text: /* $Id$ */
  /* 
   * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
   * Copyright (C) 2003-2008 Benny Prijono <benny@prijono.org>
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 
   */
  #ifndef __PJ_DOXYGEN_H__
  #define __PJ_DOXYGEN_H__
  
  /**
   * @file doxygen.h
   * @brief Doxygen's mainpage.
   */
  
  /*////////////////////////////////////////////////////////////////////////// */
  /*
  	INTRODUCTION PAGE
   */
  
  /**
   * @mainpage Welcome to PJLIB!
   *
   * @section intro_sec What is PJLIB
   *
   * PJLIB is an Open Source, small footprint framework library written in C for 
   * making scalable applications. Because of its small footprint, it can be used
   * in embedded applications (we hope so!), but yet the library is also aimed for
   * facilitating the creation of high performance protocol stacks.
   *
   * PJLIB is released under GPL terms.
   *
   * @section download_sec Download
   *
   * PJLIB and all documentation can be downloaded from 
   * http://www.pjsip.org.
   *
   *
   * @section how_to_use_sec About This Documentation
   *
   * This document is generated directly from PJLIB source file using
   * \a doxygen (http://www.doxygen.org). Doxygen is a great (and free!) 
   * tools for generating such documentation.
   *
   *
   * @subsection find_samples_subsec How to Read This Document
   *
   * This documentation is laid out more to be a reference guide instead
   * of tutorial, therefore first time users may find it difficult to
   * grasp PJLIB by reading this document alone.
   *
   * However, we've tried our best to make this document easy to follow.
   * For first time users, we would suggest that you follow these steps
   * when reading this documentation:
   *
   *  - continue reading this introduction chapter. At the end of this
   *    chapter, you'll find section called \ref pjlib_fundamentals_sec
   *    which should guide you to understand basic things about PJLIB.
   *
   *  - find information about specific features that you want to use
   *    in PJLIB. Use the <b>Module Index</b> to find out about all 
   *    features in PJLIB (if you're browsing the HTML documentation,
   *    click on the \a Module link on top of the page, or if you're
   *    reading the PDF documentation, click on \a Module \a Documentation
   *    on the navigation pane on the left).
   *
   * @subsection doc_organize_sec How To's
   *
   * Please find below links to specific tasks that you probably
   * want to do:
   *
   *  - <b>How to Build PJLIB</b>
   *\n
   * Please refer to \ref pjlib_build_sys_pg page for more information.
   *
   *  - <b>How to Use PJLIB in My Application</b>
   *\n
   * Please refer to \ref configure_app_sec for more information.
   *
   *  - <b>How to Port PJLIB</b>
   *\n
   * Please refer to \ref porting_pjlib_pg page.
   *
   *  - <b>Where to Read Samples Documentation</b>
   *\n
   * Most of the modules provide link to the corresponding sample file.
   * Alternatively, to get the list of all examples, you can click on 
   * <b>Related Pages</b> on the top of HTML document or on 
   * <b>PJLIB Page Documentation</b> on navigation pane of your PDF reader.
   *
   *  - <b>How to Submit Code to PJLIB Project</b>
   *\n
   * Please read \ref pjlib_coding_convention_page before submitting
   * your code. Send your code as patch against current Subversion tree
   * to the appropriate mailing list.
   *
   *
   * @section features_sec Features
   *
   * @subsection open_source_feat It's Open Source!
   *
   * PJLIB is currently released on GPL license, but other arrangements
   * can be made with the author.
   *
   * @subsection extreme_portable_feat Extreme Portability
   *
   * PJLIB is designed to be extremely portable. It can run on any kind
   * of processors (16-bit, 32-bit, or 64-bit, big or little endian, single
   * or multi-processors) and operating systems. Floating point or no
   * floating point. Multi-threading or not.
   * It can even run in environment where no ANSI LIBC is available. 
   *
   * Currently PJLIB is known to run on these platforms:
   *  - Win32/x86 (Win95/98/ME, NT/2000/XP/2003, mingw).
   *  - arm, WinCE and Windows Mobile.
   *  - Linux/x86, (user mode and as <b>kernel module</b>(!)).
   *  - Linux/alpha
   *  - Solaris/ultra.
   *  - MacOS X/powerpc
   *  - RTEMS (x86 and powerpc).
   *
   * And efforts is under way to port PJLIB on:
   *  - Symbian OS
   *
   *
   * @subsection small_size_feat Small in Size
   *
   * One of the primary objectives is to have library that is small in size for
   * typical embedded applications. As a rough guidance, we aim to keep the 
   * library size below 100KB for it to be considered as small.
   * As the result, most of the functionalities in the library can be tailored
   * to meet the requirements; user can enable/disable specific functionalities
   * to get the desired size/performance/functionality balance.
   *
   * For more info, please see @ref pj_config.
   *
   *
   * @subsection big_perform_feat Big in Performance
   *
   * Almost everything in PJLIB is designed to achieve the highest possible
   * performance out of the target platform. 
   *
   *
   * @subsection no_dyn_mem No Dynamic Memory Allocations
   *
   * The central idea of PJLIB is that for applications to run as fast as it can,
   * it should not use \a malloc() at all, but instead should get the memory 
   * from a preallocated storage pool. There are few things that can be 
   * optimized with this approach:
   *
   *  - \a alloc() is a O(1) operation.
   *  - no mutex is used inside alloc(). It is assumed that synchronization 
   *    will be used in higher abstraction by application anyway.
   *  - no \a free() is required. All chunks will be deleted when the pool is 
   *    destroyed.
   *
   * The performance gained on some systems can be as high as 30x speed up
   * against \a malloc() and \a free() on certain configurations, but of
   * course your mileage may vary. 
   *
   * For more information, see \ref PJ_POOL_GROUP
   *
   * 
   * @subsection os_abstract_feat Operating System Abstraction
   *
   * PJLIB has abstractions for features that are normally not portable 
   * across operating systems: 
   *  - @ref PJ_THREAD
   *\n
   *    Portable thread manipulation.
   *  - @ref PJ_TLS
   *\n
   *    Storing data in thread's private data.
   *  - @ref PJ_MUTEX
   *\n
