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G_EVENT(9)		    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);

     struct g_event *
     g_alloc_event(int flag);

     void
     g_post_event_ep(g_event_t *func, void *arg, struct g_event *ep, ...);

DESCRIPTION
     The  GEOM	framework has its own event queue to inform classes about impor-
     tant events.  The event queue can be also used by GEOM classes  themselves,
     for  example to work around some restrictions in the I/O path, where sleep-
     ing, 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  al-
     lowed  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  re-
     turns.

     The  g_post_event_ep() function posts the event with a pre-allocated struct
     g_event.  An event may be pre-allocated with g_alloc_event().

     The g_cancel_event() function cancels all event(s) identified by ref.  Can-
     cellation 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.

     g_alloc_event():

	   The argument flag has to be M_WAITOK or M_NOWAIT.

	   The returned  struct  g_event  *  must  be  freed  with  g_free()  if
	   g_post_event_ep() is not called.

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.\n", arg);
			   return;
		   }

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

ERRORS
     Possible errors for the g_post_event() function:

     [ENOMEM]		The flag argument was set to M_NOWAIT and there was  in-
			sufficient 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 in-
			sufficient memory.

SEE ALSO
     geom(4), DECLARE_GEOM_CLASS(9), g_access(9), g_attach(9), g_bio(9),  g_con-
     sumer(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>.

FreeBSD ports 15.quarterly	  July 23, 2021 		      G_EVENT(9)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=g_event&sektion=9&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>

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