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EVENTHANDLER - kernel event handling functions

 

NAME

      EVENTHANDLER - kernel event handling functions
 

SYNOPSIS

      #include <sys/eventhandler.h>
 
      EVENTHANDLER_DECLARE(name, type);
 
      EVENTHANDLER_INVOKE(name, ...);
 
      eventhandler_tag
      EVENTHANDLER_REGISTER(name, func, arg, priority);
 
      EVENTHANDLER_DEREGISTER(name, tag);
 
      eventhandler_tag
      eventhandler_register(struct eventhandler_list *list, const char *name,
              void *func, void *arg, int priority);
 
      void
      eventhandler_deregister(struct eventhandler_list *list,
              eventhandler_tag tag);
 
      struct eventhandler_list *
      eventhandler_find_list(const char *name);
 
      void
      eventhandler_prune_list(struct eventhandler_list *list);
 

DESCRIPTION

      The EVENTHANDLER mechanism provides a way for kernel subsystems to regis‐
      ter interest in kernel events and have their callback functions invoked
      when these events occur.
 
      The normal way to use this subsystem is via the macro interface.  The
      macros that can be used for working with event handlers and callback
      function lists are:
 
      EVENTHANDLER_DECLARE()
              This macro declares an event handler named by argument name with
              callback functions of type type.
 
      EVENTHANDLER_REGISTER()
              This macro registers a callback function func with event handler
              name.  When invoked, function func will be invoked with argument
              arg as its first parameter along with any additional parameters
              passed in via macro EVENTHANDLER_INVOKE() (see below).  Callback
              functions are invoked in order of priority.  The relative prior‐
              ity of each callback among other callbacks associated with an
              event is given by argument priority, which is an integer ranging
              from EVENTHANDLER_PRI_FIRST (highest priority), to
              EVENTHANDLER_PRI_LAST (lowest priority).  The symbol
              EVENTHANDLER_PRI_ANY may be used if the handler does not have a
              specific priority associated with it.  If registration is suc‐
              cessful, EVENTHANDLER_REGISTER() returns a cookie of type
              eventhandler_tag.
 
      EVENTHANDLER_DEREGISTER()
              This macro removes a previously registered callback associated
              with tag tag from the event handler named by argument name.
 
      EVENTHANDLER_INVOKE()
              This macro is used to invoke all the callbacks associated with
              event handler name.  This macro is a variadic one.  Additional
              arguments to the macro after the name parameter are passed as the
              second and subsequent arguments to each registered callback func‐
              tion.
 
      The macros are implemented using the following functions:
 
      eventhandler_register()
              The eventhandler_register() function is used to register a call‐
              back with a given event.  The arguments expected by this function
              are:
 
              list      A pointer to an existing event handler list, or NULL.
                        If list is NULL, the event handler list corresponding
                        to argument name is used.
 
              name      The name of the event handler list.
 
              func      A pointer to a callback function.  Argument arg is
                        passed to the callback function func as its first argu‐
                        ment when it is invoked.
 
              priority  The relative priority of this callback among all the
                        callbacks registered for this event.  Valid values are
                        those in the range EVENTHANDLER_PRI_FIRST to
                        EVENTHANDLER_PRI_LAST.
 
              The eventhandler_register() function returns a tag that can later
              be used with eventhandler_deregister() to remove the particular
              callback function.
 
      eventhandler_deregister()
              The eventhandler_deregister() function removes the callback asso‐
              ciated with tag tag from the event handler list pointed to by
              list.  This function is safe to call from inside an event handler
              callback.
 
      eventhandler_find_list()
              The eventhandler_find_list() function returns a pointer to event
              handler list structure corresponding to event name.
 
      eventhandler_prune_list()
              The eventhandler_prune_list() function removes all deregistered
              callbacks from the event list list.
 
    Kernel Event Handlers
      The following event handlers are present in the kernel:
 
      acpi_sleep_event
              Callbacks invoked when the system is being sent to sleep.
 
      acpi_wakeup_event
              Callbacks invoked when the system is being woken up.
 
      dev_clone
              Callbacks invoked when a new entry is created under /dev.
 
      ifaddr_event
              Callbacks invoked when an address is set up on a network inter‐
              face.
 
      if_clone_event
              Callbacks invoked when an interface is cloned.
 
      ifnet_arrival_event
              Callbacks invoked when a new network interface appears.
 
      ifnet_departure_event
              Callbacks invoked when a network interface is taken down.
 
      power_profile_change
              Callbacks invoked when the power profile of the system changes.
 
      process_exec
              Callbacks invoked when a process performs an exec() operation.
 
      process_exit
              Callbacks invoked when a process exits.
 
      process_fork
              Callbacks invoked when a process forks a child.
 
      shutdown_pre_sync
              Callbacks invoked at shutdown time, before file systems are syn‐
              chronized.
 
      shutdown_post_sync
              Callbacks invoked at shutdown time, after all file systems are
              synchronized.
 
      shutdown_final
              Callbacks invoked just before halting the system.
 
      vm_lowmem
              Callbacks invoked when virtual memory is low.
 
      watchdog_list
              Callbacks invoked when the system watchdog timer is reinitial‐
              ized.
      The macro EVENTHANDLER_REGISTER() and function eventhandler_register()
      return a cookie of type eventhandler_tag, which may be used in a subse‐
      quent call to EVENTHANDLER_DEREGISTER() or eventhandler_deregister().
 
      The eventhandler_find_list() function returns a pointer to an event han‐
      dler list corresponding to parameter name, or NULL if no such list was
      found.
 

HISTORY

      The EVENTHANDLER facility first appeared in FreeBSD 4.0.
 

AUTHORS

      This manual page was written by Joseph Koshy 〈jkoshy@FreeBSD.org〉.
 

Sections

Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.