freebsd-nq/share/man/man9/g_attach.9

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.Dd January 16, 2004
.Dt g_attach 9
.Os
.Sh NAME
.Nm g_attach ,
.Nm g_detach
.Nd "attach/detach consumer to/from provider"
.Sh SYNOPSIS
.In geom/geom.h
.Ft int
.Fn g_attach "struct g_consumer *cp" "struct g_provider *pp"
.Ft void
.Fn g_detach "struct g_consumer *cp"
.Sh DESCRIPTION
The
.Fn g_attach
function attaches given consumer to given provider.
For real provider access (ie. I/O operations), one still need to call the
.Fn g_access
function on consumer to gain access to attached provider.
.Pp
The
.Fn g_detach
function detaches the given consumer from the corresponding provider.
This function is used when we do not want to communicate with the
provider anymore.
.Sh RESTRICTIONS/CONDITIONS
.Fn g_attach :
.Bl -item -offset indent
.It
The consumer can not be attached already.
.It
The operation should not create a topology loop.
.It
The topology lock has to be held.
.El
.Pp
.Fn g_detach :
.Bl -item -offset indent
.It
The consumer has to be attached.
.It
The access count has to be 0.
.It
There must be no active requests.
.It
The topology lock has to be held.
.El
.Sh RETURN VALUES
.Fn g_attach
returns the value 0 if successful; otherwise an error code is returned.
.Sh ERRORS
Possible errors:
.Bl -tag -width Er
.It Bq Er ELOOP
The operation creates a topology loop.
.El
.Sh EXAMPLES
Create consumer, attach it to given provider, gain read access and clean up.
.Bd -literal -offset indent
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);
	if (cp == NULL)
		return;
	/* 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);
}
.Ed
.Sh SEE ALSO
.Xr DECLARE_GEOM_CLASS 9 ,
.Xr geom 4 ,
.Xr g_bio 9 ,
.Xr g_consumer 9 ,
.Xr g_data 9 ,
.Xr g_event 9 ,
.Xr g_geom 9 ,
.Xr g_provider 9 ,
.Xr g_provider_by_name 9 ,
.Xr g_wither_geom 9
.Sh AUTHORS
.An -nosplit
This manual page was written by
.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .