned int tx_evtchn,
+			unsigned long tx_ring_ref,
-		   unsigned int rx_evtchn);
+			unsigned long rx_ring_ref,
-void xenvif_disconnect(struct xenvif *vif);
+			unsigned int tx_evtchn,
+			unsigned int rx_evtchn);
+void xenvif_disconnect_data(struct xenvif *vif);
+int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref,
+			unsigned int evtchn);
+void xenvif_disconnect_ctrl(struct xenvif *vif);
 void xenvif_free(struct xenvif *vif);
 
 int xenvif_xenbus_init(void);
@@ -300,10 +310,10 @@ int xenvif_queue_stopped(struct xenvif_queue *queue);
 void xenvif_wake_queue(struct xenvif_queue *queue);
 
 /* (Un)Map communication rings. */
-void xenvif_unmap_frontend_rings(struct xenvif_queue *queue);
+void xenvif_unmap_frontend_data_rings(struct xenvif_queue *queue);
-int xenvif_map_frontend_rings(struct xenvif_queue *queue,
+int xenvif_map_frontend_data_rings(struct xenvif_queue *queue,
-			      grant_ref_t tx_ring_ref,
+				   grant_ref_t tx_ring_ref,
-			      grant_ref_t rx_ring_ref);
+				   grant_ref_t rx_ring_ref);
 
 /* Check for SKBs from frontend and schedule backend processing */
 void xenvif_napi_schedule_or_enable_events(struct xenvif_queue *queue);
@@ -318,6 +328,8 @@ void xenvif_kick_thread(struct xenvif_queue *queue);
 
 int xenvif_dealloc_kthread(void *data);
 
+int xenvif_ctrl_kthread(void *data);
+
 void xenvif_rx_queue_tail(struct xenvif_queue *queue, struct sk_buff *skb);
 
 void xenvif_carrier_on(struct xenvif *vif);

drivers/net/xen-netback/interface.c

@@ -128,6 +128,15 @@ irqreturn_t xenvif_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+irqreturn_t xenvif_ctrl_interrupt(int irq, void *dev_id)
+{
+	struct xenvif *vif = dev_id;
+
+	wake_up(&vif->ctrl_wq);
+
+	return IRQ_HANDLED;
+}
+
 int xenvif_queue_stopped(struct xenvif_queue *queue)
 {
 	struct net_device *dev = queue->vif->dev;
@@ -527,9 +536,66 @@ void xenvif_carrier_on(struct xenvif *vif)
 	rtnl_unlock();
 }
 
-int xenvif_connect(struct xenvif_queue *queue, unsigned long tx_ring_ref,
+int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref,
-		   unsigned long rx_ring_ref, unsigned int tx_evtchn,
+			unsigned int evtchn)
-		   unsigned int rx_evtchn)
+{
+	struct net_device *dev = vif->dev;
+	void *addr;
+	struct xen_netif_ctrl_sring *shared;
+	struct task_struct *task;
+	int err = -ENOMEM;
+
+	err = xenbus_map_ring_valloc(xenvif_to_xenbus_device(vif),
+				     &ring_ref, 1, &addr);
+	if (err)
+		goto err;
+
+	shared = (struct xen_netif_ctrl_sring *)addr;
+	BACK_RING_INIT(&vif->ctrl, shared, XEN_PAGE_SIZE);
+
+	init_waitqueue_head(&vif->ctrl_wq);
+
+	err = bind_interdomain_evtchn_to_irqhandler(vif->domid, evtchn,
+						    xenvif_ctrl_interrupt,
+						    0, dev->name, vif);
+	if (err < 0)
+		goto err_unmap;
+
+	vif->ctrl_irq = err;
+
+	task = kthread_create(xenvif_ctrl_kthread, (void *)vif,
+			      "%s-control", dev->name);
+	if (IS_ERR(task)) {
+		pr_warn("Could not allocate kthread for %s\n", dev->name);
+		err = PTR_ERR(task);
+		goto err_deinit;
+	}
+
+	get_task_struct(task);
+	vif->ctrl_task = task;
+
+	wake_up_process(vif->ctrl_task);
+
+	return 0;
+
+err_deinit:
+	unbind_from_irqhandler(vif->ctrl_irq, vif);
+	vif->ctrl_irq = 0;
+
+err_unmap:
+	xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(vif),
+				vif->ctrl.sring);
+	vif->ctrl.sring = NULL;
+
+err:
+	return err;
+}
+
+int xenvif_connect_data(struct xenvif_queue *queue,
+			unsigned long tx_ring_ref,
+			unsigned long rx_ring_ref,
+			unsigned int tx_evtchn,
+			unsigned int rx_evtchn)
 {
 	struct task_struct *task;
 	int err = -ENOMEM;
@@ -538,7 +604,8 @@ int xenvif_connect(struct xenvif_queue *queue, unsigned long tx_ring_ref,
 	BUG_ON(queue->task);
 	BUG_ON(queue->dealloc_task);
 
