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Manual Pages  — G_ATTACH

NAME

g_attach, g_detach – attach/detach GEOM consumers to/from providers

CONTENTS

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 <Mt pjd@FreeBSD.org>.

G_ATTACH (9) January 16, 2004

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