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-specif. data */
	 ulong_t   ks_ndata;		 /* # of type-specif. 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 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 5.11							    4 Apr 1994								 kstat(9S)