tty: stop spamming VEOF on raw terminals

There is no point in sending VEOF on PTYs that aren't interpreting them.

Simply hanging up and letting the session get killed with SIGHUP is the right
thing to do.

tty.c

@@ -125,6 +125,12 @@ static int send_veof(int ptm)
 		err(1, "send_veof: tcgetattr");
 	}
 
+	/* The terminal is is noncanonical mode; VEOF won't be interpreted. */
+	if (!(tios.c_lflag & ICANON)) {
+		errno = ENOTSUP;
+		return -1;
+	}
+
 	return write(ptm, &tios.c_cc[VEOF], 1);
 }
 
@@ -180,6 +186,11 @@ static struct buffer inbound_buffer, outbound_buffer;
 
 static int tty_handle_io(int epollfd, const struct epoll_event *ev, int fd, pid_t pid)
 {
+	/* The terminal got closed -- don't try to handle I/O any further */
+	if (info.termfd == -1) {
+		return EPOLL_HANDLER_CONTINUE;
+	}
+
 	struct epoll_handler *handler = ev->data.ptr;
 
 	if (fd == inbound_handler.fd) {
@@ -232,7 +243,12 @@ static int tty_handle_io(int epollfd, const struct epoll_event *ev, int fd, pid_
 			err(1, "epoll_ctl_mod stdin");
 		}
 	} else if ((inbound_handler.ready & (WRITE_READY | HANGUP)) == (WRITE_READY | HANGUP)) {
+		inbound_handler.ready &= ~HANGUP;
+
 		if (send_veof(inbound_handler.peer_fd) == -1) {
+			if (errno == ENOTSUP) {
+				goto hangup;
+			}
 			err(1, "send_eof: write");
 		}
 
@@ -242,15 +258,16 @@ static int tty_handle_io(int epollfd, const struct epoll_event *ev, int fd, pid_
 		   EOF. */
 		if (send_veof(inbound_handler.peer_fd) == -1) {
 			switch (errno) {
+			case ENOTSUP:
+				goto hangup;
 			case EAGAIN:
 				/* The pty device isn't ready for a second VEOF -- that's fine,
-				   we'll just send it later */
+				   we'll just send it later, so re-set the hangup flag */
+				inbound_handler.ready |= HANGUP;
 				break;
 			default:
 				err(1, "send_eof: write");
 			}
-		} else {
-			inbound_handler.ready &= ~HANGUP;
 		}
 	}
 
@@ -292,6 +309,11 @@ static int tty_handle_io(int epollfd, const struct epoll_event *ev, int fd, pid_
 	}
 
 	return EPOLL_HANDLER_CONTINUE;
+
+hangup:
+	close(info.termfd);
+	info.termfd = -1;
+	return EPOLL_HANDLER_CONTINUE;
 }
 
 void tty_parent_setup(struct tty_opts *opts, int epollfd, int socket)