freebsd-skq/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
The 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 releated to geom
.Fa gp .
The consumer is unusable prior attaching to a provider and gaining access
to it.
To serve its purpose, the consumer has to be attached to a provider
with the
.Xr g_attach 9
function.
.Pp
The
.Fn g_destroy_consumer
function destroys 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 related to the created consumer must have the
.Fa start
and
.Fa access
fields defined.
.It
The topology lock has to be held.
.El
.Pp
.Fn g_destroy_consumer :
.Bl -item -offset indent
.It
The consumer can not be attached.
.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 or
.Dv NULL
if an error occured.
.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);
	if (cp == NULL)
		return;
	/* 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_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 .