-	err = xenvif_map_frontend_rings(queue, tx_ring_ref, rx_ring_ref);
+	err = xenvif_map_frontend_data_rings(queue, tx_ring_ref,
+					     rx_ring_ref);
 	if (err < 0)
 		goto err;
 
@@ -614,7 +681,7 @@ err_tx_unbind:
 	unbind_from_irqhandler(queue->tx_irq, queue);
 	queue->tx_irq = 0;
 err_unmap:
-	xenvif_unmap_frontend_rings(queue);
+	xenvif_unmap_frontend_data_rings(queue);
 	netif_napi_del(&queue->napi);
 err:
 	module_put(THIS_MODULE);
@@ -634,7 +701,7 @@ void xenvif_carrier_off(struct xenvif *vif)
 	rtnl_unlock();
 }
 
-void xenvif_disconnect(struct xenvif *vif)
+void xenvif_disconnect_data(struct xenvif *vif)
 {
 	struct xenvif_queue *queue = NULL;
 	unsigned int num_queues = vif->num_queues;
@@ -668,12 +735,32 @@ void xenvif_disconnect(struct xenvif *vif)
 			queue->tx_irq = 0;
 		}
 
-		xenvif_unmap_frontend_rings(queue);
+		xenvif_unmap_frontend_data_rings(queue);
 	}
 
 	xenvif_mcast_addr_list_free(vif);
 }
 
+void xenvif_disconnect_ctrl(struct xenvif *vif)
+{
+	if (vif->ctrl_task) {
+		kthread_stop(vif->ctrl_task);
+		put_task_struct(vif->ctrl_task);
+		vif->ctrl_task = NULL;
+	}
+
+	if (vif->ctrl_irq) {
+		unbind_from_irqhandler(vif->ctrl_irq, vif);
+		vif->ctrl_irq = 0;
+	}
+
+	if (vif->ctrl.sring) {
+		xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(vif),
+					vif->ctrl.sring);
+		vif->ctrl.sring = NULL;
+	}
+}
+
 /* Reverse the relevant parts of xenvif_init_queue().
  * Used for queue teardown from xenvif_free(), and on the
  * error handling paths in xenbus.c:connect().

drivers/net/xen-netback/netback.c

@@ -1926,7 +1926,7 @@ static inline bool tx_dealloc_work_todo(struct xenvif_queue *queue)
 	return queue->dealloc_cons != queue->dealloc_prod;
 }
 
-void xenvif_unmap_frontend_rings(struct xenvif_queue *queue)
+void xenvif_unmap_frontend_data_rings(struct xenvif_queue *queue)
 {
 	if (queue->tx.sring)
 		xenbus_unmap_ring_vfree(xenvif_to_xenbus_device(queue->vif),
@@ -1936,9 +1936,9 @@ void xenvif_unmap_frontend_rings(struct xenvif_queue *queue)
 					queue->rx.sring);
 }
 
-int xenvif_map_frontend_rings(struct xenvif_queue *queue,
+int xenvif_map_frontend_data_rings(struct xenvif_queue *queue,
-			      grant_ref_t tx_ring_ref,
+				   grant_ref_t tx_ring_ref,
-			      grant_ref_t rx_ring_ref)
+				   grant_ref_t rx_ring_ref)
 {
 	void *addr;
 	struct xen_netif_tx_sring *txs;
@@ -1965,7 +1965,7 @@ int xenvif_map_frontend_rings(struct xenvif_queue *queue,
 	return 0;
 
 err:
-	xenvif_unmap_frontend_rings(queue);
+	xenvif_unmap_frontend_data_rings(queue);
 	return err;
 }
 
