qemu-io: fix EOF Ctrl-D handling in qemu-io readline code

qemu-io puts the TTY into non-canonical mode, which means no EOF processing is
done and thus getchar() will never return the EOF constant. Instead we have to
query the TTY attributes to determine the configured EOF character (usually
Ctrl-D / 0x4), and then explicitly check for that value. This fixes the
regression that prevented Ctrl-D from triggering an exit of qemu-io that has
existed since readline was first added in

  commit 0cf17e1817
  Author: Stefan Hajnoczi <stefanha@redhat.com>
  Date:   Thu Nov 14 11:54:17 2013 +0100

    qemu-io: use readline.c

It also ensures that a newline is printed when exiting, to complete the
line output by the "qemu-io> " prompt.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

qemu-io.c

@@ -11,6 +11,9 @@
 #include "qemu/osdep.h"
 #include <getopt.h>
 #include <libgen.h>
+#ifndef _WIN32
+#include <termios.h>
+#endif
 
 #include "qapi/error.h"
 #include "qemu-io.h"
@@ -42,6 +45,26 @@ static bool imageOpts;
 
 static ReadLineState *readline_state;
 
+static int ttyEOF;
+
+static int get_eof_char(void)
+{
+#ifdef _WIN32
+    return 0x4; /* Ctrl-D */
+#else
+    struct termios tty;
+    if (tcgetattr(STDIN_FILENO, &tty) != 0) {
+        if (errno == ENOTTY) {
+            return 0x0; /* just expect read() == 0 */
+        } else {
+            return 0x4; /* Ctrl-D */
+        }
+    }
+
+    return tty.c_cc[VEOF];
+#endif
+}
+
 static int close_f(BlockBackend *blk, int argc, char **argv)
 {
     blk_unref(qemuio_blk);
@@ -323,7 +346,8 @@ static char *fetchline_readline(void)
     readline_start(readline_state, get_prompt(), 0, readline_func, &line);
     while (!line) {
         int ch = getchar();
-        if (ch == EOF) {
+        if (ttyEOF != 0x0 && ch == ttyEOF) {
+            printf("\n");
             break;
         }
         readline_handle_byte(readline_state, ch);
@@ -593,6 +617,7 @@ int main(int argc, char **argv)
     qemuio_add_command(&close_cmd);
 
     if (isatty(STDIN_FILENO)) {
+        ttyEOF = get_eof_char();
         readline_state = readline_init(readline_printf_func,
                                        readline_flush_func,
                                        NULL,