vnc: reorganize code for reverse mode

Avoid the dance between csock and vs->lsock.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

console.h

@@ -378,7 +378,7 @@ void cocoa_display_init(DisplayState *ds, int full_screen);
 /* vnc.c */
 void vnc_display_init(DisplayState *ds);
 void vnc_display_close(DisplayState *ds);
-int vnc_display_open(DisplayState *ds, const char *display);
+void vnc_display_open(DisplayState *ds, const char *display, Error **errp);
 void vnc_display_add_client(DisplayState *ds, int csock, int skipauth);
 int vnc_display_disable_login(DisplayState *ds);
 char *vnc_display_local_addr(DisplayState *ds);

qmp.c

@@ -349,11 +349,9 @@ void qmp_change_vnc_password(const char *password, Error **errp)
     }
 }
 
-static void qmp_change_vnc_listen(const char *target, Error **err)
+static void qmp_change_vnc_listen(const char *target, Error **errp)
 {
-    if (vnc_display_open(NULL, target) < 0) {
-        error_set(err, QERR_VNC_SERVER_FAILED, target);
-    }
+    vnc_display_open(NULL, target, errp);
 }
 
 static void qmp_change_vnc(const char *target, bool has_arg, const char *arg,

ui/vnc.c

@@ -3053,19 +3053,17 @@ int vnc_display_open(DisplayState *ds, const char *display)
 
     if (reverse) {
         /* connect to viewer */
-        if (strncmp(display, "unix:", 5) == 0)
-            vs->lsock = unix_connect(display+5, NULL);
-        else
-            vs->lsock = inet_connect(display, NULL);
-        if (vs->lsock < 0) {
-            goto fail;
+        int csock;
+        vs->lsock = -1;
+        if (strncmp(display, "unix:", 5) == 0) {
+            csock = unix_connect(display+5, NULL);
         } else {
-            int csock = vs->lsock;
-            vs->lsock = -1;
-            vnc_connect(vs, csock, 0);
+            csock = inet_connect(display, NULL);
         }
-        return 0;
-
+        if (csock < 0) {
+            goto fail;
+        }
+        vnc_connect(vs, csock, 0);
     } else {
         /* listen for connects */
         char *dpy;