[20/54] tracing: Add variable support to hist triggers
diff mbox series

Message ID TY1PR01MB16929BC131156311E9781F6896090@TY1PR01MB1692.jpnprd01.prod.outlook.com
State New
Headers show
Series
  • [01/54] tracing: Remove redundant unread variable ret
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Commit Message

Motai.Hirotaka@aj.MitsubishiElectric.co.jp Aug. 29, 2018, 12:17 p.m. UTC
Add support for saving the value of a current event's event field by
assigning it to a variable that can be read by a subsequent event.

The basic syntax for saving a variable is to simply prefix a unique
variable name not corresponding to any keyword along with an '=' sign
to any event field.

Both keys and values can be saved and retrieved in this way:

    # echo 'hist:keys=next_pid:vals=$ts0:ts0=common_timestamp ...
    # echo 'hist:timer_pid=common_pid:key=$timer_pid ...'

If a variable isn't a key variable or prefixed with 'vals=', the
associated event field will be saved in a variable but won't be summed
as a value:

    # echo 'hist:keys=next_pid:ts1=common_timestamp:...

Multiple variables can be assigned at the same time:

    # echo 'hist:keys=pid:vals=$ts0,$b,field2:ts0=common_timestamp,b=field1 ...

Multiple (or single) variables can also be assigned at the same time
using separate assignments:

    # echo 'hist:keys=pid:vals=$ts0:ts0=common_timestamp:b=field1:c=field2 ...

Variables set as above can be used by being referenced from another
event, as described in a subsequent patch.

Link: http://lkml.kernel.org/r/fc93c4944d9719dbcb1d0067be627d44e98e2adc.1516069914.git.tom.zanussi@linux.intel.com

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Baohong Liu <baohong.liu@intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
(cherry picked from commit 30350d65ac5676c6d08d4fc935bc9a9cb0fd4ed3)
Signed-off-by: Hirotaka MOTAI <Motai.Hirotaka@aj.MitsubishiElectric.co.jp>
---
 kernel/trace/trace_events_hist.c | 370 +++++++++++++++++++++++++++----
 1 file changed, 331 insertions(+), 39 deletions(-)

Patch
diff mbox series

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 7f5f0b8f..8f43f24b 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -25,26 +25,34 @@ 
 #include "trace.h"
 
 struct hist_field;
 
 typedef u64 (*hist_field_fn_t) (struct hist_field *field, void *event,
 				struct ring_buffer_event *rbe);
 
 #define HIST_FIELD_OPERANDS_MAX	2
+#define HIST_FIELDS_MAX		(TRACING_MAP_FIELDS_MAX + TRACING_MAP_VARS_MAX)
+
+struct hist_var {
+	char				*name;
+	struct hist_trigger_data	*hist_data;
+	unsigned int			idx;
+};
 
 struct hist_field {
 	struct ftrace_event_field	*field;
 	unsigned long			flags;
 	hist_field_fn_t			fn;
 	unsigned int			size;
 	unsigned int			offset;
 	unsigned int                    is_signed;
 	struct hist_field		*operands[HIST_FIELD_OPERANDS_MAX];
 	struct hist_trigger_data	*hist_data;
+	struct hist_var			var;
 };
 
 static u64 hist_field_none(struct hist_field *field, void *event,
 			   struct ring_buffer_event *rbe)
 {
 	return 0;
 }
 
@@ -133,58 +141,114 @@  enum hist_field_flags {
 	HIST_FIELD_FL_SYM		= 1 << 4,
 	HIST_FIELD_FL_SYM_OFFSET	= 1 << 5,
 	HIST_FIELD_FL_EXECNAME		= 1 << 6,
 	HIST_FIELD_FL_SYSCALL		= 1 << 7,
 	HIST_FIELD_FL_STACKTRACE	= 1 << 8,
 	HIST_FIELD_FL_LOG2		= 1 << 9,
 	HIST_FIELD_FL_TIMESTAMP		= 1 << 10,
 	HIST_FIELD_FL_TIMESTAMP_USECS	= 1 << 11,
+	HIST_FIELD_FL_VAR		= 1 << 12,
+};
+
+struct var_defs {
+	unsigned int	n_vars;
+	char		*name[TRACING_MAP_VARS_MAX];
+	char		*expr[TRACING_MAP_VARS_MAX];
 };
 
