[PATCH v4 31/37] tracing: Add 'last error' error facility for hist triggers

[Tom Zanussi <tom.zanussi@linux.intel.com>]

With the addition of variables and actions, it's become necessary to
provide more detailed error information to users about syntax errors.

Add a 'last error' facility accessible via the erroring event's 'hist'
file.  Reading the hist file after an error will display more detailed
information about what went wrong, if information is available.  This
extended error information will be available until the next hist
trigger command for that event.

  # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
  echo: write error: Invalid argument

  # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist

  ERROR: Couldn't yyy: zzz
  Last command: xxx

Also add specific error messages for variable and action errors.

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
---
 Documentation/trace/histogram.txt |  20 +++++
 kernel/trace/trace_events_hist.c  | 165 +++++++++++++++++++++++++++++++++++---
 2 files changed, 172 insertions(+), 13 deletions(-)

diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt
index cd3ec00..7ae5a39 100644
--- a/Documentation/trace/histogram.txt
+++ b/Documentation/trace/histogram.txt
@@ -190,6 +190,26 @@
 				 interpreted as microseconds.
     cpu                    int - the cpu on which the event occurred.
 
+  Extended error information
+  --------------------------
+
+  For some error conditions encountered when invoking a hist trigger
+  command, extended error information is available via the
+  corresponding event's 'hist' file.  Reading the hist file after an
+  error will display more detailed information about what went wrong,
+  if information is available.  This extended error information will
+  be available until the next hist trigger command for that event.
+
+  If available for a given error condition, the extended error
+  information and usage takes the following form:
+
+    # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
+    echo: write error: Invalid argument
+
+    # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/hist
+    ERROR: Couldn't yyy: zzz
+      Last command: xxx
+
 6.2 'hist' trigger examples
 ---------------------------
 
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 7ecbbb4..acebaae 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -351,6 +351,65 @@ struct action_data {
 	};
 };
 
+
+static char last_hist_cmd[MAX_FILTER_STR_VAL];
+static char hist_err_str[MAX_FILTER_STR_VAL];
+
+static void last_cmd_set(char *str)
+{
+	if (!str)
+		return;
+
+	strncpy(last_hist_cmd, str, MAX_FILTER_STR_VAL - 1);
+}
+
+static void hist_err(char *str, char *var)
+{
+	int maxlen = MAX_FILTER_STR_VAL - 1;
+
+	if (!str)
+		return;
+
+	if (strlen(hist_err_str))
+		return;
+
+	if (!var)
+		var = "";
+
+	if (strlen(hist_err_str) + strlen(str) + strlen(var) > maxlen)
+		return;
+
+	strcat(hist_err_str, str);
+	strcat(hist_err_str, var);
+}
+
+static void hist_err_event(char *str, char *system, char *event, char *var)
+{
+	char err[MAX_FILTER_STR_VAL];
+
+	if (system && var)
+		snprintf(err, MAX_FILTER_STR_VAL, "%s.%s.%s", system, event, var);
+	else if (system)
+		snprintf(err, MAX_FILTER_STR_VAL, "%s.%s", system, event);
+	else
+		strncpy(err, var, MAX_FILTER_STR_VAL);
+
+	hist_err(str, err);
+}
+
+static void hist_err_clear(void)
+{
+	hist_err_str[0] = '\0';
+}
+
+static bool have_hist_err(void)
+{
+	if (strlen(hist_err_str))
+		return true;
+
+	return false;
+}
+
 static LIST_HEAD(synth_event_list);
 static DEFINE_MUTEX(synth_event_mutex);
 
@@ -1453,6 +1512,7 @@ static struct trace_event_file *find_var_file(struct trace_array *tr,
 		if (!system || !event_name) {
 			if (find_var(file, var_name)) {
 				if (found) {
+					hist_err_event("Variable name not unique, need to use fully qualified name (subsys.event.var) for variable: ", system, event_name, var_name);
 					return NULL;
 				}
 
@@ -1513,6 +1573,7 @@ static struct hist_field *find_file_var(struct trace_event_file *file,
 			hist_field = find_file_var(file, var_name);
 			if (hist_field) {
 				if (found) {
+					hist_err_event("Variable name not unique, need to use fully qualified name (subsys.event.var) for variable: ", system, event_name, var_name);
 					return ERR_PTR(-EINVAL);
 				}
 
