Manual Pages  — G_ACCESS

g_access – control access to GEOM consumers and their providers

SYNOPSIS DESCRIPTION RESTRICTIONS/CONDITIONS RETURN VALUES EXAMPLES ERRORS SEE ALSO AUTHORS

#include <geom/geom.h>

int
g_access(struct g_consumer *cp, int dcr, int dcw, int dce);

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.

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.

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 , 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 , 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);
}

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.

This manual page was written by Pawel Jakub Dawidek <Mt pjd@FreeBSD.org>.