terminal-util: introduce vt_release() helper

src/basic/terminal-util.c

@@ -1305,3 +1305,19 @@ int vt_restore(int fd) {
 
         return q;
 }
+
+int vt_release(int fd, bool restore) {
+        assert(fd >= 0);
+
+        /* This function releases the VT by acknowledging the VT-switch signal
+         * sent by the kernel and optionally reset the VT in text and auto
+         * VT-switching modes. */
+
+        if (ioctl(fd, VT_RELDISP, 1) < 0)
+                return -errno;
+
+        if (restore)
+                return vt_restore(fd);
+
+        return 0;
+}

src/basic/terminal-util.h

@@ -155,3 +155,4 @@ int open_terminal_in_namespace(pid_t pid, const char *name, int mode);
 int vt_default_utf8(void);
 int vt_reset_keyboard(int fd);
 int vt_restore(int fd);
+int vt_release(int fd, bool restore_vt);