   *    Mutual exclusion protection.
   *  - @ref PJ_SEM
   *\n
   *    Semaphores.
   *  - @ref PJ_ATOMIC
   *\n
   *    Atomic variables and their operations.
   *  - @ref PJ_CRIT_SEC
   *\n
   *    Fast locking of critical sections.
   *  - @ref PJ_LOCK
   *\n
   *    High level abstraction for lock objects.
   *  - @ref PJ_EVENT
   *\n
   *    Event object.
   *  - @ref PJ_TIME
   *\n
   *    Portable time manipulation.
   *  - @ref PJ_TIMESTAMP
   *\n
   *    High resolution time value.
   *  - etc.
   *
   *
   * @subsection ll_network_io_sec Low-Level Network I/O
   *
   * PJLIB has very portable abstraction and fairly complete set of API for
   * doing network I/O communications. At the lowest level, PJLIB provides:
   *
   *  - @ref PJ_SOCK
   *\n
   *    A highly portable socket abstraction, runs on all kind of
   *    network APIs such as standard BSD socket, Windows socket, Linux
   *    \b kernel socket, PalmOS networking API, etc.
   *
   *  - @ref pj_addr_resolve
   *\n
   *    Portable address resolution, which implements #pj_gethostbyname().
   *
   *  - @ref PJ_SOCK_SELECT
   *\n
   *    A portable \a select() like API (#pj_sock_select()) which can be
   *    implemented with various back-end.
   *
   *
   *
   * @subsection timer_mgmt_sec Timer Management
   *
   * A passive framework for managing timer, see @ref PJ_TIMER for more info.
   * There is also function to retrieve high resolution timestamp
   * from the system (see @ref PJ_TIMESTAMP).
   *
   *
   * @subsection data_struct_sec Various Data Structures
   *
   * Various data structures are provided in the library:
   *
   *  - @ref PJ_PSTR
   *  - @ref PJ_ARRAY
   *  - @ref PJ_HASH
   *  - @ref PJ_LIST
   *  - @ref PJ_RBTREE
   *
   *
   * @subsection exception_sec Exception Construct
   *
   * A convenient TRY/CATCH like construct to propagate errors, which by
   * default are used by the @ref PJ_POOL_GROUP "memory pool" and 
   * the lexical scanner in pjlib-util. The exception
   * construct can be used to write programs like below:
   *
   * <pre>
   *    #define SYNTAX_ERROR  1
   *
   *    PJ_TRY {
   *       msg = NULL;
   *       msg = parse_msg(buf, len);
   *    }
   *    PJ_CATCH ( SYNTAX_ERROR ) {
   *       .. handle error ..
   *    }
   *    PJ_END;
   * </pre>
   *
   * Please see @ref PJ_EXCEPT for more information.
   *
   *
   * @subsection logging_sec Logging Facility
   *
   * PJLIB @ref PJ_LOG consists of macros to write logging information to
   * some output device. Some of the features of the logging facility:
   *
   *  - the verbosity can be fine-tuned both at compile time (to control
   *    the library size) or run-time (to control the verbosity of the
   *    information).
   *  - output device is configurable (e.g. stdout, printk, file, etc.)
   *  - log decoration is configurable.
   *
   * See @ref PJ_LOG for more information.
   *
   *
   * @subsection guid_gen_sec Random and GUID Generation
   *
   * PJLIB provides facility to create random string 
   * (#pj_create_random_string()) or globally unique identifier
   * (see @ref PJ_GUID).
   *
   *
   *
   * @section configure_app_sec Configuring Application to use PJLIB
   *
   * @subsection pjlib_compil_sec Building PJLIB
   *
   * Follow the instructions in \ref pjlib_build_sys_pg to build
   * PJLIB.
   *
   * @subsection pjlib_compil_app_sec Building Applications with PJLIB
   *
   * Use the following settings when building applications with PJLIB.
   *
   * @subsubsection compil_inc_dir_sec Include Search Path
   *
   * Add this to your include search path ($PJLIB is PJLIB root directory):
   * <pre>
   *   $PJLIB/include
   * </pre>
   *
   * @subsubsection compil_inc_file_sec Include PJLIB Header
   *
   * To include all PJLIB headers:
   * \verbatim
      #include <ZadarmaPJSIP/pjlib.h>
     \endverbatim
   *
   * Alternatively, you can include individual PJLIB headers like this:
   * \verbatim
       #include <ZadarmaPJSIP/pj/log.h>
       #include <ZadarmaPJSIP/pj/os.h>
    \endverbatim
   *
   *
   * @subsubsection compil_lib_dir_sec Library Path
   *
   * Add this to your library search path:
   * <pre>
   *   $PJLIB/lib
   * </pre>
   *
   * Then add the appropriate PJLIB library to your link specification. For
   * example, you would add \c libpj-i386-linux-gcc.a when you're building
   * applications in Linux.
   *
   *
   * @subsection pjlib_fundamentals_sec Principles in Using PJLIB
   *
   * Few things that you \b MUST do when using PJLIB, to make sure that
   * you create trully portable applications.
   *
   * @subsubsection call_pjlib_init_sec Call pj_init()
   *
   * Before you do anything else, call \c pj_init(). This would make sure that
   * PJLIB system is properly set up.
   *
   * @subsubsection no_ansi_subsec Do NOT Use ANSI C
   *
   * Contrary to popular teaching, ANSI C (and LIBC) is not the most portable
   * library in the world, nor it's the most ubiquitous. For example, LIBC
   * is not available in Linux kernel. Also normally LIBC will be excluded
   * from compilation of RTOSes to reduce size.
   *
   * So for maximum portability, do NOT use ANSI C. Do not even try to include
   * any other header files outside <include/pj>. Stick with the functionalities
   * provided by PJLIB. 
   *
   *
   * @subsubsection string_rep_subsubsec Use pj_str_t instead of C Strings
   *
   * PJLIB uses pj_str_t instead of normal C strings. You SHOULD follow this
   * convention too. Remember, ANSI string-h is not always available. And
   * PJLIB string is faster!
   *
   * @subsubsection mem_alloc_subsubsec Use Pool for Memory Allocations
   *
   * You MUST NOT use \a malloc() or any other memory allocation functions.
   * Use PJLIB @ref PJ_POOL_GROUP instead! It's faster and most portable.
   *
   * @subsection logging_subsubsec Use Logging for Text Display
   *
   * DO NOT use <stdio.h> for text output. Use PJLIB @ref PJ_LOG instead.
   *
   *
   * @section porting_pjlib_sec0 Porting PJLIB
   *
   * Please see \ref porting_pjlib_pg page on more information to port
   * PJLIB to new target.
   *
   * @section enjoy_sec Enjoy Using PJLIB!
   *
   * We hope that you find PJLIB usefull for your application. If you
   * have any questions, suggestions, critics, bug fixes, or anything
   * else, we would be happy to hear it.
   *
   * Enjoy using PJLIB!
   *
   * Benny Prijono < bennylp at pjsip dot org >
   */
  
