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DECLARE_GEOM_CLASS(9)	    Kernel Developer's Manual	   DECLARE_GEOM_CLASS(9)

NAME
     DECLARE_GEOM_CLASS -- GEOM class declaration macro

SYNOPSIS
     #include <geom/geom.h>

     DECLARE_GEOM_CLASS(class, mod_name);

DESCRIPTION
     The  DECLARE_GEOM_CLASS()	macro  registers  a  GEOM class in GEOM.  A GEOM
     class itself implements one particular kind of transformation.  Typical ex-
     amples are: MBR disk partition,  BSD  disklabel  and  RAID5  classes.   DE-
     CLARE_GEOM_CLASS()  can  be  used both for compiled in and loaded as kld(4)
     modules GEOM classes and it is the only official way  for	class  registra-
     tion.

     The arguments to DECLARE_GEOM_CLASS() are:

	   class	 The g_class structure which describes a GEOM class.

	   mod_name	 A kernel module name (not a class name!).

     Structure g_class contains data describing the class.  They are:

	   const char * name
		   Class name.

	   g_taste_t * taste
		   Pointer  to function used for taste event handling.	If it is
		   non-NULL it is called in three situations:

		   -   On class activation, all existing providers  are  offered
		       for tasting.
		   -   When new provider is created it is offered for tasting.
		   -   After last write access to a provider is closed it is of-
		       fered  for  retasting  (on first write open event "spoil"
		       was sent).

	   g_config_t * config
		   This field is not used anymore,  its  functionality	was  re-
		   placed by the ctlreq field.

	   g_ctl_req_t * ctlreq
		   Pointer  to	function  used for handling events from userland
		   applications.

	   g_init_t * init
		   Pointer to function which is called right after class  regis-
		   tration.

	   g_fini_t * fini
		   Pointer to function which is called right before class dereg-
		   istration.

	   g_ctl_destroy_geom_t * destroy_geom
		   Pointer to a function which is called for every geom on class
		   unload.   If  this field is not set, the class can not be un-
		   loaded.

     Only a name field is required; the rest are optional.

RESTRICTIONS/CONDITIONS
     The fields of g_class should always be initialized  using	C99-style  field
     naming (see the initialization of example_class below).

EXAMPLES
     Example class declaration.

	   static struct g_geom *
	   g_example_taste(struct g_class *mp, struct g_provider *pp,
	       int flags __unused)
	   {
		   g_topology_assert();

		   [...]
	   }

	   static void
	   g_example_ctlreq(struct gctl_req *req, struct g_class *cp,
	       char const *verb)
	   {

		   [...]
	   }

	   static int
	   g_example_destroy_geom(struct gctl_req *req, struct g_class *cp,
	       struct g_geom *gp)
	   {

		   g_topology_assert();

		   [...]
	   }

	   static void
	   g_example_init(struct g_class *mp)
	   {

		   [...]
	   }

	   static void
	   g_example_fini(struct g_class *mp)
	   {

		   [...]
	   }

	   struct g_class example_class = {
		   .name = "EXAMPLE",
		   .taste = g_example_taste,
		   .ctlreq = g_example_ctlreq,
		   .init = g_example_init,
		   .fini = g_example_fini,
		   .destroy_geom = g_example_destroy_geom
	   };

	   DECLARE_GEOM_CLASS(example_class, g_example);

SEE ALSO
     geom(4),	g_attach(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			 August 13, 2007	   DECLARE_GEOM_CLASS(9)
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