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

# g\_access(9freebsd)

control access to GEOM consumers and their providers

## NAME

**g\_access** – control access to GEOM consumers and their providers

## SYNOPSIS

**#include \<geom/geom.h\>**

*int*\

**g\_access**(*struct g\_consumer \*cp*, *int dcr*, *int dcw*, *int dce*);

## DESCRIPTION

The **g\_access**() function allows to open, close, and generally change access to the provider which is attached to the given consumer *cp*. The arguments *dcr*, *dcw*, and *dce* represent relative read, write, and exclusive access count changes. Read and write access counts are self explanatory, and exclusive access counts deny write access to other interested parties. A provider's access count is the sum of the access counts of all attached consumers.

After attaching a consumer to a provider with [g\_attach(9)](/g_attach/9.md), the **g\_access**() function has to be called on the consumer before starting I/O requests.

## RESTRICTIONS/CONDITIONS

The consumer has to be attached to a provider.

The intended change must not result in a negative access count.

No-operation is not permitted *(*, *dcr* = *dcw* = *dce* = 0).

The provider's geom must have an access method defined (e.g., *gp-\>access*).

The topology lock has to be held.

## RETURN VALUES

The **g\_access**() function returns 0 if successful; otherwise an error code is returned. Note that **g\_access**() cannot fail when the arguments *dcr*, *dcw*, and *dce* are less than or equal to 0.

## EXAMPLES

Create a consumer, attach it to a given provider, gain read access and read first sector.

```
void
some_function(struct g_geom *mygeom, struct g_provider *pp)
{
	struct g_consumer *cp;
	void *ptr;
	int error;
	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. */
	error = g_access(cp, 1, 0, 0);
	if (error != 0) {
		printf("Cannot access provider: %s\n", error);
		g_detach(cp);
		g_destroy_consumer(cp);
		return;
	}
	/*
	 * Don't hold topology lock while reading.
	 */
	g_topology_unlock();
	ptr = g_read_data(cp, 0, pp->sectorsize, &error);
	if (ptr == NULL)
		printf("Error while reading: %d\n", error);
	/*
	 * Do something useful with data.
	 */
	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:

- \[EPERM\]

  The function is trying to open a provider with an exclusive access count, but it is already open for writing.

- \[EPERM\]

  The function is trying to open a provider for writing, but it is already exclusively open.

Any other error that can be returned by the provider's access method.

## SEE ALSO

[geom(4)](/geom/4.md), [DECLARE\_GEOM\_CLASS(9)](/DECLARE_GEOM_CLASS/9.md), [g\_attach(9)](/g_attach/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*⟩.