[for-next][PATCH 18/24] tracing: Add hist trigger comments for variable-related fields

Steven Rostedt
2018-12-21T17:58:01Z

From: Tom Zanussi <tom.zanussi@linux.intel.com>

Add a few comments to help clarify how variable and variable reference
fields are used in the code.

Link: http://lkml.kernel.org/r/ea857ce948531d7bec712bbb0f38360aa1d378ec.1545161087.git.tom.zanussi@linux.intel.com

Acked-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace_events_hist.c | 36 ++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 1b1aee944588..c5448c103770 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -40,6 +40,16 @@ enum field_op_id {
FIELD_OP_UNARY_MINUS,
};

+/*
+ * A hist_var (histogram variable) contains variable information for
+ * hist_fields having the HIST_FIELD_FL_VAR or HIST_FIELD_FL_VAR_REF
+ * flag set. A hist_var has a variable name e.g. ts0, and is
+ * associated with a given histogram trigger, as specified by
+ * hist_data. The hist_var idx is the unique index assigned to the
+ * variable by the hist trigger's tracing_map. The idx is what is
+ * used to set a variable's value and, by a variable reference, to
+ * retrieve it.
+ */
struct hist_var {
char *name;
struct hist_trigger_data *hist_data;
@@ -56,11 +66,29 @@ struct hist_field {
const char *type;
struct hist_field *operands[HIST_FIELD_OPERANDS_MAX];
struct hist_trigger_data *hist_data;
+
+ /*
+ * Variable fields contain variable-specific info in var.
+ */
struct hist_var var;
enum field_op_id operator;
char *system;
char *event_name;
+
+ /*
+ * The name field is used for EXPR and VAR_REF fields. VAR
+ * fields contain the variable name in var.name.
+ */
char *name;
+
+ /*
+ * When a histogram trigger is hit, if it has any references
+ * to variables, the values of those variables are collected
+ * into a var_ref_vals array by resolve_var_refs(). The
+ * current value of each variable is read from the tracing_map
+ * using the hist field's hist_var.idx and entered into the
+ * var_ref_idx entry i.e. var_ref_vals[var_ref_idx].
+ */
unsigned int var_ref_idx;
bool read_once;
};
@@ -365,6 +393,14 @@ struct action_data {

union {
struct {
+ /*
+ * When a histogram trigger is hit, the values of any
+ * references to variables, including variables being passed
+ * as parameters to synthetic events, are collected into a
+ * var_ref_vals array. This var_ref_idx is the index of the
+ * first param in the array to be passed to the synthetic
+ * event invocation.
+ */
unsigned int var_ref_idx;
char *match_event;
char *match_event_system;
--
2.19.2