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Subject[PATCH 3/3] tracing: Add hist_debug trace event files for histogram debugging
Date
Add a new "hist_debug" file for each trace event, which when read will
dump out a bunch of internal details about the hist triggers defined
on that event.

This is normally off but can be enabled by saying 'y' to the new
CONFIG_HIST_TRIGGERS_DEBUG config option.

This is in support of the new Documentation file describing histogram
internals, Documentation/trace/histogram-design.rst, which was
requested by developers trying to understand the internals when
extending or making use of the hist triggers for higher-level tools.

The histogram-design.rst documentation refers to the hist_debug files
and demonstrates their use with output in the test examples.

Signed-off-by: Tom Zanussi <zanussi@kernel.org>
---
kernel/trace/Kconfig | 23 +++
kernel/trace/trace.h | 1 +
kernel/trace/trace_events.c | 4 +
kernel/trace/trace_events_hist.c | 273 +++++++++++++++++++++++++++++++
4 files changed, 301 insertions(+)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 402eef84c859..357f6304e86a 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -848,6 +848,29 @@ config KPROBE_EVENT_GEN_TEST

If unsure, say N.

+config HIST_TRIGGERS_DEBUG
+ bool "Hist trigger debug support"
+ depends on HIST_TRIGGERS
+ help
+ Add "hist_debug" file for each event, which when read will
+ dump out a bunch of internal details about the hist triggers
+ defined on that event.
+
+ The hist_debug file serves a couple of purposes:
+
+ - Helps developers verify that nothing is broken.
+
+ - Provides educational information to support the details
+ of the hist trigger internals as described by
+ Documentation/trace/histogram-design.rst.
+
+ The hist_debug output only covers the data structures
+ related to the histogram definitions themselves and doesn't
+ display the internals of map buckets or variable values of
+ running histograms.
+
+ If unsure, say N.
+
endif # FTRACE

endif # TRACING_SUPPORT
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 4eb1d004d5f2..def769df5bf1 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1661,6 +1661,7 @@ extern struct list_head ftrace_events;

extern const struct file_operations event_trigger_fops;
extern const struct file_operations event_hist_fops;
+extern const struct file_operations event_hist_debug_fops;
extern const struct file_operations event_inject_fops;

#ifdef CONFIG_HIST_TRIGGERS
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 242f59e7f17d..f6f55682d3e2 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2208,6 +2208,10 @@ event_create_dir(struct dentry *parent, struct trace_event_file *file)
#ifdef CONFIG_HIST_TRIGGERS
trace_create_file("hist", 0444, file->dir, file,
&event_hist_fops);
+#endif
+#ifdef CONFIG_HIST_TRIGGERS_DEBUG
+ trace_create_file("hist_debug", 0444, file->dir, file,
+ &event_hist_debug_fops);
#endif
trace_create_file("format", 0444, file->dir, call,
&ftrace_event_format_fops);
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 1bb61c217a4a..cdb79aa84066 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -6471,6 +6471,279 @@ const struct file_operations event_hist_fops = {
.release = single_release,
};

