xen/pvcalls: implement frontend disconnect

Introduce a data structure named pvcalls_bedata. It contains pointers to
the command ring, the event channel, a list of active sockets and a list
of passive sockets. Lists accesses are protected by a spin_lock.

Introduce a waitqueue to allow waiting for a response on commands sent
to the backend.

Introduce an array of struct xen_pvcalls_response to store commands
responses.

Introduce a new struct sock_mapping to keep track of sockets.  In this
patch the struct sock_mapping is minimal, the fields will be added by
the next patches.

pvcalls_refcount is used to keep count of the outstanding pvcalls users.
Only remove connections once the refcount is zero.

Implement pvcalls frontend removal function. Go through the list of
active and passive sockets and free them all, one at a time.

Signed-off-by: Stefano Stabellini <stefano@aporeto.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: boris.ostrovsky@oracle.com
CC: jgross@suse.com
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/pvcalls-front.c

@@ -20,6 +20,51 @@
 #include <xen/xenbus.h>
 #include <xen/interface/io/pvcalls.h>
 
+#define PVCALLS_INVALID_ID UINT_MAX
+#define PVCALLS_RING_ORDER XENBUS_MAX_RING_GRANT_ORDER
+#define PVCALLS_NR_RSP_PER_RING __CONST_RING_SIZE(xen_pvcalls, XEN_PAGE_SIZE)
+
+struct pvcalls_bedata {
+	struct xen_pvcalls_front_ring ring;
+	grant_ref_t ref;
+	int irq;
+
+	struct list_head socket_mappings;
+	spinlock_t socket_lock;
+
+	wait_queue_head_t inflight_req;
+	struct xen_pvcalls_response rsp[PVCALLS_NR_RSP_PER_RING];
+};
+/* Only one front/back connection supported. */
+static struct xenbus_device *pvcalls_front_dev;
+static atomic_t pvcalls_refcount;
+
+/* first increment refcount, then proceed */
+#define pvcalls_enter() {               \
+	atomic_inc(&pvcalls_refcount);      \
+}
+
+/* first complete other operations, then decrement refcount */
+#define pvcalls_exit() {                \
+	atomic_dec(&pvcalls_refcount);      \
+}
+
+struct sock_mapping {
+	bool active_socket;
+	struct list_head list;
+	struct socket *sock;
+};
+
+static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id)
+{
+	return IRQ_HANDLED;
+}
+
+static void pvcalls_front_free_map(struct pvcalls_bedata *bedata,
+				   struct sock_mapping *map)
+{
+}
+
 static const struct xenbus_device_id pvcalls_front_ids[] = {
 	{ "pvcalls" },
 	{ "" }
@@ -27,6 +72,32 @@ static const struct xenbus_device_id pvcalls_front_ids[] = {
 
 static int pvcalls_front_remove(struct xenbus_device *dev)
 {
+	struct pvcalls_bedata *bedata;
+	struct sock_mapping *map = NULL, *n;
+
+	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
+	dev_set_drvdata(&dev->dev, NULL);
+	pvcalls_front_dev = NULL;
+	if (bedata->irq >= 0)
+		unbind_from_irqhandler(bedata->irq, dev);
+
+	smp_mb();
+	while (atomic_read(&pvcalls_refcount) > 0)
+		cpu_relax();
+	list_for_each_entry_safe(map, n, &bedata->socket_mappings, list) {
+		if (map->active_socket) {
+			/* No need to lock, refcount is 0 */
+			pvcalls_front_free_map(bedata, map);
+		} else {
+			list_del(&map->list);
+			kfree(map);
+		}
+	}
+	if (bedata->ref >= 0)
+		gnttab_end_foreign_access(bedata->ref, 0, 0);
+	kfree(bedata->ring.sring);
+	kfree(bedata);
+	xenbus_switch_state(dev, XenbusStateClosed);
 	return 0;
 }