Handle Ctrl-a x sequence to exit

Originally, the guest will be terminated when ctrl-c is pressed. This
causes the guest to exit unexpectedly.

This change addresses this issue by removing ISIG flag in c_lflag in termios
and adds a key sequence ctrl-a x to terminate the guest.

Close #25

Author: yanjiew1

README.md

@@ -42,6 +42,8 @@ containing concatenated `bootsect.o + setup.o + misc.o + piggy.o`. `initrd` is t
 initial RAM disk image, which is an optional argument.
 `disk-image` is the path to disk image which can be mounted as a block device via virtio. For the reference Linux guest, ext4 filesystem is used for disk image.
 
+To exit kvm-host, press "Ctrl-A", release both keys, and then press "x".
+
 ## License
 
 `kvm-host` is released under the BSD 2 clause license. Use of this source code is governed by

src/main.c

@@ -42,7 +42,7 @@ static void set_input_mode(void)
     atexit(reset_input_mode);
 
     tattr = saved_attributes;
-    tattr.c_lflag &= ~(ICANON | ECHO);
+    tattr.c_lflag &= ~(ICANON | ECHO | ISIG);
     tcsetattr(STDIN_FILENO, TCSANOW, &tattr);
 }
 

src/serial.c

@@ -97,14 +97,28 @@ static void *serial_thread(serial_dev_t *s)
     return NULL;
 }
 
+#define TERMINAL_ESCAPE_CHAR 0x01
+#define TERMINAL_EXIT_CHAR 'x'
+
 void serial_console(serial_dev_t *s)
 {
     struct serial_dev_priv *priv = (struct serial_dev_priv *) s->priv;
+    static bool escaped = false;
 
     while (!fifo_is_full(&priv->rx_buf) && serial_readable(s, 0)) {
         char c;
         if (read(s->infd, &c, 1) == -1)
             break;
+        if (escaped && c == TERMINAL_EXIT_CHAR) {
+            /* Terminate */
+            fprintf(stderr, "\n");
+            exit(0);
+        }
+        if (!escaped && c == TERMINAL_ESCAPE_CHAR) {
+            escaped = true;
+            continue;
+        }
+        escaped = false;
         if (!fifo_put(&priv->rx_buf, c))
             break;
         __atomic_store_n(&priv->lsr, priv->lsr | UART_LSR_DR, __ATOMIC_RELEASE);