Edit File: PLUGINS
== Introduction == Yum has a simple but powerful plugin architecture which allows external modules to add new features and/or modify Yum's behaviour. Yum plugins are Python module s (.py files) which are loaded when Yum starts. Plugins were created partially as a place to put functionality that was seen as either less common or undesirable for the main yum package. Functionality in pl ugins will generally not be moved or included in the core yum package. This document explains how to create plugins for Yum. See the {{{ yum(8) }}} and {{{ yum.conf(5) }}} man pages for information on how to install and configure p re-existing plugins. == A Basic Plugin == The following example shows a minimal Yum plugin:: {{{ #!python numbering=off from yum.plugins import PluginYumExit, TYPE_CORE, TYPE_INTERACTIVE requires_api_version = '2.3' plugin_type = (TYPE_CORE, TYPE_INTERACTIVE) def init_hook(conduit): conduit.info(2, 'Hello world') def postreposetup_hook(conduit): raise PluginYumExit('Goodbye') }}} This plugin will display "Hello world" as it loads and then will cause Yum to qu it with a "Goodbye" message once it has finished initialising its repositories. == Slots and Hooks == Plugins integrate with Yum by registering a 'hook' function that corresponds to a given 'slot'. A slot is simply a point in Yum's execution. All plugin hook fun ctions for a given slot are called as Yum reaches that slot. Registration of hook functions is automatic. The plugin module is inspected for functions named {{{ <slotname>_hook }}}. If a function matching a valid slot nam e is found then that function is automatically registered as a hook function. Hook functions all take one argument, for a {{{ conduit }}} instance. Conduits a re explained below. The following slots exist: {{{ config Called first as plugins are initialised. Plugins that need to extend Yum's configuration files or command line options should do so during this slot. postconfig Called immediately after Yum's config object is initialised. Useful for extending variables or modifying items in the config, for example the $ variables that are used in repo configuration. Note: Only available in yum 3.1.7 or later init Called early in Yum's initialisation. May be used for general plugin related initialisation. predownload Called just before Yum starts downloads of packages. Plugins may access information about the packages to be downloaded here. postdownload Called just after Yum finishes package downloads. Plugins may access error information about the packages just downloaded. prereposetup Called just before Yum initialises its repository information. postreposetup Called just after Yum initialises its repository information. exclude Called after package inclusion and exclusions are processed. Plugins may modify package exclusions here. preresolve Called before Yum begins package resolution. postresolve Called just after Yum finishes package resolution. pretrans Called before Yum begins the RPM update transation. posttrans Called just after Yum has finished the RPM update transation. close Called as Yum is performing a normal exit. Plugins may wish to perform cleanup functions here. clean Called during Yum's cleanup. This slot will be executed when Yum is run with the parameters 'clean all' or 'clean plugins'. }}} == Conduits == An object known as a conduit is passed into hook functions when they are called. This object provides methods and attributes that should be used for all interac tion that the plugin has with the rest of Yum. The conduit varies depending on the plugin slot. Different methods and attribute s are available as appropriate for the slot. See the {{{ yum.plugins.SLOT_TO_CON DUIT }}} dictionary for details on the conduit class used for a particular slot. All conduits are subclassed from the {{{ PluginConduit }}} class. == API Dependencies == The plugin API and general Yum API are subject to change. For this reason, plugi ns must state which API they were written for via the {{{ requires_api_version } }} attribute. Yum will exit with a useful error if it tries to load the plugin w hich is not compatible with its API version. In general, a plugin author should set {{{ requires_api_version }}} to the API v ersion at the time that the plugin is written. The current API version can be fo und at {{{ yum.plugins.API_VERSION }}}. The {{{ yum.plugins }}} module documents how the API version is incremented and the rules for compatibility tests. == Plugin Types == Plugins must advertise what type of plugin they are via the {{{ plugin_type }}} tuple. The advertised type(s) can be used by software using the Yum libraries to control the types of plugins that will be loaded. Yum itself will always load a ll types of plugins. A plugin may have more than one type. Two plugin types currently exist. {{{ TYPE_CORE A core plugin modifies Yum's base functionality. For example, a core plugin might modify package exclusions, dependency resolving or repository loading. TYPE_INTERACTIVE An interative plugin may modify Yum's user interface flow. For example, a TY PE_INTERACTIVE plugin might terminate Yum early in some conditions or output extra informat ion to the user. In Yum versions 2.6.x and earlier (plugin API version < 2.3) this constant w as called TYPE_INTERFACE. The purpose of TYPE_INTERFACE is the same as TYPE_INTERACTIV E but the meaning of the old name wasn't clear and so it has been deprecated. }}} == Stopping Yum == A plugin may stop Yum's execution at any point by raising the {{{ yum.plugins.Pl uginYumExit }}} exception. The argument of the exception will be displayed to th e user as Yum terminates. == Reading Private Plugin Options == Each plugin has its own configuration file in {{{ /etc/yum/pluginconf.d/ }}}. Th ese configuration files follow standard INI file conventions like Yum's own conf iguration files. Arbitrary options can be read from a plugin's configuration fil e at any time by using the following methods. These are available on any conduit instance: {{{ #!python numbering=off def confString(self, section, opt, default=None) def confInt(self, section, opt, default=None) def