text: 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 themselves, 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 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.〉.