diff options
Diffstat (limited to 'Documentation/trace/events.rst')
| -rw-r--r-- | Documentation/trace/events.rst | 63 |
1 files changed, 32 insertions, 31 deletions
diff --git a/Documentation/trace/events.rst b/Documentation/trace/events.rst index ed79b220bd07..4a2ebe0bd19b 100644 --- a/Documentation/trace/events.rst +++ b/Documentation/trace/events.rst @@ -342,7 +342,8 @@ section of Documentation/trace/ftrace.rst), but there are major differences and the implementation isn't currently tied to it in any way, so beware about making generalizations between the two. -Note: Writing into trace_marker (See Documentation/trace/ftrace.rst) +.. Note:: + Writing into trace_marker (See Documentation/trace/ftrace.rst) can also enable triggers that are written into /sys/kernel/tracing/events/ftrace/print/trigger @@ -569,14 +570,14 @@ The first creates the event in one step, using synth_event_create(). In this method, the name of the event to create and an array defining the fields is supplied to synth_event_create(). If successful, a synthetic event with that name and fields will exist following that -call. For example, to create a new "schedtest" synthetic event: +call. For example, to create a new "schedtest" synthetic event:: ret = synth_event_create("schedtest", sched_fields, ARRAY_SIZE(sched_fields), THIS_MODULE); The sched_fields param in this example points to an array of struct synth_field_desc, each of which describes an event field by type and -name: +name:: static struct synth_field_desc sched_fields[] = { { .type = "pid_t", .name = "next_pid_field" }, @@ -615,7 +616,7 @@ synth_event_gen_cmd_array_start(), the user should create and initialize a dynevent_cmd object using synth_event_cmd_init(). For example, to create a new "schedtest" synthetic event with two -fields: +fields:: struct dynevent_cmd cmd; char *buf; @@ -631,7 +632,7 @@ fields: "u64", "ts_ns"); Alternatively, using an array of struct synth_field_desc fields -containing the same information: +containing the same information:: ret = synth_event_gen_cmd_array_start(&cmd, "schedtest", THIS_MODULE, fields, n_fields); @@ -640,7 +641,7 @@ Once the synthetic event object has been created, it can then be populated with more fields. Fields are added one by one using synth_event_add_field(), supplying the dynevent_cmd object, a field type, and a field name. For example, to add a new int field named -"intfield", the following call should be made: +"intfield", the following call should be made:: ret = synth_event_add_field(&cmd, "int", "intfield"); @@ -649,7 +650,7 @@ the field is considered to be an array. A group of fields can also be added all at once using an array of synth_field_desc with add_synth_fields(). For example, this would add -just the first four sched_fields: +just the first four sched_fields:: ret = synth_event_add_fields(&cmd, sched_fields, 4); @@ -658,7 +659,7 @@ synth_event_add_field_str() can be used to add it as-is; it will also automatically append a ';' to the string. Once all the fields have been added, the event should be finalized and -registered by calling the synth_event_gen_cmd_end() function: +registered by calling the synth_event_gen_cmd_end() function:: ret = synth_event_gen_cmd_end(&cmd); @@ -691,7 +692,7 @@ trace array)), along with an variable number of u64 args, one for each synthetic event field, and the number of values being passed. So, to trace an event corresponding to the synthetic event definition -above, code like the following could be used: +above, code like the following could be used:: ret = synth_event_trace(create_synth_test, 7, /* number of values */ 444, /* next_pid_field */ @@ -715,7 +716,7 @@ trace array)), along with an array of u64, one for each synthetic event field. To trace an event corresponding to the synthetic event definition -above, code like the following could be used: +above, code like the following could be used:: u64 vals[7]; @@ -739,7 +740,7 @@ In order to trace a synthetic event, a pointer to the trace event file is needed. The trace_get_event_file() function can be used to get it - it will find the file in the given trace instance (in this case NULL since the top trace array is being used) while at the same time -preventing the instance containing it from going away: +preventing the instance containing it from going away:: schedtest_event_file = trace_get_event_file(NULL, "synthetic", "schedtest"); @@ -751,31 +752,31 @@ To enable a synthetic event from the kernel, trace_array_set_clr_event() can be used (which is not specific to synthetic events, so does need the "synthetic" system name to be specified explicitly). -To enable the event, pass 'true' to it: +To enable the event, pass 'true' to it:: trace_array_set_clr_event(schedtest_event_file->tr, "synthetic", "schedtest", true); -To disable it pass false: +To disable it pass false:: trace_array_set_clr_event(schedtest_event_file->tr, "synthetic", "schedtest", false); Finally, synth_event_trace_array() can be used to actually trace the -event, which should be visible in the trace buffer afterwards: +event, which should be visible in the trace buffer afterwards:: ret = synth_event_trace_array(schedtest_event_file, vals, ARRAY_SIZE(vals)); To remove the synthetic event, the event should be disabled, and the -trace instance should be 'put' back using trace_put_event_file(): +trace