  
  
  /*////////////////////////////////////////////////////////////////////////// */
  /*
           CODING CONVENTION
   */
  
  /**
   * @page pjlib_coding_convention_page Coding Convention
   *
   * Before you submit your code/patches to be included with PJLIB, you must
   * make sure that your code is compliant with PJLIB coding convention.
   * <b>This is very important!</b> Otherwise we would not accept your code.
   *
   * @section coding_conv_editor_sec Editor Settings
   *
   * The single most important thing in the whole coding convention is editor 
   * settings. It's more important than the correctness of your code (bugs will
   * only crash the system, but incorrect tab size is mental!).
   *
   * Kindly set your editor as follows:
   *  - tab size to \b 8.
   *  - indentation to \b 4.
   *
   * With \c vi, you can do it with:
   * <pre>
   *  :se ts=8
   *  :se sts=4
   * </pre>
   *
   * You should replace tab with eight spaces.
   *
   * @section coding_conv_detail_sec Coding Style
   *
   * Coding style MUST strictly follow K&R style. The rest of coding style
   * must follow current style. You SHOULD be able to observe the style
   * currently used by PJLIB from PJLIB sources, and apply the style to your 
   * code. If you're not able to do simple thing like to observe PJLIB
   * coding style from the sources, then logic dictates that your ability to
   * observe more difficult area in PJLIB such as memory allocation strategy, 
   * concurrency, etc is questionable.
   *
   * @section coding_conv_comment_sec Commenting Your Code
   *
   * Public API (e.g. in header files) MUST have doxygen compliant comments.
   *
   */
  
