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G_ATTACH(9)		    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 15.1			October 10, 2020		     G_ATTACH(9)
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