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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: Tom Parkin <tparkin@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tom Parkin 2020-08-22 15:59:09 +01:00 committed by David S. Miller
parent eee049c0ef
commit 9d048e5e66
1 changed files with 14 additions and 23 deletions
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37
Documentation/networking/l2tp.rst
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@ -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