  
  /*////////////////////////////////////////////////////////////////////////// */
  /*
  	BUILDING AND INSTALLING PJLIB
   */
  
  
  
  /**
   * @page pjlib_build_sys_pg Building, and Installing PJLIB
   *
   * @section build_sys_install_sec Build and Installation
   *
   * \note
   * <b>The most up-to-date information on building and installing PJLIB
   *  should be found in the website, under "Getting Started" document.
   *  More over, the new PJLIB build system is now based on autoconf,
   *  so some of the information here might not be relevant anymore 
   *  (although most still are, since the autoconf script still use
   *  the old Makefile system as the backend).</b>
   *
   * @subsection build_sys_install_win32_sec Visual Studio
   *
   * The PJLIB Visual Studio workspace supports the building of PJLIB
   * for Win32 target. Although currently only the Visual Studio 6 Workspace is
   * actively maintained, developers with later version of Visual Studio
   * can easily imports VS6 workspace into their IDE.
   *
   * To start building PJLIB projects with Visual Studio 6 or later, open
   * the \a workspace file in the corresponding \b \c build directory. You have
   * several choices on which \a dsw file to open:
   \verbatim
    $PJPROJECT/pjlib/build/pjlib.dsw
    $PJPROJECT/pjsip/build/pjsip.dsw
   ..etc
   \endverbatim
   *
   * The easiest way is to open <tt>pjsip_apps.dsw</tt> file in \b \c $PJPROJECT/pjsip-apps/build
   * directory, and build pjsua project or the samples project. 
   * However this will not build the complete projects. 
   * For example, the PJLIB test is not included in this workspace. 
   * To build the complete projects, you must
   * open and build each \a dsw file in \c build directory in each
   * subprojects. For example, to open the complete PJLIB workspace, open
   * <tt>pjlib.dsw</tt> in <tt>$PJPROJECT/pjlib/build</tt> directory.
   *
   *
   * @subsubsection config_site_create_vc_sec Create config_site.h
   *
   * The file <tt><b>$PJPROJECT/pjlib/include/pj/config_site.h</b></tt>
   * is supposed to contain configuration that is specific to your site/target.
   * This file is not part of PJLIB, so you must create it yourself. Normally
   * you just need to create a blank file.
   *
   * The reason why it's not included in PJLIB is so that you would not accidently
   * overwrite your site configuration.
   *
   * If you fail to do this, Visual C will complain with error like: 
   *
   * <b>"fatal error C1083: Cannot open include file: 'pj/config_site.h': No such file 
   * or directory"</b>.
   *
   * @subsubsection build_vc_subsubsec Build the Projects
   *
   * Just hit the build button!
   *
   *
   * @subsection build_sys_install_unix_sec Make System
   *
   * For other targets, PJLIB provides a rather comprehensive build system
   * that uses GNU \a make (and only GNU \a make will work). 
   * Currently, the build system supports building * PJLIB for these targets:
   *  - i386/Win32/mingw
   *  - i386/Linux
   *  - i386/Linux (kernel)
   *  - alpha/linux
   *  - sparc/SunOS
   *  - etc..
   *
   *
   * @subsubsection build_req_sec Requirements
   *
   * In order to use the \c make based build system, you MUST have:
   *
   *  - <b>GNU make</b>
   *\n
   *    The Makefiles heavily utilize GNU make commands which most likely
   *    are not available in other \c make system.
   *  - <b>bash</b> shell is recommended.
   *\n
   *    Specificly, there is a command <tt>"echo -n"</tt> which may not work
   *    in other shells. This command is used when generating dependencies
   *    (<tt>make dep</tt>) and it's located in 
   *    <tt>$PJPROJECT/build/rules.mak</tt>.
   *  - <b>ar</b>, <b>ranlib</b> from GNU binutils
   *\n
   *    In your system has different <tt>ar</tt> or <tt>ranlib</tt> (e.g. they
   *    may have been installed as <tt>gar</tt> and <tt>granlib</tt>), then
   *    either you create the relevant symbolic links, <b>or</b> modify
   *    <tt>$PJPROJECT/build/cc-gcc.mak</tt> and rename <tt>ar</tt> and
   *    <tt>ranlib</tt> to the appropriate names.
   *  - <b>gcc</b> to generate dependency.
   *\n
   *    Currently the build system uses <tt>"gcc -MM"</tt> to generate build
   *    dependencies. If <tt>gcc</tt> is not desired to generate dependency,
   *    then either you don't run <tt>make dep</tt>, <b>or</b> edit
   *    <tt>$PJPROJECT/build/rules.mak</tt> to calculate dependency using
   *    your prefered method. (And let me know when you do so so that I can
   *    update the file. :) )
   *
   * @subsubsection build_overview_sec Building the Project
   *
   * Generally, steps required to build the PJLIB are:
   *
   \verbatim
     $ cd /home/user/pjproject
     $ ./configure
     $ touch pjlib/include/pj/config_site.h
     $ make dep
     $ make
   \endverbatim
   *
   * The above process will build all static libraries and all applications.
   *
   * \note the <tt>configure</tt> script is not a proper autoconf script,
   * but rather a simple shell script to detect current host. This script
   * currently does not support cross-compilation.
   *
   * \note For Linux kernel target, there are additional steps required, which
   * will be explained in section \ref linux_kern_target_subsec.
   *
   * @subsubsection build_mak_sec Cross Compilation
   * 
   * For cross compilation, you will need to edit the \c build.mak file in 
   * \c $PJPROJECT root directory manually. Please see <b>README-configure</b> file
   * in the root directory for more information.
   *
