forkpty with streams

[Andrew Barton <andrevv@users.sourceforge.net>]

I've got the 2.4 kernel, and I'm trying to use the forkpty() system call
with the standard I/O stream functions. The calls to forkpty() and
fdopen() and fprintf() all return successfully, but the data never seems
to get to the child process. In this simplified example, I am trying to
open a shell in a pseudo terminal and then send it the string "exit\n"
and then wait for it to die. But the shell apparently never sees the
"exit\n", and the parent waits forever.

#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>

main()
{
	int fd;
	pid_t pid;

	pid = forkpty (&fd, 0, 0, 0);
	if (pid == 0) {
		execlp ("sh", "sh", (void *)0);
		_exit (1);
	} else if (pid == -1) {
		return 1;
	} else {
		FILE *F;

		F = fdopen (fd, "w");
		fprintf (F, "exit\n");
		fflush (F);
		wait (0);
	}
	return 0;
}