freebsd-dev/share/man/man9/g_consumer.9

.\"
.\" 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_CONSUMER 9
.Os
.Sh NAME
.Nm g_new_consumer ,
.Nm g_destroy_consumer
.Nd "GEOM consumers management"
.Sh SYNOPSIS
.In geom/geom.h
.Ft "struct g_consumer *"
.Fn g_new_consumer "struct g_geom *gp"
.Ft void
.Fn g_destroy_consumer "struct g_consumer *cp"
.Sh DESCRIPTION
A GEOM consumer is the backdoor through which a geom connects to
another GEOM provider and through which I/O requests are sent.
.Pp
The
.Fn g_new_consumer
function creates a new consumer on geom
.Fa gp .
Before using the new consumer, it has to be attached to a provider with
.Xr g_attach 9
and opened with
.Xr g_access 9 .
.Pp
The
.Fn g_destroy_consumer
function destroys the given consumer and cancels all related pending events.
This function is the last stage of killing an unwanted consumer.
.Sh RESTRICTIONS/CONDITIONS
.Fn g_new_consumer :
.Bl -item -offset indent
.It
The geom
.Fa gp
has to have an
.Va orphan
method defined.
.It
The topology lock has to be held.
.El
.Pp
.Fn g_destroy_consumer :
.Bl -item -offset indent
.It
The consumer must not be attached to a provider.
.It
The access count has to be 0.
.It
The topology lock has to be held.
.El
.Sh RETURN VALUES
The
.Fn g_new_consumer
function
returns a pointer to the newly created consumer.
.Sh EXAMPLES
Create consumer, attach it to given provider, gain read access and clean up.
.Bd -literal -offset indent
void
some_function(struct g_geom *mygeom, struct g_provider *pp)
{
	struct g_consumer *cp;

	g_topology_assert();

	/* Create new consumer on 'mygeom' geom. */
	cp = g_new_consumer(mygeom);
	/* Attach newly created consumer to given provider. */
	if (g_attach(cp, pp) != 0) {
		g_destroy_consumer(cp);
		return;
	}
	/* Open provider for reading through our consumer. */
	if (g_access(cp, 1, 0, 0) != 0) {
		g_detach(cp);
		g_destroy_consumer(cp);
		return;
	}

	g_topology_unlock();
	/*
	 * Read data from provider.
	 */
	g_topology_lock();

	/* Disconnect from provider (release access count). */
	g_access(cp, -1, 0, 0);
	/* Detach from provider. */
	g_detach(cp);
	/* Destroy consumer. */
	g_destroy_consumer(cp);
}
.Ed
.Sh SEE ALSO
.Xr geom 4 ,
.Xr DECLARE_GEOM_CLASS 9 ,
.Xr g_access 9 ,
.Xr g_attach 9 ,
.Xr g_bio 9 ,
.Xr g_data 9 ,
.Xr g_event 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 .