slcanpty: Improve the reading from pty to avoid incomplete messages in the reading buf[]

index f3628b9..037edf5 100644
@@ -31,6 +31,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <termios.h>
+#include <poll.h>
 
 #include <net/if.h>
 #include <sys/socket.h>

@@ -74,12 +75,41 @@ int pty2can(int pty, int socket, struct can_filter *fi,
 	struct can_frame frame;
 	int tmp, i;
 
-	nbytes = read(pty, &buf, sizeof(buf)-1);
+	nbytes = read(pty, &buf, sizeof(buf)-SLC_MTU-1);
 	if (nbytes < 0) {
 		perror("read pty");
 		return 1;
 	}
 
+	if (nbytes == sizeof(buf)-SLC_MTU-1) {
+		struct pollfd fds;
+		fds.fd = pty;
+		fds.events = POLLIN;
+
+		while (buf[nbytes-1] != '\r' && nbytes < (sizeof(buf)-1)) {
+			tmp = poll(&fds, 1, 0);
+			if (tmp < 0) {
+				perror("poll pty");
+				return 1;
+			}
+
+			if (fds.revents & POLLIN) {
+				tmp = read(pty, &buf[nbytes++], 1);
+				if (tmp < 0) {
+					perror("read pty");
+					return 1;
+				}
+			} else {
+				/* No further Data available */
+				break;
+			}
+		}
+	}
+
+#ifdef DEBUG
+	printf("read %d bytes from pty\n",nbytes);
+#endif
+
 rx_restart:
 	/* remove trailing '\r' characters to be robust against some apps */
 	while (buf[0] == '\r' && nbytes > 0) {