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

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: default avatarOleg Nesterov <>
Signed-off-by: default avatarSteven Rostedt <>
parent 8f768993
......@@ -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;
switch ((unsigned long)v) {
if (unlikely(list_empty(common_head)))
return NULL;
field = list_entry(common_head->prev,
struct ftrace_event_field, link);
return field;
node = common_head;
if (unlikely(list_empty(head)))
return NULL;
field = list_entry(head->prev, struct ftrace_event_field, link);
return field;
node = head;
/* all done */
return NULL;
field = v;
if (field->link.prev == common_head)
node = node->prev;
if (node == common_head)
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;
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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