g_data(9) [freebsd man page]

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

NAME

     g_read_data, g_write_data -- read/write data from/to GEOM consumer

SYNOPSIS

     #include <geom/geom.h>

     void *
     g_read_data(struct g_consumer *cp, off_t offset, off_t length, int *error);

     int
     g_write_data(struct g_consumer *cp, off_t offset, void *ptr, off_t length);

DESCRIPTION

     The g_read_data() function reads length bytes of data from the provider attached to consumer cp, starting at offset offset.  The buffer
     returned from g_read_data() is allocated with g_malloc(), so it should be freed by the caller with g_free() after use.  If the operation
     fails, an error value will be stored in the error argument if it is not NULL.

     The g_write_data() function writes length bytes of data from the buffer pointed to by ptr to the provider attached to consumer cp, starting
     at offset offset.

RESTRICTIONS
/CONDITIONS
     The length argument should be a multiple of the provider's sectorsize and less than or equal to DFLTPHYS (DFLTPHYS is defined in
     <sys/param.h>).

     The topology lock must not be held.

RETURN VALUES

     The g_read_data() function returns a pointer to a data buffer or NULL if an error occurred.  In that case an error value is stored in the
     error argument unless it is NULL.

     The g_write_data() function returns 0 if successful; otherwise an error code is returned.

ERRORS

     Possible errors:

     [EIO]		An I/O error occurred while reading from or writing to the consumer.

SEE ALSO

     geom(4), DECLARE_GEOM_CLASS(9), g_access(9), g_attach(9), g_bio(9), g_consumer(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

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