@@ -2266,9 +2327,18 @@ static struct hist_field *create_var_ref(struct hist_field *var_field,
 	return ref_field;
 }
 
+static bool is_common_field(char *var_name)
+{
+	if (strncmp(var_name, "$common_timestamp", strlen("$common_timestamp")) == 0)
+		return true;
+
+	return false;
+}
+
 static bool is_var_ref(char *var_name)
 {
-	if (!var_name || strlen(var_name) < 2 || var_name[0] != '$')
+	if (!var_name || strlen(var_name) < 2 || var_name[0] != '$' ||
+	    is_common_field(var_name))
 		return false;
 
 	return true;
@@ -2320,6 +2390,10 @@ static struct hist_field *parse_var_ref(struct hist_trigger_data *hist_data,
 	if (var_field)
 		ref_field = create_var_ref(var_field, system, event_name);
 
+	if (!ref_field)
+		hist_err_event("Couldn't find variable: $",
+			       system, event_name, var_name);
+
 	return ref_field;
 }
 
@@ -2564,8 +2638,10 @@ static int check_expr_operands(struct hist_field *operand1,
 	}
 
 	if ((operand1_flags & HIST_FIELD_FL_TIMESTAMP_USECS) !=
-	    (operand2_flags & HIST_FIELD_FL_TIMESTAMP_USECS))
+	    (operand2_flags & HIST_FIELD_FL_TIMESTAMP_USECS)) {
+		hist_err("Timestamp units in expression don't match", NULL);
 		return -EINVAL;
+	}
 
 	return 0;
 }
@@ -2811,12 +2887,17 @@ static struct trace_event_file *event_file(struct trace_array *tr,
 	char *cmd;
 	int ret;
 
-	if (target_hist_data->n_field_var_hists >= SYNTH_FIELDS_MAX)
+	if (target_hist_data->n_field_var_hists >= SYNTH_FIELDS_MAX) {
+		hist_err_event("onmatch: Too many field variables defined: ",
+			       subsys_name, event_name, field_name);
 		return ERR_PTR(-EINVAL);
+	}
 
 	file = event_file(tr, subsys_name, event_name);
 
 	if (IS_ERR(file)) {
+		hist_err_event("onmatch: Event file not found: ",
+			       subsys_name, event_name, field_name);
 		ret = PTR_ERR(file);
 		return ERR_PTR(ret);
 	}
@@ -2828,8 +2909,11 @@ static struct trace_event_file *event_file(struct trace_array *tr,
 	 * yet a registered histogram so we can't use that.
 	 */
 	hist_data = find_compatible_hist(target_hist_data, file);
-	if (!hist_data)
+	if (!hist_data) {
+		hist_err_event("onmatch: Matching event histogram not found: ",
+			       subsys_name, event_name, field_name);
 		return ERR_PTR(-EINVAL);
+	}
 
 	/* See if a synthetic field variable has already been created */
 	event_var = find_synthetic_field_var(target_hist_data, subsys_name,
@@ -2888,6 +2972,8 @@ static struct trace_event_file *event_file(struct trace_array *tr,
 		kfree(cmd);
 		kfree(var_hist->cmd);
 		kfree(var_hist);
+		hist_err_event("onmatch: Couldn't create histogram for field: ",
+			       subsys_name, event_name, field_name);
 		return ERR_PTR(ret);
 	}
 
@@ -2900,6 +2986,8 @@ static struct trace_event_file *event_file(struct trace_array *tr,
 		kfree(cmd);
 		kfree(var_hist->cmd);
 		kfree(var_hist);
+		hist_err_event("onmatch: Couldn't find synthetic variable: ",
+			       subsys_name, event_name, field_name);
 		return ERR_PTR(-EINVAL);
 	}
 
@@ -3036,18 +3124,21 @@ static struct field_var *create_field_var(struct hist_trigger_data *hist_data,
 	int ret = 0;
 
 	if (hist_data->n_field_vars >= SYNTH_FIELDS_MAX) {
+		hist_err("Too many field variables defined: ", field_name);
 		ret = -EINVAL;
 		goto err;
 	}
 
 	val = parse_atom(hist_data, file, field_name, &flags, NULL);
 	if (IS_ERR(val)) {
+		hist_err("Couldn't parse field variable: ", field_name);
 		ret = PTR_ERR(val);
 		goto err;
 	}
 
