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22.2.4.2 Type-Specific Plugin Data Structures and Functions »
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22.2.4.1. General Plugin Data Structures and Functions

Every plugin must have a general descriptor that provides information to the plugin API. The structure of the general descriptor is the same for all plugin types. This descriptor is defined by the st_mysql_plugin structure in the plugin.h file: 

struct st_mysql_plugin
{
  int type;             /* the plugin type (a MYSQL_XXX_PLUGIN value)   */
  void *info;           /* pointer to type-specific plugin descriptor   */
  const char *name;     /* plugin name                                  */
  const char *author;   /* plugin author (for SHOW PLUGINS)             */
  const char *descr;    /* general descriptive text (for SHOW PLUGINS ) */
  int license;          /* the plugin license (PLUGIN_LICENSE_XXX)      */
  int (*init)(void *);  /* the function to invoke when plugin is loaded */
  int (*deinit)(void *);/* the function to invoke when plugin is unloaded */
  unsigned int version; /* plugin version (for SHOW PLUGINS)            */
  struct st_mysql_show_var *status_vars;
  struct st_mysql_sys_var **system_vars; 
  void * __reserved1;   /* reserved for dependency checking             */
};

The st_mysql_plugin descriptor structure is common to every type of plugin. Its members should be filled in as follows:

  • type

    The plugin type. This must be one of the plugin-type values from plugin.h: 

    /*
  The allowable types of plugins
*/
#define MYSQL_UDF_PLUGIN             0  /* User-defined function        */
#define MYSQL_STORAGE_ENGINE_PLUGIN  1  /* Storage Engine               */
#define MYSQL_FTPARSER_PLUGIN        2  /* Full-text parser plugin      */
#define MYSQL_DAEMON_PLUGIN          3  /* The daemon/raw plugin type */
#define MYSQL_INFORMATION_SCHEMA_PLUGIN  4  /* The I_S plugin type */
...

    Thus, for a full-text parser plugin, the type value is MYSQL_FTPARSER_PLUGIN.

  • info

    A pointer to the type-specific descriptor for the plugin. This descriptor's structure depends on the particular type of plugin, unlike that of the general plugin descriptor structure. Each type-specific descriptor has a version number that indicates the API version for that type of plugin, plus any other members needed. The descriptor for full-text plugins is described in Section 22.2.4.2.1, “Full-Text Parser Plugin Data Structures and Functions”.

  • name

    A string that gives the plugin name. This is the name that will be listed in the plugin table and by which you refer to the plugin in SQL statements such as INSTALL PLUGIN and UNINSTALL PLUGIN, or with the --plugin-load option. The name is also visible in the INFORMATION_SCHEMA.PLUGINS table or the output from SHOW PLUGINS.

  • author

    A string naming the plugin author. This can be whatever you like.

  • desc

    A string that provides a general description of the plugin. This can be whatever you like.

  • license

    The plugin license type. The value can be one of PLUGIN_LICENSE_PROPRIETARY, PLUGIN_LICENSE_GPL, or PLUGIN_LICENSE_BSD.

  • init

    A once-only initialization function. The server executes this function when it loads the plugin, which happens for INSTALL PLUGIN or, for plugins listed in the plugin table, at server startup. The function takes no arguments. It returns zero for success and nonzero for failure. If an init function is unneeded for a plugin, it can be specified as 0.

  • deinit

    A once-only deinitialization function. The server executes this function when it unloads the plugin, which happens for UNINSTALL PLUGIN or, for plugins listed in the plugin table, at server shutdown. The function takes no arguments. It returns zero for success and nonzero for failure. If a deinit function is unneeded for a plugin, it can be specified as 0.

  • version

    The plugin version number. When the plugin is installed, this value can be retrieved from the INFORMATION_SCHEMA.PLUGINS table. The value includes major and minor numbers. If you write the value as a hex constant, the format is 0xMMNN, where MM and NN are the major and minor numbers, respectively. For example, 0x0302 represents version 3.2.

  • status_vars

    A pointer to a structure for status variables associated with the plugin, or 0 if there are no such variables. When the plugin is installed, these variables are displayed in the output of the SHOW STATUS statement.

  • system_vars

    A pointer to a structure for system variables associated with the plugin, or 0 if there are no such variables. These options and system variables can be used to help initialize variables within the plugin.

  • __reserved1

    A placeholder for the future. Currently, it should be set to NULL.

The init and deinit functions in the general plugin descriptor are invoked only when loading and unloading the plugin. They have nothing to do with use of the plugin such as happens when an SQL statement causes the plugin to be invoked.

The status_vars member, if not 0, points to an array of st_mysql_show_var structures that describe status variables. See Section 22.2.4.3, “Plugin Status and System Variables”.

The system_vars member, if not 0, points to an array of st_mysql_sys_var structures that describe sytem variables. See Section 22.2.4.3, “Plugin Status and System Variables”.