[PATCH 0/2] tracing: minor cleanups

[PATCH 0/2] tracing: minor cleanups

[Oleg Nesterov]

Steven,

As you suggested, I extracted 2/2 into the separate change.

I think that it and 1/2 makes sense in any case so I am sending
them right now. This shrinks the next series I am trying to make.

Oleg.

[PATCH 1/2] tracing: Simplify the iteration logic in f_start/f_next

[Oleg Nesterov]

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.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/trace/trace_events.c |   60 +++++++++++++++---------------------------
 1 files changed, 22 insertions(+), 38 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 9d2b499..2c3a8c5 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -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)
 {
 }
-- 
1.5.5.1

[PATCH 2/2] tracing: Do not (ab)use trace_seq in event_id_read()

[Oleg Nesterov]

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

Note: "if (*ppos) return 0" looks strange and even wrong,
simple_read_from_buffer() handles ppos != 0 case corrrectly.

And it seems that almost every user of trace_seq in this file
should be converted too. Unless you use seq_open(), trace_seq
buys nothing compared to the raw buffer, but it needs a bit
more memory and code.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/trace/trace_events.c |   17 ++++-------------
 1 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 2c3a8c5..1d2c8db 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -947,23 +947,14 @@ 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[32];
+	int len;
 
 	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", call->event.type);
+	return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
 }
 
 static ssize_t
-- 
1.5.5.1