l2tp: Add debugfs files for dumping l2tp debug info

The existing pppol2tp driver exports debug info to
/proc/net/pppol2tp. Rather than adding info to that file for the new
functionality added in this patch series, we add new files in debugfs,
leaving the old /proc file for backwards compatibility (L2TPv2 only).

Currently only one file is provided: l2tp/tunnels, which lists
internal debug info for all l2tp tunnels and sessions. More files may
be added later. The info is for debug and problem analysis only -
userspace apps should use netlink to obtain status about l2tp tunnels
and sessions.

Although debugfs does not support net namespaces, the tunnels and
sessions dumped in l2tp/tunnels are only those in the net namespace of
the process reading the file.

Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c
index d64f081f2b1..1ef10e4118d 100644
--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -597,6 +597,20 @@ out:
         return error;
 }
 
+#ifdef CONFIG_L2TP_DEBUGFS
+static void pppol2tp_show(struct seq_file *m, void *arg)
+{
+        struct l2tp_session *session = arg;
+        struct pppol2tp_session *ps = l2tp_session_priv(session);
+
+        if (ps) {
+                struct pppox_sock *po = pppox_sk(ps->sock);
+                if (po)
+                        seq_printf(m, "   interface %s\n", ppp_dev_name(&po->chan));
+        }
+}
+#endif
+
 /* connect() handler. Attach a PPPoX socket to a tunnel UDP socket
  */
 static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
@@ -734,6 +748,9 @@ static int pppol2tp_connect(struct socket *sock, struct sockaddr *uservaddr,
 
         session->recv_skb       = pppol2tp_recv;
         session->session_close  = pppol2tp_session_close;
+#ifdef CONFIG_L2TP_DEBUGFS
+        session->show           = pppol2tp_show;
+#endif
 
         /* We need to know each time a skb is dropped from the reorder
          * queue.