From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1DA0C433FE for ; Mon, 10 Oct 2022 10:11:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231582AbiJJKLi (ORCPT ); Mon, 10 Oct 2022 06:11:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52390 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230198AbiJJKLg (ORCPT ); Mon, 10 Oct 2022 06:11:36 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7B0CC3D5B8 for ; Mon, 10 Oct 2022 03:11:35 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 1D84D1F74D; Mon, 10 Oct 2022 10:11:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1665396694; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=sbH2RUMOoOwHcj2wF2XCAK9RzyeAAy8Sdt9/OUJoo44=; b=HVjQWOzzK++VmbnbAlZf+MganpGbrlOGEAy68OzvaW+2RBg0C2jOnrXVksPkiKCVwI8Inb kV/UTiDTnDq6L36Pa2CUWbBJrr0zwOL3M5MLU1bG/P9smxGM9Z/66QHpexYuhi1QjgBZF7 1gGJxG/z094rsRRgP+SycNiMUhbtVPM= Received: from suse.cz (unknown [10.100.208.146]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id BECCC2C141; Mon, 10 Oct 2022 10:11:33 +0000 (UTC) Date: Mon, 10 Oct 2022 12:11:33 +0200 From: Petr Mladek To: John Ogness Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH printk 16/18] printk: Use struct cons_text_buf Message-ID: References: <20220924000454.3319186-1-john.ogness@linutronix.de> <20220924000454.3319186-17-john.ogness@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220924000454.3319186-17-john.ogness@linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 2022-09-24 02:10:52, John Ogness wrote: > From: Thomas Gleixner > > Replace the separately allocated output buffers with a single instance of > struct cons_text_buf. > > Note that the buffer size of devkmsg_user.text_buf, when replaced with > cons_text_buf.text, reduces from CONSOLE_EXT_LOG_MAX to CONSOLE_LOG_MAX. > However, the buffer is only used to read ringbuffer records, which have > a maximum size of LOG_LINE_MAX (CONSOLE_LOG_MAX - PREFIX_MAX). > > Signed-off-by: Thomas Gleixner > Signed-off-by: John Ogness > --- > kernel/printk/printk.c | 50 ++++++++++++++++++------------------------ > 1 file changed, 21 insertions(+), 29 deletions(-) > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index 65e9903d066f..9cbd44e9fc45 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -671,11 +671,9 @@ struct devkmsg_user { > atomic64_t seq; > struct ratelimit_state rs; > struct mutex lock; > - char buf[CONSOLE_EXT_LOG_MAX]; > - > struct printk_info info; > - char text_buf[CONSOLE_EXT_LOG_MAX]; > struct printk_record record; > + struct cons_text_buf txtbuf; I think about how to make it more clear that @txtbuf is not a simple text buffer. It would help to better follow the code. What about renaming "struct cons_text_buf", for example: struct con_text_bufs; struct con_bufs; struct console_text_buffers; struct console_buffers; and use the variables, for example: ctbufs, cbufs, ct_bufs, c_bufs, con_bufs > }; > > static __printf(3, 4) __cold > @@ -758,6 +756,8 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, > { > struct devkmsg_user *user = file->private_data; > struct printk_record *r = &user->record; > + char *outbuf = user->txtbuf.ext_text; Please, use either "ext_text" or "ext_text_buf". > + const int maxlen = sizeof(user->txtbuf.ext_text); and "ext_text_size" or "ext_text_buf_size" to follow the existing style, for example: info_print_ext_header(buf, size, info). prb_rec_init_rd(r, info, text_buf, text_buf_size). > size_t len; > ssize_t ret; > > @@ -2741,13 +2742,13 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ > goto skip; > } > > - if (ext_text) { > - write_text = ext_text; > - len = info_print_ext_header(ext_text, CONSOLE_EXT_LOG_MAX, r.info); > - len += msg_print_ext_body(ext_text + len, CONSOLE_EXT_LOG_MAX - len, > + if (extmsg) { We could get this from the console flags: if (con->flags & CON_EXTENDED) { > + write_text = txtbuf->ext_text; > + len = info_print_ext_header(write_text, CONSOLE_EXT_LOG_MAX, r.info); > + len += msg_print_ext_body(write_text + len, CONSOLE_EXT_LOG_MAX - len, > &r.text_buf[0], r.info->text_len, &r.info->dev_info); I would use this opportunity and get rid of the hardcoded *_LOG_MAX lengts and something like: write_text = txtbuf->ext_text; write_text_size = sizeof(txtbuf->ext_text); len = info_print_ext_header(write_text, write_text_size, r.info); len += msg_print_ext_body(write_text + len, write_text_size - len, &r.text_buf[0], r.info->text_len, &r.info->dev_info); Using the hard coded size is error prone. It makes the review complicated especially when we are going to pass the buffers via some structures or generic pointers. I always have to check if it is still the same buffer. The only sane way is to use either sizeof(buf) or pass/store @buf_size. In addition, I would set here: dropped_text = txtbuf->ext_text; dropped_text_size = sizeof(txtbuf->ext_text); As a result, we could define as: struct con_text_bufs { char ext_text[CONSOLE_EXT_LOG_MAX]; char text[CONSOLE_LOG_MAX]; } __no_randomize_layout; and remove DROPPED_TEXT_MAX. I see that it is actually done later anyway. Adding the union is just a temporary twist that complicates the review. > } else { > - write_text = text; > + write_text = txtbuf->text; > len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time); write_text = txtbuf->text; write_text_size = sizeof(txtbuf->text); len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time); dropped_text = NULL; dropped_text_size = 0; > } > > @@ -2765,7 +2766,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_ > console_lock_spinning_enable(); > > stop_critical_timings(); /* don't trace print latency */ > - call_console_driver(con, write_text, len, dropped_text); > + call_console_driver(con, write_text, len, extmsg ? NULL : txtbuf->dropped_text); call_console_driver(con, write_text, len, dropped_text, dropped_text_size); > start_critical_timings(); > > con->seq++; Best Regards, Petr