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

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.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.
.Pp
.Sh RESTRICTIONS/CONDITIONS
.Fn g_new_consumer :
.Bl -item -offset indent
.It
The geom
.Fa gp
has to have
.Fa start
and
.Fa access
methods 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
.Fn g_new_consumer
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 DECLARE_GEOM_CLASS 9 ,
.Xr geom 4 ,
.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 .