ftrace: Create separate t_func_next() to simplify the function / hash logic

I noticed that if I use dd to read the set_ftrace_filter file that the first
hash command is repeated.

 # cd /sys/kernel/debug/tracing
 # echo schedule > set_ftrace_filter
 # echo do_IRQ >> set_ftrace_filter
 # echo schedule:traceoff >> set_ftrace_filter
 # echo do_IRQ:traceoff >> set_ftrace_filter

 # cat set_ftrace_filter
 schedule
 do_IRQ
 schedule:traceoff:unlimited
 do_IRQ:traceoff:unlimited

 # dd if=set_ftrace_filter bs=1
 schedule
 do_IRQ
 schedule:traceoff:unlimited
 schedule:traceoff:unlimited
 do_IRQ:traceoff:unlimited
 98+0 records in
 98+0 records out
 98 bytes copied, 0.00265011 s, 37.0 kB/s

This is due to the way t_start() calls t_next() as well as the seq_file
calls t_next() and the state is slightly different between the two. Namely,
t_start() will call t_next() with a local "pos" variable.

By separating out the function listing from t_next() into its own function,
we can have better control of outputting the functions and the hash of
triggers. This simplifies the code.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -3154,22 +3154,12 @@ t_hash_show(struct seq_file *m, struct ftrace_iterator *iter)
 }
 
 static void *
-t_next(struct seq_file *m, void *v, loff_t *pos)
+t_func_next(struct seq_file *m, loff_t *pos)
 {
 	struct ftrace_iterator *iter = m->private;
 	struct dyn_ftrace *rec = NULL;
 
-	if (unlikely(ftrace_disabled))
-		return NULL;
-
-	if (iter->flags & FTRACE_ITER_HASH)
-		return t_hash_next(m, pos);
-
 	(*pos)++;
-	iter->pos = iter->func_pos = *pos;
-
-	if (iter->flags & FTRACE_ITER_PRINTALL)
-		return t_hash_start(m, pos);
 
  retry:
 	if (iter->idx >= iter->pg->index) {
@@ -3192,13 +3182,40 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
 	}
 
 	if (!rec)
-		return t_hash_start(m, pos);
+		return NULL;
 
+	iter->pos = iter->func_pos = *pos;
 	iter->func = rec;
 
 	return iter;
 }
 
+static void *
+t_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	struct ftrace_iterator *iter = m->private;
+	void *ret;
+
+	if (unlikely(ftrace_disabled))
+		return NULL;
+
+	if (iter->flags & FTRACE_ITER_HASH)
+		return t_hash_next(m, pos);
+
+	if (iter->flags & FTRACE_ITER_PRINTALL) {
+		/* next must increment pos, and t_hash_start does not */
+		(*pos)++;
+		return t_hash_start(m, pos);
+	}
+
+	ret = t_func_next(m, pos);
+
+	if (!ret)
+		return t_hash_start(m, pos);
+
+	return ret;
+}
+
 static void reset_iter_read(struct ftrace_iterator *iter)
 {
 	iter->pos = 0;
@@ -3250,13 +3267,13 @@ static void *t_start(struct seq_file *m, loff_t *pos)
 	iter->pg = ftrace_pages_start;
 	iter->idx = 0;
 	for (l = 0; l <= *pos; ) {
-		p = t_next(m, p, &l);
+		p = t_func_next(m, &l);
 		if (!p)
 			break;
 	}
 
 	if (!p)
-		return NULL;
+		return t_hash_start(m, pos);
 
 	return iter;
 }