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gctl_ro_param(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

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

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);

     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 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 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
     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.

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>

FreeBSD 5.4			 March 7, 2004			   FreeBSD 5.4

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