From f59281dafb832b161133743fcf3dc29051e6fdb8 Mon Sep 17 00:00:00 2001
From: Jason Wang <jasowang@redhat.com>
Date: Tue, 21 Jun 2011 18:04:27 +0800
Subject: vhost: init used ring after backend was set

Move the used ring initialization after backend was set. This
makes it possible to disable the backend and tweak the used ring,
then restart. This will also make it possible to log the used ring
write correctly.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index f0fd52c..70ac604 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -703,6 +703,10 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 		vhost_net_disable_vq(n, vq);
 		rcu_assign_pointer(vq->private_data, sock);
 		vhost_net_enable_vq(n, vq);
+
+		r = vhost_init_used(vq);
+		if (r)
+			goto err_vq;
 	}
 
 	mutex_unlock(&vq->mutex);
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index 734e1d7..fc9a1d7 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -195,8 +195,13 @@ static long vhost_test_run(struct vhost_test *n, int test)
 						    lockdep_is_held(&vq->mutex));
 		rcu_assign_pointer(vq->private_data, priv);
 
+		r = vhost_init_used(&n->vqs[index]);
+
 		mutex_unlock(&vq->mutex);
 
+		if (r)
+			goto err;
+
 		if (oldpriv) {
 			vhost_test_flush_vq(n, index);
 		}
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 5ef2f62..9a10803 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -629,15 +629,17 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 	return 0;
 }
 
-static int init_used(struct vhost_virtqueue *vq,
-		     struct vring_used __user *used)
+int vhost_init_used(struct vhost_virtqueue *vq)
 {
-	int r = put_user(vq->used_flags, &used->flags);
+	int r;
+	if (!vq->private_data)
+		return 0;
 
+	r = put_user(vq->used_flags, &vq->used->flags);
 	if (r)
 		return r;
 	vq->signalled_used_valid = false;
-	return get_user(vq->last_used_idx, &used->idx);
+	return get_user(vq->last_used_idx, &vq->used->idx);
 }
 
 static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
@@ -752,10 +754,6 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
 			}
 		}
 
-		r = init_used(vq, (struct vring_used __user *)(unsigned long)
-			      a.used_user_addr);
-		if (r)
-			break;
 		vq->log_used = !!(a.flags & (0x1 << VHOST_VRING_F_LOG));
 		vq->desc = (void __user *)(unsigned long)a.desc_user_addr;
 		vq->avail = (void __user *)(unsigned long)a.avail_user_addr;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 1544b78..14c9abf 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -174,6 +174,7 @@ int vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
 		      struct vhost_log *log, unsigned int *log_num);
 void vhost_discard_vq_desc(struct vhost_virtqueue *, int n);
 
+int vhost_init_used(struct vhost_virtqueue *);
 int vhost_add_used(struct vhost_virtqueue *, unsigned int head, int len);
 int vhost_add_used_n(struct vhost_virtqueue *, struct vring_used_elem *heads,
 		     unsigned count);
-- 
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