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 - 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 g_stat *
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);

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 da

ta, this is
left as an excercize 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 statis

tics 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 snap

shot 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 snap

shot. 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 readonly parameters) or gctl_rw_param() (for read/write parame

ters).

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 readonly 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.

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>

BSD March 7, 2004

BSD