[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.zanu...@linux.intel.com>
---
 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