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.
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
0x
,
where MMNN
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”.
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