relay.c

linux源码

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>

#define BUFSIZE 32

int
relay(int fd1, int fd2)
{
	int r1, w2, r2, w1;
	int ret;
	int fd1save, fd2save;
	char buf12[BUFSIZE], buf21[BUFSIZE];
	int len12, pos12, len21, pos21;

	fd1save=fcntl(fd1, F_GETFL);
	ret=fcntl(fd1, F_SETFL, fd1save|O_NONBLOCK);
	if (ret==-1) {
		return -1;
	}
	fd2save=fcntl(fd2, F_GETFL);
	ret=fcntl(fd2, F_SETFL, fd2save|O_NONBLOCK);
	if (ret==-1) {
		fcntl(fd1, F_SETFL, fd1save);
		return -1;
	}

	r1=1; w2=0; r2=1; w1=0;
	while (r1+w2+r2+w1) {
		if (r1) {
			len12=read(fd1, buf12, BUFSIZE);
			pos12=0;
			if (len12==-1) {
				if (errno!=EAGAIN) {
					r1=0; w2=0;
				}
			} else if (len12==0) {
				r1=0; w2=0;
			} else {
				r1=0; w2=1;
			}
		}

		if (w2) {
			ret=write(fd2, buf12+pos12, len12);
			if (ret==-1) {
				if (errno!=EAGAIN) {
					r1=0; w2=0;
				}
			} else {
				pos12+=ret;
				len12-=ret;
				if (len12==0) {
					r1=1; w2=0;
				}
			}
		}
		if (r2) {
			len21=read(fd2, buf21, BUFSIZE);
			pos21=0;
			if (len21==-1) {
				if (errno!=EAGAIN) {
					r2=0; w1=0;
				}
			} else if (len21==0) {
				r2=0; w1=0;
			} else {
				r2=0; w1=1;
			}
		}

		if (w1) {
			ret=write(fd1, buf21+pos21, len21);
			if (ret==-1) {
				if (errno!=EAGAIN) {
					r2=0; w1=0;
				}
			} else {
				pos21+=ret;
				len21-=ret;
				if (len21==0) {
					r2=1; w1=0;
				}
			}
		}
		usleep(1);
	}

	fcntl(fd1, F_SETFL, fd1save);
	fcntl(fd2, F_SETFL, fd2save);

	return 0;
}

int
main()
{
	int ret;
	int fd1, fd2;

	fd1=open("/dev/tty5", O_RDWR);
	if (fd1==-1) {
		perror("open()");
		exit(1);
	}
	fd2=open("/dev/tty6", O_RDWR);
	if (fd2==-1) {
		perror("open()");
		exit(1);
	}

	write(fd1, "fd1\n", 4);
	write(fd2, "fd2\n", 4);
	ret=relay(fd1, fd2);

	close(fd1);
	close(fd2);

	exit(0);
}