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 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⟩.