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_providernameuserland API library for kernel GEOM subsystem


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


#include < libgeom.h>

Statistics Functions

geom_stats_close( void);

geom_stats_open( void);

geom_stats_resync( void);

void *
geom_stats_snapshot_get( 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_get_handle( void);

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 kernel. 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 previous 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() function returns NULL on failure.

The geom_stats_snapshot_timestamp() function provides access to the timestamp 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 corresponding 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 descriptor 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 provider.

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 identifier. 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 <phk@FreeBSD.org> Lukas Ertl <le@FreeBSD.org> Pawel Jakub Dawidek <pjd@FreeBSD.org>
December 4, 2010 FreeBSD