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=common_timestamp ...
    # echo 'hist:key=timer_pid=common_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=common_timestamp,b=field1,field2 ...

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

Signed-off-by: Tom Zanussi <redacted>
---
 kernel/trace/trace_events_hist.c | 160 ++++++++++++++++++++++++++++++++-------
 1 file changed, 131 insertions(+), 29 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 8d7f7dd..e707577 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c

@@ -29,6 +29,7 @@ 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_ASSIGNMENT_MAX	4
 
 struct hist_field {
 	struct ftrace_event_field	*field;

@@ -36,8 +37,10 @@ struct hist_field {
 	hist_field_fn_t			fn;
 	unsigned int			size;
 	unsigned int			offset;
-	unsigned int                    is_signed;
+	unsigned int			is_signed;

 	struct hist_field		*operands[HIST_FIELD_OPERANDS_MAX];
+	u64				var_val;
+	char				*var_name;
 };
 
 static u64 hist_field_none(struct hist_field *field, void *event,

@@ -140,12 +143,16 @@ enum hist_field_flags {
 	HIST_FIELD_FL_SYSCALL		= 128,
 	HIST_FIELD_FL_STACKTRACE	= 256,
 	HIST_FIELD_FL_LOG2		= 512,
-	HIST_FIELD_FL_TIMESTAMP		= 1024,
+	HIST_FIELD_FL_VAR		= 1024,
+	HIST_FIELD_FL_VAR_ONLY		= 2048,
+	HIST_FIELD_FL_TIMESTAMP		= 4096,

 };
 
 struct hist_trigger_attrs {
 	char		*keys_str;
 	char		*vals_str;
+	char		*assignment_str[HIST_ASSIGNMENT_MAX];
+	unsigned int	n_assignments;
 	char		*sort_key_str;
 	char		*name;
 	bool		pause;

@@ -241,9 +248,14 @@ static int parse_map_size(char *str)
 
 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);

@@ -258,9 +270,9 @@ static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
 	if ((strncmp(str, "key=", strlen("key=")) == 0) ||
 	    (strncmp(str, "keys=", strlen("keys=")) == 0))
 		attrs->keys_str = kstrdup(str, GFP_KERNEL);
-	else if ((strncmp(str, "val=", strlen("val=")) == 0) ||
-		 (strncmp(str, "vals=", strlen("vals=")) == 0) ||
-		 (strncmp(str, "values=", strlen("values=")) == 0))
+	else if (((strncmp(str, "val=", strlen("val=")) == 0) ||
+		  (strncmp(str, "vals=", strlen("vals=")) == 0) ||
+		  (strncmp(str, "values=", strlen("values=")) == 0)))

 		attrs->vals_str = kstrdup(str, GFP_KERNEL);
 	else if (strncmp(str, "sort=", strlen("sort=")) == 0)
 		attrs->sort_key_str = kstrdup(str, GFP_KERNEL);

@@ -274,8 +286,22 @@ static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
 			goto out;
 		}
 		attrs->map_bits = map_bits;
-	} else
-		ret = -EINVAL;
+	} else {
+		char *assignment;
+
+		if (attrs->n_assignments == HIST_ASSIGNMENT_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;
 }

@@ -839,8 +913,7 @@ static int create_tracing_map_fields(struct hist_trigger_data *hist_data)
 			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)

@@ -931,6 +1004,11 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
 	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) {
+			hist_field->var_val = hist_val;
+			if (hist_field->flags & HIST_FIELD_FL_VAR_ONLY)
+				continue;
+		}
 		tracing_map_update_sum(elt, i, hist_val);

 	}
 }

@@ -996,17 +1074,21 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec,
 			} else
 				key = (void *)&field_contents;
 		}
-
 		if (use_compound_key)
 			add_to_key(compound_key, key, key_field, rec);
+
+		if (key_field->flags & HIST_FIELD_FL_VAR)
+			key_field->var_val = (u64)key;
 	}
 
 	if (use_compound_key)
 		key = compound_key;
 
 	elt = tracing_map_insert(hist_data->map, key);
-	if (elt)
-		hist_trigger_elt_update(hist_data, elt, rec, rbe);
+	if (!elt)
+		return;
+
+	hist_trigger_elt_update(hist_data, elt, rec, rbe);
 }
 
 static void hist_trigger_stacktrace_print(struct seq_file *m,

@@ -1228,7 +1310,12 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
 {
 	const char *field_name = hist_field_name(hist_field);
 
-	seq_printf(m, "%s", field_name);
+	if (hist_field->var_name)
+		seq_printf(m, "%s=", hist_field->var_name);
+
+	if (field_name)
+		seq_printf(m, "%s", field_name);
+
 	if (hist_field->flags) {
 		const char *flags_str = get_hist_field_flags(hist_field);
 

@@ -1237,6 +1324,16 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
 	}
 }
 
+static bool var_only(struct hist_trigger_data *hist_data)
+{
+	unsigned int i;
+
+	for_each_hist_val_field(i, hist_data)
+		if (hist_data->fields[i]->flags & HIST_FIELD_FL_VAR_ONLY)
+			return true;
+	return false;
+}

+
 static int event_hist_trigger_print(struct seq_file *m,
 				    struct event_trigger_ops *ops,
 				    struct event_trigger_data *data)

@@ -1266,15 +1363,19 @@ static int event_hist_trigger_print(struct seq_file *m,
 			hist_field_print(m, key_field);
 	}
 
-	seq_puts(m, ":vals=");
+	if (!var_only(hist_data))
+		seq_puts(m, ":vals=");
+	else
+		seq_puts(m, ":");
 
 	for_each_hist_val_field(i, hist_data) {
-		if (i == HITCOUNT_IDX)
+		if (i == HITCOUNT_IDX && !var_only(hist_data))
 			seq_puts(m, "hitcount");

 			hist_field_print(m, hist_data->fields[i]);
 		}
 	}

@@ -1673,6 +1774,7 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	}
 
 	ret = cmd_ops->reg(glob, trigger_ops, trigger_data, file);
+
 	/*
 	 * The above returns on success the # of triggers registered,
 	 * but if it didn't register any it returns zero.  Consider no

-- 
1.9.3