Merge branch 'l2tp-replace-custom-logging-code-with-tracepoints'

Tom Parkin says:

====================
l2tp: replace custom logging code with tracepoints

The l2tp subsystem implemented custom logging macros for debugging
purposes which were controlled using a set of debugging flags in each
tunnel and session structure.

A more standard and easier-to-use approach is to use tracepoints.

This patchset refactors l2tp to:

 * remove excessive logging
 * tweak useful log messages to use the standard pr_* calls for logging
   rather than the l2tp wrappers
 * replace debug-level logging with tracepoints
 * add tracepoints for capturing tunnel and session lifetime events

I note that checkpatch.pl warns about the layout of code in the
newly-added file net/l2tp/trace.h.  When adding this file I followed the
example(s) of other tracepoint files in the net/ subtree since it seemed
preferable to adhere to the prevailing style rather than follow
checkpatch.pl's advice in this instance.  If that's the wrong
approach please let me know.

v1 -> v2

 * Fix up a build warning found by the kernel test robot
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/l2tp.rst

@@ -455,31 +455,16 @@ l2tp help`` for more information.
 Debugging
 ---------
 
-The L2TP subsystem offers a debug scheme where kernel trace messages
-may be optionally enabled per tunnel and per session. Care is needed
-when debugging a live system since the messages are not rate-limited
-and a busy system could be swamped. Userspace uses setsockopt on the
-PPPoX socket to set a debug mask, or ``L2TP_ATTR_DEBUG`` in netlink
-Create and Modify commands.
+The L2TP subsystem offers a range of debugging interfaces through the
+debugfs filesystem.
 
-The following debug mask bits are defined:-
-
-================  ==============================
-L2TP_MSG_DEBUG    verbose debug (if compiled in)
-L2TP_MSG_CONTROL  userspace - kernel interface
-L2TP_MSG_SEQ      sequence numbers handling
-L2TP_MSG_DATA     data packets
-================  ==============================
-
-Sessions inherit default debug flags from the parent tunnel.
-
-If enabled, files under a l2tp debugfs directory can be used to dump
-kernel state about L2TP tunnels and sessions. To access it, the
-debugfs filesystem must first be mounted::
+To access these interfaces, the debugfs filesystem must first be mounted::
 
     # mount -t debugfs debugfs /debug
 
-Files under the l2tp directory can then be accessed::
+Files under the l2tp directory can then be accessed, providing a summary
+of the current population of tunnel and session contexts existing in the
+kernel::
 
     # cat /debug/l2tp/tunnels
 
@@ -488,8 +473,14 @@ state information because the file format is subject to change. It is
 implemented to provide extra debug information to help diagnose
 problems. Applications should instead use the netlink API.
 
-/proc/net/pppol2tp is also provided for backwards compatibility with
-the original pppol2tp code. It lists information about L2TPv2
+In addition the L2TP subsystem implements tracepoints using the standard
+kernel event tracing API.  The available L2TP events can be reviewed as
+follows::
+
+    # find /debug/tracing/events/l2tp
+
+Finally, /proc/net/pppol2tp is also provided for backwards compatibility
+with the original pppol2tp code. It lists information about L2TPv2
 tunnels and sessions only. Its use is discouraged.
 
 Internal Implementation

include/uapi/linux/if_pppol2tp.h

@@ -75,7 +75,7 @@ struct pppol2tpv3in6_addr {
 };
 
 /* Socket options:
- * DEBUG	- bitmask of debug message categories
+ * DEBUG	- bitmask of debug message categories (not used)
  * SENDSEQ	- 0 => don't send packets with sequence numbers
  *		  1 => send packets with sequence numbers
  * RECVSEQ	- 0 => receive packet sequence numbers are optional

include/uapi/linux/l2tp.h

@@ -108,7 +108,7 @@ enum {
 	L2TP_ATTR_VLAN_ID,		/* u16 (not used) */
 	L2TP_ATTR_COOKIE,		/* 0, 4 or 8 bytes */
 	L2TP_ATTR_PEER_COOKIE,		/* 0, 4 or 8 bytes */
-	L2TP_ATTR_DEBUG,		/* u32, enum l2tp_debug_flags */
+	L2TP_ATTR_DEBUG,		/* u32, enum l2tp_debug_flags (not used) */
 	L2TP_ATTR_RECV_SEQ,		/* u8 */
 	L2TP_ATTR_SEND_SEQ,		/* u8 */
 	L2TP_ATTR_LNS_MODE,		/* u8 */
@@ -177,7 +177,9 @@ enum l2tp_seqmode {
 };
 
 /**
- * enum l2tp_debug_flags - debug message categories for L2TP tunnels/sessions
+ * enum l2tp_debug_flags - debug message categories for L2TP tunnels/sessions.
+ *
+ * Unused.
  *
  * @L2TP_MSG_DEBUG: verbose debug (if compiled in)
  * @L2TP_MSG_CONTROL: userspace - kernel interface

net/l2tp/Makefile

@@ -5,6 +5,8 @@
 
 obj-$(CONFIG_L2TP) += l2tp_core.o
 
+CFLAGS_l2tp_core.o += -I$(src)
+
 # Build l2tp as modules if L2TP is M
 obj-$(subst y,$(CONFIG_L2TP),$(CONFIG_PPPOL2TP)) += l2tp_ppp.o
 obj-$(subst y,$(CONFIG_L2TP),$(CONFIG_L2TP_IP)) += l2tp_ip.o