g_consumer9

Usage

Overview

A GEOM consumer is the backdoor through which a geom connects to another GEOM provider and through which I/O requests are sent.

The g_new_consumer() function creates a new consumer on geom gp. Before using the new consumer, it has to be attached to a provider with g_attach(9) and opened with g_access(9).

The g_destroy_consumer() function destroys the given consumer and cancels all related pending events. This function is the last stage of killing an unwanted consumer.

Restrictions/conditions

g_new_consumer():

The geom gp has to have start and access methods defined.

The topology lock has to be held.

g_destroy_consumer():

The consumer must not be attached to a provider.

The access count has to be 0.

The topology lock has to be held.

Return values

The g_new_consumer() function returns a pointer to the newly created consumer.

Examples

Create consumer, attach it to 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);
}