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From: Rich Felker <dalias@libc.org>
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Subject: Re: Add login_tty
Date: Sat, 20 Dec 2014 19:58:21 -0500
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On Mon, Nov 03, 2014 at 07:29:54PM +0100, Felix Janda wrote:
> Thanks for the review. Below a new version.

Sorry I didn't get around to reviewing this right away.

> #include <pty.h>
> #include <utmp.h>
> #include <unistd.h>
> 
> int forkpty(int *m, char *name, const struct termios *tio, const struct winsize *ws)
> {
> 	int s, ec, p[2];
> 	pid_t pid;
> 
> 	if (openpty(m, &s, name, tio, ws) < 0) return -1;
> 	if (pipe2(p, O_CLOEXEC)) {
> 		close(s);
> 		goto fail;
> 	}
> 
> 	pid = fork();
> 	if (!pid) {
> 		close(*m);
> 		close(p[0]);
> 		ec = login_tty(s);

login_tty could end up closing the pipe if stdin/out/err were
initially closed in the parent, since p[1] might be 0/1/2 in that
case. I think we need to check for this and move p[1] to a new fd in
that case (and fail if that fails) before calling login_tty.

> 		while (write(p[1], &ec, sizeof ec) < 0);
> 		if (ec) _exit(127);
> 		close(p[1]);
> 		return 0;
> 	}
> 	close(s);
> 	close(p[1]);
> 	if (pid > 0) read(p[0], &ec, sizeof ec);

This read probably needs to retry-loop, in case the parent has
interrupting signal handlers.

> 	close(p[0]);
> 	if (pid > 0) {
> 		if (!ec) return pid;
> 		waitpid(pid, &(int){0}, 0);

I think waitpid could in principle fail too, but it probably shouldn't
since the process is already dead at the time waitpid is called.

> 	}
> fail:
> 	close(*m);
> 	return -1;
> }

Otherwise it looks okay now.

Rich