+#ifdef CONFIG_HIST_TRIGGERS_DEBUG
+static void hist_field_debug_show_flags(struct seq_file *m,
+ unsigned long flags)
+{
+ seq_puts(m, " flags:\n");
+
+ if (flags & HIST_FIELD_FL_KEY)
+ seq_puts(m, " HIST_FIELD_FL_KEY\n");
+ else if (flags & HIST_FIELD_FL_HITCOUNT)
+ seq_puts(m, " VAL: HIST_FIELD_FL_HITCOUNT\n");
+ else if (flags & HIST_FIELD_FL_VAR)
+ seq_puts(m, " HIST_FIELD_FL_VAR\n");
+ else if (flags & HIST_FIELD_FL_VAR_REF)
+ seq_puts(m, " HIST_FIELD_FL_VAR_REF\n");
+ else
+ seq_puts(m, " VAL: normal u64 value\n");
+
+ if (flags & HIST_FIELD_FL_ALIAS)
+ seq_puts(m, " HIST_FIELD_FL_ALIAS\n");
+}
+
+static int hist_field_debug_show(struct seq_file *m,
+ struct hist_field *field, unsigned long flags)
+{
+ if ((field->flags & flags) != flags) {
+ seq_printf(m, "ERROR: bad flags - %lx\n", flags);
+ return -EINVAL;
+ }
+
+ hist_field_debug_show_flags(m, field->flags);
+ if (field->field)
+ seq_printf(m, " ftrace_event_field name: %s\n",
+ field->field->name);
+
+ if (field->flags & HIST_FIELD_FL_VAR) {
+ seq_printf(m, " var.name: %s\n", field->var.name);
+ seq_printf(m, " var.idx (into tracing_map_elt.vars[]): %u\n",
+ field->var.idx);
+ }
+
+ if (field->flags & HIST_FIELD_FL_ALIAS)
+ seq_printf(m, " var_ref_idx (into hist_data->var_refs[]): %u\n",
+ field->var_ref_idx);
+
+ if (field->flags & HIST_FIELD_FL_VAR_REF) {
+ seq_printf(m, " name: %s\n", field->name);
+ seq_printf(m, " var.idx (into tracing_map_elt.vars[]): %u\n",
+ field->var.idx);
+ seq_printf(m, " var.hist_data: %p\n", field->var.hist_data);
+ seq_printf(m, " var_ref_idx (into hist_data->var_refs[]): %u\n",
+ field->var_ref_idx);
+ if (field->system)
+ seq_printf(m, " system: %s\n", field->system);
+ if (field->event_name)
+ seq_printf(m, " event_name: %s\n", field->event_name);
+ }
+
+ seq_printf(m, " type: %s\n", field->type);
+ seq_printf(m, " size: %u\n", field->size);
+ seq_printf(m, " is_signed: %u\n", field->is_signed);
+
+ return 0;
+}
+
+static int field_var_debug_show(struct seq_file *m,
+ struct field_var *field_var, unsigned int i,
+ bool save_vars)
+{
+ const char *vars_name = save_vars ? "save_vars" : "field_vars";
+ struct hist_field *field;
+ int ret = 0;
+
+ seq_printf(m, "\n hist_data->%s[%d]:\n", vars_name, i);
+
+ field = field_var->var;
+
+ seq_printf(m, "\n %s[%d].var:\n", vars_name, i);
+
+ hist_field_debug_show_flags(m, field->flags);
+ seq_printf(m, " var.name: %s\n", field->var.name);
+ seq_printf(m, " var.idx (into tracing_map_elt.vars[]): %u\n",
+ field->var.idx);
+
+ field = field_var->val;
+
+ seq_printf(m, "\n %s[%d].val:\n", vars_name, i);
+ if (field->field)
+ seq_printf(m, " ftrace_event_field name: %s\n",
+ field->field->name);
+ else {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ seq_printf(m, " type: %s\n", field->type);
+ seq_printf(m, " size: %u\n", field->size);
+ seq_printf(m, " is_signed: %u\n", field->is_signed);
+out:
+ return ret;
+}
+
+static int hist_action_debug_show(struct seq_file *m,
+ struct action_data *data, int i)
+{
+ int ret = 0;
+
+ if (data->handler == HANDLER_ONMAX ||
+ data->handler == HANDLER_ONCHANGE) {
+ seq_printf(m, "\n hist_data->actions[%d].track_data.var_ref:\n", i);
+ ret = hist_field_debug_show(m, data->track_data.var_ref,
+ HIST_FIELD_FL_VAR_REF);
+ if (ret)
+ goto out;
+
+ seq_printf(m, "\n hist_data->actions[%d].track_data.track_var:\n", i);
+ ret = hist_field_debug_show(m, data->track_data.track_var,
+ HIST_FIELD_FL_VAR);
+ if (ret)
+ goto out;
+ }
+
+ if (data->handler == HANDLER_ONMATCH) {
+ seq_printf(m, "\n hist_data->actions[%d].match_data.event_system: %s\n",
+ i, data->match_data.event_system);
