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Diffstat (limited to 'doc/developer')
| -rw-r--r-- | doc/developer/tracing.rst | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/doc/developer/tracing.rst b/doc/developer/tracing.rst index d54f6c7aaa..b07c71e505 100644 --- a/doc/developer/tracing.rst +++ b/doc/developer/tracing.rst @@ -173,6 +173,77 @@ Example:: When using LTTng, you can also get zlogs as trace events by enabling the ``lttng_ust_tracelog:*`` event class. +To see available SystemTap USDT probes, run:: + + stap -L 'process("/usr/lib/frr/bgpd").mark("*")' + +Example:: + root@host ~> stap -L 'process("/usr/lib/frr/bgpd").mark("*")' + process("/usr/lib/frr/bgpd").mark("capability_process") $arg1:long $arg2:long + process("/usr/lib/frr/bgpd").mark("input_filter") $arg1:long $arg2:long $arg3:long $arg4:long $arg5:long + process("/usr/lib/frr/bgpd").mark("keepalive_process") $arg1:long $arg2:long + process("/usr/lib/frr/bgpd").mark("notification_process") $arg1:long $arg2:long + process("/usr/lib/frr/bgpd").mark("open_process") $arg1:long $arg2:long + process("/usr/lib/frr/bgpd").mark("output_filter") $arg1:long $arg2:long $arg3:long $arg4:long $arg5:long + process("/usr/lib/frr/bgpd").mark("packet_read") $arg1:long $arg2:long + process("/usr/lib/frr/bgpd").mark("process_update") $arg1:long $arg2:long $arg3:long $arg4:long $arg5:long $arg6:long + process("/usr/lib/frr/bgpd").mark("refresh_process") $arg1:long $arg2:long + process("/usr/lib/frr/bgpd").mark("update_process") $arg1:long $arg2:long + +When using SystemTap, you can also easily attach to an existing function:: + + stap -L 'process("/usr/lib/frr/bgpd").function("bgp_update_receive")' + +Example: + + root@host ~> stap -L 'process("/usr/lib/frr/bgpd").function("bgp_update_receive")' + process("/usr/lib/frr/bgpd").function("bgp_update_receive@bgpd/bgp_packet.c:1531") $peer:struct peer* $size:bgp_size_t $attr:struct attr $restart:_Bool $nlris:struct bgp_nlri[] $__func__:char const[] const + +Complete ``bgp.stp`` example using SystemTap to show BGP peer, prefix and aspath +using ``process_update`` USDT:: + + global pkt_size; + probe begin + { + ansi_clear_screen(); + println("Starting..."); + } + probe process("/usr/lib/frr/bgpd").function("bgp_update_receive") + { + pkt_size <<< $size; + } + probe process("/usr/lib/frr/bgpd").mark("process_update") + { + aspath = @cast($arg6, "attr")->aspath; + printf("> %s via %s (%s)\n", + user_string($arg2), + user_string(@cast($arg1, "peer")->host), + user_string(@cast(aspath, "aspath")->str)); + } + probe end + { + if (@count(pkt_size)) + print(@hist_linear(pkt_size, 0, 20, 2)); + } + +Output:: + + Starting... + > 192.168.0.0/24 via 192.168.0.1 (65534) + > 192.168.100.1/32 via 192.168.0.1 (65534) + > 172.16.16.1/32 via 192.168.0.1 (65534 65030) + ^Cvalue |-------------------------------------------------- count + 0 | 0 + 2 | 0 + 4 |@ 1 + 6 | 0 + 8 | 0 + ~ + 18 | 0 + 20 | 0 + >20 |@@@@@ 5 + + Concepts -------- @@ -308,6 +379,31 @@ Limitations Tracers do not like ``fork()`` or ``dlopen()``. LTTng has some workarounds for this involving interceptor libraries using ``LD_PRELOAD``. +If you're running FRR in a typical daemonizing way (``-d`` to the daemons) +you'll need to run the daemons like so: + +.. code-block:: shell + + LD_PRELOAD=liblttng-ust-fork.so <daemon> + + +If you're using systemd this you can accomplish this for all daemons by +modifying ``frr.service`` like so: + +.. code-block:: diff + + --- a/frr.service + +++ b/frr.service + @@ -7,6 +7,7 @@ Before=network.target + OnFailure=heartbeat-failed@%n.service + + [Service] + +Environment="LD_PRELOAD=liblttng-ust-fork.so" + Nice=-5 + Type=forking + NotifyAccess=all + + USDT tracepoints are relatively high overhead and probably shouldn't be used for "flight recorder" functionality, i.e. enabling and passively recording all events for monitoring purposes. It's generally okay to use LTTng like this, |