[PATCH 2/6] tracing: event_id_read() uses simple buffer instead of trace_seq

[Lai Jiangshan <laijs@cn.fujitsu.com>]

It seems that struct trace_seq is too heavy for event_id_read().
we use simple buffer instead of struct trace_seq.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 04d3f90..835b370 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -604,23 +604,16 @@ static ssize_t
 event_id_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
 {
 	struct ftrace_event_call *call = filp->private_data;
-	struct trace_seq *s;
-	int r;
+	char buf[20];
+	int len;
 
 	if (*ppos)
 		return 0;
 
-	s = kmalloc(sizeof(*s), GFP_KERNEL);
-	if (!s)
-		return -ENOMEM;
+	len = snprintf(buf, sizeof(buf), "%d\n", call->id);
+	len = simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
 
-	trace_seq_init(s);
-	trace_seq_printf(s, "%d\n", call->id);
-
-	r = simple_read_from_buffer(ubuf, cnt, ppos,
-				    s->buffer, s->len);
-	kfree(s);
-	return r;
+	return len;
 }
 
 static ssize_t