tcgetsid.c\termios\src - musl - musl - an implementation of the standard library for Linux-based systems

#include <termios.h>
#include <sys/ioctl.h>
pid_t tcgetsid(int fd)
{
	int sid;
	if (ioctl(fd, TIOCGSID, &sid) < 0)
		return -1;
	return sid;
}