[PATCH 28/32] tracing: Add hist trigger support for variable reference aliases

[Tom Zanussi]

Add support for alias=$somevar where alias can be used as
onmatch($alias).

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 46 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 904a635..799b95e 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -225,6 +225,7 @@ enum hist_field_flags {
 	HIST_FIELD_FL_EXPR		= 16384,
 	HIST_FIELD_FL_VAR_REF		= 32768,
 	HIST_FIELD_FL_CPU		= 65536,
+	HIST_FIELD_FL_ALIAS		= 131072,
 };
 
 struct hist_trigger_attrs {
@@ -1414,7 +1415,8 @@ static const char *hist_field_name(struct hist_field *field,
 
 	if (field->field)
 		field_name = field->field->name;
-	else if (field->flags & HIST_FIELD_FL_LOG2)
+	else if (field->flags & HIST_FIELD_FL_LOG2 ||
+		 field->flags & HIST_FIELD_FL_ALIAS)
 		field_name = hist_field_name(field->operands[0], ++level);
 	else if (field->flags & HIST_FIELD_FL_TIMESTAMP)
 		field_name = "$common_timestamp";
@@ -1819,7 +1821,7 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 
 	hist_field->hist_data = hist_data;
 
-	if (flags & HIST_FIELD_FL_EXPR)
+	if (flags & HIST_FIELD_FL_EXPR || flags & HIST_FIELD_FL_ALIAS)
 		goto out; /* caller will populate */
 
 	if (flags & HIST_FIELD_FL_VAR_REF) {
@@ -2013,6 +2015,34 @@ static struct hist_field *parse_var_ref(char *system, char *event_name,
 	return field;
 }
 
+static struct hist_field *create_alias(struct hist_trigger_data *hist_data,
+				       struct hist_field *var_ref,
+				       char *var_name)
+{
+	struct hist_field *alias = NULL;
+	unsigned long flags = HIST_FIELD_FL_ALIAS | HIST_FIELD_FL_VAR |
+		HIST_FIELD_FL_VAR_ONLY;
+
+	alias = create_hist_field(hist_data, NULL, flags, var_name);
+	if (!alias)
+		return NULL;
+
+	alias->fn = var_ref->fn;
+	alias->operands[0] = var_ref;
+	alias->var.idx = var_ref->var.idx;
+	alias->var.hist_data = var_ref->hist_data;
+	alias->size = var_ref->size;
+	alias->is_signed = var_ref->is_signed;
+	alias->type = kstrdup(var_ref->type, GFP_KERNEL);
+	if (!alias->type) {
+		kfree(alias->type);
+		destroy_hist_field(alias, 0);
+		return NULL;
+	}
+
+	return alias;
+}
+
 struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
 			      struct trace_event_file *file, char *str,
 			      unsigned long *flags, char *var_name)
@@ -2036,6 +2066,13 @@ struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
 	if (hist_field) {
 		hist_data->var_refs[hist_data->n_var_refs] = hist_field;
 		hist_field->var_ref_idx = hist_data->n_var_refs++;
+		if (var_name) {
+			hist_field = create_alias(hist_data, hist_field, var_name);
+			if (!hist_field) {
+				ret = -ENOMEM;
+				goto out;
+			}
+		}
 		return hist_field;
 	}
 
@@ -4152,8 +4189,11 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
 		seq_puts(m, "$common_timestamp");
 	else if (hist_field->flags & HIST_FIELD_FL_CPU)
 		seq_puts(m, "cpu");
-	else if (field_name)
+	else if (field_name) {
+		if (hist_field->flags & HIST_FIELD_FL_ALIAS)
+			seq_putc(m, '$');
 		seq_printf(m, "%s", field_name);
+	}
 
 	if (hist_field->flags) {
 		const char *flags_str = get_hist_field_flags(hist_field);
-- 
1.9.3