G_CONSUMER(9)          FreeBSD Kernel Developer's Manual         G_CONSUMER(9)

NAME
     g_new_consumer, g_destroy_consumer - GEOM consumers management

SYNOPSIS
     #include <geom/geom.h>

     struct g_consumer *
     g_new_consumer(struct g_geom *gp);

     void
     g_destroy_consumer(struct g_consumer *cp);

DESCRIPTION
     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.

RESTRICTIONS/CONDITIONS
     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.

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

EXAMPLES
     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);
           }

SEE ALSO
     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)

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

FreeBSD 13.1-RELEASE-p6        January 16, 2004        FreeBSD 13.1-RELEASE-p6