This commit adds nsh_consolechild(). I noticed that there are several examples that call nsh_consolemain.c to create to create a new NSH session. That will not always work because nsh_consolemain() performs the one-time initialization needed by the NSH library: Mounting, reading, and running the start-up script, configuring USB tracing. Some of those actions will cause failures if attempted twice.

Here are some offenders: examples/cc3000/shell.c, examples/nsh/nsh_main.c, examples/nxterm/nxterm_main.c, and examples/pty_test/pty_test.c.  It is possible that for some of those, that represents the first call to nsh_consolemain().  But probably not.

To give other initialization options, I added nsh_consolechild() which is identical to nsh_consolemain() other than it omits all of the one-time initialization.  Of course, you would not get the result that you wanted if nsh_consolechild() were called without nsh_consolemain().

nshlib/nsh_consolemain.c

@@ -55,14 +55,19 @@
  * Name: nsh_consolemain (Normal character device version)
  *
  * Description:
- *   This interfaces maybe to called or started with task_start to start a
+ *   This interfaces may be to called or started with task_start to start a
  *   single an NSH instance that operates on stdin and stdout.  This
  *   function does not normally return (see below).
  *
- *   This version of nsh_consolmain handles generic /dev/console character
+ *   This function performs all basic, one-time initialization logic as
+ *   configured.  This includes such things as mounting the romfs /etc/
+ *   file system and running the initialization script, setting up USB
+ *   tracing options.  It should be spawned only once for this reason.
+ *
+ *   This version of nsh_consolmain() handles generic /dev/console character
  *   devices (see nsh_usbconsole.c and usb_usbkeyboard for other versions
  *   for special USB console devices).
-  *
+ *
  * Input Parameters:
  *   Standard task start-up arguments.  These are not used.  argc may be
  *   zero and argv may be NULL.
@@ -79,17 +84,17 @@ int nsh_consolemain(int argc, char *argv[])
   FAR struct console_stdio_s *pstate = nsh_newconsole();
   int ret;
 
-  DEBUGASSERT(pstate);
-
-  /* Execute the start-up script */
+  DEBUGASSERT(pstate != NULL);
 
 #ifdef CONFIG_NSH_ROMFSETC
+  /* Execute the start-up script */
+
   (void)nsh_initscript(&pstate->cn_vtbl);
 #endif
 
+#ifdef CONFIG_NSH_USBDEV_TRACE
   /* Initialize any USB tracing options that were requested */
 
-#ifdef CONFIG_NSH_USBDEV_TRACE
   usbtrace_enable(TRACE_BITSET);
 #endif