1 files changed, 12 insertions, 0 deletions

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 1c116dc03e0e..77be396ca633 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -300,6 +300,18 @@ extern void xfrm_put_type(struct xfrm_type *type);
 
 struct xfrm_mode {
         int (*input)(struct xfrm_state *x, struct sk_buff *skb);
+
+        /*
+         * Add encapsulation header.
+         *
+         * On exit, the transport header will be set to the start of the
+         * encapsulation header to be filled in by x->type->output and
+         * the mac header will be set to the nextheader (protocol for
+         * IPv4) field of the extension header directly preceding the
+         * encapsulation header, or in its absence, that of the top IP
+         * header.  The value of the network header will always point
+         * to the top IP header while skb->data will point to the payload.
+         */
         int (*output)(struct xfrm_state *x,struct sk_buff *skb);
 
         struct module *owner;