Use non-blocking mode a little better by repeatedly trying to send data out to

the clients until at least one write worked and no error (other than EAGAIN)
occurred when writing to any of the clients. This way, complete data loss can
be avoided since at least one client must get all of the data.

Also make sure that stdin/stdout/stderr point to /dev/null instead of just
closing them, to avoid confusion.

master.c

@@ -82,6 +82,28 @@ die(int sig)
 	exit(1);
 }
 
+/* Sets a file descriptor to non-blocking mode. */
+static int
+setnonblocking(int fd)
+{
+	int flags;
+
+#if defined(O_NONBLOCK)
+	flags = fcntl(fd, F_GETFL);
+	if (flags < 0 || fcntl(fd, F_SETFL, flags | O_NONBLOCK) < 0)
+		return -1;
+	return 0;
+#elif defined(FIONBIO)
+	flags = 1;
+	if (ioctl(fd, FIONBIO, &flags) < 0)
+		return -1;
+	return 0;
+#else
+#warning Do not know how to set non-blocking mode.
+	return 0;
+#endif
+}
+
 /* Initialize the pty structure. */
 static int
 init_pty(char **argv)
@@ -113,116 +135,6 @@ init_pty(char **argv)
 	return 0;
 }
 
-/* Creates a new unix domain socket. */
-static int
-create_socket(char *name)
-{
-	int s;
-	struct sockaddr_un sockun;
-
-	s = socket(PF_UNIX, SOCK_STREAM, 0);
-	if (s < 0)
-		return -1;
-	sockun.sun_family = AF_UNIX;
-	strcpy(sockun.sun_path, name);
-	if (bind(s, (struct sockaddr*)&sockun, sizeof(sockun)) < 0)
-	{
-		close(s);
-		return -1;
-	}
-	if (listen(s, 128) < 0)
-	{
-		close(s);
-		return -1;
-	}
-	/* chmod it to prevent any suprises */
-	if (chmod(name, 0600) < 0)
-	{
-		close(s);
-		return -1;
-	}
-	return s;
-}
-
-/* Sets a file descriptor to non-blocking mode. */
-static int
-setnonblocking(int fd)
-{
-	int flags;
-
-#if defined(O_NONBLOCK)
-	flags = fcntl(fd, F_GETFL);
-	if (flags < 0 || fcntl(fd, F_SETFL, flags | O_NONBLOCK) < 0)
-		return -1;
-	return 0;
-#elif defined(FIONBIO)
-	flags = 1;
-	if (ioctl(fd, FIONBIO, &flags) < 0)
-		return -1;
-	return 0;
-#else
-#warning Do not know how to set non-blocking mode.
-	return 0;
-#endif
-}
-
-/* Process activity on the pty - Input and terminal changes are sent out to
-** the attached clients. If the pty goes away, we die. */
-static void
-pty_activity()
-{
-	unsigned char buf[BUFSIZE];
-	struct client *p;
-	int len;
-
-	/* Read the pty activity */
-	len = read(the_pty.fd, buf, sizeof(buf));
-
-	/* Error -> die */
-	if (len <= 0)
-		exit(1);
-
-#ifdef BROKEN_MASTER
-	/* Get the current terminal settings. */
-	if (tcgetattr(the_pty.slave, &the_pty.term) < 0)
-		exit(1);
-#else
-	/* Get the current terminal settings. */
-	if (tcgetattr(the_pty.fd, &the_pty.term) < 0)
-		exit(1);
-#endif
-
-	/* Send it out to the clients. */
-	for (p = clients; p; p = p->next)
-	{
-		if (p->attached)
-			write(p->fd, buf, len);
-	}
-}
-
-/* Process activity on the control socket */
-static void
-control_activity(int s)
-{
-	int fd;
-	struct client *p;
- 
-	/* Accept the new client and link it in. */
-	fd = accept(s, NULL, NULL);
-	if (fd < 0 || setnonblocking(fd) < 0)
-		return;
-
-	/* Link it in. */
-	p = malloc(sizeof(struct client));
-	p->fd = fd;
-	p->attached = 0;
-	p->pprev = &clients;
-	p->next = *(p->pprev);
-	if (p->next)
-		p->next->pprev = &p->next;
-	*(p->pprev) = p;
-}
-
 /* Send a signal to the slave side of a pseudo-terminal. */
 static void
 killpty(struct pty *pty, int sig)
@@ -252,6 +164,154 @@ killpty(struct pty *pty, int sig)
 	kill(-pty->pid, sig);
 }
 
