g_attach9
Attach/detach geom consumers to/from providers
Usage
#include <geom/geom.h>
int
g_attach(struct g_consumer *cp, struct g_provider *pp);
void
g_detach(struct g_consumer *cp);
Overview
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.
- [ENXIO]
-
Provider got orphaned.
Releases
52 releases since FreeBSD 5.3-RELEASE; the text changed 33 times.