G_ATTACH(9) BSD 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:
[ELOOP] The operation creates a topology loop.
SEE ALSOgeom(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⟩.
BSD January 16, 2004 BSD
