Add 5 spare VOPs as placeholders to avoid breaking the KBI in the future

when new VOPs are MFC'd to a branch.

Reviewed by:	kib, bz
MFC after:	3 days

sys/kern/vnode_if.src

@@ -50,7 +50,7 @@
 # X: locked if not nil.
 #
 # The paramater named "vpp" is assumed to be always used with double
-# indirection (**vpp) and that name is hard-codeed in vnode_if.awk !
+# indirection (**vpp) and that name is hard-coded in vnode_if.awk !
 #
 # Lines starting with %! specify a pre or post-condition function
 # to call before/after the vop call.
@@ -639,3 +639,28 @@ vop_advise {
 	IN off_t end;
 	IN int advice;
 };
+
+# The VOPs below are spares at the end of the table to allow new VOPs to be
+# added in stable branches without breaking the KBI.  New VOPs in HEAD should
+# be added above these spares.  When merging a new VOP to a stable branch,
+# the new VOP should replace one of the spares.
+
+vop_spare1 {
+	IN struct vnode *vp;
+};
+
+vop_spare2 {
+	IN struct vnode *vp;
+};
+
+vop_spare3 {
+	IN struct vnode *vp;
+};
+
+vop_spare4 {
+	IN struct vnode *vp;
+};
+
+vop_spare5 {
+	IN struct vnode *vp;
+};