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Branden Robinson" , linux-man@vger.kernel.org, linux-serial@vger.kernel.org, Alejandro Colomar , Michael Kerrisk Subject: Re: [PATCH v3] ioctl_tty.2: Add example how to get or set baudrate on the serial port Message-ID: <20210804220808.cetleob6dldpfnjk@pali> References: <20210730095333.6118-1-pali@kernel.org> <20210801135146.14849-1-pali@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210801135146.14849-1-pali@kernel.org> User-Agent: NeoMutt/20180716 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org + linux-serial + Greg Greg, could I ask you for reviewing this documentation manpage patch? 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); > +#else > +#ifdef TCGETS2 > + struct termios2 tio; > +#else > + struct termios tio; > +#endif > + int fd, rc; > + > + if (argc != 2 && argc != 3) { > + fprintf(stderr, "Usage: %s device [new_baudrate]\en", argv[0]); > + exit(EXIT_FAILURE); > + } > + > + fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY); > + if (fd < 0) { > + perror("open"); > + exit(EXIT_FAILURE); > + } > + > +#ifdef TCGETS2 > + rc = ioctl(fd, TCGETS2, &tio); > +#else > + rc = ioctl(fd, TCGETS, &tio); > +#endif > + if (rc) { > + perror("TCGETS"); > + close(fd); > + exit(EXIT_FAILURE); > + } > + > + printf("%u\en", tio.c_ospeed); > + > + if (argc == 3) { > + tio.c_cflag &= ~CBAUD; > + tio.c_cflag |= BOTHER; > + tio.c_ospeed = tio.c_ispeed = atoi(argv[2]); > + > +#ifdef TCSETS2 > + rc = ioctl(fd, TCSETS2, &tio); > +#else > + rc = ioctl(fd, TCSETS, &tio); > +#endif > + if (rc) { > + perror("TCSETS"); > + close(fd); > + exit(EXIT_FAILURE); > + } > + } > + > + close(fd); > + exit(EXIT_SUCCESS); > +#endif > +} > +.EE > .SH SEE ALSO > .BR ldattach (1), > .BR ioctl (2), > -- > 2.20.1 >