G_ATTACH(9) MidnightBSD Kernel Developer’s Manual 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 consumer 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 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);

}

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〉.

MidnightBSD 0.3 January 16, 2004 MidnightBSD 0.3