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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 con-
     sumer.

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	9.2		       January 16, 2004			   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | RESTRICTIONS/CONDITIONS | RETURN VALUES | EXAMPLES | SEE ALSO | AUTHORS

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