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Module Creation Using a Template

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Any existing Apache module can be used as a template for a new module. Mod_example.c is distributed with Apache in /APACHE/PUB/libexec and makes a useful template for a simple module. When compiled and linked as the shared library (NMXL) mod_example.so, this module is a fully working DSO. The module libexec/mod_example.so has already been pre-built.

For a more functional module, try a different module as your template. For instance, to create a new module that does authentication, starting with one of Apache's authentication modules may be more appropriate. If you want to create a module that has its own configuration directives, start with another module that already does this.

To create the module file "mod_hw.c" from file "mod_example.c", log on as MGR.APACHE so that the file is created with the right ownership: 

  :HELLO MGR.APACHE
  :XEQ SH.HPBIN.SYS -L
  shell/iX> mkdir hw
  shell/iX> cd hw
  shell/iX> cp /APACHE/PUB/libexec/mod_example.c mod_hw.c
Change all references inside mod_hw.c from mod_example, example_module, example_handler, etc. to mod_hw, hw_module, hw_handler, etc., and modify/add any other code, as needed. Creating a separate directory for the module, such as hw, separates it from other modules under development.

To compile a module, certain compile options must be specified and the Apache C header files must also be included. Below, gcc creates two object files, hw.o and mod_hw.o, using the necessary options and include files. Use the -c option for compilation: 

  shell/iX> gcc -DMPE -D_POSIX_SOURCE -D_SOCKET_SOURCE
  -DNO_DBM_REWRITEMAP -DUSE_HSREGEX -DEAPI -DSHARED_MODULE
  -I/APACHE/PUB/include -c mod_hw.c hw.c
Next, link the module. The link steps will be different when calling external functions that reside in archive or shared libraries. Other examples of linking are shown later.

To link, the MPE/iX LinkEditor can be called from the CI or the POSIX shell:

:linkedit

or 

  shell/iX> callci linkeditLinkEd> buildxl xl=./mod_hw.so;limit=5
  LinkEd> addxl from=./mod_hw.o,./hw.o;to=./mod_hw.so;
  rl=/lib/libm.a,/lib/libc.a;merge;share
  1 OBJECT FILE HAS BEEN ADDED.
The "rl=" option is used to specify which archive libraries are used to resolve external function calls. The math library (/lib/libm.a) is specified here to resolve pow() in mod_hw.o. /lib/libc.a is not actually needed by the sample code. But it is a good practice to always specify libc since most modules and other libraries are likely to need functions from this library. If libc is not specified explicitly as shown here, the MPE/iX C library will be used by default (LIBC.LIB.SYS). Since Apache is built with libc, we recommend explicitly specifying /lib/libc instead of defaulting to LIBC.LIB.SYS. /lib/libc and LIBC.LIB.SYS are not identical. The order of the libraries listed by "rl=" is important and libc should always be specified last. The merge directive is necessary when functions are called across object boundaries such as mod_hw.o calling helloworld() in hw.o. The share option is needed when global data is shared between multiple object files. The share option is not actually needed by the sample code.

The compile and link steps can be put in a Makefile to facilitate multiple builds of a module. As an example, refer to the section “Modified APXS Makefile (mod_hw)”.

Mod_hw.so is now ready to be configured into Apache. To do this, refer to the section "Creating Apache Modules".



Tools

Module Creation Using the APXS Utility