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

kstat - kernel statistics structure

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

illumos DDI specific (illumos DDI)

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 structure in any other manner.

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


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.

kstat_create(9F)

Writing Device Drivers

April 4, 1994 OmniOS