Manual Pages  — G_ATTACH

g_attach, g_detach – attach/detach GEOM consumers to/from providers

SYNOPSIS DESCRIPTION RESTRICTIONS/CONDITIONS RETURN VALUES EXAMPLES ERRORS SEE ALSO AUTHORS

#include <geom/geom.h>

int
g_attach(struct g_consumer *cp, struct g_provider *pp);

void
g_detach(struct g_consumer *cp);

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.

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.

The g_attach() function returns 0 if successful; otherwise an error code is returned.

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);
}

Possible errors:

[ELOOP]
	The operation creates a topology loop.
[ENXIO]
	Provider got orphaned.

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