tracing: Add TRACE_DEFINE_ENUM() macro to map enums to their values

Several tracepoints use the helper functions __print_symbolic() or
__print_flags() and pass in enums that do the mapping between the
binary data stored and the value to print. This works well for reading
the ASCII trace files, but when the data is read via userspace tools
such as perf and trace-cmd, the conversion of the binary value to a
human string format is lost if an enum is used, as userspace does not
have access to what the ENUM is.

For example, the tracepoint trace_tlb_flush() has:

 __print_symbolic(REC->reason,
    { TLB_FLUSH_ON_TASK_SWITCH, "flush on task switch" },
    { TLB_REMOTE_SHOOTDOWN, "remote shootdown" },
    { TLB_LOCAL_SHOOTDOWN, "local shootdown" },
    { TLB_LOCAL_MM_SHOOTDOWN, "local mm shootdown" })

Which maps the enum values to the strings they represent. But perf and
trace-cmd do no know what value TLB_LOCAL_MM_SHOOTDOWN is, and would
not be able to map it.

With TRACE_DEFINE_ENUM(), developers can place these in the event header
files and ftrace will convert the enums to their values:

By adding:

 TRACE_DEFINE_ENUM(TLB_FLUSH_ON_TASK_SWITCH);
 TRACE_DEFINE_ENUM(TLB_REMOTE_SHOOTDOWN);
 TRACE_DEFINE_ENUM(TLB_LOCAL_SHOOTDOWN);
 TRACE_DEFINE_ENUM(TLB_LOCAL_MM_SHOOTDOWN);

 $ cat /sys/kernel/debug/tracing/events/tlb/tlb_flush/format
[...]
 __print_symbolic(REC->reason,
    { 0, "flush on task switch" },
    { 1, "remote shootdown" },
    { 2, "local shootdown" },
    { 3, "local mm shootdown" })

The above is what userspace expects to see, and tools do not need to
be modified to parse them.

Link: http://lkml.kernel.org/r/20150403013802.220157513@goodmis.org

Cc: Guilherme Cox <cox@computer.org>
Cc: Tony Luck <tony.luck@gmail.com>
Cc: Xie XiuQi <xiexiuqi@huawei.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 119 insertions, 0 deletions

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index db54dda10ccc..fc58c50fbf01 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1704,6 +1704,125 @@ __register_event(struct ftrace_event_call *call, struct module *mod)
 	return 0;
 }
 
+static char *enum_replace(char *ptr, struct trace_enum_map *map, int len)
+{
+	int rlen;
+	int elen;
+
+	/* Find the length of the enum value as a string */
+	elen = snprintf(ptr, 0, "%ld", map->enum_value);
+	/* Make sure there's enough room to replace the string with the value */
+	if (len < elen)
+		return NULL;
+
+	snprintf(ptr, elen + 1, "%ld", map->enum_value);
+
+	/* Get the rest of the string of ptr */
+	rlen = strlen(ptr + len);
+	memmove(ptr + elen, ptr + len, rlen);
+	/* Make sure we end the new string */
+	ptr[elen + rlen] = 0;
+
+	return ptr + elen;
+}
+
+static void update_event_printk(struct ftrace_event_call *call,
+				struct trace_enum_map *map)
+{
+	char *ptr;
+	int quote = 0;
+	int len = strlen(map->enum_string);
+
+	for (ptr = call->print_fmt; *ptr; ptr++) {
+		if (*ptr == '\\') {
+			ptr++;
+			/* paranoid */
+			if (!*ptr)
+				break;
+			continue;
+		}
+		if (*ptr == '"') {
+			quote ^= 1;
+			continue;
+		}
+		if (quote)
+			continue;
+		if (isdigit(*ptr)) {
+			/* skip numbers */
+			do {
+				ptr++;
+				/* Check for alpha chars like ULL */
+			} while (isalnum(*ptr));
+			/*
+			 * A number must have some kind of delimiter after
+			 * it, and we can ignore that too.
+			 */
+			continue;
+		}
+		if (isalpha(*ptr) || *ptr == '_') {
+			if (strncmp(map->enum_string, ptr, len) == 0 &&
+			    !isalnum(ptr[len]) && ptr[len] != '_') {
+				ptr = enum_replace(ptr, map, len);
+				/* Hmm, enum string smaller than value */
+				if (WARN_ON_ONCE(!ptr))
+					return;
+				/*
+				 * No need to decrement here, as enum_replace()
+				 * returns the pointer to the character passed
+				 * the enum, and two enums can not be placed
+				 * back to back without something in between.
+				 * We can skip that something in between.
+				 */
+				continue;
+			}
+		skip_more:
+			do {
+				ptr++;
+			} while (isalnum(*ptr) || *ptr == '_');
+			/*
+			 * If what comes after this variable is a '.' or
+			 * '->' then we can continue to ignore that string.
+			 */
+			if (*ptr == '.' || (ptr[0] == '-' && ptr[1] == '>')) {
+				ptr += *ptr == '.' ? 1 : 2;
+				goto skip_more;
+			}
+			/*
+			 * Once again, we can skip the delimiter that came
+			 * after the string.
+			 */
+			continue;
+		}
+	}
+}
+
+void trace_event_enum_update(struct trace_enum_map **map, int len)
+{
+	struct ftrace_event_call *call, *p;
+	const char *last_system = NULL;
+	int last_i;
+	int i;
+
+	down_write(&trace_event_sem);
+	list_for_each_entry_safe(call, p, &ftrace_events, list) {
+		/* events are usually grouped together with systems */
+		if (!last_system || call->class->system != last_system) {
+			last_i = 0;
+			last_system = call->class->system;
+		}
+
+		for (i = last_i; i < len; i++) {
+			if (call->class->system == map[i]->system) {
+				/* Save the first system if need be */
+				if (!last_i)
+					last_i = i;
+				update_event_printk(call, map[i]);
+			}
+		}
+	}
+	up_write(&trace_event_sem);
+}
+
 static struct ftrace_event_file *
 trace_create_new_event(struct ftrace_event_call *call,
 		       struct trace_array *tr)