G_ATTACH(9)            FreeBSD 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.

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

FreeBSD 13.1-RELEASE-p6        October 10, 2020        FreeBSD 13.1-RELEASE-p6