LD_PRELOAD program used to prevent terminals from being write-protected by foreground process.

droptostop.c

/* This file has no copyright assigned and is placed in the Public Domain.
 * No warranty is given.
 */

#include <termios.h>
#include <dlfcn.h>
#include <stdlib.h>
#include <stdio.h>

#ifndef LIBC_PATH
// Use SysV path by default
#define LIBC_PATH "/usr/lib/libc.so.1"
#ifndef __SVR4
#warning "You may need to define macro LIBC_PATH"
#endif
#endif

static void *get_libc() {
	static void *libc;
	if(!libc) libc = dlopen(LIBC_PATH, RTLD_LAZY);
	return libc;
}

static int (*get_libc_tcsetattr())(int, int, const struct termios *) {
	static int (*f)(int, int, const struct termios *);
	if(f) return f;
	void *libc = get_libc();
	if(!libc) {
		perror("dlopen");
		abort();
	}
	*(void **)&f = dlsym(libc, "tcsetattr");
	if(!f) {
		perror("dlsym: tcsetattr");
		abort();
	}
	return f;
}

int tcsetattr(int fd, int action, const struct termios *attr) {
	if(attr->c_lflag & TOSTOP) {
		struct termios new_attr = *attr;
		new_attr.c_lflag &= ~TOSTOP;
		return get_libc_tcsetattr()(fd, action, &new_attr);
	}
	return get_libc_tcsetattr()(fd, action, attr);
}