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tracing: Simplify the iteration logic in f_start/f_next

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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.

Link: http://lkml.kernel.org/r/20130718184710.GA4783@redhat.com

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Oleg Nesterov 2013-07-18 20:47:10 +02:00 committed by Steven Rostedt
parent 8f76899339
commit 7710b63995
1 changed files with 22 additions and 38 deletions
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60
kernel/trace/trace_events.c
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@ -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)
{
}