+static int evtchn_resize_ring(struct per_user_data *u)
+{
+ unsigned int new_size;
+ evtchn_port_t *new_ring, *old_ring;
+ unsigned int p, c;
+
+ /*
+ * Ensure the ring is large enough to capture all possible
+ * events. i.e., one free slot for each bound event.
+ */
+ if (u->nr_evtchns <= u->ring_size)
+ return 0;
+
+ if (u->ring_size == 0)
+ new_size = 64;
+ else
+ new_size = 2 * u->ring_size;
+
+ new_ring = evtchn_alloc_ring(new_size);
+ if (!new_ring)
+ return -ENOMEM;
+
+ old_ring = u->ring;
+
+ /*
+ * Access to the ring contents is serialized by either the
+ * prod /or/ cons lock so take both when resizing.
+ */
+ mutex_lock(&u->ring_cons_mutex);
+ spin_lock_irq(&u->ring_prod_lock);
+
+ /*
+ * Copy the old ring contents to the new ring.
+ *
+ * If the ring contents crosses the end of the current ring,
+ * it needs to be copied in two chunks.
+ *
+ * +---------+ +------------------+
+ * |34567 12| -> | 1234567 |
+ * +-----p-c-+ +------------------+
+ */
+ p = evtchn_ring_offset(u, u->ring_prod);
+ c = evtchn_ring_offset(u, u->ring_cons);
+ if (p < c) {
+ memcpy(new_ring + c, u->ring + c, (u->ring_size - c) * sizeof(*u->ring));
+ memcpy(new_ring + u->ring_size, u->ring, p * sizeof(*u->ring));
+ } else
+ memcpy(new_ring + c, u->ring + c, (p - c) * sizeof(*u->ring));
+
+ u->ring = new_ring;
+ u->ring_size = new_size;
+
+ spin_unlock_irq(&u->ring_prod_lock);
+ mutex_unlock(&u->ring_cons_mutex);
+
+ evtchn_free_ring(old_ring);
+
+ return 0;
+}
+