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g_attach (9)

>> g_attach (9) ( FreeBSD man: Ядро )

BSD mandoc

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 Fa cp to given provider Fa 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 Fa 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);
}