 struct hist_trigger_attrs {
 	char		*keys_str;
 	char		*vals_str;
 	char		*sort_key_str;
 	char		*name;
 	bool		pause;
 	bool		cont;
 	bool		clear;
 	bool		ts_in_usecs;
 	unsigned int	map_bits;
+
+	char		*assignment_str[TRACING_MAP_VARS_MAX];
+	unsigned int	n_assignments;
+
+	struct var_defs	var_defs;
 };
 
 struct hist_trigger_data {
-	struct hist_field               *fields[TRACING_MAP_FIELDS_MAX];
+	struct hist_field               *fields[HIST_FIELDS_MAX];
 	unsigned int			n_vals;
 	unsigned int			n_keys;
 	unsigned int			n_fields;
+	unsigned int			n_vars;
 	unsigned int			key_size;
 	struct tracing_map_sort_key	sort_keys[TRACING_MAP_SORT_KEYS_MAX];
 	unsigned int			n_sort_keys;
 	struct trace_event_file		*event_file;
 	struct hist_trigger_attrs	*attrs;
 	struct tracing_map		*map;
 	bool				enable_timestamps;
+	bool				remove;
 };
 
 static u64 hist_field_timestamp(struct hist_field *hist_field, void *event,
 				struct ring_buffer_event *rbe)
 {
 	struct hist_trigger_data *hist_data = hist_field->hist_data;
 	struct trace_array *tr = hist_data->event_file->tr;
 
 	u64 ts = ring_buffer_event_time_stamp(rbe);
 
 	if (hist_data->attrs->ts_in_usecs && trace_clock_in_ns(tr))
 		ts = ns2usecs(ts);
 
 	return ts;
 }
 
+static struct hist_field *find_var_field(struct hist_trigger_data *hist_data,
+					 const char *var_name)
+{
+	struct hist_field *hist_field, *found = NULL;
+	int i;
+
+	for_each_hist_field(i, hist_data) {
+		hist_field = hist_data->fields[i];
+		if (hist_field && hist_field->flags & HIST_FIELD_FL_VAR &&
+		    strcmp(hist_field->var.name, var_name) == 0) {
+			found = hist_field;
+			break;
+		}
+	}
+
+	return found;
+}
+
+static struct hist_field *find_var(struct hist_trigger_data *hist_data,
+				   struct trace_event_file *file,
+				   const char *var_name)
+{
+	struct hist_trigger_data *test_data;
+	struct event_trigger_data *test;
+	struct hist_field *hist_field;
+
+	hist_field = find_var_field(hist_data, var_name);
+	if (hist_field)
+		return hist_field;
+
+	list_for_each_entry_rcu(test, &file->triggers, list) {
+		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			test_data = test->private_data;
+			hist_field = find_var_field(test_data, var_name);
+			if (hist_field)
+				return hist_field;
+		}
+	}
+
+	return NULL;
+}
+
 static const char *hist_field_name(struct hist_field *field,
 				   unsigned int level)
 {
 	const char *field_name = "";
 
 	if (level > 1)
 		return field_name;
 
@@ -257,19 +321,24 @@  static int parse_map_size(char *str)
 	else
 		ret = map_bits;
  out:
 	return ret;
 }
 
 static void destroy_hist_trigger_attrs(struct hist_trigger_attrs *attrs)
 {
+	unsigned int i;
+
 	if (!attrs)
 		return;
 
+	for (i = 0; i < attrs->n_assignments; i++)
+		kfree(attrs->assignment_str[i]);
+
 	kfree(attrs->name);
 	kfree(attrs->sort_key_str);
 	kfree(attrs->keys_str);
 	kfree(attrs->vals_str);
 	kfree(attrs);
 }
 
 static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
@@ -306,18 +375,32 @@  static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
 	} else if (strncmp(str, "size=", strlen("size=")) == 0) {
 		int map_bits = parse_map_size(str);
 
 		if (map_bits < 0) {
 			ret = map_bits;
 			goto out;
 		}
 		attrs->map_bits = map_bits;
-	} else
-		ret = -EINVAL;
+	} else {
+		char *assignment;
+
+		if (attrs->n_assignments == TRACING_MAP_VARS_MAX) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		assignment = kstrdup(str, GFP_KERNEL);
+		if (!assignment) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		attrs->assignment_str[attrs->n_assignments++] = assignment;
+	}
  out:
 	return ret;
 }
 
 static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
 {
 	struct hist_trigger_attrs *attrs;
 	int ret = 0;
@@ -423,22 +506,25 @@  static void destroy_hist_field(struct hist_field *hist_field,
 		return;
 
 	if (!hist_field)
 		return;
 
 	for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++)
 		destroy_hist_field(hist_field->operands[i], level + 1);
 
