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List:       glibc-alpha
Subject:    Re: [PATCH v4] ioctl_tty.2: Add example how to get or set baudrate on the serial port
From:       Pali_Rohár_via_Libc-alpha <libc-alpha () sourceware ! org>
Date:       2021-08-31 20:34:36
Message-ID: 20210831203436.hy52aimer5hozb6r () pali
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On Tuesday 10 August 2021 21:49:28 Pali Rohár wrote:
> Setting custom baudrate for which is not defined Bnnn constant is possible
> via BOTHER flag and then filling speed in c_ospeed and c_ispeed fields.
> 
> These two fields are either in struct termios or struct termios2. Former
> belongs to TCGETS/TCSETS ioctls, latter to TCGETS2/TCSETS2 ioctls.
> 
> BOTHER flag with these two fields and new struct termios2 is not supported
> by older versions of include header files.
> 
> 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).
> 
> Setting input baudrate is done via IBSHIFT macro.
> 
> Signed-off-by: Pali Rohár <pali@kernel.org>

Hello! Do you have any comments on this patch?

> ---
> Changes in v4:
> * Add SPDX-License-Identifier
> * Correctly process split baudrates (separate output and input) via IBSHIFT
> * Update commit message
> 
> 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
> ---
>  man2/ioctl_tty.2 | 100 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 100 insertions(+)
> 
> diff --git a/man2/ioctl_tty.2 b/man2/ioctl_tty.2
> index abfdc1e21fe9..7b2b03ff6757 100644
> --- a/man2/ioctl_tty.2
> +++ b/man2/ioctl_tty.2
> @@ -796,6 +796,106 @@ main(void)
>      close(fd);
>  }
>  .EE
> +.PP
> +Get or set arbitrary baudrate on the serial port.
> +.PP
> +.EX
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
> +#include <asm/termbits.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/ioctl.h>
> +#include <sys/types.h>
> +#include <unistd.h>
> +
> +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
> +    /* Declare tio structure, its type depends on supported ioctl */
> +#ifdef TCGETS2
> +    struct termios2 tio;
> +#else
> +    struct termios tio;
> +#endif
> +    int fd, rc;
> +
> +    if (argc != 2 && argc != 3 && argc != 4) {
> +        fprintf(stderr, "Usage: %s device [output [input] ]\en", argv[0]);
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY);
> +    if (fd < 0) {
> +        perror("open");
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    /* Get the current serial port settings via supported ioctl */
> +#ifdef TCGETS2
> +    rc = ioctl(fd, TCGETS2, &tio);
> +#else
> +    rc = ioctl(fd, TCGETS, &tio);
> +#endif
> +    if (rc) {
> +        perror("TCGETS");
> +        close(fd);
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    /* Change baud rate when more arguments were provided */
> +    if (argc == 3 || argc == 4) {
> +        /* Clear the current output baud rate and fill a new value */
> +        tio.c_cflag &= ~CBAUD;
> +        tio.c_cflag |= BOTHER;
> +        tio.c_ospeed = atoi(argv[2]);
> +
> +        /* Clear the current input baud rate and fill a new value */
> +        tio.c_cflag &= ~(CBAUD << IBSHIFT);
> +        tio.c_cflag |= BOTHER << IBSHIFT;
> +        /* When 4th argument is not provided reuse output baud rate */
> +        tio.c_ispeed = (argc == 4) ? atoi(argv[3]) : atoi(argv[2]);
> +
> +        /* Set new serial port settings via supported ioctl */
> +#ifdef TCSETS2
> +        rc = ioctl(fd, TCSETS2, &tio);
> +#else
> +        rc = ioctl(fd, TCSETS, &tio);
> +#endif
> +        if (rc) {
> +            perror("TCSETS");
> +            close(fd);
> +            exit(EXIT_FAILURE);
> +        }
> +
> +        /* And get new values which were really configured */
> +#ifdef TCGETS2
> +        rc = ioctl(fd, TCGETS2, &tio);
> +#else
> +        rc = ioctl(fd, TCGETS, &tio);
> +#endif
> +        if (rc) {
> +            perror("TCGETS");
> +            close(fd);
> +            exit(EXIT_FAILURE);
> +        }
> +    }
> +
> +    close(fd);
> +
> +    printf("output baud rate: %u\en", tio.c_ospeed);
> +    printf("input baud rate: %u\en", tio.c_ispeed);
> +
> +    exit(EXIT_SUCCESS);
> +#endif
> +}
> +.EE
>  .SH SEE ALSO
>  .BR ldattach (1),
>  .BR ioctl (2),
> -- 
> 2.20.1
> 
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