   * For Linux kernel target, you are also required to declare the following
   * variables in this file:
   *	- \c KERNEL_DIR: full path of kernel source tree.
   *	- \c KERNEL_ARCH: kernel ARCH options (e.g. "ARCH=um"), or leave blank
   * 	     for default.
   *	- \c PJPROJECT_DIR: full path of PJPROJECT source tree.
   *
   * Apart from these, there are also additional steps required to build
   * Linux kernel target, which will be explained in \ref linux_kern_target_subsec.
   *
   * @subsubsection build_dir_sec Files in "build" Directory
   *
   * The <tt>*.mak</tt> files in \c $PJPROJECT/build directory are used to specify
   * the configuration for the specified compiler, target machine target 
   * operating system, and host options. These files will be executed
   * (included) by \a make during building process, depending on the values
   * specified in <b>$PJPROJECT/build.mak</b> file.
   *
   * Normally you don't need to edit these files, except when you're porting
   * PJLIB to new target.
   *
   * Below are the description of some files in this directory:
   *
   *  - <tt>rules.mak</tt>: contains generic rules always included during make.
   *  - <tt>cc-gcc.mak</tt>: rules when gcc is used for compiler.
   *  - <tt>cc-vc.mak</tt>: rules when MSVC compiler is used.
   *  - <tt>host-mingw.mak</tt>: rules for building in mingw host.
   *  - <tt>host-unix.mak</tt>: rules for building in Unix/Posix host.
   *  - <tt>host-win32.mak</tt>: rules for building in Win32 command console
   *    (only valid when VC is used).
   *  - <tt>m-i386.mak</tt>: rules when target machine is an i386 processor.
   *  - <tt>m-m68k.mak</tt>: rules when target machine is an m68k processor.
   *  - <tt>os-linux.mak</tt>: rules when target OS is Linux.
   *  - <tt>os-linux-kernel.mak</tt>: rules when PJLIB is to be build as
   *    part of Linux kernel.
   *  - <tt>os-win32.mak</tt>: rules when target OS is Win32.
   *
   *
   * @subsubsection config_site_create_sec Create config_site.h
   *
   * The file <tt><b>$PJPROJECT/pjlib/include/pj/config_site.h</b></tt>
   * is supposed to contain configuration that is specific to your site/target.
   * This file is not part of PJLIB, so you must create it yourself.
   *
   * The reason why it's not included in PJLIB is so that you would not accidently
   * overwrite your site configuration.
   *
   *
   * @subsubsection invoking_make_sec Invoking make
   *
   * Normally, \a make is invoked in \c build directory under each project.
   * For example, to build PJLIB, you would invoke \a make in
   * \c $PJPROJECT/pjlib/build directory like below:
   *
   \verbatim
     $ cd pjlib/build
     $ make
   \endverbatim
   *
   * Alternatively you may invoke <tt>make</tt> in <tt>$PJPROJECT</tt> 
   * directory, to build all projects under that directory (e.g. 
   * PJLIB, PJSIP, etc.).
   *
   *
   * @subsubsection linux_kern_target_subsec Linux Kernel Target
   *
   * \note
   * <b>BUILDING APPLICATIONS IN LINUX KERNEL MODE IS A VERY DANGEROUS BUSINESS.
   * YOU MAY CRASH THE WHOLE OF YOUR SYSTEM, CORRUPT YOUR HARDISK, ETC. PJLIB
   * KERNEL MODULES ARE STILL IN EXPERIMENTAL PHASE. DO NOT RUN IT IN PRODUCTION
   * SYSTEMS OR OTHER SYSTEMS WHERE RISK OF LOSS OF DATA IS NOT ACCEPTABLE.
   * YOU HAVE BEEN WARNED.</b>
   *
   * \note
   * <b>User Mode Linux (UML)</b> provides excellent way to experiment with Linux
   * kernel without risking the stability of the host system. See
   * http://user-mode-linux.sourceforge.net for details.
   *
   * \note
   * I only use <b>UML</b> to experiment with PJLIB kernel modules.
   * <b>I wouldn't be so foolish to use my host Linux machine to experiment
   * with this.</b> 
   *
   * \note
   * You have been warned.
   *
   * For building PJLIB for Linux kernel target, there are additional steps required.
   * In general, the additional tasks are:
   *	- Declare some more variables in <b><tt>build.mak</tt></b> file (this
   *        has been explained in \ref build_mak_sec above).
   *      - Perform these two small modifications in kernel source tree.
   *
   * There are two small modification need to be applied to the kernel tree.
   *
   * <b>1. Edit <tt>Makefile</tt> in kernel root source tree.</b>
   *
   * Add the following lines at the end of the <tt>Makefile</tt> in your 
   * <tt>$KERNEL_SRC</tt> dir:
   \verbatim
  script:
         $(SCRIPT)
   \endverbatim
   *
   * \note Remember to replace spaces with <b>tab</b> in the Makefile.
   *
   * The modification above is needed to capture kernel's \c $CFLAGS and 
   * \c $CFLAGS_MODULE which will be used for PJLIB's compilation.
   *
   * <b>2. Add Additional Exports.</b>
   *
   * We need the kernel to export some more symbols for our use. So we declare
   * the additional symbols to be exported in <tt>extra-exports.c</tt> file, and add
   * a this file to be compiled into the kernel:
   *
   *	- Copy the file <tt>extra-exports.c</tt> from <tt>pjlib/src/pj</tt> 
   *	  directory to <tt>$KERNEL_SRC/kernel/</tt> directory.
   *	- Edit <tt>Makefile</tt> in that directory, and add this line
   *        somewhere after the declaration of that variable:
   \verbatim
  obj-y   += extra-exports.o
   \endverbatim
   *
   * To illustrate what have been done in your kernel source tree, below
   * is screenshot of my kernel source tree _after_ the modification.
   *
   \verbatim
  [root@vpc-linux linux-2.6.7]# pwd
  /usr/src/linux-2.6.7
  [root@vpc-linux linux-2.6.7]# 
  [root@vpc-linux linux-2.6.7]# 
  [root@vpc-linux linux-2.6.7]# tail Makefile 
  
