On Sun, Jul 21, 2024 at 02:52:31PM +0300, stsp wrote:
> Hi!
>
> I've noticed that one of my progs failed
> to work with serial ports. To distinguish
> between real serial ports and PTS nodes,
> it tried TIOCMBIC, checking errno for EINVAL.
>
> Obviously that behaviour was changed
> and now ENOTTY is returned. Besides
> being backward-incompatible, I think this
> is also wrong because isatty() returns 1
> on such FDs.
>
> Here's the test-case:
> socat PTY,link=/tmp/ttyS20,raw,echo=0,b9600
> PTY,link=/tmp/ttyS21,raw,echo=0,b9600
>
> Then run this program:
>
> #include <stdio.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <errno.h>
> #include <sys/ioctl.h>
> #include <unistd.h>
>
> int main() {
> int fd, err;
> int data = TIOCM_DTR | TIOCM_RTS;
> fd = open("/tmp/ttyS20", O_NONBLOCK);
> if (fd == -1) {
> perror("open()");
> return 1;
> }
> err = ioctl(fd, TIOCMBIC, &data);
> if (err && errno == ENOTTY && isatty(fd))
> printf("Test FAILED: ENOTTY for tty fd\n");
> return 0;
> }
>
>
What caused this change/regression? And does any real-world programs
rely on this? What exactly are you trying to determine with this ioctl
test? Is there a different way to determine that?
thanks,
greg k-h