 	var = create_var(hist_data, file, field_name, val->size, val->type);
 	if (IS_ERR(var)) {
+		hist_err("Couldn't create or find variable: ", field_name);
 		kfree(val);
 		ret = PTR_ERR(var);
 		goto err;
@@ -3192,14 +3283,18 @@ static int onmax_create(struct hist_trigger_data *hist_data,
 	int ret = 0;
 
 	onmax_var_str = data->onmax.var_str;
-	if (onmax_var_str[0] != '$')
+	if (onmax_var_str[0] != '$') {
+		hist_err("onmax: For onmax(x), x must be a variable: ", onmax_var_str);
 		return -EINVAL;
+	}
 	onmax_var_str++;
 
 	event_name = trace_event_name(call);
 	var_field = find_target_event_var(hist_data, NULL, NULL, onmax_var_str);
-	if (!var_field)
+	if (!var_field) {
+		hist_err("onmax: Couldn't find onmax variable: ", onmax_var_str);
 		return -EINVAL;
+	}
 
 	flags = HIST_FIELD_FL_VAR_REF;
 	ref_field = create_hist_field(hist_data, NULL, flags, NULL);
@@ -3219,6 +3314,7 @@ static int onmax_create(struct hist_trigger_data *hist_data,
 	data->onmax.max_var_ref_idx = var_ref_idx;
 	max_var = create_var(hist_data, file, "max", sizeof(u64), "u64");
 	if (IS_ERR(max_var)) {
+		hist_err("onmax: Couldn't create onmax variable: ", "max");
 		ret = PTR_ERR(max_var);
 		goto out;
 	}
@@ -3233,6 +3329,7 @@ static int onmax_create(struct hist_trigger_data *hist_data,
 
 		field_var = create_target_field_var(hist_data, NULL, NULL, param);
 		if (IS_ERR(field_var)) {
+			hist_err("onmax: Couldn't create field variable: ", param);
 			ret = PTR_ERR(field_var);
 			kfree(param);
 			goto out;
@@ -3265,6 +3362,7 @@ static int parse_action_params(char *params, struct action_data *data)
 
 		param = strstrip(param);
 		if (strlen(param) < 2) {
+			hist_err("Invalid action param: ", param);
 			ret = -EINVAL;
 			goto out;
 		}
@@ -3437,6 +3535,9 @@ static int check_synth_field(struct synth_event *event,
 		hist_field = find_event_var(hist_data, system, event, var);
 	}
 
+	if (!hist_field)
+		hist_err_event("onmatch: Couldn't find onmatch param: $", system, event, var);
+
 	return hist_field;
 }
 
@@ -3504,6 +3605,7 @@ static int onmatch_create(struct hist_trigger_data *hist_data,
 	mutex_lock(&synth_event_mutex);
 	event = find_synth_event(data->onmatch.synth_event_name);
 	if (!event) {
+		hist_err("onmatch: Couldn't find synthetic event: ", data->onmatch.synth_event_name);
 		mutex_unlock(&synth_event_mutex);
 		return -EINVAL;
 	}
@@ -3562,12 +3664,15 @@ static int onmatch_create(struct hist_trigger_data *hist_data,
 			continue;
 		}
 
+		hist_err_event("onmatch: Param type doesn't match synthetic event field type: ",
+			       system, event_name, param);
 		kfree(p);
 		ret = -EINVAL;
 		goto out;
 	}
 
 	if (field_pos != event->n_fields) {
+		hist_err("onmatch: Param count doesn't match synthetic event field count: ", event->name);
 		ret = -EINVAL;
 		goto out;
 	}
@@ -3592,15 +3697,22 @@ static struct action_data *onmatch_parse(struct trace_array *tr, char *str)
 		return ERR_PTR(-ENOMEM);
 
 	match_event = strsep(&str, ")");
-	if (!match_event || !str)
+	if (!match_event || !str) {
+		hist_err("onmatch: Missing closing paren: ", match_event);
 		goto free;
+	}
 
 	match_event_system = strsep(&match_event, ".");
-	if (!match_event)
+	if (!match_event) {
+		hist_err("onmatch: Missing subsystem for match event: ", match_event_system);
 		goto free;
+	}
 