+	kfree(hist_field->var.name);
+
 	kfree(hist_field);
 }
 
 static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 					    struct ftrace_event_field *field,
-					    unsigned long flags)
+					    unsigned long flags,
+					    char *var_name)
 {
 	struct hist_field *hist_field;
 
 	if (field && is_function_field(field))
 		return NULL;
 
 	hist_field = kzalloc(sizeof(struct hist_field), GFP_KERNEL);
 	if (!hist_field)
@@ -454,17 +540,17 @@  static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 	if (flags & HIST_FIELD_FL_STACKTRACE) {
 		hist_field->fn = hist_field_none;
 		goto out;
 	}
 
 	if (flags & HIST_FIELD_FL_LOG2) {
 		unsigned long fl = flags & ~HIST_FIELD_FL_LOG2;
 		hist_field->fn = hist_field_log2;
-		hist_field->operands[0] = create_hist_field(hist_data, field, fl);
+		hist_field->operands[0] = create_hist_field(hist_data, field, fl, NULL);
 		hist_field->size = hist_field->operands[0]->size;
 		goto out;
 	}
 
 	if (flags & HIST_FIELD_FL_TIMESTAMP) {
 		hist_field->fn = hist_field_timestamp;
 		hist_field->size = sizeof(u64);
 		goto out;
@@ -489,59 +575,66 @@  static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 			destroy_hist_field(hist_field, 0);
 			return NULL;
 		}
 	}
  out:
 	hist_field->field = field;
 	hist_field->flags = flags;
 
+	if (var_name) {
+		hist_field->var.name = kstrdup(var_name, GFP_KERNEL);
+		if (!hist_field->var.name)
+			goto free;
+	}
+
 	return hist_field;
+ free:
+	destroy_hist_field(hist_field, 0);
+	return NULL;
 }
 
 static void destroy_hist_fields(struct hist_trigger_data *hist_data)
 {
 	unsigned int i;
 
-	for (i = 0; i < TRACING_MAP_FIELDS_MAX; i++) {
+	for (i = 0; i < HIST_FIELDS_MAX; i++) {
 		if (hist_data->fields[i]) {
 			destroy_hist_field(hist_data->fields[i], 0);
 			hist_data->fields[i] = NULL;
 		}
 	}
 }
 
 static int create_hitcount_val(struct hist_trigger_data *hist_data)
 {
 	hist_data->fields[HITCOUNT_IDX] =
-		create_hist_field(hist_data, NULL, HIST_FIELD_FL_HITCOUNT);
+		create_hist_field(hist_data, NULL, HIST_FIELD_FL_HITCOUNT, NULL);
 	if (!hist_data->fields[HITCOUNT_IDX])
 		return -ENOMEM;
 
 	hist_data->n_vals++;
+	hist_data->n_fields++;
 
 	if (WARN_ON(hist_data->n_vals > TRACING_MAP_VALS_MAX))
 		return -EINVAL;
 
 	return 0;
 }
 
-static int create_val_field(struct hist_trigger_data *hist_data,
-			    unsigned int val_idx,
-			    struct trace_event_file *file,
-			    char *field_str)
+static int __create_val_field(struct hist_trigger_data *hist_data,
+			      unsigned int val_idx,
+			      struct trace_event_file *file,
+			      char *var_name, char *field_str,
+			      unsigned long flags)
 {
 	struct ftrace_event_field *field = NULL;
-	unsigned long flags = 0;
 	char *field_name;
 	int ret = 0;
 
-	if (WARN_ON(val_idx >= TRACING_MAP_VALS_MAX))
-		return -EINVAL;
-
 	field_name = strsep(&field_str, ".");
 	if (field_str) {
 		if (strcmp(field_str, "hex") == 0)
 			flags |= HIST_FIELD_FL_HEX;
 		else {
 			ret = -EINVAL;
 			goto out;
 		}
@@ -553,35 +646,68 @@  static int create_val_field(struct hist_trigger_data *hist_data,
 	} else {
 		field = trace_find_event_field(file->event_call, field_name);
 		if (!field || !field->size) {
 			ret = -EINVAL;
 			goto out;
 		}
 	}
 
