EN JA
G_ATTACH(9)
G_ATTACH(9) FreeBSD Kernel Developer's Manual G_ATTACH(9)

NAME

g_attach, g_detachattach/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.

AUTHORS

This manual page was written by Pawel Jakub Dawidek <pjd@FreeBSD.org>.
January 16, 2004 FreeBSD