tracing: Add hist trigger support for variable reference aliases

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

Aliases are a way of creating a new name for an existing variable, for
flexibly in making naming more clear in certain cases.  For example in
the below the user perhaps feels that using $new_lat in the synthetic
event invocation is opaque or doesn't fit well stylistically with
previous triggers, so creates an alias of $new_lat named $latency and
uses that in the call instead:

  # echo 'hist:keys=next_pid:new_lat=common_timestamp.usecs' >
    /sys/kernel/debug/tracing/events/sched/sched_switch/trigger

  # echo 'hist:keys=pid:latency=$new_lat:
    onmatch(sched.sched_switch).wake2($latency,pid)' >
    /sys/kernel/debug/tracing/events/synthetic/wake1/trigger

Link: http://lkml.kernel.org/r/ef20a65d921af3a873a6f1e8c71407c926d5586f.1516069914.git.tom.zanussi@linux.intel.com
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 98be6ad..32af523 100644 (file)
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -228,6 +228,7 @@ enum hist_field_flags {
        HIST_FIELD_FL_EXPR              = 1 << 13,
        HIST_FIELD_FL_VAR_REF           = 1 << 14,
        HIST_FIELD_FL_CPU               = 1 << 15,
+       HIST_FIELD_FL_ALIAS             = 1 << 16,
 };
 
 struct var_defs {
@@ -1609,7 +1610,8 @@ 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";
@@ -2080,7 +2082,7 @@ 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) {
@@ -2217,10 +2219,18 @@ static int init_var_ref(struct hist_field *ref_field,
                }
        }
 
-       ref_field->name = kstrdup(var_field->var.name, GFP_KERNEL);
-       if (!ref_field->name) {
-               err = -ENOMEM;
-               goto free;
+       if (var_field->var.name) {
+               ref_field->name = kstrdup(var_field->var.name, GFP_KERNEL);
+               if (!ref_field->name) {
+                       err = -ENOMEM;
+                       goto free;
+               }
+       } else if (var_field->name) {
+               ref_field->name = kstrdup(var_field->name, GFP_KERNEL);
+               if (!ref_field->name) {
+                       err = -ENOMEM;
+                       goto free;
+               }
        }
 
        ref_field->type = kstrdup(var_field->type, GFP_KERNEL);
@@ -2382,6 +2392,28 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
        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;
+
+       alias = create_hist_field(hist_data, NULL, flags, var_name);
+       if (!alias)
+               return NULL;
+
+       alias->fn = var_ref->fn;
+       alias->operands[0] = var_ref;
+
+       if (init_var_ref(alias, var_ref, var_ref->system, var_ref->event_name)) {
+               destroy_hist_field(alias, 0);
+               return NULL;
+       }
+
+       return alias;
+}
+
 static struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
                                     struct trace_event_file *file, char *str,
                                     unsigned long *flags, char *var_name)
@@ -2415,6 +2447,13 @@ static 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;
                }
        } else
@@ -2515,6 +2554,26 @@ static int check_expr_operands(struct hist_field *operand1,
        unsigned long operand1_flags = operand1->flags;
        unsigned long operand2_flags = operand2->flags;
 
+       if ((operand1_flags & HIST_FIELD_FL_VAR_REF) ||
+           (operand1_flags & HIST_FIELD_FL_ALIAS)) {
+               struct hist_field *var;
+
+               var = find_var_field(operand1->var.hist_data, operand1->name);
+               if (!var)
+                       return -EINVAL;
+               operand1_flags = var->flags;
+       }
+
+       if ((operand2_flags & HIST_FIELD_FL_VAR_REF) ||
+           (operand2_flags & HIST_FIELD_FL_ALIAS)) {
+               struct hist_field *var;
+
+               var = find_var_field(operand2->var.hist_data, operand2->name);
+               if (!var)
+                       return -EINVAL;
+               operand2_flags = var->flags;
+       }
+
        if ((operand1_flags & HIST_FIELD_FL_TIMESTAMP_USECS) !=
            (operand2_flags & HIST_FIELD_FL_TIMESTAMP_USECS))
                return -EINVAL;
@@ -4646,7 +4705,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
        else if (hist_field->flags & HIST_FIELD_FL_CPU)
                seq_puts(m, "cpu");
        else if (field_name) {
-               if (hist_field->flags & HIST_FIELD_FL_VAR_REF)
+               if (hist_field->flags & HIST_FIELD_FL_VAR_REF ||
+                   hist_field->flags & HIST_FIELD_FL_ALIAS)
                        seq_putc(m, '$');
                seq_printf(m, "%s", field_name);
        }