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)