kstat(9S)						    Data Structures for Drivers 						 kstat(9S)

NAME

       kstat - kernel statistics structure

SYNOPSIS

       #include <sys/types.h>
       #include <sys/kstat.h>
       #include <sys/ddi.h>
       #include <sys/sunddi.h>

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI)

DESCRIPTION

       Each kernel statistic (kstat) exported by device drivers consists of a header section and a data section. The kstat structure is the header
       portion of the statistic.

       A driver receives a pointer to a kstat structure from a successful call to kstat_create(9F). Drivers should never allocate a  kstat  struc-
       ture in any other manner.

       After  allocation,  the	driver	should	perform  any further initialization needed before calling kstat_install(9F) to actually export the
       kstat.

STRUCTURE MEMBERS

       void	 *ks_data;	       /* kstat type-specific data */
       ulong_t	 ks_ndata;	       /* # of type-specific data records */
       ulong_t	 ks_data_size;	       /* total size of kstat data section */
       int	 (*ks_update)(struct kstat *, int);
       void	 *ks_private;	       /* arbitrary provider-private data */
       void	 *ks_lock;	       /* protects this kstat's data */

       The members of the kstat structure available to examine or set by a driver are as follows:

       ks_data	       Points to the data portion of the kstat.  Either allocated by kstat_create(9F) for the drivers use, or by the driver if	it
		       is using virtual kstats.

       ks_ndata        The number of data records in this kstat. Set by the ks_update(9E) routine.

       ks_data_size    The amount of data pointed to by ks_data. Set by the ks_update(9E) routine.

       ks_update       Pointer	to  a  routine	that dynamically updates kstat. This is useful for drivers where the underlying device keeps cheap
		       hardware statistics, but where extraction is expensive. Instead of constantly keeping the kstat data section  up  to  date,
		       the  driver  can  supply  a ks_update(9E) function that updates the kstat data section on demand. To take advantage of this
		       feature, set the ks_update field before calling kstat_install(9F).

       ks_private      Is a private field for the driver's use. Often used in ks_update(9E).

       ks_lock	       Is a pointer to a mutex that protects this kstat. kstat data sections are optionally protected by the per-kstat ks_lock. If
		       ks_lock	is  non-NULL, kstat clients (such as /dev/kstat) will acquire this lock for all of their operations on that kstat.
		       It is up to the kstat provider to decide whether guaranteeing consistent data to kstat clients is sufficiently important to
		       justify	the locking cost. Note, however, that most statistic updates already occur under one of the provider's mutexes. If
		       the provider sets ks_lock to point to that mutex, then kstat data locking is free. ks_lock is really  of  type  (kmutex_t*)
		       and  is	declared  as  (void*)  in the kstat header. That way, users do not have to be exposed to all of the kernel's lock-
		       related data structures.

SEE ALSO

       kstat_create(9F)

       Writing Device Drivers

SunOS 5.10							    4 Apr 1994								 kstat(9S)