-	hist_data->fields[val_idx] = create_hist_field(hist_data, field, flags);
+	hist_data->fields[val_idx] = create_hist_field(hist_data, field, flags, var_name);
 	if (!hist_data->fields[val_idx]) {
 		ret = -ENOMEM;
 		goto out;
 	}
 
 	++hist_data->n_vals;
+	++hist_data->n_fields;
 
-	if (WARN_ON(hist_data->n_vals > TRACING_MAP_VALS_MAX))
+	if (WARN_ON(hist_data->n_vals > TRACING_MAP_VALS_MAX + TRACING_MAP_VARS_MAX))
 		ret = -EINVAL;
  out:
 	return ret;
 }
 
+static int create_val_field(struct hist_trigger_data *hist_data,
+			    unsigned int val_idx,
+			    struct trace_event_file *file,
+			    char *field_str)
+{
+	if (WARN_ON(val_idx >= TRACING_MAP_VALS_MAX))
+		return -EINVAL;
+
+	return __create_val_field(hist_data, val_idx, file, NULL, field_str, 0);
+}
+
+static int create_var_field(struct hist_trigger_data *hist_data,
+			    unsigned int val_idx,
+			    struct trace_event_file *file,
+			    char *var_name, char *expr_str)
+{
+	unsigned long flags = 0;
+
+	if (WARN_ON(val_idx >= TRACING_MAP_VALS_MAX + TRACING_MAP_VARS_MAX))
+		return -EINVAL;
+	if (find_var(hist_data, file, var_name) && !hist_data->remove) {
+		return -EINVAL;
+	}
+
+	flags |= HIST_FIELD_FL_VAR;
+	hist_data->n_vars++;
+	if (WARN_ON(hist_data->n_vars > TRACING_MAP_VARS_MAX))
+		return -EINVAL;
+
+	return __create_val_field(hist_data, val_idx, file, var_name, expr_str, flags);
+}
+
 static int create_val_fields(struct hist_trigger_data *hist_data,
 			     struct trace_event_file *file)
 {
 	char *fields_str, *field_str;
-	unsigned int i, j;
+	unsigned int i, j = 1;
 	int ret;
 
 	ret = create_hitcount_val(hist_data);
 	if (ret)
 		goto out;
 
 	fields_str = hist_data->attrs->vals_str;
 	if (!fields_str)
@@ -591,47 +717,52 @@  static int create_val_fields(struct hist_trigger_data *hist_data,
 	if (!fields_str)
 		goto out;
 
 	for (i = 0, j = 1; i < TRACING_MAP_VALS_MAX &&
 		     j < TRACING_MAP_VALS_MAX; i++) {
 		field_str = strsep(&fields_str, ",");
 		if (!field_str)
 			break;
+
 		if (strcmp(field_str, "hitcount") == 0)
 			continue;
+
 		ret = create_val_field(hist_data, j++, file, field_str);
 		if (ret)
 			goto out;
 	}
+
 	if (fields_str && (strcmp(fields_str, "hitcount") != 0))
 		ret = -EINVAL;
  out:
 	return ret;
 }
 
 static int create_key_field(struct hist_trigger_data *hist_data,
 			    unsigned int key_idx,
 			    unsigned int key_offset,
 			    struct trace_event_file *file,
 			    char *field_str)
 {
 	struct ftrace_event_field *field = NULL;
+	struct hist_field *hist_field = NULL;
 	unsigned long flags = 0;
 	unsigned int key_size;
 	int ret = 0;
 
-	if (WARN_ON(key_idx >= TRACING_MAP_FIELDS_MAX))
+	if (WARN_ON(key_idx >= HIST_FIELDS_MAX))
 		return -EINVAL;
 
 	flags |= HIST_FIELD_FL_KEY;
 
 	if (strcmp(field_str, "stacktrace") == 0) {
 		flags |= HIST_FIELD_FL_STACKTRACE;
 		key_size = sizeof(unsigned long) * HIST_STACKTRACE_DEPTH;
+		hist_field = create_hist_field(hist_data, NULL, flags, NULL);
 	} else {
 		char *field_name = strsep(&field_str, ".");
 
 		if (field_str) {
 			if (strcmp(field_str, "hex") == 0)
 				flags |= HIST_FIELD_FL_HEX;
 			else if (strcmp(field_str, "sym") == 0)
 				flags |= HIST_FIELD_FL_SYM;
@@ -667,32 +798,33 @@  static int create_key_field(struct hist_trigger_data *hist_data,
 
 			if (is_string_field(field))
 				key_size = MAX_FILTER_STR_VAL;
 			else
 				key_size = field->size;
 		}
 	}
 