instance should be 'put' back using trace_put_event_file():: trace_array_set_clr_event(schedtest_event_file->tr, "synthetic", "schedtest", false); trace_put_event_file(schedtest_event_file); If those have been successful, synth_event_delete() can be called to -remove the event: +remove the event:: ret = synth_event_delete("schedtest"); @@ -784,7 +785,7 @@ remove the event: To trace a synthetic using the piecewise method described above, the synth_event_trace_start() function is used to 'open' the synthetic -event trace: +event trace:: struct synth_trace_state trace_state; @@ -809,7 +810,7 @@ along with the value to set the next field in the event. After each field is set, the 'cursor' points to the next field, which will be set by the subsequent call, continuing until all the fields have been set in order. The same sequence of calls as in the above examples using -this method would be (without error-handling code): +this method would be (without error-handling code):: /* next_pid_field */ ret = synth_event_add_next_val(777, &trace_state); @@ -837,7 +838,7 @@ used. Each call is passed the same synth_trace_state object used in the synth_event_trace_start(), along with the field name of the field to set and the value to set it to. The same sequence of calls as in the above examples using this method would be (without error-handling -code): +code):: ret = synth_event_add_val("next_pid_field", 777, &trace_state); ret = synth_event_add_val("next_comm_field", (u64)"silly putty", @@ -855,7 +856,7 @@ can be used but not both at the same time. Finally, the event won't be actually traced until it's 'closed', which is done using synth_event_trace_end(), which takes only the -struct synth_trace_state object used in the previous calls: +struct synth_trace_state object used in the previous calls:: ret = synth_event_trace_end(&trace_state); @@ -878,7 +879,7 @@ function. Before calling kprobe_event_gen_cmd_start(), the user should create and initialize a dynevent_cmd object using kprobe_event_cmd_init(). -For example, to create a new "schedtest" kprobe event with two fields: +For example, to create a new "schedtest" kprobe event with two fields:: struct dynevent_cmd cmd; char *buf; @@ -900,18 +901,18 @@ Once the kprobe event object has been created, it can then be populated with more fields. Fields can be added using kprobe_event_add_fields(), supplying the dynevent_cmd object along with a variable arg list of probe fields. For example, to add a -couple additional fields, the following call could be made: +couple additional fields, the following call could be made:: ret = kprobe_event_add_fields(&cmd, "flags=%cx", "mode=+4($stack)"); Once all the fields have been added, the event should be finalized and registered by calling the kprobe_event_gen_cmd_end() or kretprobe_event_gen_cmd_end() functions, depending on whether a kprobe -or kretprobe command was started: +or kretprobe command was started:: ret = kprobe_event_gen_cmd_end(&cmd); -or +or:: ret = kretprobe_event_gen_cmd_end(&cmd); @@ -920,13 +921,13 @@ events. Similarly, a kretprobe event can be created using kretprobe_event_gen_cmd_start() with a probe name and location and -additional params such as $retval: +additional params such as $retval:: ret = kretprobe_event_gen_cmd_start(&cmd, "gen_kretprobe_test", "do_sys_open", "$retval"); Similar to the synthetic event case, code like the following can be -used to enable the newly created kprobe event: +used to enable the newly created kprobe event:: gen_kprobe_test = trace_get_event_file(NULL, "kprobes", "gen_kprobe_test"); @@ -934,7 +935,7 @@ used to enable the newly created kprobe event: "kprobes", "gen_kprobe_test", true); Finally, also similar to synthetic events, the following code can be -used to give the kprobe event file back and delete the event: +used to give the kprobe event file back and delete the event:: trace_put_event_file(gen_kprobe_test); @@ -963,7 +964,7 @@ are described below. The first step in building a new command string is to create and initialize an instance of a dynevent_cmd. Here, for instance, we -create a dynevent_cmd on the stack and initialize it: +create a dynevent_cmd on the stack and initialize it:: struct dynevent_cmd cmd; char *buf; @@ -989,7 +990,7 @@ calls to argument-adding functions. To add a single argument, define and initialize a struct dynevent_arg or struct dynevent_arg_pair object. Here's an example of the simplest possible arg addition, which is simply to append the given string as -a whitespace-separated argument to the command: +a whitespace-separated argument to the command:: struct dynevent_arg arg; @@ -1007,7 +1008,7 @@ the arg. Here's another more complicated example using an 'arg pair', which is used to create an argument that consists of a couple components added together as a unit, for example, a 'type field_name;' arg or a simple -expression arg e.g. 'flags=%cx': +expression arg e.g. 'flags=%cx':: struct dynevent_arg_pair arg_pair; @@ -1031,7 +1032,7 @@ Any number of dynevent_*_add() calls can be made to build up the string (until its length surpasses cmd->maxlen). When all the arguments have been added and the command string is complete, the only thing left to do is run the command, which happens by simply calling -dynevent_create(): +dynevent_create():: ret = dynevent_create(&cmd); |