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>.

Debian                                          January 16, 2004                                     G_ATTACH(9)