+/* Creates a new unix domain socket. */
+static int
+create_socket(char *name)
+{
+	int s;
+	struct sockaddr_un sockun;
+
+	s = socket(PF_UNIX, SOCK_STREAM, 0);
+	if (s < 0)
+		return -1;
+	sockun.sun_family = AF_UNIX;
+	strcpy(sockun.sun_path, name);
+	if (bind(s, (struct sockaddr*)&sockun, sizeof(sockun)) < 0)
+	{
+		close(s);
+		return -1;
+	}
+	if (listen(s, 128) < 0)
+	{
+		close(s);
+		return -1;
+	}
+	if (setnonblocking(s) < 0)
+	{
+		close(s);
+		return -1;
+	}
+	/* chmod it to prevent any suprises */
+	if (chmod(name, 0600) < 0)
+	{
+		close(s);
+		return -1;
+	}
+	return s;
+}
+
+/* Process activity on the pty - Input and terminal changes are sent out to
+** the attached clients. If the pty goes away, we die. */
+static void
+pty_activity(int s)
+{
+	unsigned char buf[BUFSIZE];
+	int len;
+	struct client *p;
+	fd_set readfds, writefds;
+	int highest_fd, nclients;
+
+	/* Read the pty activity */
+	len = read(the_pty.fd, buf, sizeof(buf));
+
+	/* Error -> die */
+	if (len <= 0)
+		exit(1);
+
+#ifdef BROKEN_MASTER
+	/* Get the current terminal settings. */
+	if (tcgetattr(the_pty.slave, &the_pty.term) < 0)
+		exit(1);
+#else
+	/* Get the current terminal settings. */
+	if (tcgetattr(the_pty.fd, &the_pty.term) < 0)
+		exit(1);
+#endif
+
+top:
+	/*
+	** Wait until at least one client is writable. Also wait on the control
+	** socket in case a new client tries to connect.
+	*/
+	FD_ZERO(&readfds);
+	FD_ZERO(&writefds);
+	FD_SET(s, &readfds);
+	highest_fd = s;
+	for (p = clients, nclients = 0; p; p = p->next)
+	{
+		if (!p->attached)
+			continue;
+		FD_SET(p->fd, &writefds);
+		if (p->fd > highest_fd)
+			highest_fd = p->fd;
+		nclients++;
+	}
+	if (nclients == 0)
+		return;
+	if (select(highest_fd + 1, &readfds, &writefds, NULL, NULL) < 0)
+		return;
+
+	/* Send the data out to the clients. */
+	for (p = clients, nclients = 0; p; p = p->next)
+	{
+		int written;
+
+		if (!FD_ISSET(p->fd, &writefds))
+			continue;
+
+		written = 0;
+		while (written < len)
+		{
+			int n = write(p->fd, buf + written, len - written);
+
+			if (n > 0)
+			{
+				written += n;
+				continue;
+			}
+			else if (n < 0 && errno == EINTR)
+				continue;
+			else if (n < 0 && errno != EAGAIN)
+				nclients = -1;
+			break;
+		}
+		if (nclients != -1 && written == len)
+			nclients++;
+	}
+
+	/* Try again if nothing happened. */
+	if (!FD_ISSET(s, &readfds) && nclients == 0)
+		goto top;
+}
+
+/* Process activity on the control socket */
+static void
+control_activity(int s)
+{
+	int fd;
+	struct client *p;
+ 
+	/* Accept the new client and link it in. */
+	fd = accept(s, NULL, NULL);
+	if (fd < 0)
+		return;
+	else if (setnonblocking(fd) < 0)
+	{
+		close(fd);
+		return;
+	}
+
+	/* Link it in. */
+	p = malloc(sizeof(struct client));
+	p->fd = fd;
+	p->attached = 0;
+	p->pprev = &clients;
+	p->next = *(p->pprev);
+	if (p->next)
+		p->next->pprev = &p->next;
+	*(p->pprev) = p;
+}
+
 /* Process activity from a client. */
 static void
 client_activity(struct client *p)
@@ -261,6 +321,9 @@ client_activity(struct client *p)
 
 	/* Read the activity. */
 	len = read(p->fd, &pkt, sizeof(struct packet));
+	if (len < 0 && (errno == EAGAIN || errno == EINTR))
+		return;
+
 	/* Close the client on an error. */
 	if (len <= 0)
 	{
@@ -333,6 +396,7 @@ master_process(int s, char **argv)
 	struct client *p, *next;
 	fd_set readfds;
 	int highest_fd;
+	int nullfd;
 
 	/* Okay, disassociate ourselves from the original terminal, as we
 	** don't care what happens to it. */
@@ -355,10 +419,14 @@ master_process(int s, char **argv)
 	signal(SIGTERM, die);
 	signal(SIGCHLD, die);
 
-	/* Close the original terminal. We are now a daemon. */
+	/* Make sure stdin/stdout/stderr point to /dev/null. We are now a
-	fclose(stdin);
+	** daemon. */
-	fclose(stdout);
+	nullfd = open("/dev/null", O_RDWR);
-	fclose(stderr);
+	dup2(nullfd, 0);
+	dup2(nullfd, 1);
+	dup2(nullfd, 2);
+	if (nullfd > 2)
+		close(nullfd);
 
 	/* Set a trap to unlink the socket when we die. */
 	atexit(unlink_socket);
@@ -390,7 +458,7 @@ master_process(int s, char **argv)
 		}	
 		/* pty activity? */
 		if (FD_ISSET(the_pty.fd, &readfds))
-			pty_activity(&the_pty);
+			pty_activity(s);
 		/* New client? */
 		if (FD_ISSET(s, &readfds))
 			control_activity(s);