380710a5c8
g_alloc_event will allocate storage for an opaque event. g_post_event_ep can use memory returned by g_alloc_event to send an event from a context that might not be able to allocate the event. Occasionally, we can alloate memory when we create an object, but not while we're destroy it. This allows one to allocate at creation time memory to use when destorying the object. Reviewed by: jhb Sponsored by: Netflix Differential Revision: https://reviews.freebsd.org/D30544
220 lines
4.9 KiB
Groff
220 lines
4.9 KiB
Groff
.\"
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.\" Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 23, 2021
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.Dt G_EVENT 9
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.Os
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.Sh NAME
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.Nm g_post_event ,
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.Nm g_waitfor_event ,
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.Nm g_cancel_event
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.Nd "GEOM events management"
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.Sh SYNOPSIS
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.In geom/geom.h
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.Ft int
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.Fn g_post_event "g_event_t *func" "void *arg" "int flag" ...
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.Ft int
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.Fn g_waitfor_event "g_event_t *func" "void *arg" "int flag" ...
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.Ft void
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.Fn g_cancel_event "void *ref"
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.Ft "struct g_event *"
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.Fn g_alloc_event "int flag"
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.Ft void
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.Fn g_post_event_ep "g_event_t *func" "void *arg" "struct g_event *ep" ...
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.Sh DESCRIPTION
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The GEOM framework has its own event queue to inform classes about important
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events.
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The event queue can be also used by GEOM classes themselves, for example
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to work around some restrictions in the I/O path, where sleeping, heavy weight
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tasks, etc.\& are not permitted.
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.Pp
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The
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.Fn g_post_event
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function tells the GEOM framework to call function
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.Fa func
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with argument
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.Fa arg
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from the event queue.
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The
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.Fa flag
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argument is passed to
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.Xr malloc 9
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for memory allocations inside of
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.Fn g_post_event .
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The only allowed flags are
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.Dv M_WAITOK
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and
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.Dv M_NOWAIT .
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The rest of the arguments are used as references to identify the event.
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An event can be canceled by using any of the given references as an
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argument to
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.Fn g_cancel_event .
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The list of references has to end with a
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.Dv NULL
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value.
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.Pp
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The
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.Fn g_waitfor_event
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function is a blocking version of the
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.Fn g_post_event
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function.
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It waits until the event is finished or canceled and then returns.
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.Pp
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The
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.Fn g_post_event_ep
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function posts the event with a pre-allocated
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.Va struct g_event .
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An event may be pre-allocated with
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.Fn g_alloc_event .
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.Pp
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The
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.Fn g_cancel_event
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function cancels all event(s) identified by
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.Fa ref .
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Cancellation is equivalent to calling the requested function
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with requested arguments and argument
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.Fa flag
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set to
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.Dv EV_CANCEL .
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.Sh RESTRICTIONS/CONDITIONS
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.Fn g_post_event :
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.Bl -item -offset indent
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.It
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The argument
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.Fa flag
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has to be
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.Dv M_WAITOK
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or
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.Dv M_NOWAIT .
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.It
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The list of references has to end with a
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.Dv NULL
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value.
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.El
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.Pp
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.Fn g_waitfor_event :
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.Bl -item -offset indent
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.It
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The argument
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.Fa flag
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has to be
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.Dv M_WAITOK
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or
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.Dv M_NOWAIT .
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.It
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The list of references has to end with a
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.Dv NULL
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value.
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.It
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The
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.Fn g_waitfor_event
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function cannot be called from an event, since doing so would result
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in a deadlock.
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.El
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.Pp
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.Fn g_alloc_event :
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.Bl -item -offset indent
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.It
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The argument
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.Fa flag
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has to be
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.Dv M_WAITOK
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or
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.Dv M_NOWAIT .
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.It
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The returned
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.Va struct g_event *
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must be freed with
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.Fn g_free
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if
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.Fn g_post_event_ep
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is not called.
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.El
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.Sh RETURN VALUES
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The
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.Fn g_post_event
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and
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.Fn g_waitfor_event
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functions
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return 0 if successful; otherwise an error code is returned.
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.Sh EXAMPLES
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Example of a function called from the event queue.
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.Bd -literal -offset indent
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void
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example_event(void *arg, int flag)
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{
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if (flag == EV_CANCEL) {
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printf("Event with argument %p canceled.\\n", arg);
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return;
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}
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printf("Event with argument %p called.\\n", arg);
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}
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.Ed
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.Sh ERRORS
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Possible errors for the
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.Fn g_post_event
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function:
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.Bl -tag -width Er
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.It Bq Er ENOMEM
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The
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.Fa flag
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argument was set to
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.Dv M_NOWAIT
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and there was insufficient memory.
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.El
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.Pp
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Possible errors for the
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.Fn g_waitfor_event
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function:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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The event was canceled.
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.It Bq Er ENOMEM
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The
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.Fa flag
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argument was set to
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.Dv M_NOWAIT
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and there was insufficient memory.
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.El
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.Sh SEE ALSO
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.Xr geom 4 ,
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.Xr DECLARE_GEOM_CLASS 9 ,
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.Xr g_access 9 ,
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.Xr g_attach 9 ,
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.Xr g_bio 9 ,
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.Xr g_consumer 9 ,
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.Xr g_data 9 ,
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.Xr g_geom 9 ,
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.Xr g_provider 9 ,
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.Xr g_provider_by_name 9 ,
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.Xr g_wither_geom 9
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.Sh AUTHORS
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.An -nosplit
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This manual page was written by
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.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org .
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