Including <termios.h> and <asm/termios.h> in the same project

Question

What I want to achieve: I want to set custom baud rate values for some tty*-like UART-mapped terminals.

How: The only way I found by far is to use the struct termios2 structure which is located in<asm/termios> header (as mentioned here, first answer).

My solution works very well by far, but now I need to use some functions:

speed_t cfgetispeed(const struct termios *);
int     tcdrain(int);
int     tcflow(int, int);
int     tcflush(int, int);
int     tcgetattr(int, struct termios *);
pid_t   tcgetsid(int);
int     tcsendbreak(int, int);
int     tcsetattr(int, int, struct termios *);

The problem is that in <asm/termios.h> there are no such functions, and I need to include <termios.h> for being able to use them.

Problem: If I include both headers (<asm/termios.h> and <termios.h>) the compiler will scream about functions and structure re-declaration, and he's right.

How can I solve this without using some obscure practice (like wrapping one of headers in a namespace, like mentioned here)?

Answer 1

How can I solve this without using some obscure practice (like wrapping one of headers in a namespace, like mentioned here)?

If you find namespaces obscure, I don't know how you'd call this:

#define termios asmtermios
#include <asm/termios.h>
#undef  termios
#include <termios.h>

Anyway, this too gets you rid of the error: redefinition of 'struct termios'.

Answer 2

I had a similar issue - wanted custom baud rate support with definitions like termios2, TCGETS2 and BOTHER, while still making use of the traditional termios calls. I instinctively wrapped the termios2 stuff in its own compilation unit and had no problems. So my structure looks like this:

serial_driver.c/.h

#include <termios.h>
#include <fcntl.h>
#include <dirent.h>

int open_port(int fd, int baudrate, eParitySetting parity, int numStopBits)
{
  if(baudrate_is_non_standard(baudrate)
    setNonStandardBaudRateTermios(fd, baudrate, parity, numStopBits);
  else
    //all the normal tcgetattr/cfsetospeed/tcsetattr
}

int do_other_things(void)
{
  //all the normal tcsendbreak/tcflush/etc things
}

serial_driver_abr.c/.h

#include <asm/termios.h> /* asm gives us the all important BOTHER and TCGETS2 */
#include <fcntl.h>
#include <dirent.h>
#include <stropts.h> /* Oddly, for ioctl, because ioctl.h causes include dramas */

setNonStandardBaudRateTermios(int fd, int baudrate, eParitySetting parity, int numStopBits)
{
  //All the termios2/ioctl/TCGETS2/BOTHER things
}

Works well for me.

Answer 3

I hit the same problem with an old arm cross compiler, but found the latest one, gcc-arm-10.2-2020.11-x86_64-arm-none-linux-gnueabihf, solved the problem with a different header file. Here is my code:

[uart_config.c]
#include <asm/termbits.h>
#include <sys/ioctl.h>

/* functions */
int uart_config_baudrate(int fd)
{
    struct termios2 tio;

    ioctl(fd, TCGETS2, &tio);
    tio.c_cflag &= ~CBAUD;
    tio.c_cflag |= BOTHER;
    tio.c_ispeed = MY_SPECIAL_BAUDRATE_NUMBER;
    tio.c_ospeed = MY_SPECIAL_BAUDRATE_NUMBER;
    return ioctl(fd, TCSETS2, &tio);
}

[main.c]
static int init_uart(void)
{
    struct termios tp;
    int rc;

    memset(&tp, 0, sizeof(tp));
    tp.c_cflag = MY_SPECIAL_BAUDRATE | CS8 | CLOCAL | CREAD | PARENB | PARODD;
    tp.c_iflag = IGNPAR;
    tp.c_oflag = 0;

    tp.c_lflag = 0;     /* set input mode to non-canonical */

    tp.c_cc[VTIME] = 0; /* inter-character timer unused */
    tp.c_cc[VMIN] = 1;  /* blocking read until 5 chars received */

    tcflush(fd, TCIFLUSH);
    rc = tcsetattr(fd, TCSANOW, &tp);

    return rc;
}

int main()
{
    int fd;

    fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY);
    init_uart(fd);  // add your error handling
    uart_config_baudrate(fd); // add your error handling
    ...
}