G_CONSUMER(9) BSD Kernel Developer's Manual G_CONSUMER(9)NAME
g_new_consumer, g_destroy_consumer — GEOM consumers management
SYNOPSIS
#include <geom/geom.h>
struct g_consumer *
g_new_consumer(struct g_geom *gp);
void
g_destroy_consumer(struct g_consumer *cp);
DESCRIPTION
A GEOM consumer is the backdoor through which a geom connects to another
GEOM provider and through which I/O requests are sent.
The g_new_consumer() function creates a new consumer on geom gp. Before
using the new consumer, it has to be attached to a provider with
g_attach(9) and opened with g_access(9).
The 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.
RESTRICTIONS/CONDITIONS
g_new_consumer():
The geom gp has to have an orphan method defined.
The topology lock has to be held.
g_destroy_consumer():
The consumer must not be attached to a provider.
The access count has to be 0.
The topology lock has to be held.
RETURN VALUES
The g_new_consumer() function returns a pointer to the newly created con‐
sumer.
EXAMPLES
Create consumer, attach it to given provider, gain read access and clean
up.
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);
}
SEE ALSOgeom(4), DECLARE_GEOM_CLASS(9), g_access(9), g_attach(9), g_bio(9),
g_data(9), g_event(9), g_geom(9), g_provider(9), g_provider_by_name(9),
g_wither_geom(9)AUTHORS
This manual page was written by Pawel Jakub Dawidek ⟨pjd@FreeBSD.org⟩.
BSD January 16, 2004 BSD
