From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS17314 8.43.84.0/22 X-Spam-Status: No, score=-4.2 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id D044C1F8C6 for ; Thu, 5 Aug 2021 05:52:29 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 7E43C398641F for ; Thu, 5 Aug 2021 05:52:28 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 7E43C398641F DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1628142748; bh=xRBacfBJs9ANTq1wk+Wfi+bi8ze7FoDGjMbSj4xgSUY=; h=Date:To:Subject:References:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=lREhA5Df2EIFF3amWw0/qhBLgPYQtgAOamTOmKmkJl1Vo2pZBjTBA4gp2RVILHaFQ ZipzYzExSTXjqV7PmUYkBGO1NqAPZB9u93tx4CF1FsecrGDg/+GqA5H87efOjgklWK r2DVN77ypXNOvkbmXzn7DZao6U1O8yUdup0t+CMg= Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by sourceware.org (Postfix) with ESMTPS id DC5D53986427 for ; Thu, 5 Aug 2021 05:52:08 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org DC5D53986427 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5970760EBB; Thu, 5 Aug 2021 05:52:06 +0000 (UTC) Date: Thu, 5 Aug 2021 07:52:03 +0200 To: Pali =?iso-8859-1?Q?Roh=E1r?= Subject: Re: [PATCH v3] ioctl_tty.2: Add example how to get or set baudrate on the serial port Message-ID: References: <20210730095333.6118-1-pali@kernel.org> <20210801135146.14849-1-pali@kernel.org> <20210804220808.cetleob6dldpfnjk@pali> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210804220808.cetleob6dldpfnjk@pali> X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Greg Kroah-Hartman via Libc-alpha Reply-To: Greg Kroah-Hartman Cc: Marek =?iso-8859-1?Q?Beh=FAn?= , Alejandro Colomar , libc-alpha@sourceware.org, linux-man@vger.kernel.org, Michael Kerrisk , linux-serial@vger.kernel.org, "G. Branden Robinson" Errors-To: libc-alpha-bounces+e=80x24.org@sourceware.org Sender: "Libc-alpha" On Thu, Aug 05, 2021 at 12:08:08AM +0200, Pali Rohár wrote: > + linux-serial > + Greg > > Greg, could I ask you for reviewing this documentation manpage patch? If it is submitted in a format I can review, sure (i.e. not top-post...) But I will dig down below to say one thing... > > On Sunday 01 August 2021 15:51:45 Pali Rohár wrote: > > Signed-off-by: Pali Rohár > > > > --- > > Changes in v3: > > * Check support for custom baudrate only based on BOTHER macro > > * Use TCGETS/TCSETS/termios when TCGETS2/TCSETS2/termios2 is not available > > > > Changes in v2: > > * Use \e for backslash > > * Use exit(EXIT_*) instead of return num > > * Sort includes > > * Add comment about possible fallback > > --- > > > > Hello Alejandro! > > > > I found out that this stuff is more complicated as I originally thought. > > And seems that additional documentation on this topic is needed... > > > > For setting custom baudrate it is needed to set BOTHER flag in c_cflag > > field and baudrate value itself in c_ospeed and c_ispeed fields. > > > > So when BOTHER flag is not provided by then setting custom > > baudrate is not possible, fields c_ospeed and c_ispeed do not exist (and > > only some predefined Bnnn baudrate values are supported). This applies when > > compiling application with older version of header files (prior support for > > custom baudrate was introduced into header files). > > > > First caveat: BOTHER constant is different for different architectures. > > So it is not possible to provide fallback #ifndef..#define BOTHER. > > > > And now the biggest issue: Some architectures have these c_ospeed and > > c_ispeed fields in struct termios and some in struct termios2. > > > > TCGETS/TCSETS ioctls use struct termios and TCGETS/TCSETS2 use > > struct termios2. > > > > Some architectures (e.g. amd64) provide both struct termios and struct > > termios2, but c_ospeed and c_ispeed are only in struct termios2. > > > > Some other architectures (e.g. alpha) provide both struct termios and struct > > termios2 and both have c_ospeed and c_ispeed fields. > > > > And some other architectures (e.g. powerpc) provide only struct termios > > (no struct termios2) and it has c_ospeed and c_ispeed fields. > > > > So basically to support all architectures it is needed to use > > struct termios2 when TCGETS2/TCSETS2 is supported. Otherwise it is needed > > to use struct termios with TCGETS/TCSETS (case for e.g. powerpc). > > > > I updated v3 patch to handle this logic. > > --- > > man2/ioctl_tty.2 | 73 ++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 73 insertions(+) > > > > diff --git a/man2/ioctl_tty.2 b/man2/ioctl_tty.2 > > index 3020f9984872..d83cbd17225b 100644 > > --- a/man2/ioctl_tty.2 > > +++ b/man2/ioctl_tty.2 > > @@ -764,6 +764,79 @@ main(void) > > close(fd); > > } > > .EE > > +.PP > > +Get or set arbitrary baudrate on the serial port. > > +.PP > > +.EX > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +int > > +main(int argc, char *argv[]) > > +{ > > +#ifndef BOTHER > > + fprintf(stderr, "BOTHER is unsupported\en"); > > + /* Program may fallback to TCGETS/TCSETS with Bnnn constants */ > > + exit(EXIT_FAILURE); So this is a BOTHER test only? What is the goal of this program? Don't throw a bunch of #ifdef in here for no good reason. These options should all be present on all normal kernels, why wouldn't they be? thanks, greg k-h