[PATCH v5 30/37] tracing: Add hist trigger support for variable reference aliases

[Tom Zanussi]

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

Signed-off-by: Tom Zanussi 
---
 kernel/trace/trace_events_hist.c | 58 +---
 1 file changed, 55 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 30da21c..bd3f03f 100644
--- 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 {
@@ -1624,7 +1625,8 @@ 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";
@@ -2091,7 +2093,7 @@ 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) {
@@ -2375,6 +2377,28 @@ static struct hist_field *parse_var_ref(struct 
hist_trigger_data *hist_data,
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;
+}
+
 struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
  struct trace_event_file *file, char *str,
  unsigned long *flags, char *var_name)
@@ -2408,6 +2432,13 @@ 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;
}
} else
@@ -2512,6 +2543,26 @@ 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) !=

[PATCH v5 30/37] tracing: Add hist trigger support for variable reference aliases

[Tom Zanussi]

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

Signed-off-by: Tom Zanussi 
---
 kernel/trace/trace_events_hist.c | 58 +---
 1 file changed, 55 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 30da21c..bd3f03f 100644
--- 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 {
@@ -1624,7 +1625,8 @@ 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";
@@ -2091,7 +2093,7 @@ 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) {
@@ -2375,6 +2377,28 @@ static struct hist_field *parse_var_ref(struct 
hist_trigger_data *hist_data,
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;
+}
+
 struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
  struct trace_event_file *file, char *str,
  unsigned long *flags, char *var_name)
@@ -2408,6 +2432,13 @@ 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;
}
} else
@@ -2512,6 +2543,26 @@ 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 &