kstat(9S) Data Structures for Drivers kstat(9S)NAMEkstat - 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 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 allo‐
cated 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 con‐
sistent data to kstat clients is sufficiently impor‐
tant 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 ALSOkstat_create(9F)
Writing Device Drivers
SunOS 5.11 4 Apr 1994 kstat(9S)