@@ -2164,6 +2164,95 @@ int xenvif_dealloc_kthread(void *data)
 	return 0;
 }
 
+static void make_ctrl_response(struct xenvif *vif,
+			       const struct xen_netif_ctrl_request *req,
+			       u32 status, u32 data)
+{
+	RING_IDX idx = vif->ctrl.rsp_prod_pvt;
+	struct xen_netif_ctrl_response rsp = {
+		.id = req->id,
+		.type = req->type,
+		.status = status,
+		.data = data,
+	};
+
+	*RING_GET_RESPONSE(&vif->ctrl, idx) = rsp;
+	vif->ctrl.rsp_prod_pvt = ++idx;
+}
+
+static void push_ctrl_response(struct xenvif *vif)
+{
+	int notify;
+
+	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->ctrl, notify);
+	if (notify)
+		notify_remote_via_irq(vif->ctrl_irq);
+}
+
+static void process_ctrl_request(struct xenvif *vif,
+				 const struct xen_netif_ctrl_request *req)
+{
+	make_ctrl_response(vif, req, XEN_NETIF_CTRL_STATUS_NOT_SUPPORTED,
+			   0);
+	push_ctrl_response(vif);
+}
+
+static void xenvif_ctrl_action(struct xenvif *vif)
+{
+	for (;;) {
+		RING_IDX req_prod, req_cons;
+
+		req_prod = vif->ctrl.sring->req_prod;
+		req_cons = vif->ctrl.req_cons;
+
+		/* Make sure we can see requests before we process them. */
+		rmb();
+
+		if (req_cons == req_prod)
+			break;
+
+		while (req_cons != req_prod) {
+			struct xen_netif_ctrl_request req;
+
+			RING_COPY_REQUEST(&vif->ctrl, req_cons, &req);
+			req_cons++;
+
+			process_ctrl_request(vif, &req);
+		}
+
+		vif->ctrl.req_cons = req_cons;
+		vif->ctrl.sring->req_event = req_cons + 1;
+	}
+}
+
+static bool xenvif_ctrl_work_todo(struct xenvif *vif)
+{
+	if (likely(RING_HAS_UNCONSUMED_REQUESTS(&vif->ctrl)))
+		return 1;
+
+	return 0;
+}
+
+int xenvif_ctrl_kthread(void *data)
+{
+	struct xenvif *vif = data;
+
+	for (;;) {
+		wait_event_interruptible(vif->ctrl_wq,
+					 xenvif_ctrl_work_todo(vif) ||
+					 kthread_should_stop());
+		if (kthread_should_stop())
+			break;
+
+		while (xenvif_ctrl_work_todo(vif))
+			xenvif_ctrl_action(vif);
+
+		cond_resched();
+	}
+
+	return 0;
+}
+
 static int __init netback_init(void)
 {
 	int rc = 0;

drivers/net/xen-netback/xenbus.c

@@ -38,7 +38,8 @@ struct backend_info {
 	const char *hotplug_script;
 };
 
-static int connect_rings(struct backend_info *be, struct xenvif_queue *queue);
+static int connect_data_rings(struct backend_info *be,
+			      struct xenvif_queue *queue);
 static void connect(struct backend_info *be);
 static int read_xenbus_vif_flags(struct backend_info *be);
 static int backend_create_xenvif(struct backend_info *be);
@@ -367,6 +368,12 @@ static int netback_probe(struct xenbus_device *dev,
 	if (err)
 		pr_debug("Error writing multi-queue-max-queues\n");
 
+	err = xenbus_printf(XBT_NIL, dev->nodename,
+			    "feature-ctrl-ring",
+			    "%u", true);
+	if (err)
+		pr_debug("Error writing feature-ctrl-ring\n");
+
 	script = xenbus_read(XBT_NIL, dev->nodename, "script", NULL);
 	if (IS_ERR(script)) {
 		err = PTR_ERR(script);
@@ -457,7 +464,8 @@ static void backend_disconnect(struct backend_info *be)
 #ifdef CONFIG_DEBUG_FS
 		xenvif_debugfs_delif(be->vif);
 #endif /* CONFIG_DEBUG_FS */
-		xenvif_disconnect(be->vif);
+		xenvif_disconnect_data(be->vif);
+		xenvif_disconnect_ctrl(be->vif);
 	}
 }
 
