About module struct in Apache

在写apache模块的时候，会用到 module这个结构体。module这个结构体实际上是module_struct，后面附上了定义。使用的时候通常都是定义一个这个结构体的变量并赋初值，如：
module AP_MODULE_DECLARE_DATA proxy_module =
{
STANDARD20_MODULE_STUFF,
create_proxy_dir_config, /* create per-directory config structure */
merge_proxy_dir_config, /* merge per-directory config structures */
create_proxy_config, /* create per-server config structure */
merge_proxy_config, /* merge per-server config structures */
proxy_cmds, /* command table */
register_hooks
};
其中STANDARD20_MODULE_STUFF这个宏为module_struct中的API version, minor version, module index, name, danamic load handle, next, magic, rewrite_args赋了初值。随后是per-directory configuration structure的初始化、合并函数和per-server configuration structure的初始化、合并函数。command table是command_rec结构的一个数组，依然是宏展开，描述这个模块在配置文件里面的信息。最后的register_hooks指向用于注册hook的函数。

typedef struct module_struct module;

/**
 * Module structures.  Just about everything is dispatched through
 * these, directly or indirectly (through the command and handler
 * tables).
 */ struct module_struct {
    /** API version, *not* module version; check that module is 
     * compatible with this version of the server.
     */
    int version;
    /** API minor version. Provides API feature milestones. Not checked 
     *  during module init */
    int minor_version;
    /** Index to this modules structures in config vectors.  */
    int module_index;

    /** The name of the module's C file */
    const char *name;
    /** The handle for the DSO.  Internal use only */
    void *dynamic_load_handle;

    /** A pointer to the next module in the list
     *  @defvar module_struct *next */
    struct module_struct *next;

    /** Magic Cookie to identify a module structure;  It's mainly 
     *  important for the DSO facility (see also mod_so).  */
    unsigned long magic;

    /** Function to allow MPMs to re-write command line arguments.  This
     *  hook is only available to MPMs.
     *  @param The process that the server is running in.
     */
    void (*rewrite_args) (process_rec *process);
    /** Function to allow all modules to create per directory configuration
     *  structures.
     *  @param p The pool to use for all allocations.
     *  @param dir The directory currently being processed.
     *  @return The per-directory structure created
     */
    void *(*create_dir_config) (apr_pool_t *p, char *dir);
    /** Function to allow all modules to merge the per directory configuration
     *  structures for two directories.
     *  @param p The pool to use for all allocations.
     *  @param base_conf The directory structure created for the parent directory.
     *  @param new_conf The directory structure currently being processed.
     *  @return The new per-directory structure created
     */
    void *(*merge_dir_config) (apr_pool_t *p, void *base_conf, void *new_conf);
    /** Function to allow all modules to create per server configuration
     *  structures.
     *  @param p The pool to use for all allocations.
     *  @param s The server currently being processed.
     *  @return The per-server structure created
     */
    void *(*create_server_config) (apr_pool_t *p, server_rec *s);
    /** Function to allow all modules to merge the per server configuration
     *  structures for two servers.
     *  @param p The pool to use for all allocations.
     *  @param base_conf The directory structure created for the parent directory.
     *  @param new_conf The directory structure currently being processed.
     *  @return The new per-directory structure created
     */
    void *(*merge_server_config) (apr_pool_t *p, void *base_conf, 
                                  void *new_conf);

    /** A command_rec table that describes all of the directives this module
     * defines. */
    const command_rec *cmds;

    /** A hook to allow modules to hook other points in the request processing.
     *  In this function, modules should call the ap_hook_*() functions to
     *  register an interest in a specific step in processing the current
     *  request.
     *  @param p the pool to use for all allocations
     */
    void (*register_hooks) (apr_pool_t *p);
};