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

g_new_geomf, g_destroy_geom
geom management

#include <geom/geom.h>
struct g_geom *
g_new_geomf(struct g_class *mp, const char *fmt, ...);
g_destroy_geom(struct g_geom *gp);

The geom (do not confuse “geom” with “GEOM”) is an instance of a GEOM class. For example: in a typical i386 FreeBSD system, there will be one geom of class MBR for each disk. The geom's name is not really important, it is only used in the XML dump and for debugging purposes. There can be many geoms with the same name.
The g_new_geomf() function creates a new geom, which will be an instance of the class mp. The geom's name is created in a printf(3)-like way from the rest of the arguments.
The g_destroy_geom() function destroys the given geom immediately and cancels all related pending events.
The g_geom structure contains fields that should be set by the caller after geom creation, but before creating any providers or consumers related to this geom (not all are required):
g_start_t * start
Pointer to a function used for I/O processing.
g_spoiled_t * spoiled
Pointer to a function used for consumers spoiling.
g_dumpconf_t * dumpconf
Pointer to a function used for configuration in XML format dumping.
g_access_t * access
Pointer to a function used for access control.
g_orphan_t * orphan
Pointer to a function used to inform about orphaned consumer.
g_ioctl_t * ioctl
Pointer to a function used for handling ioctl requests.
void * softc
Field for private use.

If you intend to use providers in this geom you must set field start of your geom.
If you are planning to use consumers in your geom you must set fields orphan and access for it.
  • Class mp must be valid (registered in GEOM).
  • The topology lock has to be held.
  • The geom cannot possess any providers.
  • The geom cannot possess any consumers.
  • The topology lock has to be held.

The g_new_geomf() function returns a pointer to the newly created geom.

Create an example geom.
static void 
g_example_start(struct bio *bp) 
static void 
g_example_orphan(struct g_consumer *cp) 
static void 
g_example_spoiled(struct g_consumer *cp) 
static int 
g_example_access(struct g_provider *pp, int dr, int dw, int de) 
static struct g_geom * 
create_example_geom(struct g_class *myclass) 
	struct g_geom *gp; 
	gp = g_new_geomf(myclass, "example_geom"); 
	gp->start = g_example_start; 
	gp->orphan = g_example_orphan; 
	gp->spoiled = g_example_spoiled; 
	gp->access = g_example_access; 
	gp->softc = NULL; 
	return (gp); 
static int 
destroy_example_geom(struct g_geom *gp) 
	if (!LIST_EMPTY(&gp->provider) || 
	    !LIST_EMPTY(&gp->consumer)) { 
		return (EBUSY); 
	return (0); 

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

This manual page was written by Pawel Jakub Dawidek <>.
April 24, 2016 FreeBSD 12.0-RELEASE

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