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-specific data */
ulong_t ks_ndata; /* # of type-specific 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 this 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 sec‐
tion 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 struc‐
tures.
SEE ALSOkstat_create(9F)
Writing Device Drivers
SunOS 5.10 4 Apr 1994 kstat(9S)