@@ -825,6 +833,48 @@ static void hotplug_status_changed(struct xenbus_watch *watch,
 	kfree(str);
 }
 
+static int connect_ctrl_ring(struct backend_info *be)
+{
+	struct xenbus_device *dev = be->dev;
+	struct xenvif *vif = be->vif;
+	unsigned int val;
+	grant_ref_t ring_ref;
+	unsigned int evtchn;
+	int err;
+
+	err = xenbus_gather(XBT_NIL, dev->otherend,
+			    "ctrl-ring-ref", "%u", &val, NULL);
+	if (err)
+		goto done; /* The frontend does not have a control ring */
+
+	ring_ref = val;
+
+	err = xenbus_gather(XBT_NIL, dev->otherend,
+			    "event-channel-ctrl", "%u", &val, NULL);
+	if (err) {
+		xenbus_dev_fatal(dev, err,
+				 "reading %s/event-channel-ctrl",
+				 dev->otherend);
+		goto fail;
+	}
+
+	evtchn = val;
+
+	err = xenvif_connect_ctrl(vif, ring_ref, evtchn);
+	if (err) {
+		xenbus_dev_fatal(dev, err,
+				 "mapping shared-frame %u port %u",
+				 ring_ref, evtchn);
+		goto fail;
+	}
+
+done:
+	return 0;
+
+fail:
+	return err;
+}
+
 static void connect(struct backend_info *be)
 {
 	int err;
@@ -861,6 +911,12 @@ static void connect(struct backend_info *be)
 	xen_register_watchers(dev, be->vif);
 	read_xenbus_vif_flags(be);
 
+	err = connect_ctrl_ring(be);
+	if (err) {
+		xenbus_dev_fatal(dev, err, "connecting control ring");
+		return;
+	}
+
 	/* Use the number of queues requested by the frontend */
 	be->vif->queues = vzalloc(requested_num_queues *
 				  sizeof(struct xenvif_queue));
@@ -896,11 +952,12 @@ static void connect(struct backend_info *be)
 		queue->remaining_credit = credit_bytes;
 		queue->credit_usec = credit_usec;
 
-		err = connect_rings(be, queue);
+		err = connect_data_rings(be, queue);
 		if (err) {
-			/* connect_rings() cleans up after itself on failure,
+			/* connect_data_rings() cleans up after itself on
-			 * but we need to clean up after xenvif_init_queue() here,
+			 * failure, but we need to clean up after
-			 * and also clean up any previously initialised queues.
+			 * xenvif_init_queue() here, and also clean up any
+			 * previously initialised queues.
 			 */
 			xenvif_deinit_queue(queue);
 			be->vif->num_queues = queue_index;
@@ -935,15 +992,17 @@ static void connect(struct backend_info *be)
 
 err:
 	if (be->vif->num_queues > 0)
-		xenvif_disconnect(be->vif); /* Clean up existing queues */
+		xenvif_disconnect_data(be->vif); /* Clean up existing queues */
 	vfree(be->vif->queues);
 	be->vif->queues = NULL;
 	be->vif->num_queues = 0;
+	xenvif_disconnect_ctrl(be->vif);
 	return;
 }
 
 
-static int connect_rings(struct backend_info *be, struct xenvif_queue *queue)
+static int connect_data_rings(struct backend_info *be,
+			      struct xenvif_queue *queue)
 {
 	struct xenbus_device *dev = be->dev;
 	unsigned int num_queues = queue->vif->num_queues;
@@ -1007,8 +1066,8 @@ static int connect_rings(struct backend_info *be, struct xenvif_queue *queue)
 	}
 
 	/* Map the shared frame, irq etc. */
-	err = xenvif_connect(queue, tx_ring_ref, rx_ring_ref,
+	err = xenvif_connect_data(queue, tx_ring_ref, rx_ring_ref,
-			     tx_evtchn, rx_evtchn);
+				  tx_evtchn, rx_evtchn);
 	if (err) {
 		xenbus_dev_fatal(dev, err,
 				 "mapping shared-frames %lu/%lu port tx %u rx %u",