Update the plugins documentation

1 files changed, 93 insertions, 8 deletions

diff --git a/PLUGINS b/PLUGINS
index 75c404c..2cbb427 100644
--- a/PLUGINS
+++ b/PLUGINS
@@ -3,9 +3,7 @@ pieces of code which can be loaded into pppd at runtime and which can
 affect its behaviour in various ways.  The idea of plugins is to
 provide a way for people to customize the behaviour of pppd without
 having to either apply local patches to each version or get their
-patches accepted into the standard distribution.  My aim is that
-plugins will be able to be used with successive versions of pppd
-without needing to recompile the plugins.
+patches accepted into the standard distribution.
 
 A plugin is a standard shared library object, typically with a name
 ending in .so.  They are loaded using the standard dlopen() library
@@ -15,8 +13,11 @@ plugin support only under Linux and Solaris.
 
 Plugins are loaded into pppd using the `plugin' option, which takes
 one argument, the name of a shared object file.  The plugin option is
-a privileged option.  I suggest that you give the full path name of
-the shared object file; if you don't, it may be possible for
+a privileged option.  If the name given does not contain a slash, pppd
+will look in the /usr/lib/pppd/<version> directory for the file, where
+<version> is the version number of pppd, for example, 2.4.2.  I
+suggest that you either give the full path name of the shared object
+file or just the base name; if you don't, it may be possible for
 unscrupulous users to substitute another shared object file for the
 one you mean to load, e.g. by setting the LD_LIBRARY_PATH variable.
 
@@ -38,9 +39,15 @@ them to #include "pppd.h" from the pppd source directory.
 
 Every plugin must contain a global procedure called `plugin_init'.
 This procedure will get called (with no arguments) immediately after
-the plugin is loaded.
+the plugin is loaded.  Every plugin should also contain a variable
+called pppd_version declared as follows:
 
-Plugins can affect the behaviour of pppd in at least three ways:
+char pppd_version[] = VERSION;
+
+If this declaration is included, pppd will not load the module if its
+version number differs from that compiled into the plugin binary.
+
+Plugins can affect the behaviour of pppd in at least four ways:
 
 1. They can add extra options which pppd will then recognize.  This is
    done by calling the add_options() procedure with a pointer to an
@@ -56,6 +63,13 @@ Plugins can affect the behaviour of pppd in at least three ways:
 3. Plugin code can call any global procedures and access any global
    variables in pppd.
 
+4. Plugins can register procedures to be called when particular events
+   occur, using the `notifier' mechanism in pppd.  The differences
+   between hooks and notifiers are that a hook will only call one
+   function, whereas a notifier can call an arbitrary number, and that
+   a hook usually returns some value to pppd, whereas a notifier
+   function returns nothing.
+
 Here is a list of the currently implemented hooks in pppd.
 
 
@@ -89,6 +103,7 @@ int (*pap_auth_hook)(char *user, int userlen,
 		     char **msgp, int *msglenp,
 		     struct wordlist **paddrs,
 		     struct wordlist **popts);
+void (*pap_logout_hook)(void);
 
 These hooks are designed to allow a plugin to replace the normal PAP
 password processing in pppd with something different (e.g. contacting
@@ -127,5 +142,75 @@ permitted to use, formatted as in the pap-secrets file.  It can also
 set *popts to a wordlist containing any extra options for this user
 which pppd should apply at this point.
 
+The pap_logout_hook is called when the link is terminated, instead of
+pppd's internal `plogout' function.  It can be used for accounting
+purposes.  This hook is deprecated and will be replaced by a notifier.
+
+
+int (*null_auth_hook)(struct wordlist **paddrs,
+		      struct wordlist **popts);
+
+This hook allows a plugin to determine what the policy should be if
+the peer refuses to authenticate when it is requested to.  If the
+return value is 0, the link will be terminated; if it is 1, the
+connection is allowed to proceed, and in this case *paddrs and *popts
+can be set as for pap_auth_hook, to specify what IP addresses are
+permitted and any extra options to be applied.  If the return value is
+-1, pppd will look in the pap-secrets file as usual.
+
+
+void (*ip_choose_hook)(u_int32_t *addrp);
+
+This hook is called at the beginning of IPCP negotiation.  It gives a
+plugin the opportunity to set the IP address for the peer; the address
+should be stored in *addrp.  If nothing is stored in *addrp, pppd will
+determine the peer's address in the usual manner.
+
+
+A plugin registers itself with a notifier by declaring a procedure of
+the form:
+
+void my_notify_proc(void *opaque, int arg);
+
+and then registering the procedure with the appropriate notifier with
+a call of the form
+
+	add_notifier(&interesting_notifier, my_notify_proc, opaque);
+
+The `opaque' parameter in the add_notifier call will be passed to
+my_notify_proc every time it is called.  The `arg' parameter to
+my_notify_proc depends on the notifier.
+
+A notify procedure can be removed from the list for a notifier with a
+call of the form
+
+	remove_notifier(&interesting_notifier, my_notify_proc, opaque);
+
+Here is a list of the currently-implemented notifiers in pppd.
+
+* pidchange.  This notifier is called in the parent when pppd has
+  forked and the child is continuing pppd's processing, i.e. when pppd
+  detaches from its controlling terminal.  The argument is the pid of
+  the child.
+
+* phasechange.  This is called when pppd moves from one phase of
+  operation to another.  The argument is the new phase number.
+
+* exitnotify.  This is called just before pppd exits.  The argument is
+  the status with which pppd will exit (i.e. the argument to exit()).
+
+* sigreceived.  This is called when a signal is received, from within
+  the signal handler.  The argument is the signal number.
+
+* ip_up_notifier.  This is called when IPCP has come up.
+
+* ip_down_notifier.  This is called when IPCP goes down.
+
+* auth_up_notifier.  This is called when the peer has successfully
+  authenticated itself.
+
+* link_down_notifier.  This is called when the link goes down.
+
+
 
-## $Id: PLUGINS,v 1.2 1999/09/17 06:02:45 paulus Exp $ ##
+## $Id: PLUGINS,v 1.3 2001/05/21 08:34:33 paulus Exp $ ##