tree 4319a3e6fe143e6404420f885275cb1f7c87a1a4
parent 883a1e867e0fe7c2dc2e5844ef692f80177631d5
author Steven Rostedt (Red Hat) <rostedt@goodmis.org> 1442956399 -0400
committer Steven Rostedt <rostedt@goodmis.org> 1445823234 -0400

tracepoint: Give priority to probes of tracepoints

In order to guarantee that a probe will be called before other probes that
are attached to a tracepoint, there needs to be a mechanism to provide
priority of one probe over the others.

Adding a prio field to the struct tracepoint_func, which lets the probes be
sorted by the priority set in the structure. If no priority is specified,
then a priority of 10 is given (this is a macro, and perhaps may be changed
in the future).

Now probes may be added to affect other probes that are attached to a
tracepoint with a guaranteed order.

One use case would be to allow tracing of tracepoints be able to filter by
pid. A special (higher priority probe) may be added to the sched_switch
tracepoint and set the necessary flags of the other tracepoints to notify
them if they should be traced or not. In case a tracepoint is enabled at the
sched_switch tracepoint too, the order of the two are not random.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>