1Deterministic Automata Instrumentation
2======================================
3
4The RV monitor file created by dot2k, with the name "$MODEL_NAME.c"
5includes a section dedicated to instrumentation.
6
7In the example of the wip.dot monitor created on [1], it will look like::
8
9  /*
10   * This is the instrumentation part of the monitor.
11   *
12   * This is the section where manual work is required. Here the kernel events
13   * are translated into model's event.
14   *
15   */
16  static void handle_preempt_disable(void *data, /* XXX: fill header */)
17  {
18	da_handle_event_wip(preempt_disable_wip);
19  }
20
21  static void handle_preempt_enable(void *data, /* XXX: fill header */)
22  {
23	da_handle_event_wip(preempt_enable_wip);
24  }
25
26  static void handle_sched_waking(void *data, /* XXX: fill header */)
27  {
28	da_handle_event_wip(sched_waking_wip);
29  }
30
31  static int enable_wip(void)
32  {
33	int retval;
34
35	retval = da_monitor_init_wip();
36	if (retval)
37		return retval;
38
39	rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_disable);
40	rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_enable);
41	rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_sched_waking);
42
43	return 0;
44  }
45
46The comment at the top of the section explains the general idea: the
47instrumentation section translates *kernel events* into the *model's
48event*.
49
50Tracing callback functions
51--------------------------
52
53The first three functions are the starting point of the callback *handler
54functions* for each of the three events from the wip model. The developer
55does not necessarily need to use them: they are just starting points.
56
57Using the example of::
58
59 void handle_preempt_disable(void *data, /* XXX: fill header */)
60 {
61        da_handle_event_wip(preempt_disable_wip);
62 }
63
64The preempt_disable event from the model connects directly to the
65preemptirq:preempt_disable. The preemptirq:preempt_disable event
66has the following signature, from include/trace/events/preemptirq.h::
67
68  TP_PROTO(unsigned long ip, unsigned long parent_ip)
69
70Hence, the handle_preempt_disable() function will look like::
71
72  void handle_preempt_disable(void *data, unsigned long ip, unsigned long parent_ip)
73
74In this case, the kernel event translates one to one with the automata
75event, and indeed, no other change is required for this function.
76
77The next handler function, handle_preempt_enable() has the same argument
78list from the handle_preempt_disable(). The difference is that the
79preempt_enable event will be used to synchronize the system to the model.
80
81Initially, the *model* is placed in the initial state. However, the *system*
82might or might not be in the initial state. The monitor cannot start
83processing events until it knows that the system has reached the initial state.
84Otherwise, the monitor and the system could be out-of-sync.
85
86Looking at the automata definition, it is possible to see that the system
87and the model are expected to return to the initial state after the
88preempt_enable execution. Hence, it can be used to synchronize the
89system and the model at the initialization of the monitoring section.
90
91The start is informed via a special handle function, the
92"da_handle_start_event_$(MONITOR_NAME)(event)", in this case::
93
94  da_handle_start_event_wip(preempt_enable_wip);
95
96So, the callback function will look like::
97
98  void handle_preempt_enable(void *data, unsigned long ip, unsigned long parent_ip)
99  {
100        da_handle_start_event_wip(preempt_enable_wip);
101  }
102
103Finally, the "handle_sched_waking()" will look like::
104
105  void handle_sched_waking(void *data, struct task_struct *task)
106  {
107        da_handle_event_wip(sched_waking_wip);
108  }
109
110And the explanation is left for the reader as an exercise.
111
112enable and disable functions
113----------------------------
114
115dot2k automatically creates two special functions::
116
117  enable_$(MONITOR_NAME)()
118  disable_$(MONITOR_NAME)()
119
120These functions are called when the monitor is enabled and disabled,
121respectively.
122
123They should be used to *attach* and *detach* the instrumentation to the running
124system. The developer must add to the relative function all that is needed to
125*attach* and *detach* its monitor to the system.
126
127For the wip case, these functions were named::
128
129 enable_wip()
130 disable_wip()
131
132But no change was required because: by default, these functions *attach* and
133*detach* the tracepoints_to_attach, which was enough for this case.
134
135Instrumentation helpers
136-----------------------
137
138To complete the instrumentation, the *handler functions* need to be attached to a
139kernel event, at the monitoring enable phase.
140
141The RV interface also facilitates this step. For example, the macro "rv_attach_trace_probe()"
142is used to connect the wip model events to the relative kernel event. dot2k automatically
143adds "rv_attach_trace_probe()" function call for each model event in the enable phase, as
144a suggestion.
145
146For example, from the wip sample model::
147
148  static int enable_wip(void)
149  {
150        int retval;
151
152        retval = da_monitor_init_wip();
153        if (retval)
154                return retval;
155
156        rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_enable);
157        rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_sched_waking);
158        rv_attach_trace_probe("wip", /* XXX: tracepoint */, handle_preempt_disable);
159
160        return 0;
161  }
162
163The probes then need to be detached at the disable phase.
164
165[1] The wip model is presented in::
166
167  Documentation/trace/rv/deterministic_automata.rst
168
169The wip monitor is presented in::
170
171  Documentation/trace/rv/da_monitor_synthesis.rst
172