confFloat(self, section, opt, default=None) def confBool(self, section, opt, default=None) }}} If the option is missing from the configuration file then the default value pass ed to method will be returned. See {{{ yum.plugins }}} for more documentation on these methods and see the {{{ yum(8) }}} and {{{ yum.conf(5) }}} man pages for general information on plugin configuration files. == Extending Yum's Configuration Options == In addition to having their own configuration file, plugins may modify the options available in Yum's own configuration files. A plugin can add new options or modify the existing options by modifying the {{{ YumConf }}} and {{{ RepoConf }}} classes defined in {{{ yum.config }}}. The {{{ YumConf }}} class defines options that are available in the {{{ [main] } }} section of {{{ yum.conf }}}. The {{{ RepoConf }}} class defines options that are available in each repository sections of Yum's configuration file(s). Modifications to {{{ YumConf }}} and {{{ RepoConf }}} should occur in the {{{ co nfig }}} slot. Here is a simple example of how options can be added to Yum's configuration files. {{{ #!python numbering=off from yum import config from yum.plugins import TYPE_INTERACTIVE requires_api_version = '2.4' plugin_type = (TYPE_INTERACTIVE,) def config_hook(conduit): # Add a boolean option to the [main] section config.YumConf.enable_foo = config.BoolOption(False) # Add a URL option to repository sections config.RepoConf.foo_url = config.UrlOption() # Add an option to to [main] and the repository sections. The # repository options will inherit the properties of the [main] option # and will use the value from [main] if the option is not specified in # the repo section. config.YumConf.max_foo = config.IntOption(10) config.RepoConf.max_foo = config.Inherit(config.YumConf.max_foo) def init_hook(conduit): conf = conduit.getConf() # Display the options from the [main] section conduit.info(2, "enable_foo = %r" % conf.enable_foo) conduit.info(2, "max_foo = %r" % conf.max_foo) # Display the options from the repository sections for repo in conduit.getRepos().listEnabled(): conduit.info(2, "%s.foo_url = %r" % (repo.id, repo.foo_url)) conduit.info(2, "%s.max_foo = %r" % (repo.id, repo.max_foo)) }}} Note how different types of options are defined ({{{ IntOption }}}, {{{ UrlOptio n }}}, {{{ BoolOption }}}). A wide variety of option types are available in {{{ yum.config }}}. It is even possible for plugins to define their own option types by subclassing {{{ Option }}} if the existing types aren't sufficient. See the source code for the {{{ yum.config }}} module for further details. == Extending Yum's Configuration Options (pre Yum 2.9.x, deprecated) == In addition to having their own configuration file, plugins may add extra option s to Yum's main configuration files. A plugin must register new options in the { {{ config }}} slot using the {{{ registerOpt() }}} conduit method: {{{ #!python numbering=off registerOpt(name, valuetype, where, default) }}} where the arguments are... {{{ name The name of the new option. valuetype The type of the option. Valid values are PLUG_OPT_STRING, PLUG_OPT_INT, PLUG_OPT_FLOAT and PLUG_OPT_BOOL (defined in yum.constants). The value returned for the option will be automatically parsed according to the type. where Defines where the option should be available in configuration files. Valid values are: - PLUG_OPT_WHERE_MAIN: the option only exists in the [main] section - PLUG_OPT_WHERE_REPO: the option only exists in repository sections - PLUG_OPT_WHERE_ALL: the option exists in both [main] and repository sections default The default value returned for the option if it isn't present. }}} The option values defined in the {{{ [main] }}} section may be read by calling t he {{{ getConf() }}} repository method. The options will be available as attributes of the returned object. New repository options will be available as attributes of the repository objects returned via the {{{ getRepos() }}} conduit method. The following example plugin shows how a custom option may be defined and read: {{{ #!python numbering=off from yum.constants import * from yum.plugins import TYPE_INTERACTIVE requires_api_version = '2.3' plugin_type = (TYPE_INTERACTIVE,) def config_hook(conduit): conduit.registerOpt('foo', PLUG_OPT_BOOL, PLUG_OPT_WHERE_ALL, False) def init_hook(conduit): conduit.info(2, "[main] foo=%r" % conduit.getConf().foo) def exclude_hook(conduit): for repo in conduit.getRepos().listEnabled(): conduit.info(2, "[%s] foo=%r" % (repo.id, repo.foo)) }}} == Extending Yum's Command Line Options == A plugin may add extra command line options to Yum. To do this the plugin should call the {{{ getOptParser() }}} conduit method during the {{{ config }}} or {{{ init }}} slot. This will return an {{{ OptionParser }}} instance which the p lugin may modify. See the Python standard library {{{ optparse }}} module documentati on for information on how to manipulate this object. The parsed command line options may be read in any slot after the {{{ init }}} slot. The values returned are as for {{{ OptionParser.parse_args() }}}. Options added by plugins will show up in Yum's command line help output (ie. {{{ yum --help }}}) The following plugin demonstrates the addition of new command line options by ad ding a {{{ --downloadonly }}} option: {{{ #!python numbering=off from yum.plugins import PluginYumExit, TYPE_INTERACTIVE requires_api_version = '2.3' plugin_type = (TYPE_INTERACTIVE,) def config_hook(conduit): parser = conduit.getOptParser() parser.add_option('', '--downloadonly', dest='dlonly', action='store_true', default=False, help="don't update, just download") def postdownload_hook(conduit): opts, commands = conduit.getCmdLine() if opts.dlonly: raise PluginYumExit('exiting because --downloadonly specified ') }}} == More Examples == The easiest way to get started writing Yum plugins is to look at some examples. The yum-utils package contains a number of useful plugins which will act as a useful starting point. The yum-utils git tree can be viewed here: [http://yum.ba seurl.org/gitweb/?p=yum-utils.git;a=tree] ----