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 9EE13C4332F for ; Wed, 9 Nov 2022 12:02:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229533AbiKIMCw (ORCPT ); Wed, 9 Nov 2022 07:02:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41638 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229447AbiKIMCv (ORCPT ); Wed, 9 Nov 2022 07:02:51 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 795842D76B; Wed, 9 Nov 2022 04:02:50 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 2BD19B81C98; Wed, 9 Nov 2022 12:02:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3AEC8C433D6; Wed, 9 Nov 2022 12:02:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1667995367; bh=/yQM/f090OAeWMsA4JwUWTtZHi+F0/lBIpwhZOAAhCY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=y3ey7U9icl93mDMBa9apturhQJNCymQjL44QehXBLY56m/SuGtzHvxpgRkIreQY/4 6hDDba2M3Yk0F4Njub8O9P6aUsZkACgJZnLjbYwjltcVz4+ewslKOFb+7ywDnGG4/K OI9X584CNF8cqZg/Jj8gzQGRmaWAQysf2L01L0QU= Date: Wed, 9 Nov 2022 13:02:43 +0100 From: Greg KH To: Ilpo =?iso-8859-1?Q?J=E4rvinen?= Cc: linux-serial , Jiri Slaby , LKML Subject: Re: [PATCH v2 1/2] tty: Convert tty_buffer flags to bool Message-ID: References: <20221019105504.16800-1-ilpo.jarvinen@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On Thu, Nov 03, 2022 at 12:11:26PM +0200, Ilpo Järvinen wrote: > On Thu, 3 Nov 2022, Greg KH wrote: > > > On Wed, Oct 19, 2022 at 01:55:03PM +0300, Ilpo Järvinen wrote: > > > The struct tty_buffer has flags which is only used for storing TTYB_NORMAL. > > > There is also a few quite confusing operations for checking the presense > > > of TTYB_NORMAL. Simplify things by converting flags to bool. > > > > > > Despite the name remaining the same, the meaning of "flags" is altered > > > slightly by this change. Previously it referred to flags of the buffer > > > (only TTYB_NORMAL being used as a flag). After this change, flags tell > > > whether the buffer contains/should be allocated with flags array along > > > with character data array. It is much more suitable name that > > > TTYB_NORMAL was for this purpose, thus the name remains. > > > > > > Signed-off-by: Ilpo Järvinen > > > --- > > > > > > v2: > > > - Make it more obvious why flags is not renamed (both in kerneldoc > > > comment and commit message). > > > > > > drivers/tty/tty_buffer.c | 28 ++++++++++++++-------------- > > > include/linux/tty_buffer.h | 5 +---- > > > include/linux/tty_flip.h | 4 ++-- > > > 3 files changed, 17 insertions(+), 20 deletions(-) > > > > > > diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c > > > index 5e287dedce01..b408d830fcbc 100644 > > > --- a/drivers/tty/tty_buffer.c > > > +++ b/drivers/tty/tty_buffer.c > > > @@ -107,7 +107,7 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size) > > > p->commit = 0; > > > p->lookahead = 0; > > > p->read = 0; > > > - p->flags = 0; > > > + p->flags = true; > > > } > > > > > > /** > > > @@ -249,7 +249,7 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld) > > > * __tty_buffer_request_room - grow tty buffer if needed > > > * @port: tty port > > > * @size: size desired > > > - * @flags: buffer flags if new buffer allocated (default = 0) > > > + * @flags: buffer has to store flags along character data > > > * > > > * Make at least @size bytes of linear space available for the tty buffer. > > > * > > > @@ -260,19 +260,19 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld) > > > * Returns: the size we managed to find. > > > */ > > > static int __tty_buffer_request_room(struct tty_port *port, size_t size, > > > - int flags) > > > + bool flags) > > > { > > > struct tty_bufhead *buf = &port->buf; > > > struct tty_buffer *b, *n; > > > int left, change; > > > > > > b = buf->tail; > > > - if (b->flags & TTYB_NORMAL) > > > + if (!b->flags) > > > left = 2 * b->size - b->used; > > > else > > > left = b->size - b->used; > > > > > > - change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL); > > > + change = !b->flags && flags; > > > if (change || left < size) { > > > /* This is the slow path - looking for new buffers to use */ > > > n = tty_buffer_alloc(port, size); > > > @@ -300,7 +300,7 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size, > > > > > > int tty_buffer_request_room(struct tty_port *port, size_t size) > > > { > > > - return __tty_buffer_request_room(port, size, 0); > > > + return __tty_buffer_request_room(port, size, true); > > > > Did this logic just get inverted? > > > > Maybe it's the jet-lag, but this feels like it's not correct anymore. > > As you can see, the old way is sooo confusing :-). I'll admit I stumbled > myself with this same default thing first. It's even more confusing than > the other places. > > This check is true when flag bytes are present / required to be present: > (~flags & TTYB_NORMAL) > It's very very confusing way to check such condition due to layered > reverse logic. > > With old code, the per character flag bytes won't be there in the buffer > if TTYB_NORMAL is present. Thus, the old default of 0 means > __tty_buffer_request_room will allocate room for those flag bytes. > > If you think about it carefully, the old code passed 0. Therefore, ~0 & > TTYB_NORMAL is going to be true. After my change true is passed and true > matches to the original code. > > So the logic was not inverted. I just cleared those layered reverse logic > traps the original had which makes my patch look it's inverting things. > > I really appreciate you took your time to find out this little detail > from it! This is far from a simple change because of how trappy the old > way of doing things is. > > > Maybe a commet up above where you calculate "left" would make more sense > > as to what is going on? > > Do you mean you want me to add a comment there? I don't see any > pre-existing comments that you could be pointing me to. > > > Should I resubmit it since you probably dropped the patch? No need, I took is as-is now, thanks. greg k-h