g_new_consumer, g_destroy_consumer — GEOM consumers management

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

Debian                                          January 16, 2004                                   G_CONSUMER(9)

       A  GEOM consumer is the backdoor through which a geom connects to another GEOM provider and through which
       I/O requests are sent.

       The g_new_consumer() function creates a new consumer on geom gp.  Before using the new consumer,  it  has
       to be attached to a provider with g_attach(9) and opened with g_access(9).

       The  g_destroy_consumer()  function  destroys  the given consumer and cancels all related pending events.
       This function is the last stage of killing an unwanted consumer.

       Create consumer, attach it to 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);
             }

       g_new_consumer, g_destroy_consumer — GEOM consumers management

g_new_consumer():

             The geom gp has to have an orphan method defined.

             The topology lock has to be held.

       g_destroy_consumer():

             The consumer must not be attached to a provider.

             The access count has to be 0.

             The topology lock has to be held.

       The g_new_consumer() function returns a pointer to the newly created consumer.

geom(4), DECLARE_GEOM_CLASS(9), g_access(9), g_attach(9),  g_bio(9),  g_data(9),  g_event(9),  g_geom(9),
       g_provider(9), g_provider_by_name(9), g_wither_geom(9)

#include<geom/geom.h>structg_consumer*g_new_consumer(structg_geom*gp);

       voidg_destroy_consumer(structg_consumer*cp);