Commit 9d048e5e authored by Tom Parkin's avatar Tom Parkin Committed by David S. Miller
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docs: networking: add tracepoint info to l2tp.rst 



Update l2tp.rst to:

 * remove information about the obsolete debug flags and their use
 * include information about tracepoints for l2tp

Signed-off-by: default avatarTom Parkin <tparkin@katalix.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent eee049c0

Documentation/networking/l2tp.rst

+14 −23
Original line number Diff line number Diff line
@@ -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