  endif   # skip-makefile
  
  FORCE:
  
  .PHONY: script
  
  script:
          $(SCRIPT)
  
  [root@vpc-linux linux-2.6.7]# 
  [root@vpc-linux linux-2.6.7]# 
  [root@vpc-linux linux-2.6.7]# head kernel/extra-exports.c 
  #include <ZadarmaPJSIP/linux/module.h>
  #include <ZadarmaPJSIP/linux/syscalls.h>
  
  EXPORT_SYMBOL(sys_select);
  
  EXPORT_SYMBOL(sys_epoll_create);
  EXPORT_SYMBOL(sys_epoll_ctl);
  EXPORT_SYMBOL(sys_epoll_wait);
  
  EXPORT_SYMBOL(sys_socket);
  [root@vpc-linux linux-2.6.7]# 
  [root@vpc-linux linux-2.6.7]# 
  [root@vpc-linux linux-2.6.7]# head -15 kernel/Makefile 
  #
  # Makefile for the linux kernel.
  #
  
  obj-y     = sched.o fork.o exec_domain.o panic.o printk.o profile.o \
              exit.o itimer.o time.o softirq.o resource.o \
              sysctl.o capability.o ptrace.o timer.o user.o \
              signal.o sys.o kmod.o workqueue.o pid.o \
              rcupdate.o intermodule.o extable.o params.o posix-timers.o \
              kthread.o
  
  obj-y   +=  extra-exports.o
  
  obj-$(CONFIG_FUTEX) += futex.o
  obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
  [root@vpc-linux linux-2.6.7]# 
  
