freebsd man page for g_waitfor_event

G_EVENT(9)						   BSD Kernel Developer's Manual						G_EVENT(9)

NAME
     g_post_event, g_waitfor_event, g_cancel_event -- GEOM events management

SYNOPSIS
     #include <geom/geom.h>

     int
     g_post_event(g_event_t *func, void *arg, int flag, ...);

     int
     g_waitfor_event(g_event_t *func, void *arg, int flag, ...);

     void
     g_cancel_event(void *ref);

DESCRIPTION
     The GEOM framework has its own event queue to inform classes about important events.  The event queue can be also used by GEOM classes them-
     selves, for example to work around some restrictions in the I/O path, where sleeping, heavy weight tasks, etc. are not permitted.

     The g_post_event() function tells the GEOM framework to call function func with argument arg from the event queue.  The flag argument is
     passed to malloc(9) for memory allocations inside of g_post_event().  The only allowed flags are M_WAITOK and M_NOWAIT.  The rest of the
     arguments are used as references to identify the event.  An event can be canceled by using any of the given references as an argument to
     g_cancel_event().	The list of references has to end with a NULL value.

     The g_waitfor_event() function is a blocking version of the g_post_event() function.  It waits until the event is finished or canceled and
     then returns.

     The g_cancel_event() function cancels all event(s) identified by ref.  Cancellation is equivalent to calling the requested function with
     requested arguments and argument flag set to EV_CANCEL.

RESTRICTIONS
/CONDITIONS
     g_post_event():

	   The argument flag has to be M_WAITOK or M_NOWAIT.

	   The list of references has to end with a NULL value.

     g_waitfor_event():

	   The argument flag has to be M_WAITOK or M_NOWAIT.

	   The list of references has to end with a NULL value.

	   The g_waitfor_event() function cannot be called from an event, since doing so would result in a deadlock.

RETURN VALUES
     The g_post_event() and g_waitfor_event() functions return 0 if successful; otherwise an error code is returned.

EXAMPLES
     Example of a function called from the event queue.

	   void
	   example_event(void *arg, int flag)
	   {

		   if (flag == EV_CANCEL) {
			   printf("Event with argument %p canceled.
", arg);
			   return;
		   }

		   printf("Event with argument %p called.
", arg);
	   }

ERRORS
     Possible errors for the g_post_event() function:

     [ENOMEM]		The flag argument was set to M_NOWAIT and there was insufficient memory.

     Possible errors for the g_waitfor_event() function:

     [EAGAIN]		The event was canceled.

     [ENOMEM]		The flag argument was set to M_NOWAIT and there was insufficient memory.

SEE ALSO
     geom(4), DECLARE_GEOM_CLASS(9), g_access(9), g_attach(9), g_bio(9), g_consumer(9), g_data(9), g_geom(9), g_provider(9),
     g_provider_by_name(9), g_wither_geom(9)

AUTHORS
     This manual page was written by Pawel Jakub Dawidek <pjd@FreeBSD.org>.

BSD
								 January 16, 2004							       BSD