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From: Rich Felker <dalias@libc.org>
Newsgroups: gmane.linux.lib.musl.general
Subject: Re: Add login_tty
Date: Sat, 20 Dec 2014 21:59:07 -0500
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On Sat, Dec 20, 2014 at 08:38:58PM -0500, Rich Felker wrote:
> I've got a draft based on these comments that I'll post soon for
> review.

Here's the draft. While I was at it I added protection against
cancellation. openpty should have this too but I'll do that
separately.

Rich

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#include <pty.h>
#include <utmp.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <pthread.h>

int forkpty(int *pm, char *name, const struct termios *tio, const struct winsize *ws)
{
	int m, s, ec=0, p[2], cs;
	pid_t pid=-1;
	sigset_t set, oldset;

	if (openpty(&m, &s, name, tio, ws) < 0) return -1;

	sigfillset(&set);
	pthread_sigmask(SIG_BLOCK, &set, &oldset);
	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);

	if (pipe2(p, O_CLOEXEC)) {
		close(s);
		goto out;
	}

	pid = fork();
	if (!pid) {
		close(m);
		close(p[0]);
		if (login_tty(s)) {
			write(p[1], &errno, sizeof errno);
			_exit(127);
		}
		close(p[1]);
		pthread_setcancelstate(cs, 0);
		pthread_sigmask(SIG_SETMASK, &oldset, 0);
		return 0;
	}
	close(s);
	close(p[1]);
	if (read(p[0], &ec, sizeof ec) > 0) {
		int status;
		waitpid(pid, &status, 0);
		pid = -1;
		errno = ec;
	}
	close(p[0]);

out:
	if (pid > 0) *pm = m;
	else close(m);

	pthread_setcancelstate(cs, 0);
	pthread_sigmask(SIG_SETMASK, &oldset, 0);

	return pid;
}

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