From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757077Ab3GQTfj (ORCPT ); Wed, 17 Jul 2013 15:35:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5725 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755455Ab3GQTfi (ORCPT ); Wed, 17 Jul 2013 15:35:38 -0400 Date: Wed, 17 Jul 2013 21:30:17 +0200 From: Oleg Nesterov To: Steven Rostedt , Masami Hiramatsu Cc: "zhangwei(Jovi)" , Jiri Olsa , Peter Zijlstra , Arnaldo Carvalho de Melo , Srikar Dronamraju , Frederic Weisbecker , Ingo Molnar , Andrew Morton , linux-kernel@vger.kernel.org Subject: [RFC PATCH 5/4] tracing: Simplify the ftrace_event_field iteration in f_next/f_show Message-ID: <20130717193017.GA15312@redhat.com> References: <20130716185658.GA21167@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130716185658.GA21167@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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 f4a86f9..6c3e4e6 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -806,59 +806,33 @@ 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) @@ -884,8 +858,7 @@ 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: @@ -912,6 +885,17 @@ 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 (p && l < *pos) + p = f_next(m, p, &l); + + return p; +} + static void f_stop(struct seq_file *m, void *p) { } -- 1.5.5.1