-	hist_data->fields[key_idx] = create_hist_field(hist_data, field, flags);
+	hist_data->fields[key_idx] = create_hist_field(hist_data, field, flags, NULL);
 	if (!hist_data->fields[key_idx]) {
 		ret = -ENOMEM;
 		goto out;
 	}
 
 	key_size = ALIGN(key_size, sizeof(u64));
 	hist_data->fields[key_idx]->size = key_size;
 	hist_data->fields[key_idx]->offset = key_offset;
 	hist_data->key_size += key_size;
 	if (hist_data->key_size > HIST_KEY_SIZE_MAX) {
 		ret = -EINVAL;
 		goto out;
 	}
 
 	hist_data->n_keys++;
+	hist_data->n_fields++;
 
 	if (WARN_ON(hist_data->n_keys > TRACING_MAP_KEYS_MAX))
 		return -EINVAL;
 
 	ret = key_size;
  out:
 	return ret;
 }
@@ -726,31 +858,121 @@  static int create_key_fields(struct hist_trigger_data *hist_data,
 		ret = -EINVAL;
 		goto out;
 	}
 	ret = 0;
  out:
 	return ret;
 }
 
+static int create_var_fields(struct hist_trigger_data *hist_data,
+			     struct trace_event_file *file)
+{
+	unsigned int i, j = hist_data->n_vals;
+	int ret = 0;
+
+	unsigned int n_vars = hist_data->attrs->var_defs.n_vars;
+
+	for (i = 0; i < n_vars; i++) {
+		char *var_name = hist_data->attrs->var_defs.name[i];
+		char *expr = hist_data->attrs->var_defs.expr[i];
+
+		ret = create_var_field(hist_data, j++, file, var_name, expr);
+		if (ret)
+			goto out;
+	}
+ out:
+	return ret;
+}
+
+static void free_var_defs(struct hist_trigger_data *hist_data)
+{
+	unsigned int i;
+
+	for (i = 0; i < hist_data->attrs->var_defs.n_vars; i++) {
+		kfree(hist_data->attrs->var_defs.name[i]);
+		kfree(hist_data->attrs->var_defs.expr[i]);
+	}
+
+	hist_data->attrs->var_defs.n_vars = 0;
+}
+
+static int parse_var_defs(struct hist_trigger_data *hist_data)
+{
+	char *s, *str, *var_name, *field_str;
+	unsigned int i, j, n_vars = 0;
+	int ret = 0;
+
+	for (i = 0; i < hist_data->attrs->n_assignments; i++) {
+		str = hist_data->attrs->assignment_str[i];
+		for (j = 0; j < TRACING_MAP_VARS_MAX; j++) {
+			field_str = strsep(&str, ",");
+			if (!field_str)
+				break;
+
+			var_name = strsep(&field_str, "=");
+			if (!var_name || !field_str) {
+				ret = -EINVAL;
+				goto free;
+			}
+
+			if (n_vars == TRACING_MAP_VARS_MAX) {
+				ret = -EINVAL;
+				goto free;
+			}
+
+			s = kstrdup(var_name, GFP_KERNEL);
+			if (!s) {
+				ret = -ENOMEM;
+				goto free;
+			}
+			hist_data->attrs->var_defs.name[n_vars] = s;
+
+			s = kstrdup(field_str, GFP_KERNEL);
+			if (!s) {
+				kfree(hist_data->attrs->var_defs.name[n_vars]);
+				ret = -ENOMEM;
+				goto free;
+			}
+			hist_data->attrs->var_defs.expr[n_vars++] = s;
+
+			hist_data->attrs->var_defs.n_vars = n_vars;
+		}
+	}
+
+	return ret;
+ free:
+	free_var_defs(hist_data);
+
+	return ret;
+}
+
 static int create_hist_fields(struct hist_trigger_data *hist_data,
 			      struct trace_event_file *file)
 {
 	int ret;
 
+	ret = parse_var_defs(hist_data);
+	if (ret)
+		goto out;
+
 	ret = create_val_fields(hist_data, file);
 	if (ret)
 		goto out;
 
-	ret = create_key_fields(hist_data, file);
+	ret = create_var_fields(hist_data, file);
 	if (ret)
 		goto out;
 
