[RFC PATCH 2/4] tracing: Turn "id"->i_private into call->event.type

[Oleg Nesterov]

ftrace_event_id_fops and event_id_read() is overcomplicated.

1. Change event_create_dir() to pass "data = call->event.type"
   to debugfs_create_file().

   This means that ftrace_event_id_fops doesn't need .open()
   and event_id_read() can simply print (int)i_private

2. event_id_read() has no reason to kmalloc "struct trace_seq"
   (more than PAGE_SIZE!), it can use a small buffer.

Note: "if (*ppos) return 0" looks strange and unneeded,
simple_read_from_buffer(ppos) should handle this case corrrectly.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 kernel/trace/trace_events.c |   26 +++++++++-----------------
 1 files changed, 9 insertions(+), 17 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index cbd1a57..cefbe85 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -962,24 +962,17 @@ static int trace_format_open(struct inode *inode, struct file *file)
 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;
+	int id = (long)ACCESS_ONCE(file_inode(filp)->i_private);
+	char buf[32];
+	int len;
 
+	if (!id)
+		return -ENODEV;
 	if (*ppos)
 		return 0;
 
-	s = kmalloc(sizeof(*s), GFP_KERNEL);
-	if (!s)
-		return -ENOMEM;
-
-	trace_seq_init(s);
-	trace_seq_printf(s, "%d\n", call->event.type);
-
-	r = simple_read_from_buffer(ubuf, cnt, ppos,
-				    s->buffer, s->len);
-	kfree(s);
-	return r;
+	len = sprintf(buf, "%d\n", id);
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
 }
 
 static ssize_t
@@ -1264,7 +1257,6 @@ static const struct file_operations ftrace_event_format_fops = {
 };
 
 static const struct file_operations ftrace_event_id_fops = {
-	.open = tracing_open_generic,
 	.read = event_id_read,
 	.llseek = default_llseek,
 };
@@ -1496,8 +1488,8 @@ event_create_dir(struct dentry *parent,
 
 #ifdef CONFIG_PERF_EVENTS
 	if (call->event.type && call->class->reg)
-		trace_create_file("id", 0444, file->dir, call,
-		 		  id);
+		trace_create_file("id", 0444, file->dir,
+				  (void*)(long)call->event.type, id);
 #endif
 
 	/*
-- 
1.5.5.1

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