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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:
[]
The operation creates a topology loop.

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>.
January 16, 2004 Linux 4.19.0-10-amd64