   \endverbatim
   *
   * Then you must rebuild the kernel.
   * If you fail to do this, you won't be able to <b>insmod</b> pjlib.
   *
   * \note You will see a lots of warning messages during pjlib-test compilation.
   * The warning messages complain about unresolved symbols which are defined
   * in pjlib module. You can safely ignore these warnings. However, you can not
   * ignore warnings about non-pjlib unresolved symbols.
   *
   * 
   * @subsection makefile_explained_sec Makefile Explained
   *
   * The \a Makefile for each project (e.g. PJLIB, PJSIP, etc) should be
   * very similar in the contents. The Makefile is located under \c build
   * directory in each project subdir.
   *
   * @subsubsection pjlib_makefile_subsec PJLIB Makefile.
   *
   * Below is PJLIB's Makefile:
   *
   * \include build/Makefile
   *
   * @subsubsection pjlib_os_makefile_subsec PJLIB os-linux.mak.
   *
   * Below is file <tt><b>os-linux.mak</b></tt> file in 
   * <tt>$PJPROJECT/pjlib/build</tt> directory,
   * which is OS specific configuration file for Linux target that is specific 
   * for PJLIB project. For \b global OS specific configuration, please see
   * <tt>$PJPROJECT/build/os-*.mak</tt>.
   *
   * \include build/os-linux.mak
   *
   */
  
  
  /*////////////////////////////////////////////////////////////////////////// */
  /*
           PORTING PJLIB
   */
  
  
  