-	hist_data->n_fields = hist_data->n_vals + hist_data->n_keys;
+	ret = create_key_fields(hist_data, file);
+	if (ret)
+		goto out;
  out:
+	free_var_defs(hist_data);
+
 	return ret;
 }
 
 static int is_descending(const char *str)
 {
 	if (!str)
 		return 0;
 
@@ -763,17 +985,17 @@  static int is_descending(const char *str)
 	return -EINVAL;
 }
 
 static int create_sort_keys(struct hist_trigger_data *hist_data)
 {
 	char *fields_str = hist_data->attrs->sort_key_str;
 	struct tracing_map_sort_key *sort_key;
 	int descending, ret = 0;
-	unsigned int i, j;
+	unsigned int i, j, k;
 
 	hist_data->n_sort_keys = 1; /* we always have at least one, hitcount */
 
 	if (!fields_str)
 		goto out;
 
 	strsep(&fields_str, "=");
 	if (!fields_str) {
@@ -811,36 +1033,44 @@  static int create_sort_keys(struct hist_trigger_data *hist_data)
 			if (descending < 0) {
 				ret = descending;
 				break;
 			}
 			sort_key->descending = descending;
 			continue;
 		}
 
-		for (j = 1; j < hist_data->n_fields; j++) {
+		for (j = 1, k = 1; j < hist_data->n_fields; j++) {
+			unsigned int idx;
+
 			hist_field = hist_data->fields[j];
+			if (hist_field->flags & HIST_FIELD_FL_VAR)
+				continue;
+
+			idx = k++;
+
 			test_name = hist_field_name(hist_field, 0);
 
 			if (strcmp(field_name, test_name) == 0) {
-				sort_key->field_idx = j;
+				sort_key->field_idx = idx;
 				descending = is_descending(field_str);
 				if (descending < 0) {
 					ret = descending;
 					goto out;
 				}
 				sort_key->descending = descending;
 				break;
 			}
 		}
 		if (j == hist_data->n_fields) {
 			ret = -EINVAL;
 			break;
 		}
 	}
+
 	hist_data->n_sort_keys = i;
  out:
 	return ret;
 }
 
 static void destroy_hist_data(struct hist_trigger_data *hist_data)
 {
 	destroy_hist_trigger_attrs(hist_data->attrs);
@@ -871,22 +1101,29 @@  static int create_tracing_map_fields(struct hist_trigger_data *hist_data)
 			else if (is_string_field(field))
 				cmp_fn = tracing_map_cmp_string;
 			else
 				cmp_fn = tracing_map_cmp_num(field->size,
 							     field->is_signed);
 			idx = tracing_map_add_key_field(map,
 							hist_field->offset,
 							cmp_fn);
-
-		} else
+		} else if (!(hist_field->flags & HIST_FIELD_FL_VAR))
 			idx = tracing_map_add_sum_field(map);
 
 		if (idx < 0)
 			return idx;
+
+		if (hist_field->flags & HIST_FIELD_FL_VAR) {
+			idx = tracing_map_add_var(map);
+			if (idx < 0)
+				return idx;
+			hist_field->var.idx = idx;
+			hist_field->var.hist_data = hist_data;
+		}
 	}
 
 	return 0;
 }
 
 static bool need_tracing_map_ops(struct hist_trigger_data *hist_data)
 {
 	struct hist_field *key_field;
@@ -900,27 +1137,29 @@  static bool need_tracing_map_ops(struct hist_trigger_data *hist_data)
 	}
 
 	return false;
 }
 
 static struct hist_trigger_data *
 create_hist_data(unsigned int map_bits,
 		 struct hist_trigger_attrs *attrs,
-		 struct trace_event_file *file)
+		 struct trace_event_file *file,
+		 bool remove)
 {
 	const struct tracing_map_ops *map_ops = NULL;
 	struct hist_trigger_data *hist_data;
 	int ret = 0;
 
 	hist_data = kzalloc(sizeof(*hist_data), GFP_KERNEL);
 	if (!hist_data)
 		return ERR_PTR(-ENOMEM);
 
 	hist_data->attrs = attrs;
+	hist_data->remove = remove;
 
 	ret = create_hist_fields(hist_data, file);
 	if (ret)
 		goto free;
 
 	ret = create_sort_keys(hist_data);
 	if (ret)
 		goto free;
@@ -957,24 +1196,38 @@  create_hist_data(unsigned int map_bits,
 	goto out;
 }
 
