NAME
g_attach, g_detach — attach/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)
{
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struct g_consumer *cp; |
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g_topology_assert(); |
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/* Create new consumer on ’mygeom’ geom. */ |
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cp = g_new_consumer(mygeom); |
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/* Attach newly created consumer to given provider. */ |
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if (g_attach(cp, pp) != 0) { |
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g_destroy_consumer(cp); |
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return; |
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} |
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/* Open provider for reading through our consumer. */ |
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if (g_access(cp, 1, 0, 0) != 0) { |
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g_detach(cp); |
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g_destroy_consumer(cp); |
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return; |
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} |
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g_topology_unlock(); |
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/* |
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* Read data from provider. |
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*/ |
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g_topology_lock(); |
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/* Disconnect from provider (release access count). */ |
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g_access(cp, -1, 0, 0); |
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/* Detach from provider. */ |
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g_detach(cp); |
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/* Destroy consumer. */ |
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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 <pjd [AT] FreeBSD.org>.
BSD January 16, 2004 BSD