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

illumos DDI specific (illumos 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
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.

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

April 4, 1994 KSTAT(9S)