g_attach(9)

NAME

g_attach, g_detach - attach/detach GEOM consumers to/from

providers

SYNOPSIS

#include <geom/geom.h>
int
g_attach(struct g_consumer *cp, struct g_provider *pp);
void
g_detach(struct g_consumer *cp);

DESCRIPTION

The g_attach() function attaches given consumer cp to given

provider pp,
thus establishing a communication channel between the con

sumer and the
provider that allows to change access counts and perform I/O

operations.

The g_detach() function detaches given consumer cp from its

corresponding
provider, tearing down the communication channel between

them.

RESTRICTIONS/CONDITIONS

g_attach():

The consumer must not be attached to a provider.

The operation must not create a topology loop.

The topology lock has to be held.

g_detach():

The consumer has to be attached.

The access count has to be 0.

There must be no active requests.

The topology lock has to be held.

RETURN VALUES

The g_attach() function returns 0 if successful; otherwise

an error code
is returned.

EXAMPLES

Create a consumer, attach it to a 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 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);

}

ERRORS

Possible errors:

[ELOOP] The operation creates a topology loop.

SEE ALSO

geom(4), DECLARE_GEOM_CLASS(9), g_access(9), g_bio(9),

g_consumer(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