LIBGEOM(3) BSD Library Functions Manual LIBGEOM(3)NAME
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
LIBRARY
library “libgeom”
SYNOPSIS
#include <libgeom.h>
Statistics Functions
void
geom_stats_close(void);
int
geom_stats_open(void);
void
geom_stats_resync(void);
void *
geom_stats_snapshot_get(void);
void
geom_stats_snapshot_free(void *arg);
void
geom_stats_snapshot_timestamp(void *arg, struct timespec *tp);
void
geom_stats_snapshot_reset(void *arg);
struct devstat *
geom_stats_snapshot_next(void *arg);
Control Functions
struct gctl_req *
gctl_get_handle(void);
void
gctl_ro_param(struct gctl_req *req, const char *name, int len,
const void *value);
void
gctl_rw_param(struct gctl_req *req, const char *name, int len,
void *value);
const char *
gctl_issue(struct gctl_req *req);
void
gctl_free(struct gctl_req *req);
void
gctl_dump(struct gctl_req *req, FILE *f);
Utility Functions
int
g_open(const char *name, int dowrite);
int
g_close(int fd);
off_t
g_mediasize(int fd);
ssize_t
g_sectorsize(int fd);
ssize_t
g_stripeoffset(int fd);
ssize_t
g_stripesize(int fd);
int
g_flush(int fd);
int
g_delete(int fd, off_t offset, off_t length);
char *
g_device_path(const char *devpath);
int
g_get_ident(int fd, char *ident, size_t size);
int
g_get_name(const char *ident, char *name, size_t size);
int
g_open_by_ident(const char *ident, int dowrite, char *name, size_t size);
char *
g_providername(int fd);
DESCRIPTION
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
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 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.
EXAMPLES
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);
gctl_free(H);
SEE ALSO
http://ezine.daemonnews.org/200308/blueprints.html
HISTORY
The geom library appeared in FreeBSD 5.1.
AUTHORS
Poul-Henning Kamp ⟨phk@FreeBSD.org⟩
Lukas Ertl ⟨le@FreeBSD.org⟩
Pawel Jakub Dawidek pjd@FreeBSD.org
BSD January 16, 2010 BSD
