Make tip exit if the device disappears, for instance when unplugging

or resetting USB serial devices.

Somebody[tm] should rewrite tip(1) to use two thread instead of two
processes or maybe even use that new-fangled "select(2)" or positively
futuristic "poll(2)" system call.

usr.bin/tip/tip/tip.c

@@ -584,7 +584,7 @@ parwrite(int fd, char *buf, size_t n)
 			bp++;
 		}
 	if (write(fd, buf, n) < 0) {
-		if (errno == EIO)
+		if (errno == EIO || errno == ENXIO)
 			tipabort("Lost carrier.");
 		/* this is questionable */
 		perror("write");

usr.bin/tip/tip/tipout.c

@@ -148,11 +148,12 @@ tipout(void)
 		scnt = read(FD, buf, BUFSIZ);
 		if (scnt <= 0) {
 			/* lost carrier */
-			if (scnt == 0 || (scnt < 0 && errno == EIO)) {
+			if (scnt == 0 ||
+			    (scnt < 0 && (errno == EIO || errno == ENXIO))) {
 				sigemptyset(&mask);
 				sigaddset(&mask, SIGTERM);
 				sigprocmask(SIG_BLOCK, &mask, NULL);
-				intTERM(0);
+				intTERM(SIGHUP);
 				/*NOTREACHED*/
 			}
 			continue;