 static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
 				    struct tracing_map_elt *elt, void *rec,
 				    struct ring_buffer_event *rbe)
 {
 	struct hist_field *hist_field;
-	unsigned int i;
+	unsigned int i, var_idx;
 	u64 hist_val;
 
 	for_each_hist_val_field(i, hist_data) {
 		hist_field = hist_data->fields[i];
 		hist_val = hist_field->fn(hist_field, rec, rbe);
+		if (hist_field->flags & HIST_FIELD_FL_VAR) {
+			var_idx = hist_field->var.idx;
+			tracing_map_set_var(elt, var_idx, hist_val);
+			continue;
+		}
 		tracing_map_update_sum(elt, i, hist_val);
 	}
+
+	for_each_hist_key_field(i, hist_data) {
+		hist_field = hist_data->fields[i];
+		if (hist_field->flags & HIST_FIELD_FL_VAR) {
+			hist_val = hist_field->fn(hist_field, rec, rbe);
+			var_idx = hist_field->var.idx;
+			tracing_map_set_var(elt, var_idx, hist_val);
+		}
+	}
 }
 
 static inline void add_to_key(char *compound_key, void *key,
 			      struct hist_field *key_field, void *rec)
 {
 	size_t size = key_field->size;
 
 	if (key_field->flags & HIST_FIELD_FL_STRING) {
@@ -1139,16 +1392,19 @@  hist_trigger_entry_print(struct seq_file *m,
 	seq_puts(m, "}");
 
 	seq_printf(m, " hitcount: %10llu",
 		   tracing_map_read_sum(elt, HITCOUNT_IDX));
 
 	for (i = 1; i < hist_data->n_vals; i++) {
 		field_name = hist_field_name(hist_data->fields[i], 0);
 
+		if (hist_data->fields[i]->flags & HIST_FIELD_FL_VAR)
+			continue;
+
 		if (hist_data->fields[i]->flags & HIST_FIELD_FL_HEX) {
 			seq_printf(m, "  %s: %10llx", field_name,
 				   tracing_map_read_sum(elt, i));
 		} else {
 			seq_printf(m, "  %s: %10llu", field_name,
 				   tracing_map_read_sum(elt, i));
 		}
 	}
@@ -1260,16 +1516,19 @@  static const char *get_hist_field_flags(struct hist_field *hist_field)
 
 	return flags_str;
 }
 
 static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
 {
 	const char *field_name = hist_field_name(hist_field, 0);
 
+	if (hist_field->var.name)
+		seq_printf(m, "%s=", hist_field->var.name);
+
 	if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP)
 		seq_puts(m, "common_timestamp");
 	else if (field_name)
 		seq_printf(m, "%s", field_name);
 
 	if (hist_field->flags) {
 		const char *flags_str = get_hist_field_flags(hist_field);
 
@@ -1278,68 +1537,97 @@  static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
 	}
 }
 
 static int event_hist_trigger_print(struct seq_file *m,
 				    struct event_trigger_ops *ops,
 				    struct event_trigger_data *data)
 {
 	struct hist_trigger_data *hist_data = data->private_data;
-	struct hist_field *key_field;
+	struct hist_field *field;
+	bool have_var = false;
 	unsigned int i;
 
 	seq_puts(m, "hist:");
 
 	if (data->name)
 		seq_printf(m, "%s:", data->name);
 
 	seq_puts(m, "keys=");
 
 	for_each_hist_key_field(i, hist_data) {
-		key_field = hist_data->fields[i];
+		field = hist_data->fields[i];
 
 		if (i > hist_data->n_vals)
 			seq_puts(m, ",");
 
-		if (key_field->flags & HIST_FIELD_FL_STACKTRACE)
+		if (field->flags & HIST_FIELD_FL_STACKTRACE)
 			seq_puts(m, "stacktrace");
 		else
-			hist_field_print(m, key_field);
+			hist_field_print(m, field);
 	}
 
 	seq_puts(m, ":vals=");
 
