Commit 7710b639 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Steven Rostedt
Browse files

tracing: Simplify the iteration logic in f_start/f_next 

f_next() looks overcomplicated, and it is not strictly correct
even if this doesn't matter.

Say, FORMAT_FIELD_SEPERATOR should not return NULL (means EOF)
if trace_get_fields() returns an empty list, we should simply
advance to FORMAT_PRINTFMT as we do when we find the end of list.

1. Change f_next() to return "struct list_head *" rather than
   "ftrace_event_field *", and change f_show() to do list_entry().

   This simplifies the code a bit, only f_show() needs to know
   about ftrace_event_field, and f_next() can play with ->prev
   directly

2. Change f_next() to not play with ->prev / return inside the
   switch() statement. It can simply set node = head/common_head,
   the prev-or-advance-to-the-next-magic below does all work.

While at it. f_start() looks overcomplicated too. I don't think
*pos == 0 makes sense as a separate case, just change this code
to do "while" instead of "do/while".

The patch also moves f_start() down, close to f_stop(). This is
purely cosmetic, just to make the locking added by the next patch
more clear/visible.

Link: http://lkml.kernel.org/r/20130718184710.GA4783@redhat.com



Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 8f768993

kernel/trace/trace_events.c

+22 −38
Original line number Diff line number Diff line
@@ -826,59 +826,33 @@ enum { 
static void *f_next(struct seq_file *m, void *v, loff_t *pos)

{

	struct ftrace_event_call *call = m->private;

	struct ftrace_event_field *field;

	struct list_head *common_head = &ftrace_common_fields;

	struct list_head *head = trace_get_fields(call);

	struct list_head *node = v;



	(*pos)++;



	switch ((unsigned long)v) {

	case FORMAT_HEADER:

		if (unlikely(list_empty(common_head)))

			return NULL;



		field = list_entry(common_head->prev,

				   struct ftrace_event_field, link);

		return field;

		node = common_head;

		break;



	case FORMAT_FIELD_SEPERATOR:

		if (unlikely(list_empty(head)))

			return NULL;



		field = list_entry(head->prev, struct ftrace_event_field, link);

		return field;

		node = head;

		break;



	case FORMAT_PRINTFMT:

		/* all done */

		return NULL;

	}



	field = v;

	if (field->link.prev == common_head)

	node = node->prev;

	if (node == common_head)

		return (void *)FORMAT_FIELD_SEPERATOR;

	else if (field->link.prev == head)

	else if (node == head)

		return (void *)FORMAT_PRINTFMT;



	field = list_entry(field->link.prev, struct ftrace_event_field, link);



	return field;

}



static void *f_start(struct seq_file *m, loff_t *pos)

{

	loff_t l = 0;

	void *p;



	/* Start by showing the header */

	if (!*pos)

		return (void *)FORMAT_HEADER;



	p = (void *)FORMAT_HEADER;

	do {

		p = f_next(m, p, &l);

	} while (p && l < *pos);



	return p;

	else

		return node;

}



static int f_show(struct seq_file *m, void *v)
@@ -904,8 +878,7 @@ static int f_show(struct seq_file *m, void *v) 
		return 0;

	}



	field = v;



	field = list_entry(v, struct ftrace_event_field, link);

	/*

	 * Smartly shows the array type(except dynamic array).

	 * Normal:
@@ -932,6 +905,17 @@ static int f_show(struct seq_file *m, void *v) 
	return 0;

}



static void *f_start(struct seq_file *m, loff_t *pos)

{

	void *p = (void *)FORMAT_HEADER;

	loff_t l = 0;



	while (l < *pos && p)

		p = f_next(m, p, &l);



	return p;

}



static void f_stop(struct seq_file *m, void *p)

{

}

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