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SubjectRe: [PATCH] tracing: Simplify seqfile code for format file
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On Tue, 2010-08-17 at 13:53 +0800, Li Zefan wrote:
> We don't have to use the trick that marks a pointer's LSB to
> distinguish event fields from common fields.
>

Hehe, you don't like tricks. I find it as a certain art to the magic of
programming ;-)


> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

I'll pull this in and see if we can get this into 2.6.36 too.

Thanks!

-- Steve

> ---
> kernel/trace/trace_events.c | 55 ++++++++++++++-----------------------------
> 1 files changed, 18 insertions(+), 37 deletions(-)
>
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 4c758f1..398c0e8 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -600,21 +600,29 @@ out:
>
> enum {
> FORMAT_HEADER = 1,
> - FORMAT_PRINTFMT = 2,
> + FORMAT_FIELD_SEPERATOR = 2,
> + FORMAT_PRINTFMT = 3,
> };
>
> 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 *head;
> + struct list_head *common_head = &ftrace_common_fields;
> + struct list_head *head = trace_get_fields(call);
>
> (*pos)++;
>
> switch ((unsigned long)v) {
> case FORMAT_HEADER:
> - head = &ftrace_common_fields;
> + if (unlikely(list_empty(common_head)))
> + return NULL;
> +
> + field = list_entry(common_head->prev,
> + struct ftrace_event_field, link);
> + return field;
>
> + case FORMAT_FIELD_SEPERATOR:
> if (unlikely(list_empty(head)))
> return NULL;
>
> @@ -626,31 +634,10 @@ static void *f_next(struct seq_file *m, void *v, loff_t *pos)
> return NULL;
> }
>
> - head = trace_get_fields(call);
> -
> - /*
> - * To separate common fields from event fields, the
> - * LSB is set on the first event field. Clear it in case.
> - */
> - v = (void *)((unsigned long)v & ~1L);
> -
> field = v;
> - /*
> - * If this is a common field, and at the end of the list, then
> - * continue with main list.
> - */
> - if (field->link.prev == &ftrace_common_fields) {
> - if (unlikely(list_empty(head)))
> - return NULL;
> - field = list_entry(head->prev, struct ftrace_event_field, link);
> - /* Set the LSB to notify f_show to print an extra newline */
> - field = (struct ftrace_event_field *)
> - ((unsigned long)field | 1);
> - return field;
> - }
> -
> - /* If we are done tell f_show to print the format */
> - if (field->link.prev == head)
> + if (field->link.prev == common_head)
> + return (void *)FORMAT_FIELD_SEPERATOR;
> + else if (field->link.prev == head)
> return (void *)FORMAT_PRINTFMT;
>
> field = list_entry(field->link.prev, struct ftrace_event_field, link);
> @@ -688,22 +675,16 @@ static int f_show(struct seq_file *m, void *v)
> seq_printf(m, "format:\n");
> return 0;
>
> + case FORMAT_FIELD_SEPERATOR:
> + seq_putc(m, '\n');
> + return 0;
> +
> case FORMAT_PRINTFMT:
> seq_printf(m, "\nprint fmt: %s\n",
> call->print_fmt);
> return 0;
> }
>
> - /*
> - * To separate common fields from event fields, the
> - * LSB is set on the first event field. Clear it and
> - * print a newline if it is set.
> - */
> - if ((unsigned long)v & 1) {
> - seq_putc(m, '\n');
> - v = (void *)((unsigned long)v & ~1L);
> - }
> -
> field = v;
>
> /*




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