[PATCH v3 14/17] tracing: Add kho serialization of trace events

@@ -9364,7 +9364,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer);
 
 static int trace_kho_off_tr(struct trace_array *tr)
 {
-	const char *name = tr->name ? tr->name : "global_trace";
+	const char *name = tr->name ? tr->name : "global-trace";
 	const void *fdt = kho_get_fdt();
 	char *path;
 	int off;

@@ -10648,6 +10648,7 @@ static int trace_kho_notifier(struct notifier_block *self,
 
 	err |= fdt_begin_node(fdt, "ftrace");
 	err |= fdt_property(fdt, "compatible", compatible, sizeof(compatible));
+	err |= trace_kho_write_events(fdt);
 	err |= trace_kho_write_trace_array(fdt, &global_trace);
 	err |= fdt_end_node(fdt);
 

@@ -12,6 +12,8 @@
 #include <linux/sched/clock.h>
 #include <linux/sched/mm.h>
 #include <linux/idr.h>
+#include <linux/kexec.h>
+#include <linux/crc32.h>
 
 #include "trace_output.h"
 

@@ -669,6 +671,93 @@ int trace_print_lat_context(struct trace_iterator *iter)
 	return !trace_seq_has_overflowed(s);
 }
 
+/**
+ * event2fp - Return fingerprint of an event
+ * @event: The event to fingerprint
+ *
+ * For KHO, we need to match events before and after kexec to recover its type
+ * id. This function returns a hash that combines an event's name, and all of
+ * its fields' lengths.
+ */
+static u32 event2fp(struct trace_event *event)
+{
+	struct ftrace_event_field *field;
+	struct trace_event_call *call;
+	struct list_head *head;
+	const char *name;
+	u32 crc32 = ~0;
+
+	/* Low type numbers are static, nothing to checksum */
+	if (event->type && event->type < __TRACE_LAST_TYPE)
+		return event->type;
+
+	call = container_of(event, struct trace_event_call, event);
+	name = trace_event_name(call);
+	if (name)
+		crc32 = crc32_le(crc32, name, strlen(name));
+
+	head = trace_get_fields(call);
+	list_for_each_entry(field, head, link)
+		crc32 = crc32_le(crc32, (char *)&field->size, sizeof(field->size));
+
+	return crc32;
+}
+
+struct trace_event_map {
+	u32 crc32;
+	u32 type;
+};
+
+static int __maybe_unused _trace_kho_write_events(void *fdt)
+{
+	struct trace_event_call *call;
+	int count = __TRACE_LAST_TYPE - 1;
+	struct trace_event_map *map;
+	int err = 0;
+	int i;
+
+	down_read(&trace_event_sem);
+	/* Allocate an array that we can place all maps into */
+	list_for_each_entry(call, &ftrace_events, list)
+		count++;
+
+	map = vmalloc(count * sizeof(*map));
+	if (!map)
+		return -ENOMEM;
+
+	/* Then fill the array with all crc32 values */
+	count = 0;
+	for (i = 1; i < __TRACE_LAST_TYPE; i++)
+		map[count++] = (struct trace_event_map) {
+			.crc32 = count,
+			.type = count,
+		};
+
+	list_for_each_entry(call, &ftrace_events, list) {
+		struct trace_event *event = &call->event;
+
+		map[count++] = (struct trace_event_map) {
+			.crc32 = event2fp(event),
+			.type = event->type,
+		};
+	}
+	up_read(&trace_event_sem);
+
+	/* And finally write it into a DT variable */
+	err |= fdt_property(fdt, "events", map, count * sizeof(*map));
+
+	vfree(map);
+	return err;
+}
+
+#ifdef CONFIG_FTRACE_KHO
+int trace_kho_write_events(void *fdt)
+{
+	return _trace_kho_write_events(fdt);
+}
+#endif
+
+
 /**
  * ftrace_find_event - find a registered event
  * @type: the type of event to look for

@@ -25,6 +25,11 @@ extern enum print_line_t print_event_fields(struct trace_iterator *iter,
 extern void trace_event_read_lock(void);
 extern void trace_event_read_unlock(void);
 extern struct trace_event *ftrace_find_event(int type);
+#ifdef CONFIG_FTRACE_KHO
+extern int trace_kho_write_events(void *fdt);
+#else
+static inline int trace_kho_write_events(void *fdt) { return -EINVAL; }
+#endif
 
 extern enum print_line_t trace_nop_print(struct trace_iterator *iter,
 					 int flags, struct trace_event *event);