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.\"
.\" Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd January 16, 2004
.Dt g_event 9
.Os
.Sh NAME
.Nm g_post_event ,
.Nm g_waitfor_event ,
.Nm g_cancel_event
.Nd "events management"
.Sh SYNOPSIS
.In geom/geom.h
.Ft int
.Fn g_post_event "g_event_t *func" "void *arg" "int flag" ...
.Ft int
.Fn g_waitfor_event "g_event_t *func" "void *arg" "int flag" ...
.Ft void
.Fn g_cancel_event "void *ref"
.Sh DESCRIPTION
The GEOM has its own event queue to inform classes about important things.
The event queue can be also used by classes, mostly for running away
from I/O path.
Sleeping, heavy weight tasks, etc. are not permitted on I/O path and
events are the cure to avoid such situations.
.Pp
The
.Fn g_post_event
function tells GEOM to call function
.Fa func
with argument
.Fa arg
from the event queue.
The
.Fa flag
argument is a flag for
.Xr malloc 9
that should be used by GEOM.
Only the flags
.Dv M_WAITOK
or
.Dv M_NOWAIT
can be used.
The rest of the arguments are used as references.
An event can be canceled by using any of given references as an
argument to the
.Fn g_cancel_event
function.
The list of references has to end with a
.Dv NULL
value.
.Pp
The
.Fn g_waitfor_event
function is a blocking version of the
.Fn g_post_event
function.
It waits until the event is finished or canceled and then returns.
.Pp
The
.Fn g_cancel_event
function cancels event(s) identified by
.Fa ref .
Cancellation is equivalent to calling the requested function
with requested arguments and argument
.Fa flag
set to
.Dv EV_CANCEL .
.Sh RESTRICTIONS/CONDITIONS
.Fn g_post_event :
.Bl -item -offset indent
.It
The argument
.Fa flag
has to be
.Dv M_WAITOK
or
.Dv M_NOWAIT .
.It
The list of references has to end with a
.Dv NULL
value.
.El
.Pp
.Fn g_waitfor_event :
.Bl -item -offset indent
.It
The argument
.Fa flag
has to be
.Dv M_WAITOK
or
.Dv M_NOWAIT .
.It
The list of references has to end with a
.Dv NULL
value.
.It
The
.Fn g_waitfor_event
function can not be called from an event, since doing so would result
in a deadlock.
.El
.Sh RETURN VALUES
.Fn g_post_event
and
.Fn g_waitfor_event
returns the value 0 if successful; otherwise an error code is returned.
.Sh ERRORS
Possible errors for
.Fn g_post_event
function:
.Bl -tag -width Er
.It Bq Er ENOMEM
There was insufficient memory.
.El
.Pp
Possible errors for
.Fn g_waitfor_event
function:
.Bl -tag -width Er
.It Bq Er EAGAIN
The event was canceled.
.It Bq Er ENOMEM
There was insufficient memory.
.El
.Sh EXAMPLES
Example of a function called from the event queue.
.Bd -literal -offset indent
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);
}
.Ed
.Sh SEE ALSO
.Xr DECLARE_GEOM_CLASS 9 ,
.Xr geom 4 ,
.Xr g_attach 9 ,
.Xr g_bio 9 ,
.Xr g_consumer 9 ,
.Xr g_data 9 ,
.Xr g_geom 9 ,
.Xr g_provider 9 ,
.Xr g_provider_by_name 9 ,
.Xr g_wither_geom 9
.Sh AUTHORS
.An -nosplit
This manual page was written by
.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .
|