+ seq_printf(m, " hist_data->actions[%d].match_data.event: %s\n",
+ i, data->match_data.event);
+ }
+out:
+ return ret;
+}
+
+static int hist_actions_debug_show(struct seq_file *m,
+ struct hist_trigger_data *hist_data)
+{
+ int i, ret = 0;
+
+ if (hist_data->n_actions)
+ seq_puts(m, "\n action tracking variables (for onmax()/onchange()/onmatch()):\n");
+
+ for (i = 0; i < hist_data->n_actions; i++) {
+ struct action_data *action = hist_data->actions[i];
+
+ ret = hist_action_debug_show(m, action, i);
+ if (ret)
+ goto out;
+ }
+
+ if (hist_data->n_save_vars)
+ seq_puts(m, "\n save action variables (save() params):\n");
+
+ for (i = 0; i < hist_data->n_save_vars; i++) {
+ ret = field_var_debug_show(m, hist_data->save_vars[i], i, true);
+ if (ret)
+ goto out;
+ }
+out:
+ return ret;
+}
+
+static void hist_trigger_debug_show(struct seq_file *m,
+ struct event_trigger_data *data, int n)
+{
+ struct hist_trigger_data *hist_data;
+ int i, ret;
+
+ if (n > 0)
+ seq_puts(m, "\n\n");
+
+ seq_puts(m, "# event histogram\n#\n# trigger info: ");
+ data->ops->print(m, data->ops, data);
+ seq_puts(m, "#\n\n");
+
+ hist_data = data->private_data;
+
+ seq_printf(m, "hist_data: %p\n\n", hist_data);
+ seq_printf(m, " n_vals: %u\n", hist_data->n_vals);
+ seq_printf(m, " n_keys: %u\n", hist_data->n_keys);
+ seq_printf(m, " n_fields: %u\n", hist_data->n_fields);
+
+ seq_puts(m, "\n val fields:\n\n");
+
+ seq_puts(m, " hist_data->fields[0]:\n");
+ ret = hist_field_debug_show(m, hist_data->fields[0],
+ HIST_FIELD_FL_HITCOUNT);
+ if (ret)
+ return;
+
+ for (i = 1; i < hist_data->n_vals; i++) {
+ seq_printf(m, "\n hist_data->fields[%d]:\n", i);
+ ret = hist_field_debug_show(m, hist_data->fields[i], 0);
+ if (ret)
+ return;
+ }
+
+ seq_puts(m, "\n key fields:\n");
+
+ for (i = hist_data->n_vals; i < hist_data->n_fields; i++) {
+ seq_printf(m, "\n hist_data->fields[%d]:\n", i);
+ ret = hist_field_debug_show(m, hist_data->fields[i],
+ HIST_FIELD_FL_KEY);
+ if (ret)
+ return;
+ }
+
+ if (hist_data->n_var_refs)
+ seq_puts(m, "\n variable reference fields:\n");
+
+ for (i = 0; i < hist_data->n_var_refs; i++) {
+ seq_printf(m, "\n hist_data->var_refs[%d]:\n", i);
+ ret = hist_field_debug_show(m, hist_data->var_refs[i],
+ HIST_FIELD_FL_VAR_REF);
+ if (ret)
+ return;
+ }
+
+ if (hist_data->n_field_vars)
+ seq_puts(m, "\n field variables:\n");
+
+ for (i = 0; i < hist_data->n_field_vars; i++) {
+ ret = field_var_debug_show(m, hist_data->field_vars[i], i, false);
+ if (ret)
+ return;
+ }
+
+ ret = hist_actions_debug_show(m, hist_data);
+ if (ret)
+ return;
+}
+
+static int hist_debug_show(struct seq_file *m, void *v)
+{
+ struct event_trigger_data *data;
+ struct trace_event_file *event_file;
+ int n = 0, ret = 0;
+
+ mutex_lock(&event_mutex);
+
+ event_file = event_file_data(m->private);
+ if (unlikely(!event_file)) {
+ ret = -ENODEV;
+ goto out_unlock;
+ }
+
+ list_for_each_entry(data, &event_file->triggers, list) {
+ if (data->cmd_ops->trigger_type == ETT_EVENT_HIST)
+ hist_trigger_debug_show(m, data, n++);
+ }
+
+ out_unlock:
+ mutex_unlock(&event_mutex);
+
+ return ret;
+}
+
+static int event_hist_debug_open(struct inode *inode, struct file *file)
+{
+ int ret;
+
+ ret = security_locked_down(LOCKDOWN_TRACEFS);
+ if (ret)
+ return ret;
+
+ return single_open(file, hist_debug_show, file);
+}
+
+const struct file_operations event_hist_debug_fops = {
+ .open = event_hist_debug_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+#endif
+
static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
{
const char *field_name = hist_field_name(hist_field, 0);
--
2.17.1
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