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Man Pages
G_ATTACH(9) FreeBSD Kernel Developer's Manual G_ATTACH(9)

g_attach, g_detach
attach/detach GEOM consumers to/from providers

#include <geom/geom.h>
int
g_attach(struct g_consumer *cp, struct g_provider *pp);
void
g_detach(struct g_consumer *cp);

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.

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.

The g_attach() function returns 0 if successful; otherwise an error code is returned.

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); 
}

Possible errors:
[]
The operation creates a topology loop.

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)

This manual page was written by Pawel Jakub Dawidek <pjd@FreeBSD.org>.
January 16, 2004 FreeBSD 12.0-RELEASE

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