 	for_each_hist_val_field(i, hist_data) {
+		field = hist_data->fields[i];
+		if (field->flags & HIST_FIELD_FL_VAR) {
+			have_var = true;
+			continue;
+		}
+
 		if (i == HITCOUNT_IDX)
 			seq_puts(m, "hitcount");
 		else {
 			seq_puts(m, ",");
-			hist_field_print(m, hist_data->fields[i]);
+			hist_field_print(m, field);
+		}
+	}
+
+	if (have_var) {
+		unsigned int n = 0;
+
+		seq_puts(m, ":");
+
+		for_each_hist_val_field(i, hist_data) {
+			field = hist_data->fields[i];
+
+			if (field->flags & HIST_FIELD_FL_VAR) {
+				if (n++)
+					seq_puts(m, ",");
+				hist_field_print(m, field);
+			}
 		}
 	}
 
 	seq_puts(m, ":sort=");
 
 	for (i = 0; i < hist_data->n_sort_keys; i++) {
 		struct tracing_map_sort_key *sort_key;
-		unsigned int idx;
+		unsigned int idx, first_key_idx;
+
+		/* skip VAR vals */
+		first_key_idx = hist_data->n_vals - hist_data->n_vars;
 
 		sort_key = &hist_data->sort_keys[i];
 		idx = sort_key->field_idx;
 
 		if (WARN_ON(idx >= TRACING_MAP_FIELDS_MAX))
 			return -EINVAL;
 
 		if (i > 0)
 			seq_puts(m, ",");
 
 		if (idx == HITCOUNT_IDX)
 			seq_puts(m, "hitcount");
-		else
+		else {
+			if (idx >= first_key_idx)
+				idx += hist_data->n_vars;
 			hist_field_print(m, hist_data->fields[idx]);
+		}
 
 		if (sort_key->descending)
 			seq_puts(m, ".descending");
 	}
 	seq_printf(m, ":size=%u", (1 << hist_data->map->map_bits));
 
 	if (data->filter_str)
 		seq_printf(m, " if %s", data->filter_str);
@@ -1626,17 +1914,17 @@  static void hist_unregister_trigger(char *glob, struct event_trigger_ops *ops,
 			break;
 		}
 	}
 
 	if (unregistered && test->ops->free)
 		test->ops->free(test->ops, test);
 
 	if (hist_data->enable_timestamps) {
-		if (unregistered)
+		if (!hist_data->remove || unregistered)
 			tracing_set_time_stamp_abs(file->tr, false);
 	}
 }
 
 static void hist_unreg_all(struct trace_event_file *file)
 {
 	struct event_trigger_data *test, *n;
 	struct hist_trigger_data *hist_data;
@@ -1659,35 +1947,39 @@  static int event_hist_trigger_func(struct event_command *cmd_ops,
 				   struct trace_event_file *file,
 				   char *glob, char *cmd, char *param)
 {
 	unsigned int hist_trigger_bits = TRACING_MAP_BITS_DEFAULT;
 	struct event_trigger_data *trigger_data;
 	struct hist_trigger_attrs *attrs;
 	struct event_trigger_ops *trigger_ops;
 	struct hist_trigger_data *hist_data;
+	bool remove = false;
 	char *trigger;
 	int ret = 0;
 
 	if (!param)
 		return -EINVAL;
 
+	if (glob[0] == '!')
+		remove = true;
+
 	/* separate the trigger from the filter (k:v [if filter]) */
 	trigger = strsep(&param, " \t");
 	if (!trigger)
 		return -EINVAL;
 
 	attrs = parse_hist_trigger_attrs(trigger);
 	if (IS_ERR(attrs))
 		return PTR_ERR(attrs);
 
 	if (attrs->map_bits)
 		hist_trigger_bits = attrs->map_bits;
 
-	hist_data = create_hist_data(hist_trigger_bits, attrs, file);
+	hist_data = create_hist_data(hist_trigger_bits, attrs, file, remove);
 	if (IS_ERR(hist_data)) {
 		destroy_hist_trigger_attrs(attrs);
 		return PTR_ERR(hist_data);
 	}
 
 	trigger_ops = cmd_ops->get_trigger_ops(cmd, trigger);
 
 	ret = -ENOMEM;
@@ -1706,17 +1998,17 @@  static int event_hist_trigger_func(struct event_command *cmd_ops,
 
 	/* if param is non-empty, it's supposed to be a filter */
 	if (param && cmd_ops->set_filter) {
 		ret = cmd_ops->set_filter(param, trigger_data, file);
 		if (ret < 0)
 			goto out_free;
 	}
 
-	if (glob[0] == '!') {
+	if (remove) {
 		cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
 		ret = 0;
 		goto out_free;
 	}
 
 	ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
 	/*
 	 * The above returns on success the # of triggers registered,