---
name: "g_attach"
section: "9freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/g_attach/9freebsd"
---

# g\_attach(9freebsd)

attach/detach GEOM consumers to/from providers

## 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)](/geom/4.md), [DECLARE\_GEOM\_CLASS(9)](/DECLARE_GEOM_CLASS/9.md), [g\_access(9)](/g_access/9.md), [g\_bio(9)](/g_bio/9.md), [g\_consumer(9)](/g_consumer/9.md), [g\_data(9)](/g_data/9.md), [g\_event(9)](/g_event/9.md), [g\_geom(9)](/g_geom/9.md), [g\_provider(9)](/g_provider/9.md), [g\_provider\_by\_name(9)](/g_provider_by_name/9.md), [g\_wither\_geom(9)](/g_wither_geom/9.md)

## AUTHORS

This manual page was written by Pawel Jakub Dawidek ⟨*pjd@FreeBSD.org*⟩.