  /**
   * @page porting_pjlib_pg Porting PJLIB
   *
   * \note
   * <b>Since version 0.5.8, PJLIB build system is now based on autoconf, so
   * most of the time we shouldn't need to apply the tweakings below to get
   * PJLIB working on a new platform. However, since the autoconf build system
   * still uses the old Makefile build system, the information below may still
   * be useful for reference.
   * </b>
   *
   * @section new_arch_sec Porting to New CPU Architecture
   *
   * Below is step-by-step guide to add support for new CPU architecture.
   * This sample is based on porting to Alpha architecture; however steps for 
   * porting to other CPU architectures should be pretty similar. 
   *
   * Also note that in this example, the operating system used is <b>Linux</b>.
   * Should you wish to add support for new operating system, then follow
   * the next section \ref porting_os_sec.
   *
   * Step-by-step guide to port to new CPU architecture:
   *  - decide the name for the new architecture. In this case, we choose
   *    <tt><b>alpha</b></tt>.
   *  - edit file <tt>$PJPROJECT/build.mak</tt>, and add new section for
   *    the new target:
   *    <pre>
   *      #
   *      # Linux alpha, gcc
   *      #
   *      export MACHINE_NAME := <b>alpha</b>
   *      export OS_NAME := linux
   *      export CC_NAME := gcc
   *      export HOST_NAME := unix
   *    </pre>
   *
   *  - create a new file <tt>$PJPROJECT/build/<b>m-alpha</b>.mak</tt>.
   *    Alternatively create a copy from other file in this directory.
   *    The contents of this file will look something like:
   *    <pre>
   *      export M_CFLAGS := $(CC_DEF)<b>PJ_M_ALPHA=1</b>
   *      export M_CXXFLAGS :=
   *      export M_LDFLAGS :=
   *      export M_SOURCES :=
   *    </pre>
   *  - create a new file <tt>$PJPROJECT/pjlib/include/pj/compat/<b>m_alpha.h</b></tt>.
   *    Alternatively create a copy from other header file in this directory.
   *    The contents of this file will look something like:
   *    <pre>
   *      #define PJ_HAS_PENTIUM          0
   *      #define PJ_IS_LITTLE_ENDIAN     1
   *      #define PJ_IS_BIG_ENDIAN        0
   *    </pre>
   *  - edit <tt>pjlib/include/pj/<b>config.h</b></tt>. Add new processor
   *    configuration in this header file, like follows:
   *    <pre>
   *      ...
   *      #elif defined (PJ_M_ALPHA) && PJ_M_ALPHA != 0
   *      #   include <ZadarmaPJSIP/pj/compat/m_alpha.h>
   *      ...
   *    </pre>
   *  - done. Build PJLIB with:
   *    <pre>
   *      $ cd $PJPROJECT/pjlib/build
   *      $ make dep
   *      $ make clean
   *      $ make
   *    </pre>
   *
   * @section porting_os_sec Porting to New Operating System Target
   *
   * This section will try to give you rough guideline on how to
   * port PJLIB to a new target. As a sample, we give the target a name tag, 
   * for example <tt><b>xos</b></tt> (for X OS). 
   *
   * @subsection new_compat_os_h_file_sec Create New Compat Header File
   *
   * You'll need to create a new header file 
   * <b><tt>include/pj/compat/os_xos.h</tt></b>. You can copy as a 
   * template other header file and edit it accordingly.
   *
   * @subsection modify_config_h_file_sec Modify config.h
   *
   * Then modify file <b><tt>include/pj/config.h</tt></b> to include
   * this file accordingly (e.g. when macro <tt><b>PJ_XOS</b></tt> is
   * defined):
   *
   \verbatim
   ...
   #elif defined(PJ_XOS)
   #  include <ZadarmaPJSIP/pj/compat/os_xos.h>
   #else
   #...
   \endverbatim
   * 
   * @subsection new_target_mak_file_sec Create New Global Make Config File
   *
   * Then you'll need to create global configuration file that
   * is specific for this OS, i.e. <tt><b>os-xos.mak</b></tt> in 
   * <tt><b>$PJPROJECT/build</b></tt> directory.
   *
   * At very minimum, the file will normally need to define
   * <tt><b>PJ_XOS=1</b></tt> in the \c CFLAGS section:
   *
   \verbatim
  #
  # $PJPROJECT/build/os-xos.mak:
  #
  export OS_CFLAGS   := $(CC_DEF)PJ_XOS=1
  export OS_CXXFLAGS := 
  export OS_LDFLAGS  :=
  export OS_SOURCES  := 
   \endverbatim
   *
   *
   * @subsection new_target_prj_mak_file_sec Create New Project's Make Config File
   *
   * Then you'll need to create xos-specific configuration file
   * for PJLIB. This file is also named <tt><b>os-xos.mak</b></tt>,
   * but its located in <tt><b>pjlib/build</b></tt> directory.
   * This file will specify source files that are specific to
   * this OS to be included in the build process.
   *
   * Below is a sample:
   \verbatim
  #
  # pjlib/build/os-xos.mak:
  #  XOS specific configuration for PJLIB.
  #
  export PJLIB_OBJS += 	os_core_xos.o \
                          os_error_unix.o \
                          os_time_ansi.o
  export TEST_OBJS +=	main.o
  export TARGETS	    =	pjlib pjlib-test
   \endverbatim
   *
   * @subsection new_target_src_sec Create and Edit Source Files
   *
   * You'll normally need to create at least these files:
   *  - <tt><b>os_core_xos.c</b></tt>: core OS specific
   *    functionality.
   *  - <tt><b>os_timestamp_xos.c</b></tt>: how to get timestamp
   *    in this OS.
   *
   * Depending on how things are done in your OS, you may need
   * to create these files:
   *  - <tt><b>os_error_*.c</b></tt>: how to manipulate
   *    OS error codes. Alternatively you may use existing
   *    <tt>os_error_unix.c</tt> if the OS has \c errno and
   *    \c strerror() function.
   *  - <tt><b>ioqueue_*.c</b></tt>: if the OS has specific method
   *    to perform asynchronous I/O. Alternatively you may
   *    use existing <tt>ioqueue_select.c</tt> if the OS supports
   *    \c select() function call.
   *  - <tt><b>sock_*.c</b></tt>: if the OS has specific method
   *    to perform socket communication. Alternatively you may
   *    use existing <tt>sock_bsd.c</tt> if the OS supports
   *    BSD socket API, and edit <tt>include/pj/compat/socket.h</tt>
   *    file accordingly.
   *
   * You will also need to check various files in 
   * <tt><b>include/pj/compat/*.h</b></tt>, to see if they're 
   * compatible with your OS.
   *
   * @subsection new_target_build_file_sec Build The Project
   *
   * After basic building blocks have been created for the OS, then
   * the easiest way to see which parts need to be fixed is by building
   * the project and see the error messages.
   *
   * @subsection new_target_edit_vs_new_file_sec Editing Existing Files vs Creating New File
   *
   * When you encounter compatibility errors in PJLIB during porting,
   * you have three options on how to fix the error:
   *  - edit the existing <tt>*.c</tt> file, and give it <tt>#ifdef</tt>
   *    switch for the new OS, or
   *  - edit <tt>include/pj/compat/*.h</tt> instead, or
   *  - create a totally new file.
   *
   * Basicly there is no strict rule on which approach is the best
   * to use, however the following guidelines may be used:
   *  - if the file is expected to be completely different than
   *    any existing file, then perhaps you should create a completely
   *    new file. For example, file <tt>os_core_xxx.c</tt> will 
   *    normally be different for each OS flavour.
   *  - if the difference can be localized in <tt>include/compat</tt>
   *    header file, and existing <tt>#ifdef</tt> switch is there,
   *    then preferably you should edit this <tt>include/compat</tt>
   *    header file.
   *  - if the existing <tt>*.c</tt> file has <tt>#ifdef</tt> switch,
   *    then you may add another <tt>#elif</tt> switch there. This
   *    normally is used for behaviors that are not totally
   *    different on each platform.
   *  - other than that above, use your own judgement on whether
   *    to edit the file or create new file etc.
   */
  
  #endif	/* __PJ_DOXYGEN_H__ */
  
  