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)