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g_access(9) [freebsd man page]

G_ACCESS(9)						   BSD Kernel Developer's Manual					       G_ACCESS(9)

NAME
g_access -- control access to GEOM consumers and their providers SYNOPSIS
#include <geom/geom.h> int g_access(struct g_consumer *cp, int dcr, int dcw, int dce); DESCRIPTION
The g_access() function allows to open, close, and generally change access to the provider which is attached to the given consumer cp. The arguments dcr, dcw, and dce represent relative read, write, and exclusive access count changes. Read and write access counts are self explanatory, and exclusive access counts deny write access to other interested parties. A provider's access count is the sum of the access counts of all attached consumers. After attaching a consumer to a provider with g_attach(9), the g_access() function has to be called on the consumer before starting I/O requests. RESTRICTIONS
/CONDITIONS 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. RETURN VALUES
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. EXAMPLES
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); } ERRORS
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. SEE ALSO
geom(4), DECLARE_GEOM_CLASS(9), g_attach(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@FreeBSD.org>. BSD
January 16, 2004 BSD

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G_CONSUMER(9)						   BSD Kernel Developer's Manual					     G_CONSUMER(9)

NAME
g_new_consumer, g_destroy_consumer -- GEOM consumers management SYNOPSIS
#include <geom/geom.h> struct g_consumer * g_new_consumer(struct g_geom *gp); void g_destroy_consumer(struct g_consumer *cp); DESCRIPTION
A GEOM consumer is the backdoor through which a geom connects to another GEOM provider and through which I/O requests are sent. The g_new_consumer() function creates a new consumer on geom gp. Before using the new consumer, it has to be attached to a provider with g_attach(9) and opened with g_access(9). The g_destroy_consumer() function destroys the given consumer and cancels all related pending events. This function is the last stage of killing an unwanted consumer. RESTRICTIONS
/CONDITIONS g_new_consumer(): The geom gp has to have an orphan method defined. The topology lock has to be held. g_destroy_consumer(): The consumer must not be attached to a provider. The access count has to be 0. The topology lock has to be held. RETURN VALUES
The g_new_consumer() function returns a pointer to the newly created consumer. EXAMPLES
Create consumer, attach it to 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); } SEE ALSO
geom(4), DECLARE_GEOM_CLASS(9), g_access(9), g_attach(9), g_bio(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@FreeBSD.org>. BSD
January 16, 2004 BSD
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