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LIBGEOM(3)	       FreeBSD Library Functions Manual		    LIBGEOM(3)

     geom_stats_open, geom_stats_close,	geom_stats_resync,
     geom_stats_snapshot_get, geom_stats_snapshot_free,
     geom_stats_snapshot_timestamp, geom_stats_snapshot_reset,
     geom_stats_snapshot_next, gctl_get_handle,	gctl_ro_param, gctl_rw_param,
     gctl_issue, gctl_free, gctl_dump, g_open, g_close,	g_mediasize,
     g_sectorsize, g_stripeoffset, g_stripesize, g_flush, g_delete,
     g_device_path, g_get_ident, g_get_name, g_open_by_ident, g_providername
     --	userland API library for kernel	GEOM subsystem

     Userland API Library for kernel GEOM subsystem (libgeom, -lgeom)

     #include <libgeom.h>

   Statistics Functions



     void *

     geom_stats_snapshot_free(void *arg);

     geom_stats_snapshot_timestamp(void	*arg, struct timespec *tp);

     geom_stats_snapshot_reset(void *arg);

     struct devstat *
     geom_stats_snapshot_next(void *arg);

   Control Functions
     struct gctl_req *

     gctl_ro_param(struct gctl_req *req, const char *name, int len,
	 const void *value);

     gctl_rw_param(struct gctl_req *req, const char *name, int len,
	 void *value);

     const char	*
     gctl_issue(struct gctl_req	*req);

     gctl_free(struct gctl_req *req);

     gctl_dump(struct gctl_req *req, FILE *f);

   Utility Functions
     g_open(const char *name, int dowrite);

     g_close(int fd);

     g_mediasize(int fd);

     g_sectorsize(int fd);

     g_stripeoffset(int	fd);

     g_stripesize(int fd);

     g_flush(int fd);

     g_delete(int fd, off_t offset, off_t length);

     char *
     g_device_path(const char *devpath);

     g_get_ident(int fd, char *ident, size_t size);

     g_get_name(const char *ident, char	*name, size_t size);

     g_open_by_ident(const char	*ident,	int dowrite, char *name, size_t	size);

     char *
     g_providername(int	fd);

     The geom library contains the official and	publicized API for interacting
     with the GEOM subsystem in	the kernel.

   Statistics Functions
     GEOM collects statistics data for all consumers and providers, but	does
     not perform any normalization or presentation on the raw data, this is
     left as an	exercise for user-land presentation utilities.

     The geom_stats_open() and geom_stats_close() functions open and close the
     necessary pathways	to access the raw statistics information in the	ker-
     nel.  These functions are likely to open one or more files	and cache the
     file descriptors locally.	The geom_stats_open() function returns zero on
     success, and sets errno if	not.

     The geom_stats_resync() function will check if more statistics collection
     points have been added in the kernel since	geom_stats_open() or the pre-
     vious call	to geom_stats_resync().

     The geom_stats_snapshot_get() function will acquire a snapshot of the raw
     data from the kernel, and while a reasonable effort is made to make this
     snapshot as atomic	and consistent as possible, no guarantee is given that
     it	will actually be so.  The snapshot must	be freed again using the
     geom_stats_snapshot_free()	function.  The geom_stats_snapshot_get() func-
     tion returns NULL on failure.

     The geom_stats_snapshot_timestamp() function provides access to the time-
     stamp acquired in the snapshot.

     The geom_stats_snapshot_reset() and geom_stats_snapshot_next() functions
     provide an	iterator over the statistics slots in the snapshot.  The
     geom_stats_snapshot_reset() function forces the internal pointer in the
     snapshot back to before the first item.  The geom_stats_snapshot_next()
     function returns the next item, and NULL if there are no more items in
     the snapshot.

   Control Functions
     The gctl_*() functions are	used to	send requests to GEOM classes.	In
     order for a GEOM class to actually	be able	to receive these requests, it
     must have defined a "ctlreq" method.

     A struct gctl_req *, obtained with	gctl_get_handle(), can hold any	number
     of	parameters, which must be added	to it with gctl_ro_param() (for	read-
     only parameters) or gctl_rw_param() (for read/write parameters).

     Both gctl_ro_param() and gctl_rw_param() take a string name, which	is
     used to identify the parameter, and a value, which	contains, in the read-
     only case,	the data to be passed to the GEOM class, or, in	the read/write
     case, a pointer to	preallocated memory that the GEOM class	should fill
     with the desired data.  If	len is negative, it is assumed that value is
     an	ASCII string and the actual length is taken from the string length of
     value; otherwise it must hold the size of value.

     A parameter with a	name containing	the string "class" is mandatory	for
     each request, and the corresponding value must hold the name of the GEOM
     class where the request should be sent to.

     Also mandatory for	each request is	a parameter with a name	called "verb",
     and the corresponding value needs to hold the command string that the
     GEOM class	should react upon.

     Once all desired parameters are filled in,	the request must be sent to
     the GEOM subsystem	with gctl_issue(), which returns NULL on success, or a
     string containing the error message on failure.

     After the request is finished, the	allocated memory should	be released
     with gctl_free().

     The gctl_dump() function can be used to format the	contents of req	to the
     open file handle pointed to by f, for debugging purposes.

     Error handling for	the control functions is postponed until the call to
     gctl_issue(), which returns NULL on success, or an	error message corre-
     sponding to the first error which happened.

   Utility Functions
     The g_*() functions are used to communicate with GEOM providers.

     The g_open() function opens the given provider and	returns	file descrip-
     tor number, which can be used with	other functions.  The dowrite argument
     indicates if operations that modify the provider (like g_flush() or
     g_delete()) are going to be called.

     The g_close() function closes the provider.

     The g_mediasize() function	returns	size of	the given provider.

     The g_sectorsize()	function returns sector	size of	the given provider.

     The g_stripeoffset() function returns stripe offset of the	given

     The g_stripesize()	function returns stripe	size of	the given provider.

     The g_flush() function sends BIO_FLUSH request to flush write cache of
     the provider.

     The g_delete() function tells the provider	that the given data range is
     no	longer used.

     The g_device_path() function returns the full path	to a provider given a
     partial or	full path to the device	node.  If the device can not be	found
     or	is not a valid geom provider, NULL is returned.

     The g_get_ident() function	returns	provider's fixed and unique identi-
     fier.  The	ident argument should be at least DISK_IDENT_SIZE big.

     The g_get_name() function returns name of the provider, which identifier
     is	equal to the ident string.

     The g_open_by_ident() function opens provider using its ident, unlike
     g_open() which uses provider's name.  If the name argument	is not NULL,
     the function will store provider's	name there.

     The g_providername() function returns the provider	name of	an open	file
     descriptor.  If the file descriptor does not point	to a valid geom
     provider, NULL is returned.

     All functions except g_providername() and g_device_path() return a	value
     greater than or equal to 0	on success or -1 on failure.

     Create a request that is to be sent to the	CCD class, and tell it to
     destroy a specific	geom:

	   H = gctl_get_handle();
	   gctl_ro_param(H, "verb", -1,	"destroy geom");
	   gctl_ro_param(H, "class", -1, "CCD");
	   sprintf(buf,	"ccd%d", ccd);
	   gctl_ro_param(H, "geom", -1,	buf);
	   errstr = gctl_issue(H);
	   if (errstr != NULL)
	       err(1, "could not destroy ccd: %s", errstr);

     The geom library appeared in FreeBSD 5.1.

     Poul-Henning Kamp <>
     Lukas Ertl	<>
     Pawel Jakub Dawidek <>

FreeBSD	10.2		       December	4, 2010			  FreeBSD 10.2


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