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().

include/nshlib/nshlib.h

@@ -115,16 +115,21 @@ void nsh_initialize(void);
  * Name: nsh_consolemain
  *
  * 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 return.
  *
+ *   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 function handles generic /dev/console character devices, or
  *   special USB console devices.  The USB console requires some special
  *   operations to handle the cases where the session is lost when the
  *   USB device is unplugged and restarted when the USB device is plugged
  *   in again.
-  *
+ *
  * Input Parameters:
  *   Standard task start-up arguments.  These are not used.  argc may be
  *   zero and argv may be NULL.
@@ -138,6 +143,35 @@ void nsh_initialize(void);
 
 int nsh_consolemain(int argc, char *argv[]);
 
+/****************************************************************************
+ * Name: nsh_consolechild
+ *
+ * Description:
+ *   This interfaces maybe to called or started with task_start to start a
+ *   single a new NSH instance that operates on stdin and stdout.  This
+ *   function does not normally return (see below).
+ *
+ *   This function equivalent to nsh_consolemain(), except it assumes that
+ *   all one-time, NSH has already been perfroemd by nsh_consolemain().  It
+ *   simply startes a NSH session with no re-initialization.
+ *
+ *   Like nsh_consolmain(), this functions 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.
+ *
+ * Returned Values:
+ *   This function does not normally return.  exit() is usually called to
+ *   terminate the NSH session.  This function will return in the event of
+ *   an error.  In that case, a non-zero value is returned (EXIT_FAILURE=1).
+ *
+ ****************************************************************************/
+
+int nsh_consolechild(int argc, char *argv[]);
+
 /****************************************************************************
  * Name: nsh_telnetstart
  *

nshlib/Makefile

@@ -90,7 +90,7 @@ endif
 endif
 
 ifeq ($(CONFIG_NSH_CONSOLE),y)
-CSRCS += nsh_consolemain.c
+CSRCS += nsh_consolemain.c nsh_consolechild.c
 endif
 
 ifeq ($(CONFIG_NSH_TELNET),y)

nshlib/nsh_consolechild.c

@@ -0,0 +1,98 @@
+/****************************************************************************
+ * apps/nshlib/nsh_consolechild.c
+ *
+ *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name Gregory Nutt nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <stdio.h>
+#include <assert.h>
+
+#include "nsh.h"
+#include "nsh_console.h"
+
+#if !defined(HAVE_USB_CONSOLE) && !defined(HAVE_USB_KEYBOARD)
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: nsh_consolechild
+ *
+ * Description:
+ *   This interfaces maybe to called or started with task_start to start a
+ *   single a new NSH instance that operates on stdin and stdout.  This
+ *   function does not normally return (see below).
+ *
+ *   This function equivalent to nsh_consolemain(), except it assumes that
+ *   all one-time, NSH has already been perfroemd by nsh_consolemain().  It
+ *   simply startes a NSH session with no re-initialization.
+ *
+ *   Like nsh_consolmain(), this functions 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.
+ *
+ * Returned Values:
+ *   This function does not normally return.  exit() is usually called to
+ *   terminate the NSH session.  This function will return in the event of
+ *   an error.  In that case, a non-zero value is returned (EXIT_FAILURE=1).
+ *
+ ****************************************************************************/
+
+int nsh_consolechild(int argc, char *argv[])
+{
+  FAR struct console_stdio_s *pstate = nsh_newconsole();
+  int ret;
+
+  DEBUGASSERT(pstate != NULL);
+
+  /* Execute the session */
+
+  ret = nsh_session(pstate);
+
+  /* Exit upon return */
+
+  nsh_exit(&pstate->cn_vtbl, ret);
+  return ret;
+}
+
+#endif /* !HAVE_USB_CONSOLE && !HAVE_USB_KEYBOARD */

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);
+  DEBUGASSERT(pstate != NULL);
-
-  /* Execute the start-up script */
 
 #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
 

nshlib/nsh_session.c

@@ -59,12 +59,13 @@
  * Name: nsh_session
  *
  * Description:
- *   This is the common session logic or any NSH session.  This function
+ *   This is the common session login or each NSH session.  This function
- *   return when an error reading from the input stream occurs, presumably
+ *   returns when an error reading from the input stream occurs, presumably
  *   signaling the end of the session.
  *
  *   This function:
- *   - Executes the NSH logic script
+ *   - Performs the logic sequence if so configured.
+ *   - Executes the NSH login script
  *   - Presents a greeting
  *   - Then provides a prompt then gets and processes the command line.
  *   - This continues until an error occurs, then the session returns.