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.

[ENXIO]
    Provider got orphaned.

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
-nosplit This manual page was written by Pawel Jakub Dawidek <pjd@FreeBSD.org>.