-	if (IS_ERR(event_file(tr, match_event_system, match_event)))
+	if (IS_ERR(event_file(tr, match_event_system, match_event))) {
+		hist_err_event("onmatch: Invalid subsystem or event name: ",
+			       match_event_system, match_event, NULL);
 		goto free;
+	}
 
 	data->onmatch.match_event = kstrdup(match_event, GFP_KERNEL);
 	if (!data->onmatch.match_event) {
@@ -3615,12 +3727,16 @@ static struct action_data *onmatch_parse(struct trace_array *tr, char *str)
 	}
 
 	strsep(&str, ".");
-	if (!str)
+	if (!str) {
+		hist_err("onmatch: Missing . after onmatch(): ", str);
 		goto free;
+	}
 
 	synth_event_name = strsep(&str, "(");
-	if (!synth_event_name || !str)
+	if (!synth_event_name || !str) {
+		hist_err("onmatch: Missing opening paramlist paren: ", synth_event_name);
 		goto free;
+	}
 
 	data->onmatch.synth_event_name = kstrdup(synth_event_name, GFP_KERNEL);
 	if (!data->onmatch.synth_event_name) {
@@ -3629,8 +3745,10 @@ static struct action_data *onmatch_parse(struct trace_array *tr, char *str)
 	}
 
 	params = strsep(&str, ")");
-	if (!params || !str || (str && strlen(str)))
+	if (!params || !str || (str && strlen(str))) {
+		hist_err("onmatch: Missing closing paramlist paren: ", params);
 		goto free;
+	}
 
 	ret = parse_action_params(params, data);
 	if (ret)
@@ -3707,12 +3825,14 @@ static int create_var_field(struct hist_trigger_data *hist_data,
 		return -EINVAL;
 
 	if (find_var(file, var_name) && !hist_data->remove) {
+		hist_err("Variable already defined: ", var_name);
 		return -EINVAL;
 	}
 
 	flags |= HIST_FIELD_FL_VAR;
 	hist_data->n_vars++;
 	if (hist_data->n_vars > TRACING_MAP_VARS_MAX) {
+		hist_err("Too many variables defined: ", var_name);
 		return -EINVAL;
 	}
 
@@ -3788,6 +3908,7 @@ static int create_key_field(struct hist_trigger_data *hist_data,
 		}
 
 		if (hist_field->flags & HIST_FIELD_FL_VAR_REF) {
+			hist_err("Using variable references as keys not supported: ", field_str);
 			destroy_hist_field(hist_field, 0);
 			ret = -EINVAL;
 			goto out;
@@ -3901,6 +4022,7 @@ static int parse_var_defs(struct hist_trigger_data *hist_data)
 
 			var_name = strsep(&field_str, "=");
 			if (!var_name || !field_str) {
+				hist_err("Malformed assignment: ", var_name);
 				ret = -EINVAL;
 				goto free;
 			}
@@ -4655,6 +4777,11 @@ static int hist_show(struct seq_file *m, void *v)
 			hist_trigger_show(m, data, n++);
 	}
 
+	if (have_hist_err()) {
+		seq_printf(m, "\nERROR: %s\n", hist_err_str);
+		seq_printf(m, "  Last command: %s\n", last_hist_cmd);
+	}
+
  out_unlock:
 	mutex_unlock(&event_mutex);
 
@@ -5002,6 +5129,7 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
 		if (named_data) {
 			if (!hist_trigger_match(data, named_data, named_data,
 						true)) {
+				hist_err("Named hist trigger doesn't match existing named trigger (includes variables): ", hist_data->attrs->name);
 				ret = -EINVAL;
 				goto out;
 			}
@@ -5021,13 +5149,16 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
 				test->paused = false;
 			else if (hist_data->attrs->clear)
 				hist_clear(test);
-			else
+			else {
+				hist_err("Hist trigger already exists", NULL);
 				ret = -EEXIST;
+			}
 			goto out;
 		}
 	}
  new:
 	if (hist_data->attrs->cont || hist_data->attrs->clear) {
+		hist_err("Can't clear or continue a nonexistent hist trigger", NULL);
 		ret = -ENOENT;
 		goto out;
 	}
@@ -5199,6 +5330,11 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	char *trigger, *p;
 	int ret = 0;
 
+	if (glob && strlen(glob)) {
+		last_cmd_set(param);
+		hist_err_clear();
+	}
+
 	if (!param)
 		return -EINVAL;
 
@@ -5333,6 +5469,9 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 	/* Just return zero, not the number of registered triggers */
 	ret = 0;
  out:
+	if (ret == 0)
+		hist_err_clear();
+
 	return ret;
  out_unreg:
 	cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
-- 
1.9.3