g_consumer(9)

NAME

g_new_consumer, g_destroy_consumer - GEOM consumers manage

ment

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 con

nects 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 con

sumer 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 start and access methods de

fined.

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 consumer.

EXAMPLES

Create consumer, attach it to given provider, gain read ac

cess 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 con

sumer. */
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 ALSO

geom(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